BEARING LATERITIC ORE

PRIORITY CROSS-REFERENCE

[001] The present application claims priority from Australian provisional patent application No. 2021903170 filed on 5 October 2021 , the contents of which should be understood to be incorporated into this specification by this reference.

TECHNICAL FIELD

[002] The present invention generally relates to a process for the recovery of value metals from nickel and cobalt bearing lateritic ore or associated material. The invention is particularly applicable for recovering at least nickel and cobalt from a nickel and cobalt bearing lateritic ore or ore concentrate and it will be convenient to hereinafter disclose the invention in relation to that exemplary application. However, it is to be appreciated that the invention is not limited to that application and could be used to recover a number of further value metals from nickel and cobalt bearing lateritic ore, ore concentrate or associated material including but not limited to value metals such as iron, manganese, aluminium and chromium.

BACKGROUND TO THE INVENTION

[003] The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[004] Lateritic nickel ores represent nearly 70% of the global nickel resources. The beneficiation of nickel laterite can have difficulties due to the occurrence of nickel inside the lattice of: i) limonitic type iron oxide minerals such as goethite, hematite, maghemite; ii) smectite type clay-based minerals (for example nontronite); and iii) saprolite type silicate-based magnesium minerals, instead of forming discrete nickel mineral in the ore. [005] Hydrometallurgical processes for nickel recovery from laterites have been developed both in acidic and ammoniacal media. In most cases, leaching processes involve direct acid leaching of the laterite ore using mineral acids such as sulphuric, hydrochloric and nitric. Sulphuric acid leaching of lateritic ore is generally performed through high pressure acid leaching (HPAL) or atmospheric leaching. Atmospheric leaching is generally performed through agitating leaching and heap leaching using sulphuric acid lixiviant. Atmospheric acid leaching in nitric acid and hydrochloric acid media are also being investigated. However, no commercial operations have yet been established in using nitric or hydrochloric acid.

[006] Only the HPAL process has been successfully used in commercial operations. This is due to its better iron control by rejecting most of the iron as solid during leaching at high temperature and pressure, and simultaneously extracting more than 90% Ni and Co. In comparison, atmospheric acid leaching of lateritic nickel ores has the disadvantage of high iron dissolution during leaching which causes:

• high nickel and cobalt losses during its removal through normal precipitation route and generates significant solid waste for disposal;

• major issues of material of construction typically in chloride media for atmospheric iron hydrolysis at high temperature with simultaneous HCI regeneration; and

• higher cost for iron removal through solvent extraction technique due to lower value of iron product.

[007] Another important issue for the HCI leaching route for any ore/mineral/concentrate is the cost of the HCI, and therefore its regeneration from the process liquor to ensure the process is economically viable. This importance is increased where impurities such as iron, aluminium and magnesium consume a substantial amount of the hydrochloric acid during leaching forming respective metal salts.

[008] The regeneration of hydrochloric acid from these salts in many HCI leaching process, including nickel and cobalt bearing lateritic ore, is traditionally through pyrolysis or high temperature hydrolysis (pyro-hydrolysis) techniques. Both of these processes are energy intensive, requiring high temperatures: 400 to 800 °C for pyrolysis decomposition where metal chloride salts are decomposed to metal oxide; and 170 to 180 °C for high temperature hydrolysis to enable the hydrothermal reaction to precipitate remaining metals as metal oxide, for example iron as hematite. Both processes also require expensive furnace/reactor construction materials due to highly corrosive gaseous HCI produced at these temperatures.

[009] Alternate regeneration processes can use solvent extraction processes to separate value metals and/or impurities from the leach solution prior to HCI regeneration. For example, European patent publication No. EP1809778B1 teaches a process to recover metal values from laterite and other variety of ore bodies using a mixed solution of hydrochloric acid and magnesium chloride and/or zinc chloride or other metal chloride solution. The laterite leaching was performed at 85 °C and 30 % w/w pulp density using mixed solution of 1500 kg HCI/t of ore with 2M MgCk. The soluble value metals (Ni, Co, etc) and Fe and/or other impurities (Al, Cr, etc) were removed by solvent extraction (SX) or hydrolysis. The intermediate Fe removal product generated by SX was subjected to pyro-hydrolysis technique. The soluble value metals (Ni, Co, etc) and Fe and/or other impurity removed solution was treated with 30% w/w H2SO4 to separate metal sulphate typically as MgSC .xH2O by evaporation and crystallisation and thus regenerating HCI in the final liquor for recycling to leaching.

[010] Whilst value metals have a good recovery rate (reporting >95% Ni and >80% Co extractions), the use of solvent extraction is an expensive process step that adds unwanted cost and complexity to the recovery process.

[01 1] It would therefore be desirable to provide an improved or at least alternative process to recover value metals including nickel and cobalt from a nickel and cobalt bearing lateritic ore or concentrates.

SUMMARY OF THE INVENTION

[012] A first aspect of the present invention provides a process of recovering value metals from a nickel and cobalt bearing lateritic ore, the process including the steps of: leaching the nickel and cobalt bearing lateritic ore with a lixiviant in an ore leaching step at a temperature of 80 to 97 °C to produce a leach solution comprising undissolved leach solids and a leach liquor that includes a nickel and cobalt content, the lixiviant comprising hydrochloric acid at a concentration of less than or equal to 25% w/w; separating the leach liquor and the undissolved leach solids; reduction of the leach liquor at 45 to 60 °C by the addition of metallic iron, preferably iron powder, to convert ferric chloride in the leach liquor to ferrous chloride; separating the reduced leach liquor into a liquid fraction comprising a reduced liquor and a solid fraction comprising any unreacted solid iron powder; adding a neutralising agent to the reduced leach liquor at a temperature of 60 to 90 °C to raise the pH of the liquor to pH 4.5 to 5.5 thereby precipitating a nickel/cobalt/iron solid; separating the ni eke l/co bait/ iron solid from a ni eke l/co bait/ iron removed liquor; leaching the nickel/cobalt/iron containing solid with a lixiviant in at least one pH leaching step at a temperature of 50 to 70 °C to produce a second leach solution comprising acid leach solids and an acid leach liquor that includes a nickel, cobalt and iron (II) content, the lixiviant comprising hydrochloric acid at a concentration of less than or equal to 25% w/w; separating the acid leach solids and the acid leach liquor; adding an oxidant to the acid leach liquor at a temperature of 50 to 70 °C, thereby oxidising an iron(ll) content to iron(lll) in the acid leach liquor, to produce an oxidised acid leach liquor; adding a neutralising agent to the oxidised acid leach liquor at a temperature of 50 to 70 °C to raise the pH of the liquor to pH 2 to 4, thereby precipitating iron to produce an iron removed slurry; separating the iron removed slurry into a liquid fraction comprising the iron removed liquor and a solid fraction comprising the precipitated iron solid; precipitating a mixed Ni/Co hydroxide from the iron removed liquor by adding a neutralising agent, preferably at least one of lime or MgO, to the iron removed liquor at a temperature of 50 to 70 °C, to raise the pH of the liquor to 7 to 9 thereby producing a Ni/Co mixed hydroxide slurry including a mixed hydroxide solid precipitate; separating the Ni/Co mixed hydroxide slurry into a liquid fraction comprising an Ni/Co removed liquor and a solid fraction comprising the precipitated mixed Ni/Co hydroxide solid; and regenerating the lixiviant and recycling the lixiviant to the ore leaching step; wherein nickel and cobalt is recovered from the leach solution as a mixed Ni/Co hydroxide solid.

[013] The process of the present invention therefore provides a leaching process using a hydrochloric acid leach which leaches value metals from the nickel and cobalt bearing lateritic ore to recover nickel and cobalt content of the ore as a nickel-cobalt mixed hydroxide precipitate. The value metal recovery process is enhanced through the use of iron reduction and/or recovery process steps that can be configured to recover iron mainly as magnetite (FeaC ). Moreover, the lixiviant is regenerated after the Ni/Co recovery step and the regenerated lixiviant is recycled to the ore leaching step.

[014] It should be appreciated that the “nickel and cobalt bearing lateritic ore” can be any material containing nickel or cobalt values comprising one or more of: a. a nickel and cobalt bearing ore material including an ore or orebody, concentrate thereof, modified, ore thereof and tailings thereof, and mixtures thereof; b. nickel and cobalt bearing leach residues and slags; or c. mineral processing residues.

[015] The process of the present invention can process various nickel and cobalt bearing lateritic ores including but not limited to limonite, saprolite, smectite, silicious or other type of laterite ore containing nickel and/or cobalt. The nickel and cobalt bearing lateritic ore material may be an ore per se or can be a concentrate thereof. It should be appreciated that it may not be necessary to concentrate laterite ore unless there is magnetite or chromite proportions are higher in the ore which can go through gravity or magnetic separation steps as known in the art. The ore may have been subjected to a roasting step, for example an alkali roasting step with at least one of NaOH, Na2COs or Na2SC . The ore could also be in the form of roasted and/or reduced concentrates or other intermediates, all of which discussed above being referred to herein as modified ore. The ore may also be in the form of tailings of a nickel and cobalt bearing lateritic ore. It is understood that the expression "ore" also includes any other form of the ore, and that mixtures of the various forms of the ore may be used. The process of the present invention may be operated without pre- treatment of the nickel and cobalt bearing lateritic ore. In particular, the process may be operated with or without roasting or reduction of the ore.

[016] In many embodiments, pre-treatment of the ore, for example roasting, oxidation and/or reduction of the ore, is typically not required prior to leaching. The process operates with a relatively low concentration of hydrochloric acid, especially with the concentration of hydrochloric acid being less than or equal to 25% w/w (weight ratio). The process may be described as a direct process for leaching and recovery of nickel and cobalt bearing lateritic ore, as pre-treatment of the ore is not required, and the leaching step produces a solution of value metal concentrations. The process of the present invention is considered to be friendly to the environment, not requiring extensive pre-treatment procedures.

[017] The ore leaching step leaches out the value metals into the leach solution, leaving a leach solid which contains mostly silica-based quartz or silicate minerals with some undissolved impurities which can be disposed as tailings after washing. The leaching step is preferably carried out at atmospheric (ambient) pressure i.e. it is not necessary to conduct the leaching step under pressure. To achieve this, the ore leaching step is conducted with the lixiviant comprising less than or equal to 25 % w/w HCI solution, preferably 20 to 25% w/w. The temperature of the leach is between 80 to 97° C, and preferably between 90 to 95 °C. The free acid in the leach liquor is preferably about 10 g/L or less. In embodiments, a further neutralisation step may be required to minimise the free acid from the liquor to a desired level, preferably about 10 g/L or less, prior to the reduction step with Fe powder (as detailed below). In embodiments, the ore leaching step is performed for a duration of 1 to 4 h, preferably for a duration of 2 to 3 h.

[018] The ore leaching step may be conducted continuously as a co-current step, a counter-current step or in another manner, or the leaching step may be conducted as a batch step.

[019] A value metal-rich solution (leach liquor) is obtained in the ore leaching step. The residue (undissolved leach solids) may be in the form of a suspension. The leach mixture is fed to a solid/liquid separation step to effect separation of the leach liquor from the leach solids, for example leach residue and other gangue. Techniques for such separation are known in the art for example using a pressure or vacuum filter, counter-current decantation, thickener or centrifuge.

[020] Iron is added to the process in the reduction step and may also be included as a value material/ impurity in the ore. In the step of reduction of the leach liquor, metallic iron, preferably iron powder, is added to convert ferric chloride in the leach liquor to ferrous chloride. Reduction is preferably conducted under an inert gas or nitrogen atmosphere, preferably under a nitrogen blanket and achieves an oxidation-reduction potential (ORP) of the liquor below 100 mV.

[021] Following the step of reduction of the leach liquid, a number of process steps are undertaken to separate an iron content from the value metal-rich solution (leach liquor) which comprises a Ni/Co bearing leach solution. In general, Fe is removed first from the Ni/Co bearing leach solution prior generating the Ni/Co bearing mixed hydroxide solid precipitate. However, the inventors have found that a single/ simple Fe separation stage may not provide the desired Ni and Co recovery. A multistage Fe removal process has therefore been established to substantially remove the Fe content from the reduced leach liquor (the Ni/Co bearing leach solution).

[022] Whilst not wishing to be limited to any one theory, the Inventors have surprisingly found that the iron content of the reduced leach liquor (the Ni/Co bearing leach solution) can be successfully removed by firstly precipitating a Ni/Co/Fe precipitate solid from the reduced leach liquor, and then adopting a secondary leaching process for the dissolution of Ni and Co from the Ni/Co/Fe precipitated solid. As part of this iron removal/ recovery process, iron can be removed as a solid residue using a oxidation/pH controlled precipitation strategy.

[023] In a first step, nickel/cobalt/iron precipitation is performed by raising the pH of the reduced leach liquor to 4.5 to 5.5, preferably 4.8 to 5.3 by adding the neutralising agent to the reduced leach liquor at a reaction temperature of 60 to 90 °C, preferably at 70 to 80 °C and most preferably at around or at 75 °C. The nickel/cobalt/iron solid is then separated from a nickel/cobalt/iron removed liquor. The nickel/cobalt/iron removed liquor is then preferably fed into a further Fe removal/ recovery step (see below). [024] Nickel/cobalt/iron precipitation is then followed by one or more pH leaching steps to preferentially dissolve nickel and cobalt from the nickel/cobalt/iron precipitation solid. In these leaching steps, each of the leaching steps is conducted with the lixiviant comprising less than or equal to 25 % w/w HCI solution, preferably from 20 to 25 % w/w HCI solution, and more preferably 20 % w/w HCI solution. Furthermore, each leaching step is preferably conducted at a temperature of 50 to 70 °C, preferably 55 to 65 °C, and more preferably around 60 °C.

[025] Whilst a single leaching step could be used, it has been found that at least two different leaching steps are preferably used, with different pH conditions to control preferential dissolution of species. In each leaching stage, leaching of the nickel/cobalt/iron precipitate is performed at between 50 to 70 °C, for example at 60 °C, using the leach solids, for example a leach cake or other solid form, from the preceding stage. The pH of the reaction at each stage is controlled by adding the HCI solution. In embodiments, the at least one pH leaching step comprises at least two acid leaching stages, comprising: a first pH leach stage in which pH is controlled to between 5.4 and 5.7 to maximise dissolution of iron(ll) from the nickel/cobalt/iron containing solid; and at least one subsequent pH leach stage in which pH is lowered to below 1 to dissolve nickel and cobalt content from the nickel/cobalt/iron containing solid.

[026] In some embodiments, the at least one pH leaching step comprises at least three acid leaching stages, comprising: a first pH leach stage in which the pH is controlled to between 5.4 and 5.7, preferably 5.5 to 5.6; a second pH leach stage in which the pH is controlled to between 5.4 and 5.7, preferably 5.5 to 5.6; and at least one subsequent pH leach stage in which the pH of the reaction is below 1 , preferably a pH of 0.7 to 0.8.

[027] In each of these embodiments, the purpose of the first pH leach stage was to obtain a maximum dissolution of Fe as Fe(ll) with a minimum dissolution of Ni from the Ni/Co/Fe precipitate. The subsequent pH leach stages (second pH leach stage and/or the at least one subsequent pH leach stages) are used to dissolve remaining Ni and Co from the Ni/Co/Fe precipitate. Optimal Ni and Co dissolution from the Ni/Co/Fe precipitate was found at a pH of 0.7 to 0.8. However, it should be appreciated that dissolution within the scope of the present invention could still be adequately accomplished at pH values outside that range.

[028] Similar to the ore leaching step, the pH leaching step or steps is preferably carried out at atmospheric (ambient) pressure i.e. it is not necessary to conduct the leaching step under pressure. In embodiments, the pH leaching step(s)/ regime is performed for a duration of 1 to 3 h, preferably for a duration of 2 to 3 h. Each leaching stage of the pH leaching step may be conducted continuously as a co-current step, a counter-current step or in another manner, or each leaching step/ stage may be conducted as a batch step.

[029] A nickel/cobalt-rich solution (acid leach liquor) is obtained in one or more of the pH leaching steps. The residue (undissolved leach solids) may be in the form of a suspension. The leach mixture is fed to a solid/liquid separation step to effect separation of the acid leach liquor from the leach solids, for example leach residue and other gangue. Techniques for such separation are known in the art for example using a pressure or vacuum filter, counter-current decantation, thickener or centrifuge.

[030] Where the at least one pH leaching step includes two or more leaching steps, the first pH leaching step comprises the above discussed first pH leach stage. As noted above, the first pH leach stage is conducted to obtain a maximum dissolution of Fe as Fe(ll) with a minimum dissolution of Ni from the Ni/Co/Fe precipitate. This first pH leach stage therefore produces an iron(ll) rich leach liquid and nickel/cobalt/iron containing solid. In many embodiments, the nickel and cobalt content of the iron(ll) rich leach liquid is recovered using ion exchange. Ion exchange is typically conducted using an ion exchange resin suitable for Ni and Co separation from the iron(ll) rich leach liquid. As should be appreciated, the Ni and Co rich resin is treated, for example using an acid such as HCI, to recover the Ni and Co bearing elute liquor. This ion exchange step produces a Ni and Co bearing elute liquor which is fed into the iron(ll) oxidation step, and an iron bearing raffinate. That iron bearing raffinate is preferably fed into a further Fe removal/ recovery step (see below). [031] The acid leach liquor, preferably the acid leach liquid from the subsequent pH leach stages (second pH leach stage and/or the at least one subsequent pH leach stages) undergo an oxidation step to convert any iron(ll) content to iron(lll), and then a final iron removal step, conducted by adding a neutralisation agent, to precipitate out iron(lll) to produce an iron removed slurry.

[032] In this multi-step iron removal stage, the neutralising agent added to the (i) reduced leach liquor to precipitate the nickel/cobalt/iron solid therefrom; and/or (ii) the oxidised acid leach liquor to precipitate iron therefrom preferably comprises at least one of limestone, lime or MgO. In addition, the oxidant added to the acid leach liquor to precipitate the iron content therefrom preferably comprises at least one of: alkali metal peroxide, alkali metal perchlorate, ammonium perchlorate, magnesium perchlorate, magnesium chlorate, alkali metal chlorate, chlorine, alkali metal hypochlorite, hydrogen peroxide, perchloric acid, an oxygen containing gas, or mixtures thereof. Preferred oxidants are H2O2 or an oxygen containing gas, such as oxygen, air, or the like. In some embodiments, the oxidant is oxygen or air.

[033] As noted above, the nickel/cobalt/iron removed liquor and/or the iron bearing raffinate from the ion exchange is preferably fed into a further Fe removal/ recovery step. In some embodiments, the process further comprises: adding a neutralising agent and an oxidant to the nickel/cobalt/iron removed liquor at a temperature of 70 to 90 °C to raise the pH of the liquor to pH 3 to 5, and 70 to 90 °C in the presence of air thereby precipitating iron; and separating the precipitated iron solid from an iron removed liquor. However, in many embodiments, the neutralising agent and the oxidant is added to a mixture of the nickel/cobalt/iron removed liquor and the iron bearing raffinate from the ion exchange. This iron removal step therefore comprises: adding a neutralising agent and an oxidant to the nickel/cobalt/iron removed liquor and the iron bearing raffinate at a temperature of 70 to 90 °C to raise the pH of the liquor to pH 3 to 5, and 70 to 90 °C in the presence of air thereby precipitating iron; and separating the precipitated iron solid from an iron removed liquor. In this iron removal step, the neutralising agent added to the nickel/cobalt/iron removed liquor or combination with the iron bearing raffinate can comprise at least one of limestone, lime or MgO; and the oxidant added to the nickel/cobalt/iron removed liquor or combination with the iron bearing raffinate can comprise at least one of: alkali metal peroxide, alkali metal perchlorate, ammonium perchlorate, magnesium perchlorate, magnesium chlorate, alkali metal chlorate, chlorine, alkali metal hypochlorite, hydrogen peroxide, perchloric acid, an oxygen containing gas, or mixtures thereof. In embodiments the oxidant is selected from at least one of hydrogen peroxide or an oxygen containing gas such as oxygen or air.

[034] It should be appreciated that the iron precipitation solid can comprise one or more of goethite (a-FeOOH), akaganeite ([3-FeOOH), magnetite (FeaC ), or mixture thereof. Each of the above described iron precipitation (removal) steps is preferably configured to precipitate iron as goethite or magnetite and/or akageneite, and preferably mainly as magnetite (FesC ) using an oxidant such as air. In this regard, magnetite is the preferred form for the iron removed solid. Thus, in exemplary embodiments, iron is substantially precipitated as magnetite, preferably precipitated as magnetite only in particular from steps of the process (following pH leach stages and when recovered from the Ni/Co/Fe removed liquor in the further Fe removal/ recovery step). The iron precipitate, preferably mainly magnetite, can be used to produce Fe powder for example by reacting the precipitated magnetite with carbon/charcoal/coke/coal or hydrogen at high temperature, typically -800 to 1000 °C. The Fe powder produced can be recycled for use in the process, for example in the reduction step of the leach process stream. Iron removal from the process liquid occurs prior to the recovery of the mixed nickel and cobalt hydroxide solid. It is noted that iron recovery from the iron removed slurry (precipitated from the pH/acid leach liquor after the oxidation step) is typically not magnetite, rather it is mainly goethite type iron oxy-hydroxide.

[035] A mixed Ni/Co hydroxide solid product is precipitated from this process in the nickel and cobalt recovery stage by adding a neutralising agent such as lime or MgO as the precipitating agent at a pH of 7 to 9, preferably from 8 to 9, more preferably about 8.6, and a temperature of 60 to 90 °C. In some embodiments, the temperature may be from 50 to 70 °C, preferably 55 to 65 °C, more preferably about 60 °C. Lime or MgO are used as these can provide the pH required for Ni/Co precipitation from the liquor. A solid-liquid separation is conducted of the resulting Ni/Co mixed hydroxide slurry to separate a Ni/ Co mixed hydroxide precipitated solid and a Ni/Co removed liquor. The mixed Ni/Co hydroxide solid can be further processed to recover the separate nickel and cobalt value metals using any number of nickel and cobalt separation processes known in the art.

[036] The nickel and cobalt bearing lateritic ore may also include one or more additional value metals such as iron, chromium, manganese, magnesium or aluminium. Other trace elements, species or impurities may also be present. The process of the present invention can therefore include steps of removing and recovering any iron, chromium, manganese, magnesium or aluminium from the leach liquor in this leach processing stream. In these embodiments, the leach liquor is subjected to steps to recover the at least one value metal therefrom.

[037] In embodiments, the value metals in the nickel and cobalt bearing lateritic ore include at least chromium and/or aluminium. In such embodiments, the process further comprises a chromium and/or aluminium removal step comprising: adding a neutralising agent, preferably at least one of limestone, lime or MgO, to the leach liquor at a temperature of 60 to 90 °C under an inert gas or nitrogen atmosphere, to raise the pH of the liquor to 3 to 4, preferably at 3.5, thereby precipitating chromium and aluminium to produce an Al/Cr removed slurry; and separating the Al/Cr removed slurry into a liquid fraction comprising an Al/Cr removed liquor and a solid fraction comprising the Al/Cr precipitated solid.

[038] Chromium and/or aluminium separation from the leach liquor is therefore a precipitation technique resulting for a pH rise of the liquor caused by the addition of limestone, lime or MgO.

[039] This process step is preferably conducted under an inert gas or nitrogen atmosphere, preferably under a nitrogen blanket to prevent oxidation of ferrous iron to ferric iron and hinder precipitation of any iron content (in the form of ferric iron) that may be in the leach liquor. Chromium and/or aluminium precipitation is preferably conducted prior to removal/ recovery of other value metals that may be in the leach liquor. In particular, the chromium and/or aluminium removal step is preferably conducted before the iron removal/recovery steps, and preferably before the nickel/cobalt/iron precipitation step. [040] Recovery of chromium and aluminium from the Al/Cr precipitated solid can be conducted by any suitable method known in the art, for example by leaching using either a caustic or HCI solution, followed by precipitation and optional calcination steps. The details of these process steps are described in more detail later in the specification.

[041] As noted above, the nickel and cobalt bearing lateritic ore may include an iron content (i.e. one of the value metals). Alternatively, or in addition, the leach liquor includes an iron content from Fe addition in the leach process stream. In such embodiments, Fe powder is added because Fe(lll) is present in the leach liquor. Fe powder reduces Fe(lll) to Fe(ll), and Fe(ll) does not precipitate and remains in solution during Al/Cr reduction due to the preferable use of a nitrogen blanket. In these embodiments, this iron content is removed in the defined iron removal/ recovery steps of the process. In the overall leach process stream, the iron removal/ recovery steps are preferably conducted after the chromium and/or aluminium removal step.

[042] The nickel and cobalt bearing lateritic ore may also include a manganese and/or magnesium content (i.e. one of the value metals). Alternatively, or in addition, the leach liquor may include a manganese and/or magnesium content from Mg or Mn addition at some point in the leach process stream, for example MgO addition. In these embodiments, the process further comprises a manganese and/or magnesium removal step comprising: adding a neutralising agent, preferably lime, and an oxidant, preferably H2O2 or an oxygen containing gas, more preferably air, to the iron removed liquor separated from the nickel/cobalt/ iron removed liquor at a temperature of 60 to 90 °C to raise the pH of the liquor to 8 to 10 thereby precipitating Mg and/or Mn to produce a Mg/Mn removed slurry; and separating the removed Mg/Mn slurry into a liquid fraction comprising a Mg/Mn removed liquor and a solid fraction comprising the precipitated Mg and/or Mn solid.

[043] The precipitation step is conducted in the presence of an oxidant, which may preferably be H2O2 or an oxygen containing gas such as oxygen, air or similar for the oxidation of Mn(ll) to Mn(IV). In this step, lime is preferably used as the neutralisation agent. The precipitated Mg and/or Mn solid will typically comprise Mg(OH)2 and a mixture of Mn-oxide/hydroxide/oxy-hydroxide. The Mg/Mn removed liquor which will be mainly a chloride solution, for example calcium chloride where limestone and/or lime is used in the preceding steps. In the overall leach process stream, the manganese and/or magnesium removal step is preferably conducted after the iron precipitation step.

[044] In some embodiments, the neutralising agent in the various process steps/ stages comprises MgO. In these embodiments, the process typically further comprises a Mg removal step in which Mg(OH)2 is precipitated using lime and an MgO regeneration stage in which the Mg(OH)2 is calcined preferably at 400 to 600 °C to regenerate MgO for recycling as the neutralising agent in the process. In exemplary embodiments wherein the neutralising agent in at least one step of the process comprises MgO, and the process preferably further comprises a Mn removal step and a separate Mg removal step. In such embodiments, the process includes:

(A) a manganese removal step comprising: adding a neutralising agent, preferably lime or MgO, and an oxidant, preferably H2O2 or an oxygen containing gas, more preferably air, to the iron removed liquor separated from the ni eke l/co bait/ iron removed liquor at a temperature of 60 to 90 °C to raise the pH of the liquor to 8 to 9, preferably at 8.5, thereby precipitating Mn to produce a Mn removed slurry; and separating the removed Mn slurry into a liquid fraction comprising a Mn removed liquor and a solid fraction comprising the precipitated Mn solid; and

(B) a magnesium removal step comprising: adding a neutralising agent, preferably lime to the Mn removed liquor at a temperature of 60 to 90 °C to raise the pH of the liquor to 9 to 10 thereby precipitating Mg to produce a Mg removed slurry; and separating the removed Mg slurry into a liquid fraction comprising a Mg removed liquor and a solid fraction comprising the precipitated Mg solid; and

(C) an MgO regeneration stage in which the precipitated Mg solid is calcined, preferably at 400 to 600 °C, to regenerate MgO for recycling as the neutralising agent in the process.

[045] The manganese and/or magnesium removal step is preferably conducted after the ni eke l/co balt/iron precipitation step. [046] In a number of embodiments, the process can further include at least one evaporation step (i) before, (ii) after or (iii) both before and after the manganese and/or magnesium removal step to remove a water content from the process liquid.

[047] To assist with process economics, it is preferable that the lixiviant is regenerated and recycled to the ore leaching step. In embodiments, the lixiviant is regenerated by: concentrating the chloride content of a final process liquor through water removal, preferably boiling and/or evaporation, to produce an evaporated liquor; reacting the evaporated liquor with at least 98% w/w sulphuric acid to produce 20 to 25% w/w hydrochloric acid and a solid precipitate, separating the precipitated solid and hydrochloric acid liquor; and recycling the hydrochloric acid liquor to the ore leaching step.

[048] The step of reacting the evaporated liquor with at least 98% w/w sulphuric acid is preferably conducted at a temperature of 30 to 90 °C under atmospheric conditions. In some embodiments, the step of reacting the evaporated liquor with at least 98% w/w sulphuric acid is preferably conducted at a temperature of 70 to 90 °C under atmospheric conditions. Furthermore, the reaction is preferably conducted at a stoichiometric ratio of calcium chloride in the liquor to required sulphuric acid. The composition of the chloride content will depend on the composition of the additives to this leach process stream. In many cases, the chloride content will comprise a calcium chloride solution/liquor. The evaporated liquor will therefore comprise a calcium chloride liquor. In such embodiments, the evaporated liquor is reacted with concentrate sulphuric acid (98 % w/w) at a stoichiometric ratio of calcium chloride to sulphuric acid to produce HCI and a precipitate comprising at least one of gypsum, hemihydrate or an anhydrite compound. Furthermore, in these embodiments the reaction between the evaporated liquor and concentrate sulphuric acid is preferably performed in a temperature range of 80 to 85 °C aiming to precipitate anhydrite only. It should be appreciated that the production of gypsum during HCI regeneration at the back end of the circuit can assist in providing an environmentally friendly by-product of the process. [049] In some embodiments, the process of the present invention includes a sulphuric acid production plant that produces sulphuric acid from elemental sulphur to produce concentrated sulphuric acid (98% w/w) for the lixiviant regeneration step. This additional process can provide significant energy credit for power generation and heat required for various steps in the process.

[050] The lixiviant regeneration step is conducted on the final process liquor. In many cases that final process liquor will be the Mg/Mn removed liquor, or the Mg removed liquor as Mn and/or Mg removal is typically the last separation stage in the process after recovering the nickel and cobalt from the leach solution as a mixed Ni/Co hydroxide solid. However, it should be appreciated that where the process does not include a Mn and/or Mg removal step the final process liquor would comprise the Ni/Co removed liquor and the Fe removed liquor from the filtrate of nickel/cobalt/iron precipitation.

[051 ] The leach process stream preferably includes a number of treatment processes prior to value metal recovery steps, more particularly prior to the chromium and/or aluminium precipitation step. In these embodiments, the process further comprises the following steps prior to reduction of the leach liquor by the addition of metallic iron of: neutralising at least part of the free acid (HCI) in the leach liquor by adding to the leach liquor a neutralising agent comprising at least one of: the feed nickel and cobalt bearing lateritic ore, limestone, lime or MgO, at a temperature of 80 to 97 °C, preferably 90 to 95 °C to produce a first liquor neutralised slurry including a neutralised leach solid; and separating the first liquor neutralised slurry into a solid fraction comprising the neutralised leach solid and a liquid fraction comprising the neutralised leach liquor.

[052] The neutralising step preferably neutralises/reduces free acid in the leach liquor to about 10 g/L or less prior to the reduction step with Fe powder. It should be appreciated that other neutralisation agents could also be used such as sodium hydroxide or the like. In some embodiments, the leach liquor neutralisation stage solid or leach solid (when ore is used) is fed into the leaching stage. [053] In order to optimise value metal extraction, where the neutralising agent comprises nickel and cobalt bearing lateritic ore, the separated neutralising agent is fed into the ore leaching step.

[054] It should be appreciated that separation of solid and liquid elements in the process can be performed using any suitable method. Techniques for such separation are known for example using a pressure or vacuum filter, counter-current decantation, thickener or centrifuge.

[055] The process of the present invention and process steps therein are preferably carried out at atmospheric (ambient) pressure. The whole process therefore can be designed to operate below 100 °C under atmospheric conditions. This enables the process to be based on atmospheric precipitation techniques conducted at temperatures below 100 °C.

[056] A second aspect of the present invention provides a process system for recovering value metals from a nickel and cobalt bearing lateritic ore, the system including the steps of: a leaching vessel for leaching the nickel and cobalt bearing lateritic ore in an ore leaching step at a temperature of 80 to 97 °C with a lixiviant to produce a leach solution comprising undissolved leach solids and a leach liquor that includes a nickel and cobalt content, the lixiviant comprising hydrochloric acid at a concentration of less than or equal to 25% w/w; a first solid-liquid separator for separating the leach liquor and the undissolved leach solids; a reduction vessel for reduction of the leach liquor at 45 to 60 °C by the addition of metallic iron, preferably iron powder, to convert ferric chloride in the leach liquor to ferrous chloride; a second solid-liquid separator for separating the reduced leach liquor into a liquid fraction comprising a reduced liquor and a solid fraction comprising any unreacted solid iron powder; a first precipitation vessel for precipitating a nickel/cobalt/iron solid from the treated second leach liquor by adding a neutralising agent to the treated second leach liquor at a temperature of 50 to 70 °C to raise the pH of the second leach liquor to 4.5 to 5.5 to produce a slurry comprising an nickel/cobalt/iron removed liquor and a nickel/cobalt/iron solid; a third solid-liquid separator for separating the nickel/cobalt/iron solid from the nickel/cobalt/iron removed liquor; at least one secondary leaching vessel for leaching the nickel/cobalt/iron containing solid with a lixiviant in at least one pH leaching step at a temperature of 50 to 70 °C to produce a second leach solution comprising acid leach solids and an acid leach liquor that includes a nickel, cobalt and iron (II) content, the lixiviant comprising hydrochloric acid at a concentration of less than or equal to 25% w/w; a fourth solid-liquid separator for separating the acid leach solids and the acid leach liquor; an oxidation vessel in which an oxidant is added to the acid leach liquor at a temperature of 50 to 70 °C, thereby oxidising an iron(ll) content to iron(lll) in the acid leach liquor, to produce an oxidised acid leach liquor; a second precipitation vessel for precipitating iron from the oxidised acid leach liquor by adding a neutralising agent to the oxidised acid leach liquor at a temperature of 50 to 70 °C to raise the pH of the liquor to pH 2 to 4; a firth solid-liquid separator for separating the iron removed slurry into a liquid fraction comprising the iron removed liquor and a solid fraction comprising the precipitated iron solid; a third precipitation vessel for precipitating a mixed Ni/Co hydroxide from the iron removed liquor by adding a neutralising agent, preferably at least one of lime or MgO, to the iron removed liquor at a temperature of 50 to 70 °C, to raise the pH of the liquor to 7 to 9 thereby producing a Ni/Co mixed hydroxide slurry including a mixed hydroxide solid precipitate; a sixth solid-liquid separator for separating the Ni/Co mixed hydroxide slurry into a liquid fraction comprising an Ni/Co removed liquor and a solid fraction comprising the precipitated mixed Ni/Co hydroxide solid; and a regenerator stage for regenerating the second lixiviant for recycle to the second leaching step, wherein nickel and cobalt is recovered from the leach solution as a mixed Ni/Co hydroxide solid. [057] In this second aspect, the neutralising agent added in at least one of the first precipitation vessel, the second precipitation vessel, or the third precipitation vessel can comprise any suitable neutralising species or compound, and preferably comprises at least one of limestone, lime or MgO. Furthermore, the oxidant in the oxidation vessel precipitation vessel can comprise one of alkali metal peroxide, alkali metal perchlorate, ammonium perchlorate, magnesium perchlorate, magnesium chlorate, alkali metal chlorate, chlorine, alkali metal hypochlorite, hydrogen peroxide, perchloric acid, an oxygen containing gas such as air or oxygen, other non-sulphur containing oxidants, or mixtures thereof. Preferred oxidants are H2O2 or an oxygen containing gas, such as oxygen, air, or the like.

[058] Again, a number of treatment processes can be included prior to value metal recovery stages/ vessels. In these embodiments, the process system further comprises prior to the reduction vessel: a neutralisation vessel in which at least part of the free acid (HCI) in the leach liquor can be neutralised through the addition of a neutralising agent to the leach liquor comprising at least one of: the feed nickel and cobalt bearing lateritic ore, limestone, lime or MgO, preferably at a temperature of 80 to 97 °C, more preferably 90 to 95 °C to produce a first liquor neutralised slurry including a neutralised leach solid; and a solid-liquid separator for separating the first liquor neutralised slurry into a solid fraction comprising the neutralised leach solid and a liquid fraction comprising the neutralised leach liquor. It should be appreciated that for limestone, lime or MgO, a temperature of below 50 °C can be used for neutralisation (these conditions are okay for neutralisation). However, when this neutralisation step is conducted with ore a temperature of 80 to 97 °C is preferred to produce effective acid neutralisation.

[059] It should be appreciated that the process system of the second aspect of the present invention can perform the process of the first aspect of the present invention. The features and additional process steps/ stages taught for the first aspect of the present invention equally apply to this second aspect of the present invention. In particular, the process system can include separation stages for value metals such as iron, chromium, manganese, magnesium or aluminium as described in relation to the first aspect of the present invention. In each case these process steps/stages comprise precipitation vessels coupled with a solid-liquid separator. [060] A third aspect of the present invention provides a plant which includes a process according to the first aspect of the present invention and/or a process system according to the second aspect of the present invention.

[061] The present invention also provides a fourth aspect of the present invention comprising nickel and cobalt and/or other value metals (for example iron, chromium, manganese, magnesium or aluminium) produced from the process according to the first aspect of the present invention.

[062] Some advantages of this leaching process are as follows: i) The process of the present invention is based on atmospheric precipitation techniques below 100 °C, which implies low capital investment compared to the process having high temperature extraction processes and/or solvent extraction process step. ii) No specialised material of construction is required for the reactor design criteria in this process. Standard fibre glass and/or high-density polyethylene (HDPE) and/or polypropylene (PP) tanks can be used to meet the reactor/equipment requirement. iii) Compared to prior art nickel-cobalt laterite ore leaching processes, the lixiviant regeneration in the present invention is a simpler process where energy requirement is comparatively much lower than those systems and (as in ii) the material of construction is not critical (i.e. not requiring high temperature operation and high temperature corrosion resistant materials). iv) The whole process operates with low or reduced concentration of hydrochloric acid within a concentration range of less than 25% w/w HCI. v) The HCI required in the process is regenerated from the process liquor containing calcium chloride under atmospheric conditions using sulphuric acid. vi) The iron removal/recovery product from steps of the process in particular from steps of the process (following pH leach stages and when recovered from the Ni/Co/Fe removed liquor in the further Fe removal/ recovery step) is preferably mainly magnetite which can be used to produce required Fe powder by reacting the precipitated magnetite with carbon/charcoal/coke/coal/hydrogen at high temperature, -700 to 1000 °C. The excess magnetite can be a saleable by-product which can be used in other processes for example, steel making. It is noted that iron recovery from the iron removed slurry (from the pH/acid leach liquor after the oxidation step) is typically not magnetite, rather it is mainly goethite type iron oxy-hydroxide. vii) Major reagents consumption in this technology are limestone which is a very low-price reagent, and lime and elemental sulphur that are in-expensive reagent.

BRIEF DESCRIPTION OF THE DRAWINGS

[063] The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein:

[064] Figure 1 is a general process flow diagram showing the overall process steps of the process of recovering value metals from a nickel and cobalt bearing lateritic ore according to the present invention.

[065] Figure 1 A provides the established process flow diagram showing the process steps, and in particular the iron recovery process steps, for one preferred embodiment of the process according to the present invention.

[066] Figure 2 provides a plot illustrating leach extraction of Ni and Fe from three different laterite ores at 20% w/w HCI, 20% w/w pulp density and 90 °C for 4 h.

[067] Figure 3 provides a plot illustrating leach extraction of Co and Mn from three different laterite ores at 20% w/w HCI, 20% w/w pulp density and 90 °C for 4 h.

[068] Figure 4 provides a plot of leach extraction of Al and Mg from three different laterite ores at 20% w/w HCI, 20% w/w pulp density and 90 °C for 4 h.

[069] Figure 5 provides a plot illustrating leach extraction of Ni and Fe from three different laterite ores at 24.5% w/w HCI, 25% w/w pulp density and 90 °C for 4 h.

[070] Figure 6 provides a plot illustrating leach extraction of Co and Mn from three different laterite ores at 24.5% w/w HCI, 25% w/w pulp density and 90 °C for 4 h.

[071] Figure 7 provides a plot illustrating leach extraction of Al and Mg from three different laterite ores at 24.5% w/w HCI, 25% w/w pulp density and 90 °C for 4 h. [072] Figure 8 provides a plot of online pH and ORP vs time for Fe(lll) reduction test at 60 °C using 1.17 times stoichiometric addition of Fe powder.

[073] Figure 9 provides a plot of the precipitation behaviour of Ni/Co/Fe from Al/Cr removed liquor at 75 °C by lime slurry addition.

[074] Figure 10 provides a plot of the dissolution behaviour of Ni, Co and Fe during acid (pH) leach-1 at 60 °C and 10% pulp density using 20% w/w HCI solution.

[075] Figure 11 provides a plot of the dissolution behaviour of Ni, Co and Fe during acid (pH) leach-3 at 60 °C and 10% pulp density using 20% w/w HCI solution.

DETAILED DESCRIPTION

[076] The process of the present invention relates to the recovery of value metals from a nickel and cobalt bearing lateritic ore. Such nickel and cobalt bearing lateritic ore may typically also include iron, chromium, aluminium, magnesium and manganese, which can also be solubilised in a lixiviant applied during a leaching step. The nickel and cobalt bearing lateritic ore can be a Ni/Co-bearing ore material including an ore or orebody, concentrate thereof, modified, ore thereof and tailings thereof, and mixtures thereof. Various types of Ni/Co-bearing laterite ore include limonite, saprolite, smectite, silicious or other type of laterite ore containing nickel and/or cobalt. The nickel and cobalt bearing lateritic ore can also be a material including nickel and cobalt-bearing leach residues and slags. However, it should be appreciated that the invention should not be limited to any one of those materials.

[077] The process of the present invention is a leaching process which recovers value metals including nickel (Ni), cobalt (Co), aluminium (Al), manganese (Mn), magnesium (Mg) and iron (Fe) from nickel and cobalt bearing lateritic ore through a hydrochloric acid (HCI) leaching route. The overall process is described to operate with HCI concentration, below or equal to 25% w/w.

[078] The process steps of the present invention are illustrated in Figures 1 and 1 A. Figure 1 provides a general/ conceptual process flow diagram of the invention. Figure 1 A provides one embodiment of the established process flow diagram showing the process steps, and in particular the iron recovery process steps, of the process of the present invention.

[079] Starting with the overall process steps - Figure 1 shows the general flow diagram of one embodiment of the process of the present invention showing a leaching led process 100 for the recovery of value metals from a nickel and cobalt bearing lateritic ore or concentrate 101. As discussed above, the nickel and cobalt bearing lateritic ore or concentrate 101 includes nickel and cobalt, and in this case additional value metals including iron, chromium, aluminium, manganese and magnesium. The process described and illustrated has been tailored to recover each of those value metals. It should be appreciated that different process steps may be used depending in the value metal composition of a particular nickel and cobalt bearing lateritic ore. The process of the present invention can therefore include but should not be strictly limited to the following steps as shown in Figure 1 : i) An ore leaching step 120 of the nickel and cobalt bearing lateritic ore, in this embodiment a nickel and cobalt (Ni/Co) bearing ore 101 , is conducted in an HCI lixiviant solution 105 typically comprising 20 to 25% w/w HCI at 80 to 97 °C, preferably at 90 to 95 °C to leach the value metals including nickel, cobalt, along with amounts of one or more of aluminium, chromium, manganese, magnesium and iron depending on the composition of the ore. The ore leaching step 120 is preferably conducted at atmospheric (ambient) pressure. The leaching process is followed by solid-liquid separation (part of step 120) of the leach slurry to separate the leach solids 125 and leach liquor 126. The leach solid will contain mostly silica-based quartz or silicate minerals with some undissolved impurities which can be disposed as tailings after washing. The leach liquor 126 comprises a mixed chloride species solution of the nickel, cobalt, along with amounts of one or more of aluminium, chromium, manganese, magnesium and iron depending on the composition of the ore. ii) The excessive free acid (HCI) remaining in the leach liquor 126 after leaching is preferably neutralised in neutralisation stage 130 conducted at a temperature of 80 to 97 °C, preferably at 90 to 95 °C. Here the leach liquor 126 is fed into a neutralisation vessel, a neutralisation agent 131 is added to minimise the free acid concentration in the leach liquor to approximately 10 g/L or less. The neutralisation agent 131 is preferably the feed Ni/Co bearing laterite ore or concentrate to minimise the free acid concentration in the leach liquor 126. This stage will also result in partial extraction of the metal values present in that feed ore. However, another neutralisation agent such as limestone, lime or MgO could be used, with the knowledge that reagent consumption may be high to achieve the required free acid concentration. Where limestone, lime or MgO is used, the feed Ni/Co bearing ore or concentrate is preferably initially used followed by minor amount of the other neutralisation agent to achieve the required free acid concentration in the leach liquor.

A solid-liquid separation is then conducted of the first liquor neutralised slurry to provide a solid 135 and an acid neutralised leach liquor 136 which is fed to a Fe powder reduction stage 140. Where feed ore is used, the solid 135 is fed to the leaching stage 120 to extract undissolved value metals from that solid. iii) In the Fe powder reduction stage 140, the acid neutralised leach liquor 136 is reduced at 45 to 60 °C under nitrogen blanket through the addition of metallic Fe powder 141 to convert ferric chloride present in the liquor to ferrous chloride. The step is conducted to achieve an oxidation-reduction potential (ORP) of the liquor below 100 mV. A solid-liquid separation is then conducted of the produced reduced leach liquor to remove any unreacted solid Fe powder 145 and to obtain a reduced liquor 146. The unreacted solid Fe powder 145 can be recycled for use in the reduction stage 140. iv) The reduced liquor 146 is then fed into an aluminium and chromium removal stage 150 in which chromium and aluminium are precipitated from the reduced liquor 146 under nitrogen blanket by raising pH of the reduced liquor 146 to ~3 to 4, preferably at 3.5 at 60 to 90 °C by adding limestone or lime as the neutralising agent 151. A solid-liquid separation is then conducted of the produced chromium (Cr) and aluminium (Al) removed slurry to separate precipitated solid 155 and the Al/Cr removed liquor 156. v) Fe is then removed/ recovered from the Ni/Co bearing leach solution prior generating the Ni/Co bearing mixed hydroxide solid precipitate. As shown in Figure 1 , the Al/Cr removed liquor 156 is fed to an iron recovery stage 160 in which iron is precipitated from the Al/Cr removed liquor 156. Figure 1 illustrates this stage as a single process step which includes the addition of limestone or lime as the neutralising agent 161 and also the addition of an oxidant such as air 162 (an oxidant for the precipitation reaction). As shown in Figure 1 A (described in more detail below), this iron recovery stage typically comprises a number of process steps in practice, in order to achieve an effective recovery and separation of nickel and cobalt from the iron content from the Al/Cr removed liquor 156 (a Ni/Co bearing leach solution). Figure 1 A shows that a multistage Fe removal process is preferably used to substantially remove the Fe content from the reduced leach liquor (the Ni/Co bearing leach solution). The detail of this iron recovery stage 360 is described in more detail below. Iron recovered from this stage 160 is as an iron precipitation solid 165 mostly comprises magnetite, goethite and/or akageneite. However, magnetite is the most preferable precipitated from this stage. This general iron removal step 160 produces a recovered Fe solid

165 and a Fe removed liquor 166. vi) Again, following the general process illustrated in Figure 1 , the Fe removed liquor 166 is then fed into a nickel and cobalt recovery stage 170, in which Ni and Co is precipitated in a precipitation vessel as a mixed hydroxide from Fe removed liquor

166 by adding lime or MgO as the precipitating agent 171 to reach an equilibrium reaction pH of 7 to 9, preferably about 8.6, and a temperature of 50 to 70 °C, preferably about 60 °C. A solid-liquid separation is then conducted of the resulting Ni/Co mixed hydroxide slurry to separate a Ni/Co mixed hydroxide precipitated solid 175 and a Ni/Co removed liquor 176. vii) The Ni/Co removed liquor 176 can then fed into a Mg/Mn removal stage 180, in which magnesium and/or manganese is precipitated from the liquor at a pH ~8 to 10 and at a temperature of 60 to 90 °C using lime as a neutralising agent 181 and air (as illustrated) or oxygen or hydrogen peroxide (H2O2) as an oxidant 182. The precipitated Mg/Mn removal solid 185 will comprise Mg(OH)2 and a mixture of Mn- oxide/hydroxide/oxy-hydroxide. A solid-liquid separation is then conducted of the produced Mg/Mn removed slurry to separate precipitated solid 185 and the Mg/Mn removed liquor 186 which will be mainly calcium chloride solution. In some embodiments, for example as illustrated in Figure 1 A, the Ni/Co removed liquor 176 may be fed directly to the evaporation state 190 described below, with a secondary process stream being processed in the Mg/Mn removal stage 180. viii) The Mg/Mn removed liquor 186 having mainly calcium chloride is fed into an evaporation stage 190 to evaporate a water content to get a suitable calcium chloride concentration prior to the subsequent HCI regeneration stage 200. The produced evaporated calcium chloride liquor 196 typically has a concentration below its saturation concentration to avoid calcium chloride crystallisation in the liquor. Evaporation is typically achieved by heating/ boiling the Mg/Mn removed liquor 186 through the addition of heat 191 and produces steam/ water vapour 195 and an evaporated calcium chloride liquor 196. ix) The evaporated calcium chloride liquor 196 is reacted with concentrated sulphuric acid (98% w/w) 201 in regeneration stage 200 at a stoichiometric ratio of calcium chloride to sulphuric acid, to produce the leaching step concentration (20 to 25% w/w) hydrochloric acid and precipitate calcium as one or more of gypsum, hemihydrate, or anhydrite compounds. The reaction can be performed at a temperature range of 30 to 90 °C under atmospheric conditions, and preferably at a temperature of 70 to 90 °C. In some embodiments, the reaction between the evaporated liquor 196 and concentrate sulphuric acid 201 is preferably performed in a temperature range of 80 to 85 °C aiming to precipitate anhydrite only. A solid-liquid separation is then conducted of the produced regenerated hydrochloric acid slurry to separate precipitated solid 205 and hydrochloric acid liquor 206, which is recycled back to the ore leach stage 120 for use as the lixiviant solution 105.

[080] In some embodiments, the process can have a sulphuric acid production plant from elemental sulphur (not included in the flowsheet given in Figure 1 ) to produce concentrated sulphuric acid (98% w/w) for the lixiviant (HCI) regeneration step. The inclusion of a sulphuric acid production plant can give significant energy credit for power generation and heat required for various steps of the process.

[081] It should be appreciated that recovery of chromium and aluminium from the Al/Cr precipitated solid 155 can be conducted by any suitable method known in the art, for example by leaching using either a caustic or HCI solution, followed by precipitation and optional calcination steps. In particular embodiments, Al can be recovered from Al/Cr precipitate using Bayer process (caustic leaching) where Al goes in solution and Cr solid remain in residue. The Cr residue after Al separation, can be treated for Cr recovery either through hydro or pyrometallurgy. By HCI route, both Al and Cr dissolves as AlCh and CrCh. In the leach solution, Cr need to oxidise from Cr(lll) to Cr(VI) as chromate/dichromate which is soluble and precipitate Al as AI(OH)3 solid by increasing pH to ~3 - 5.

[082] The details of the process steps comprising the iron recovery stage 160 in Figure 1 are illustrated in the process flow diagram illustrated in Figure 1 A. It should be appreciated that similar features and elements in Figure 1 A have been given the same reference numeral as used in Figure 1 plus 200. It is to be understood that the above description of similar elements in Figure 1 equally apply for those similar elements in Figure 1 A. i) As with Figure 1 A, the process 300 starts with an ore leaching step 320 of the nickel and cobalt bearing lateritic ore, as described above in relation to Figure 1 . ii) The excessive free acid (HCI) remaining in the leach liquor 326 after leaching is preferably neutralised in neutralisation stage 330 using a neutralisation agent 331 is added to minimise the free acid concentration in the leach liquor to approximately 10 g/L or less as described above. A solid-liquid separation is then conducted of the first liquor neutralised slurry to provide a solid 335 and an acid neutralised leach liquor 336 which is fed to a Fe powder reduction stage 340. Where feed ore is used, the solid 335 is fed to the leaching stage 320 to extract undissolved value metals from that solid. iii) In the Fe powder reduction stage 340, the acid neutralised leach liquor 336 is reduced at 45 to 60 °C under nitrogen blanket through the addition of metallic Fe powder 341 to convert ferric chloride present in the liquor to ferrous chloride. A solidliquid separation is then conducted of the produced reduced leach liquor to remove any unreacted solid Fe powder 345 and to obtain a reduced liquor 346. The unreacted solid Fe powder 345 can be recycled for use in the reduction stage 340. iv) The reduced liquor 346 is then fed into an aluminium and chromium removal stage 350 in which chromium and aluminium are precipitated and then the precipitated solid 355 is separated from the liquid/slurry leaving an Al/Cr removed liquor 356 as described above. v) Fe is then removed from the Al/Cr removed liquor 356 in a multistep iron removal stage 360 (Figure 1 A) prior generating the Ni/Co bearing mixed hydroxide solid precipitate 375. As shown in Figure 1 A, the iron recovery stage 360 (the broken line box in Figure 1 A) comprises a multistage Fe removal process which aims to substantially remove the Fe content from the Al/Cr removed liquor 356 (the Ni/Co bearing leach solution).

(a) In a first step, Ni/Co/Fe precipitation is performed by raising the pH of the reduced leach liquor to 4.5 to 5.5 by adding a neutralising agent, for example lime 501 to the Al/Cr removed liquor 356 at a reaction temperature of 60 to 90 °C, preferably at around or at 75 °C. A solid-liquid separation is then conducted to provide a solid Ni/Co/Fe precipitate 506 and a Ni/Co/Fe removed liquor 505. The Ni/Co/Fe removed liquor 505 is fed to a Fe recovery stage 570 (described below).

(b) The Ni/Co/Fe solid 506 is subjected to one or more acid leaching stages (designated as pH leaching stages in Figure 1 A) - illustrated as three pH leaching stages 510, 520, 530 in Figure 1 A designed to preferentially dissolve nickel and cobalt from the Ni/Co/Fe precipitation solid. Each of these pH leaching stages 510, 520, 530 is conducted with a lixiviant comprising 20 to 25 % w/w HCI solution, preferably 20 % w/w HCI solution and at a temperature of 55 to 65 °C, preferably around 60 °C. Each pH leaching stages 510, 520, 530 is preferably carried out at atmospheric (ambient) pressure.

• pH leach-1 : The Ni/Co/Fe solid 506 is subjected to a first pH leach stage 510 in which the pH is controlled to between 5.4 and 5.7, preferably 5.5 to 5.6 to maximise dissolution of iron(ll) from the nickel/cobalt/iron containing solid with a minimum dissolution of Ni. The leachate 515 from that step is then fed to an ion exchange step (described below). The leach solids 516 are then subjected to a second pH leach stage 520 in which the pH is controlled to between 5.4 and 5.7, preferably 5.5 to 5.6. • pH leach-2: The leachate 525 from that second pH leach stage 520 is then fed to an oxidation step 540.

• pH leach-3: The leach solids 526 are then subjected to a third pH leach stage 530 in which the pH of the reaction is below 1 , preferably a pH of 0.7 to 0.8 aimed at dissolving any remaining nickel and cobalt content from the leach solids 526. The leachate 535 from that third pH leach stage 530 is also fed to the oxidation step 540. The leach solids 536 from the third pH leach stage 530 substantially comprises un-leached Fe-oxide solid. It should be understood that each leach stage may also include a solid-liquid separation step to separate the leach solids from the leachate. For example, a nickel/cobalt-rich solution (leachate 525, 535) is obtained in the second and third pH leaching stages 520, 530. The residue (undissolved leach solids) may be in the form of a suspension.

The leach mixture is fed to a solid/liquid separation step to effect separation of the acid leach liquor from the leach solids, for example leach residue and other gangue. Techniques for such separation are known in the art for example using a pressure or vacuum filter, counter-current decantation, thickener or centrifuge.

(c) As illustrated in Figure 1 A, the nickel and cobalt content of the iron(ll) rich leachate 515 from the first pH leach stage 510 is fed to an ion exchange (resin treatment 560). Ion exchange is conducted using an ion exchange resin suitable for Ni and Co separation from the iron(ll) rich leachate 515 such as Lewatit MonoPlus TP220 available from Lanxess. This ion exchange step produces a Ni and Co bearing elute liquor 566 which is fed into the iron(ll) oxidation step 540, and an iron bearing raffinate 565. That iron bearing raffinate 565 is preferably fed into a further Fe removal/ recovery step (see below).

(d) The leachate 525, 535 undergo an iron(ll) oxidation step 540 to convert any iron(ll) content to iron(lll). Here, an oxidant, such as air, oxygen and/or hydrogen peroxide 541 is added to the acid leach liquor at a temperature of 50 to 70 °C, thereby oxidising an iron(ll) content to iron(lll) in the acid leach liquor, to produce an oxidised acid leach liquor 545. (e) The oxidised acid leach liquor 545 is fed into a final iron removal step 550 in iron(lll) is precipitated from the oxidised acid leach liquor 545 at a temperature of 50 to 70 °C through the addition of limestone or lime as the neutralising agent 551 to change the solution pH to ~2 to 4, and preferably a pH of 3.0. The iron precipitation solid 555 mostly comprises goethite type Fe oxy-hydroxide and/or akageneite. However, goethite is the most preferable precipitated solid from this stage. A solid-liquid separation is then conducted of the produced iron removed slurry to separate the precipitated Fe solid 555 and the Fe removed liquor 556. vi) The Fe removed liquor 556 is then fed into a nickel and cobalt recovery stage 370, in which Ni and Co is precipitated in a precipitation vessel as a mixed hydroxide from Fe removed liquor 556 by adding lime or MgO as the precipitating agent 371 to reach an equilibrium reaction pH of 7 to 9, preferably about 8 to 9, more preferably about 8.6, and a temperature of 50 to 70 °C, preferably about 60 °C. A solid-liquid separation is then conducted of the resulting Ni/Co mixed hydroxide slurry to separate a Ni/ Co mixed hydroxide precipitated solid 375 and a Ni/Co removed liquor 376. vii) The iron bearing raffinate 565 from the ion exchange stage (resin treatment 560) and the Ni/Co/Fe removed liquor 505 from the Ni/Co/Fe precipitation step 500 is fed into a further Fe recovery stage 570. In this stage, iron is precipitated from the liquor mixture (iron bearing raffinate 565 and Ni/Co/Fe removed liquor 505) at a temperature of 70 to 90 °C through the addition of limestone or lime as the neutralising agent 571 in the presence of air 572 (an oxidant for the precipitation reaction) to change the solution pH to ~3 to 5, and preferably a pH of 3.5 to 4.5. Again, the iron precipitation solid 575 mostly comprises magnetite, goethite and akageneite. However, magnetite is the most preferable precipitated solid from this stage. A solidliquid separation is then conducted of the produced iron removed slurry to separate the precipitated Fe solid 575 and the Fe removed liquor 576. viii) The Fe removed liquor 576 is fed into an evaporation stage 580 to evaporate a water content to concentrate the value metal content prior to the Mg/Mn removal stage 380. Evaporation is typically achieved by heating/ boiling the Fe removed liquor 576 through the addition of heat 581 and produces steam/ water vapour 585 and an evaporated liquor 586. ix) The evaporated liquor 586 can then fed into a Mg/Mn removal stage 380, in which magnesium and/or manganese is precipitated from the evaporated liquor 586 at a pH ~8 to 10 and at a temperature of 60 to 90 °C using lime as a neutralising agent 381 and air (as illustrated) or oxygen or hydrogen peroxide (H2O2) as an oxidant 382 The precipitated Mg/Mn removal solid 385 will comprise Mg(OH)2 and a mixture of Mn- oxide/hydroxide/oxy-hydroxide. A solid-liquid separation is then conducted of the produced Mg/Mn removed slurry to separate precipitated solid 385 and the Mg/Mn removed liquor 386 which will be mainly calcium chloride solution. x) The Mg/Mn removed liquor 386 having mainly calcium chloride and the Ni/Co removed liquor 376 is fed into an evaporation stage 390 to evaporate a water content to get a suitable calcium chloride concentration prior to the subsequent HCI regeneration stage 400. The produced evaporated calcium chloride liquor 396 typically has a concentration below its saturation concentration to avoid calcium chloride crystallisation in the liquor. Evaporation is typically achieved by heating/ boiling the Mg/Mn removed liquor 386 through the addition of heat 391 and produces steam/ water vapour 395 and an evaporated calcium chloride liquor 396. xi) As described above in relation to Figure 1 , the evaporated calcium chloride liquor 396 (Figure 1 A) is reacted with concentrated sulphuric acid (98% w/w) 401 in regeneration stage 400 at a stoichiometric ratio of calcium chloride to sulphuric acid, to produce the leaching step concentration (20 to 25% w/w) hydrochloric acid and precipitate calcium as one or more of gypsum, hemihydrate, or anhydrite compounds. A solid-liquid separation is then conducted of the produced regenerated hydrochloric acid slurry to separate precipitated solid 405 and hydrochloric acid liquor 406, which is recycled back to the ore leach stage 320 for use as the lixiviant solution 305.

[083] Figures 1 and 1 A exemplifies the use of limestone or lime as neutralising/ precipitation agent 151 , 161 , 171 , 181 , 351 , 371 , 381 , 501 , 551 , 571. However, it should be appreciated that if MgO is added for neutralisation/ precipitation for these steps 150, 160, 170, 350, 370, 500, 550 it will form MgCh in the relevant liquor. For example, in some embodiments MgO is used as precipitating agent 171 , 371 in the Ni/Co mixed hydroxide precipitation step 170, 370. Therefore, where MgO is used in the process 100, 300, the process liquors will comprise a MgCh bearing solution. Any Mg content will need to be removed using the described Mn/Mg removal steps 180, 380 in the process 100, 300. However, in these steps MgO should ideally be regenerated from the Mg-removal steps 180, 380 and the regenerated solid is recycled back to the relevant neutralisation/ precipitation steps 150, 160, 170, 350, 370, 500, 550.

[084] The following process steps could be used after the Ni/Co mixed hydroxide precipitation step 170, 370 when MgO is used a neutralising agent:

[085] If Mn is present in the liquor obtained after Ni/Co mixed hydroxide precipitation step 170, 370, then the Ni/Co mixed hydroxide precipitation step 170, 370 liquor is fed to the Mn and Mg removal stage 180 and 380 and the Mn-removal and Mg-removal steps 180, 380 are preferably performed separately (i.e. as two separate steps) using lime as the neutralising agent. In this process: a) First a Mn-removal step will be performed using the Ni/Co removed liquor 176, 376 in the presence of an oxidant (for example air, oxygen, H2O2) at pH between 8 and 9 and 60 to 90 °C by adding lime to precipitate Mn as oxide/hydroxide/oxy- hydroxide or as a mixture. Solid-liquid separation will be performed to obtain a Mn- removed liquor and Mn-rich precipitate. b) Mg removal can then be performed after Mn-removal using Mn-removed liquor at pH 9 to 10 at and 60 to 90 °C by adding lime to precipitate Mg as Mg(OH)2 and the liquor will mainly have CaCh (for HCI regeneration). Mg(OH)2 obtained after solidliquid separation will be subjected to calcination at -400 to 600 °C to regenerate MgO for recycling into the appropriate neutralisation/ precipitation step or steps that use MgO. c) In the embodiments, where Mn is not present in the Ni/Co removed liquor 176, 376, only a single Mg-removal step will be required as explained above.

[086] Each of the described stages of the process illustrated in Figures 1 and 1 A can be performed in suitable process vessels suitable for leaching, precipitation, boiling, mixing and the like process steps. As previously noted, no specialised material of construction is required for the reactor design criteria in this process. Standard fibre glass and/or high-density polyethylene (HDPE) and/or polypropylene (PP) tanks can be used to meet the reactor/equipment requirement. Compared to prior art pyrolysis or high temperature hydrolysis technique, the lixiviant regeneration in the present invention is a simpler process where energy requirement is low and the material of construction is not critical (i.e. not requiring high temperature and corrosion resistant materials).

[087] It should be appreciated that the solid/liquid separation for all the stages can be operated using any suitable method and process equipment. Techniques for such separation are known, for example using a pressure or vacuum filter, counter-current decantation, thickener or centrifuge. In particular embodiments, solid/liquid separation can be operated using a thickener operation. Washing stages will only be applicable for the solids that are going out of the circuit such as: i) final leach solid from leach; ii) Ni/Co mixed hydroxide precipitate; iii) Al/Cr precipitate; iv) Fe precipitate; v) Mg/Mn removal solid; and vi) gypsum solids. It would not be essential to wash an intermediate solid which is moved from one stage to another inside the process as the respective stages of the process should be able to accommodate any entrained liquor coming with the intermediate solids.

[088] The product from this process is a mixed Ni/Co hydroxide solid, along with one or more additional value metals selected from chromium, aluminium, iron, magnesium or manganese. The mixed Ni/Co hydroxide solid can be further processed to recover the separate nickel and cobalt value metals using any number of nickel and cobalt separation processes known in the art.

[089] Compared to prior art processes, the process of the present invention comprises:

(A) Iron removal/ recovery through iron precipitation where iron may be precipitated as goethite (a-FeOOH), akaganeite ([3-FeOOH), magnetite (FeaC ), or mixture thereof, or preferably as magnetite only from the un-leached solid Fe 536 recovered following pH leach stages and further Fe recovery stage 570. Most prior art processes mainly focus on expensive techniques of pyrolysis or high temperature hydrolysis (pyro-hydrolysis) of iron as hematite (Fe2Oa) only. (B) The HCI regeneration from a CaCh solution using concentrate H2SO4 (at least 98% w/w) to produce 20 to 25% w/w HCI. In prior art processes, the HCI regeneration is generally focussed though expensive pyrolysis or high temperature iron hydrolysis techniques.

(C) The HCI regeneration step focusses on only 20 to 25% w/w HCI from CaCh solution by reacting with concentrated H2SO4 (at least 98% w/w) at 30 to 90 °C, and preferably more than 70 °C (only if required) to produce mainly anhydrite calcium sulphate or as a mixture of anhydrite, hemi-hydrate and di-hydrate calcium sulphate.

(D) The Ni/Co/Fe precipitation step to generate a Ni/Co/Fe precipitated solid and the dissolution of Ni and Co from the Ni/Co/Fe precipitated solid through one or more pH (acid) leaching stages. There is no data reported in the literature to precipitate Ni/Co//Fe together from laterite leach solution for further separation of Ni/Co from a Ni/Co/Fe bearing precipitated solid.

EXAMPLES

[090] Aspects of the process of the present invention is illustrated by the following examples:

EXAMPLE 1 - Preliminary Leach Testing

1. Laterite ores

[091] Three different types of laterite ores of West Australian origin were used in this leaching investigation. These were smectite, saprolite and limonite type ores. The chemical analyses of these ores are given in Table 1 which was obtained by fusing the sample ore with lithium metaborate, dissolving the fused mass in dilute HCI followed by the liquor was analysed using ICP-OES technique. Smectite and limonite ores were of high-grade having 1 .43% and 1 .78% Ni, respectively with 0.1 1% Co in both the ores. Saprolite ore gave relatively lower Ni (1 .1 %) and Co (0.03%) analyses with high Mg (~9%). The Fe and Si analyses for the smectite and saprolite ores were -16.5 to 19.5% and 20 to 26%, respectively. Limonite ore reported very high silica (Si ~17%) along with other major elements of ~29% Fe, 2.4% Al and 3.1 % Mg. Sodium analysis for limonite sample was also very high (~1%) due to presence of halite (NaCI) mineral in the ore.

[092] Table 1 . Analyses of the three different laterite ores.

[093] An x-ray powder diffraction (XRD) analysis of the smectite ore reported nontronite as the major mineral phase with the presence of goethite, hematite, maghemite, quartz and kaolinite phases. Antigorite was the major mineral phase for saprolite ore with a moderate amount of nontronite phase along with the minor phases of maghemite and hematite phases. Goethite, maghemite and quartz were the major mineral phases for limonite ore with the minor mineral phases of nontronite, kaolinite, hematite, and halite.

2. Leaching procedure

[094] Laterite leaching tests were conducted in 2 L and 5 L baffled glass reactors using 20 to 24.5% w/w HCI concentration at 90 °C with 20 to 25% w/w pulp density for 2 to 4 h duration. Each reactor was fitted with a glass lid connected to a condenser. For the initial tests, a required amount of HCI solution and ore were taken in a 2 L reactor and the reactor was placed in an oil (PEG 400) bath. Once the reaction temperature was attained (~90 °C), a sample was collected (zero hour sample), and the reaction was continued for 4 hours collecting samples at every hour. Samples were filtered, and the solids were repulped/washed with deionised (DI) water. At the end of the reaction the final slurry was filtered, cake was washed thoroughly and dried in an oven at 60 °C.

[095] Bulk leach tests were performed in a 5 L reactor for 2-3 h duration without sampling. Required amounts of ore and HCI solution were taken in the reactor and heated to the test temperature. At the end of the test the bulk slurry was filtered in a pressure filter. The bulk cake was repulped three times with one-time initial cake volume of DI water and filtered in the filter press. The third repulp cake was dried in the oven at 60 °C until a constant weight was attained. The solid, final liquor and wash liquors were analysed for Ni, Co, Fe, Al, Mg, Cr, Mn, Si, Zn, Cu, Na, K and Ca using Xray Diffraction analysis. The free acid was analysed in the liquor samples.

[096] XRD measurements were carried out using a PANalytical high resolution multipurpose powder diffractometer (Empyrean) applying Co Ka radiation and operating at 45 kV and 40 mA. A PIXcel3D proton counting X-ray detector was used to collect the data over an angular range of 10-90° 29 with a continuous scan mode for 1 h. The XRD data was interpreted with XPLOT and HighScore Plus software using the ICDD and ICSD database. The same procedure adopted for analysis of the liquor as used for the solid. For liquor, the liquors were diluted appropriately, and the elemental analysis was performed by ICP-OES.

[097] The final liquor and wash liquors from the bulk leach tests were stored separately in the air-tight containers.

3. Leaching results

3.1 Initial leaching results

[098] Initial leaching tests were performed at 90 °C to examine the leaching efficiency of smectite, saprolite and limonite ores at 20% w/w HCI and 20% w/w pulp density for 4 h. The extraction behaviour of Ni, Fe, Co, Mn Al and Mg are given in Figures 2 to 4. Most of the Ni and Fe extractions from these ores took place within first hour of the reaction and gave 96 to 99% Ni and Fe extraction by 2 h for smectite and saprolite ores (Figure 2). Leaching of limonite was slightly slower compared to smectite and saprolite ores where -95% Ni extraction was obtained at 3 h with -88% Fe dissolution. Continuing reaction to 4 h for limonite ore did not improve the Ni and Fe extractions significantly. Lower Fe leaching for limonite was possibly due to lower free acid concentration remained in the final liquor (-47 g/L) at the end of the reaction (4 h) compared to the free acid remained in the liquors of smectite (87 g/L) and saprolite (65 g/L) ores.

[099] Most of the Co and Mn leaching took place during heating period (>89%) from all the three ores giving >95% Co and Mn extractions within one hour of reaction (Figure 3). These test results indicate that 2 h reaction time for smectite and saprolite ores and 3 h reaction time for limonite ore were sufficient to achieve >95% Ni and Co extractions under the leach conditions of 20% w/w HCI concentration and 20% w/w pulp density.

[100] The dissolution of Al and Mg were 32 to 74% during heating which increased slowly up to 3 h with nil/minor further increase to 4 h (Figure 4). Saprolite gave highest Al dissolution (-91%) and lowest Mg dissolution (70%) within 3 h among the three ores used. Maximum dissolution of Mg was from smectite ore (-97%) and minimum dissolution of Al was from limonite ore (-72%).

3.2 Leaching at higher acid concentration and pulp density

[101] Based on the initial test results, further tests were performed at higher pulp density (25% w/w) and higher HCI concentration (24.5% w/w) with all the three ores keeping the other conditions constant. The leach extractions are given in Figures 5 to 7 for Ni, Fe, Co, Mn, Al and Mg which were found to be very similar to the leach extractions obtained at 20% w/w pulp density and 20% w/w HCI leaching. This confirms that 94 to 98% Ni and 97 to 99% Co extractions are possible to achieve for 2 h leaching of smectite and saprolite ore and 3 h leaching of limonite ore at 25% w/w pulp density.

3.3 Bulk leaching

[102] Bulk leaching was performed with all the three ores using 1 .174 kg ore material (dry basis at 60 °C) per test in 5 L reactor at 24.5% w/w HCI, 25% w/w pulp density and 90 °C. Leaching time for smectite and saprolite was 2 h and for limonite was 3 h. The leach extractions for these bulk tests are given in Table 2. The extraction of Ni, Co, Fe, Al, Mg and Mn were found to be consistent with the extractions obtained from the previous tests with 20% w/w and 25% w/w pulp densities.

[103] Table 2 shows -97 to 99% Ni/Co extraction with -97% Fe dissolution from smectite and saprolite ores whereas leach efficiency for limonite ore was lower for Ni (-94%) and Fe (88%). The free acid analyses in the final liquors were 80 g/L, 53 g/L and 27 g/L for smectite, saprolite and limonite, respectively. The lower Ni and Fe leaching for limonite ore may be attributed due to the lower free acid concentration towards the end of the reaction which was not very effective to dissolve the higher crystalline fraction of the iron oxide minerals remained in the unreacted solid. The Al, Cr and Mn dissolution for these ores were -70 to 86%, -37 to 49% and -97 to 98%, respectively. The Mg leaching was -83 to 95% for smectite and limonite whereas saprolite gave only 61 % leaching. The lower Mg leaching for saprolite was due to a higher proportion of antigorite remained unreacted as determined by XRD analysis. The dissolution of silica from these ores was negligible.

[104] Table 2. Bulk leach extraction for smectite, saprolite and limonite ores at 24.5% w/w HCI, 25% w/w pulp density and 90 °C for 2 to 3 h (2 h for smectite and saprolite ores and 3 h for limonite ore).

[105] The leach residue and leach liquor analyses of the bulk leach tests are given in Table 3 to 4. Table 3 shows <0.1 % Ni in the leach residues of smectite and saprolite ores, whereas limonite residue reported >0.2% Ni with higher Fe analysis (-6.5%). As silica did not dissolve during leaching, therefore, it was reported in the leach residues (-31 -38%).

[106] Table 3. Leach residue analysis of the bulk leach tests of smectite, saprolite and limonite ores at 24.5% w/w HCI, 25% w/w pulp density and 90 °C for 2 to 3 h (2 h for smectite and saprolite ores and 3 h for limonite ore).

[107] Table 4 shows relatively good Ni tenor 4.2 to 6.5 g/L in the leach liquors obtained from smectite, saprolite and limonite ore leaching. The Co analysis was -0.35 g/L for smectite and limonite ores whereas it was 0.08 g/L for saprolite as feed saprolite ore had very low Co analysis. The analyses of major impurities Fe, Al, Mg, Cr and Mn in the liquor from these ores were -57 to 85 g/L, 4.2 to 6.5 g/L, 6.4 to 19.1 g/L, 0.5 to 1 .5 g/L and 0.8 to 1 .8 g/L, respectively. Minor impurities analyses were <30 mg/L for Si and Cu, <70 mg/L for Zn, <0.17 g/L for K and 0.2 to 3.7 g/L for Na. High Na analysis for limonite leach liquor was due the presence of halite (NaCI) in the limonite ore.

[108] Table 4. Leach liquor analysis of the bulk leach tests of smectite, saprolite and limonite ores at 24.5% w/w HCI, 25% w/w pulp density and 90 °C for 2 to 3 h (2 h for smectite and saprolite ores and 3 h for limonite ore).

4. Conclusions

[109] The HCI leach test results of laterite ores confirm that it is possible to achieve >97% Ni and Co extractions for smectite and saprolite ores and -94% Ni extraction from limonite ore under the leaching conditions of 24.5% w/w HCI, 25% w/w pulp density, 90 °C and 2 h leach time for smectite and saprolite ores and 3 h leach time for limonite ore. Nickel analysis in the leach residue was <0.1 % for smectite and saprolite ores and -0.23% for limonite ore.

EXAMPLE 2 - Leaching and Value Metal Recovery Experiments

1. Bulk leaching of limonite and washing of the leach cake

[1 10] A bulk leach test was performed using 0.98 kg limonite ore material in a 5 L reactor at 23.9% w/w HCI, 21 .3% w/w pulp density and 90 °C for 3 h. Analysis of the ore, leach extraction, leach liquor and residue analyses are given in Table 5. The leach extraction for the limonite ore was -96.5-98% for Ni, Co, and Mn, 93% for Fe, -72% for Al, -87% for Mg and -67% for Cr with a liquor analysis of 5 g/L Ni, 0.27g/L Co, -69 g/L Fe, 4.8 g/L Al, 8.1 g/L Mg, -1 .3-1 .4 g/L Cr and Mn. The free acid analysis in the leach liquor was 59.2 g/L. The leach cake analysis reported 0.16% Ni, 0.01 % Co, 4.4% Fe, -0.5-1.6% Cr/Mg/AI and -34% Si in the solid. [1 1 1] Table 5. Analyses of limonite ore, leach residue, leach liquor and percentage metals extraction for the bulk leach test at 23.9% w/w HCI, 21.3% w/w pulp density and 90 °C for 3 h.

[1 12] The bulk leach slurry was pressure filtered to generate wet filter cake which was repulped with equal amount of deionised (DI) water to the wet cake volume. First repulped slurry was filtered to obtain the wash-1 liquor and wash-1 cake. This process was repeated 4 times to generate wash liquors from each repulp. The wash liquors analyses are given in Table 6. The metal concentration in the wash liquors gradually decreased with the subsequent washing stages giving -0.17 g/L Ni, -2.4 g/L Fe and 0.17-0.29 g/L Al/Mg in Wash-4 liquor. The Wash-1 liquor reported high metal analysis -1 .7 g/L Ni, 0.1 g/L Co, -25 g/L Fe, -3 g/L Mg and -0.5 g/L Cr/Mn. Due to high metal analysis in the Wash-1 liquor, it was mixed with the leach liquor prior neutralising the free acid in the neutralisation step.

[1 13] Table 6. Repulp/wash liquors analyses for the wet leach cake. 2. Neutralisation of leach/wash-1 mixed liquor

[1 14] The purpose of the neutralisation step was to reduce the free acid in the leach/Wash-1 mixed liquor to <10 g/L by using laterite ore prior using the liquor in the Fe powder reduction stage. The advantages of the ore neutralisation are - i) reducing free acid in the liquor, and ii) partial leaching of the ore to increase the Ni tenor in the liquor.

[1 15] The neutralisation test was performed using 3.9 L of the mixed solution and adding 0.55 kg limonite ore material in a 5 L reactor at 10.5% w/w pulp density and 90 °C for 2 h. The metal extraction was -49% Ni, 86% Co, 27% Fe, 28% Al, 44% Mg, 17% Cr and 88% Mn. The analyses of feed and final liquors are given in Table 7. The final liquor analysis was 5.1 g/L Ni, 0.33 g/L Co, -70 g/L Fe, -4.4 g/L Al, 7.8 g/L Mg, ~1.2 g/L Cr, -1.8 g/L Mn, 2.7 g/L Na and 0.1 -0.3 g/L K/Ca. The residue generated from the neutralisation test can be recycled to the ore leaching stage to extract the remaining metal values.

[1 16] Table 7. Feed and final liquor analysis of the ore neutralisation test performed with 3.9 L of leach/Wash-1 mixed solution adding 0.55 kg limonite ore at 10.5% w/w pulp density and 90 °C for 2 h.

3. Fe(lll) reduction of the neutralised liquor

[1 17] The Fe in the ore neutralised liquor is present as Fe(lll) which is required to reduce to Fe(ll) for further downstream processing. The ore neutralised liquor having 9.3 g/L free acid (Table 7) was further neutralised with limestone to reduce the free acid concentration to <1 g/L prior Fe(lll) reduction.

[1 18] The Fe(lll) in the limestone neutralised liquor was reduced to Fe(ll) using Fe metal powder. For a typical test, the Fe ( 111) reduction test was performed at 60 °C using 3.2 L of neutralised liquor adding 1.17 times stoichiometric requirement of Fe powder under a nitrogen blanket to prevent the aerial oxidation of Fe(ll). The pH and oxidationreduction potential (ORP) profiles are given in Figure 8 which shows an increase of pH (to 1 .81 ) and decrease of ORP (to -291 mV) with time. There was a loss of -2% Ni in the solid which possibly occurred due to the adsorption of Ni on the minor Fe(lll) precipitate that formed by aerial oxidation of Fe(ll) during bulk slurry handling and filtration. The final liquor pH and ORP were 2.34 and 251 mV, respectively. However, this Ni loss is recoverable by dissolving the precipitate in HCI solution and recycling the liquor to ore neutralisation stage. The Fe concentration [as Fe(ll)] in the reduced liquor was -95 g/L. The analyses of the feed and final liquors for the Fe reduction test are given in Table 8.

[1 19] Table 8. Feed and final liquor analysis of the Fe(lll) reduction test at 60 °C using 1.17 times stoichiometric addition of Fe powder.

[120] The reduced liquor was treated for Al and Cr removal at 60 °C under nitrogen blanket to precipitate both Al and Cr together by increasing the pH with limestone addition.

4. Aluminium and chromium removal from the reduced liquor

[121] Aluminium and chromium removal from the Fe(lll) reduced liquor can be performed by precipitating the Al and Cr as hydroxides at -60-90 °C by raising the pH of the liquor up to pH 4 using limestone slurry. For a typical test, Al and Cr removal was performed using 3.5L of reduced liquor having 4.5 g/L Ni, 0.28 g/L Co, -95 g/L Fe, 4.2 g/L Al, -1 g/L Cr, 7.2 g/L Mg, -1 .5 g/L Mn and -5 g/L Ca, at 60 °C by raising the pH of the liquor to -3.6 under nitrogen blanket adding limestone slurry (-31 % w/w). Almost 98% Al and Cr precipitated along with -1 % Fe during the reaction giving 74 mg/L Al and 20 mg/L Cr in the final liquor. The Ni loss during the precipitation was -1.3% whereas Co loss was negligible, (-0.1 %). The Ni, Co, Al, Cr, Fe and Ca analyses in the precipitated solid were 0.32%, <0.01 %, 22.1 %, -5.46%, -4.36% and -0.1 % respectively. The final liquor analysis reported 4.1 g/L Ni, 0.25 g/L Co, -84 g/L Fe, -6.7 g/L Mg, 1 .28 g/L Mn and 11 g/L Ca.

5. Nickel, cobalt and iron precipitation from the Al/Cr removed liquor

[122] As outlined for the general process flow diagram (Figure 1 ), Fe is removed first from the Ni/Co bearing laterite leach solution prior generating the Ni/Co bearing mixed hydroxide intermediate. However, in practice this process step comprises a multistep process as a significant Ni and Co loss was found to occur when a neutralising agent (lime/ limestone) was added with an oxidant during a single Fe removal stage which had led to precipitate both Ni and Co with Fe from the high Fe(ll) bearing Al/Cr removed liquor. The multistep process steps are illustrated in Figure 1 A as described previously. Here, a Ni/Co/Fe precipitation step 500 is conducted before a combination of pH (acid) leach steps (510, 520, 530), ion exchange (560) and Fe-removal steps (540, 550) are used to remove Fe from the process liquid.

[123] For experimental purposes, the Ni/Co/Fe precipitation was performed by raising the pH of the Al/Cr removed liquor to 4.5 to 5.5 (preferably 4.8 to 5.3) by adding lime slurry at 60 to 90 °C (preferably at 70 to 80 °C and most preferably at 75 °C).

[124] An initial Ni/Co/Fe precipitation was performed using -1 L of the Al/Cr removed liquor having 4.1 g/L Ni, 0.26 g/L Co, 94 g/L Fe, 7.1 g/L Mg, 1 .35 g/L Mn, 2.6 g/L Na and 12.3 g/L Ca, at 75 °C by adding 15.5% w/w lime slurry. Figure 9 shows the precipitation behaviour of Ni, Co and Fe which increased with time due the increase of pH from 4.85 to -5.3 giving 99.6% Ni, 93.2% Co and -85% Fe precipitation at pH -5.3. The final liquor analysis reported 19 mg/L Ni, 13 mg/L Co, 8.6 g/L Fe, 4.7 g/L Mg, 0.88 g/L Mn, 1 .87 g/L Na and 36.3 g/L Ca. The rate of the metal precipitation was found to be in the order of Ni>Co>Fe. The iron in the precipitated solid was reported to be present mainly as iron chloride hydroxide [Fe2(OH)3CI]. The formation of akageneite ([3-FeOOH) and/or magnetite (FeaC ) also occurred in some of the reactions due to partial aerial oxidation of Fe(ll) during the reaction as the reaction was not performed under the nitrogen blanket. [125] A typical bulk Ni/Co/Fe precipitation test was performed using 2.78L of Al/Cr removed liquor at 75 °C by adding 15.9% w/w lime slurry at pH 5.2-5.3 for 105 min. The precipitation of Ni, Co and Fe were 98.3%, 96.8% Co and 88.3% Fe, respectively giving 49 mg/L Ni, 4 mg/L Co and ~7g/L Fe in the final liquor. Partial Mn precipitation (-17.5%) also took place during Ni/Co/Fe precipitation. The precipitated solid was repulped and washed twice to remove the entrained mother liquor and stored as wet cake for further processing. The analyses of the feed and final liquors and the precipitated solid including percentage of metal precipitation are given in Table 9. The major analyses of the precipitated solid were 2.49% Ni, 0.16% Co, 49.2% Fe, 0.12% Mn. This precipitated wet cake was used for Ni/Co extraction through pH leach stages followed by its recovery in the downstream processing as given below.

[126] Table 9. Feed liquor, final liquor and precipitated solid analyses with percentage metals precipitation for the bulk Ni/Co/Fe precipitation test at 75 °C with 15.9% w/w lime slurry addition at pH of 5.2 to 5.3 for 105 min.

6. pH Leaching of the Ni/Co/Fe precipitated solid

[127] Leaching of the Ni/Co/Fe precipitate was performed at 60 °C in three stages - pH leach-1 , pH leach-2 and pH leach-3 using the leach cake from the first stage to the next stage by controlling the pH of the reaction at each stage by adding 20% w/w HCI solution. Details of the pH leach stages are given below:

6.1 pH leach-1

[128] The purpose of the pH leach-1 was to obtain a maximum dissolution of Fe as Fe(ll) with a minimum dissolution of Ni from the Ni/Co/Fe precipitate. Initially a pH leach-1 test was performed to understand the metal dissolution behaviour using the bulk precipitation test solid (wet cake) at 10.1 % w/w pulp density (dry basis) by controlling the pH between 5.7 to 5.2 adding HCI solution. The profile of metal dissolution versus pH is given in - i) Figure 10 for percentage metal dissolution and ii) Table 10 for leach liquor analysis. Figure 10 shows that the metal dissolution increased with the decrease of pH where 53.5% Ni, 84% Co and 75.3% Fe dissolution took place at pH 5.22.

[129] Table 10. Analyses of Ni, Co and Fe in the pH leach-1 liquors at different pH.

[130] As the pH leach-1 liquor will be used for ion-exchange (IX) resin treatment for Ni and Co separation from Fe [present as Fe(ll)] in the liquor, therefore it is intended to keep the Ni concentration ~0.5 to 0.8 g/L (preferably 0.5 to 0.6 g/L) in the pH-1 leach liquor. Based on the liquor analysis, the pH of the reaction for pH leach-1 test was chosen between 5.5 to 5.7 and preferably between -5.5 to 5.6. However, the pH value should not be strictly limited for a reaction and will depend on the lower Ni concentration (preferably 0.5 to 0.6 g/L) to high Fe concentration in the leach liquor that is suitable to run the IX resin treatment.

[131] A bulk pH leach-1 was performed using 603.9 g of bulk precipitation test Ni/Co/Fe wet cake (208.5 dry solid) at 10% w/w pulp density and 60 °C targeting the final pH of the reaction -5.5. The metal dissolution, final liquor analysis and un-leached cake analysis are given in Table 11 . The Ni, Co and Fe dissolution were 20.3%, -42% Co and -42% Fe, respectively. The leach liquor analysis reported -0.59 g/L Ni, 0.073 g/L Co and -23 g/L Fe. The un-leached wet cake from pH leach-1 was used in the pH leach-2 test. Un-leached cake analysis was 3.73% Ni, 0.16% Co and 51 .6% Fe.

[132] Table 1 1. Metal dissolution, final liquor and un-leached cake analyses of pH leach-1 test using bulk precipitation test Ni/Co/Fe wet cake at 60 °C and 10% pulp density adding 20% w/w HCI solution.

6.2 pH leach-2

[133] Similar to pH leach-1 , a bulk pH leach-2 was performed at pH -5.5 using the pH leach-1 wet cake at 60 °C and 10% pulp density adding 20% w/w HCI solution. The analysis of the final liquor and the un-leached cake of pH leach-2 test are given in Table 12. The leach liquor analysis reported -0.71 g/L Ni, 0.08 g/L Co and -19 g/L Fe which indicates that this pH leach-2 liquor could possibly be used for the resin treatment to recover Ni/Co by separating from Fe. However, it was decided to remove the Fe from this typical pH leach-2 liquor as Fe oxy-hydroxide (goethite type) by limestone neutralisation reaction. The un-leached wet cake from pH leach-2 was used for pH leach-3 test. Un-leached cake analysis was 5.21 % Ni, 0.16% Co and 53.2% Fe.

[134] Table 12. Final liquor and un-leached cake analysis of pH leach-2 test using bulk pH leach-1 wet cake at 60 °C, 10% pulp density and pH -5.5 by adding 20% w/w HCI solution. 6.3 pH leach-3

[135] The pH leach-3 was aimed to dissolve remaining Ni and Co from the pH leach- 2 cake by lowering the pH of the reaction to below 1 . Initially, Ni dissolution profile was studied in the pH leach-3 test similar to pH leach-1 , by lowering the pH of the reaction to pH 0.5. The profile of metal dissolution versus pH is given in: i) Figure 1 1 for percentage metal dissolution, and ii) Table 13 for leach liquor analysis. Figure 1 1 shows that -92% Ni and 82% Co dissolved at pH 4.2 and the dissolution slowly increased for Ni and Co with the decrease of pH to -0.7 followed by Ni dissolution decreased with decreasing pH from 0.6 to ~0.5. The decrease of Ni dissolution from pH 0.6 to pH 0.5 was possibly due to very low dissolution of Ni where significant amount of 20% HCI solution was added (-15% of total HCI addition) that diluted the Ni concentration in the liquor (Table 13) affecting metal dissolution percentage.

[136] The Fe dissolution was -58% at pH 4.2 which increased rapidly after pH 2 giving -73% Fe dissolution at pH -0.7 after which Fe dissolution remained nearly similar. The XRD of the pH leach-3 residue reported mainly magnetite phase. This indicates that magnetite dissolution was very slow with 20% w/w HCI concentration at 60 °C with controlled low pH leach and possibly required higher temperature and higher HCI concentration to enhance the magnetite leaching.

[137] The maximum dissolution of Ni was found to be at -0.7 to 0.8 pH giving 4.2 to 4.3 g/L Ni analysis (Table 13), therefore, the pH of 0.75 was decided to be a suitable pH for the bulk pH leach-3 test.

[138] Table 13. Analyses of Ni, Co and Fe in the pH leach-3 liquors at different pH.

[139] A bulk pH leach-3 test was performed using 214.3 g of pH leach-2 wet cake (dry mass 85.6 g) at 60 °C and 10% pulp density by lowering the reaction pH to 0.75 with 20% w/w HCI addition. The metal dissolution in the pH leach-3 test was 93.5% Ni, 77.5% Co and 62.3% Fe. The analysis of the final liquor and the un-leached residue of the pH leach-3 test are given in Table 14. The leach liquor analysis reported 4.2 g/L Ni, 0.12 g/L Co and ~28 g/L Fe. The leach residue analysis was 1.16% Ni, 0.14% Co and 67.4% Fe. The XRD of the leach residue reported mainly magnetite phase. The leach liquor was treated for Ni and Co recovery after Fe removal by limestone neutralisation. The iron rich pH leach-3 residue can be considered as a saleable iron by-product.

[140] Table 14. Final liquor and un-leached cake analysis of pH leach-3 test at pH 0.75 using bulk pH leach-2 wet cake at 60 °C and 10% pulp density adding 20% w/w HCI solution.

[141] An overview of the metal dissolution including the solid mass loss in the three stages of pH leaching using Ni/Co/Fe precipitate is given in Table 15 which shows a total of -96% Ni, -93% Co and -87% Fe dissolution from the Ni/Co/Fe precipitate giving -91 % mass loss.

[142] Table 15. Metal dissolution and solid mass loss behaviour of the Ni/Co/Fe precipitated solid during pH leach-1 to pH leach-3 reaction at different pH with 10% pulp density and 20% w/w HCI solution addition at 60 °C.

[143] The processing of the liquors from the three stages of pH leaching was performed in the following way and details are given in the respective sections:

(i) pH leach-1 liquor treated through IX resin to generate Fe bearing raffinate and Ni and Co bearing elute liquor.

(ii) pH leach-2 and pH leach-3 liquors were combined along with the Ni/Co bearing elute liquor from resin treatment for Fe removal by limestone neutralisation. The Ni/Co elute liquor reported -1 g/L Fe that was required to remove. For this reason, elute liquor was mixed with pH leach-2 and pH leach-3 liquors for Fe removal treatment.

7. Ion exchange (IX) resin treatment of pH leach-1 liquor

[144] A preliminary study was performed with few different ion exchange resins such as Puralite S903, Dowex M4195, Lewatit TP207 and Lewatit TP 220 to identify a resin suitable for Ni and Co separation from the pH leach-1 liquor. TP 220 (Lewatit MonoPlus TP220) was found to the best among the resin used giving 98% Ni and 91 % Co loading. Therefore, TP 220 resin was used in this research for Ni and Co separation from Fe present as Fe(ll) in the pH leach-1 liquor. [145] Initially TP220 resin was treated with HCI solution followed by washed thoroughly with DI water to prepare the resin for loading of Ni and Co. A mini column for IX resin testing was constructed using a cylindrical glass tube having an outer glass jacket for hot water circulation to control the resin bed temperature. The column test was performed with a resin bed volume of 90 ml Lewatit TP 220 resin. The column test was performed in 4 stages - loading, loaded resin washing/scrubbing, elution and eluted resin washing. The parameters used for the different steps of the column test are given in Table 16. In this test, 6 BV per hour of the liquor was passed through the column with a flowrate of 9 ml/min.

[146] Table 16. Test parameters used for the resin column test.

[147] The test results for each of the stages are given below.

7.1 Loading

[148] The analysis of the feed solution (pH leach-1 liquor) used for the column loading test reported 0.59 g/L Ni and 0.76 g/L Co and 23.7 g/L Fe analyses. A total of 38 BV of the feed liquor was passed through the column in 380 min to obtain Ni/Co loading profile (Table 17). The loading efficiency for both Ni and Co decreased after 30 BV. Therefore, 30 BV can be considered as optimum BV for the loading test of the resin where raffinate analysis for Ni/Co was <2 mg/L giving >99% loading efficiency.

[149] Table 17. Ni/Co loading test details for the IX column test with TP 220 resin.

[150] The raffinate of the loading test was stored and used for Fe removal in the Fe removal-2 stage.

7.2 Washing and scrubbing of the loaded resin

[151] The loaded resin was washed by passing through 3 BV of DI water within an hour to remove the Fe present in the entrained raffinate liquor. After water washing, the resin was scrubbed with 0.5 M HCI solution to remove any loaded Fe. The washing data profile given in T able 18 indicates that 3 BV of wash water was required to remove majority of the Fe. The scrubbing profile of Fe indicates that there was some Fe loading with Ni/Co loading as the first BV of scrub raffinate reported higher Fe concentration than the Fe concentration of the third BV of water wash. During scrubbing with 0.5 M HCI, slight elution of Ni and Co also took place with the increase of scrub BV from 1 to 3. This indicates that a total of 4-6 BV of wash water and scrub feed (2 to 3 BV for each) can be considered as requirement to minimise the Fe concentration in the loaded resin. The Fe analysis in the third BV of scrub raffinate was ~281 mg/L.

[152] Table 18. Washing and scrubbing profile of the Ni/Co loaded TP 220 resin in the column test.

7.3 Elution of the washed/scrubbed resin

[153] The elution of the washed/scrubbed loaded resin was performed using 2 M HCI at ambient temperature by passing 6 BV of acid solution with an hour. Table 19 shows the elution data profile which indicates that 8 BV of 2 M acid solution was not able to elute completely the loaded Ni, whereas, Co showed better elution behaviour compared to Ni. The high Fe analysis in the first BV of elute liquor confirms that there was some Fe loading occurred in the metal loading stage. The eluted liquor analysis after eighth BV of acid solution was -137 mg/L Ni, and 4 mg/L Co and 30 mg/L Fe. Elution data indicates that a minimum of 8 BV acid solution is essential; however, more than 8 BV may be a better option for the process. [154] Table 19. Elution profile of the Ni/Co loaded TP 220 resin in the column test.

[155] The first four BV of the eluted liquor was combined where analysis of the combined liquor reported 4.5 g/L Ni, 0.76 g/L Co and 1.03 g/L Fe. Due to high Fe concentration (1.03 g/L) in combined eluted liquor, Fe removal was essential for the Ni/Co recovery. Therefore, the liquor was stored for Fe removal in the Fe removal-1 stage.

[156] In actual practice the second four BV of the eluted liquor can be recycled as a feed for first four BV to a fresh elution reaction after making up the required acid concentration to increase the Ni/Co tenor in the eluted liquor.

7.4 Washing of the eluted resin

[157] The washing of the eluted resin was performed with 8 BV water to remove the entrained acid solution from the eluted resin. The pH of the wash solution increased with the number of the wash water BVs (Table 20). Elution wash data indicates that more than 8 BV of wash water is required to minimise the acid concentration (i.e., to increase the pH) of the wash resin to obtain a pH of the wash liquor >2. Possibly 12 BV of water wash will mostly remove all the entrained acid from the eluted resin; however, this needs further test work to confirm. [158] Table 20. Washing profile of the eluted TP 220 resin in the column test.

[159] The column test data indicates that the BV of liquor required at different stages of resin treatment should be:

Loading: 30 BV of feed liquor

Loaded resin wash: 2-3 BV of water

Loaded wash resin scrub 2-3 BV of 0.5 M HCI solution

Elution: > 8 BV of 2 M HCI solution

Eluted resin wash: >8 BV of water

8. Fe removal-1 from pH leach-2/pH leach-3 liquors

[160] The liquors obtained from the pH leach-2, pH leach-3 and IX resin elution contained Fe, therefore, these liquors were homogenised to obtain a feed liquor having -2.16 g/L Ni, 0.16 g/L Co, -21 g/L Fe, -0.05 g/L Al, 0.01 g/L Cr, -0.07 g/L Mn and 0.13 g/L Ca analysis. This liquor was purified by removing Fe to obtain a Ni/Co solution for the mixed Ni/Co hydroxide precipitation. Most of the Fe present in the feed liquor was found to be Fe(ll), therefore, Fe(ll) was oxidised with a required amount of H2O2 addition to convert to Fe(lll) prior precipitating the Fe(lll) by limestone neutralisation. This Fe removal is considered as Fe removal-1 stage in the process flowsheet. [161] In a typical test, 2.47L of feed liquor was taken in a 5 L reactor and Fe(ll) was oxidised at ambient temperature by adding -87 g of 30% H2O2. Fe removal was performed using oxidised liquor at 60 °C by adding 13.6% w/w limestone to obtain an equilibrium pH of the reaction at 3. The reaction was continued at the equilibrium pH 3 for few hours to improve the particle growth for better filtration behaviour. The Fe precipitation in the reaction was 99.9% giving -12 mg/L Fe in the final liquor. As small amount of Al and Cr reported in the feed liquor, these were also removed (92-96%) along with Fe giving 1 -2 mg/L Al/Cr analysis in the final liquor. A minor Ni and Co loss (1 .4% for Ni and 0.8% for Co) occurred due to possible co-precipitation or adsorption of Ni and Co on the Fe oxy-hydroxide surface. The final liquor analysis reported 1 .87 g/L Ni, 0.14 g/L Co, 13.57 g/L Ca along with minor impurities of 12 mg/L Fe, 1 -2 mg/L Al/Cr and 33 mg/L Mn. The Fe oxy-hydroxide solid analysis was 51 .4% Fe, 0.07% Ni, 0.003% Co, 0.12% Al, 0.03% Cr, 0.002% Mn and 0.03% Ca. The analysis of feed liquor, final liquor and precipitated solid along with percentage of metal precipitation are given in Table 21. The Fe oxy-hydroxide solid generated from the Fe removal-1 stage appeared to be good a quality Fe-oxy-hydroxide material and can be used as saleable by-product after calcining at -200 to 400 °C.

[162] The Fe precipitated liquor from Fe removal-1 stage gave 12 mg/L Fe which was further treated with a drop of H2O2 and <0.2 g of limestone at ambient temperature and filtered to generate a feed liquor for Ni/Co mixed hydroxide precipitation

[163] Table 21. Feed liquor, final liquor and precipitated solid analyses with percentage metals precipitation for the bulk Fe precipitation test at 60 °C with 13.6% w/w limestone slurry at pH 3. 9. Nickel/cobalt mixed hydroxide precipitation

[164] The Ni and Co mixed hydroxide precipitation was performed using 2.94 L of feed liquor having 1 .87 g/L Ni and 0.14 g/L Co analysis, at 60 °C adding 20.3% w/w lime slurry until an equilibrium reaction pH of 8.6 was obtained. A complete precipitation of Ni and Co was obtained along with some of the minor impurities such Mn and Si. Analysis of feed and final liquors along with percentage of metal precipitation are given in Table 22.

[165] The final liquor gave -15.5 g/L Ca analysis having minor or trace elemental analysis of other impurities; therefore, this liquor can directly be added to the evaporation stage before HCI regeneration.

[166] Table 22. Feed and final liquors analyses with percentage metals precipitation of the bulk Ni/Co mixed hydroxide precipitation test at 60 °C with 20.3% w/w lime slurry at pH 8.6.

[167] The analysis of the Ni/Co mixed hydroxide product is given in Table 23 which shows a good quality mixed hydroxide product produced having 53% Ni, 3.5% Co, -0.4% Mg and Si, 0.9% Mn and -1.1 % Cl. Impurities such as Fe and Al were <0.035%, Zn and Ca were <0.025%, B and S were <0.01 % and Cr, Cu, Na and K were <0.005%. The chloride content (-1.1 %) in the Ni/Co mixed hydroxide solid can possibly be reduced by improving the washing efficiency. [168] Table 23. Analysis of precipitated Ni/Co mixed hydroxide (dried at 60 °C).

10. Fe removal-2 from Ni/Co/Fe precipitation stage filtrate

[169] The Fe(ll) bearing solutions from Ni/Co/Fe precipitation filtrate and IX column raffinate were homogenised prior to the Fe removal-2 reaction. The Fe removal-2 was performed using 1.6 L of feed solution [having -13.6 g/L Fe(ll)] at 80 °C by adding 33.3% w/w limestone slurry as a neutralising agent and air as an oxidant at a flow rate of 2 L/min. A complete Fe precipitation took place within 80 minutes of reaction giving 2 mg/L Fe in the final liquor. Details of the feed liquor, final liquor and precipitated solid analyses with percentage Fe precipitation for Fe removal-2 are given in Table 24.

[170] Table 24. Feed liquor, final liquor and precipitated solid analyses with percentage Fe precipitation for Fe removal-2 test at 80 °C adding 33.3% w/w limestone slurry and 2 L/min air flow.

[171] The Fe removal-2 test was focussed to precipitate Fe as goethite or magnetite and preferably magnetite only. The higher Ca analysis in the precipitated solid can be reduced either by controlling the excess limestone addition or by removing the excess limestone from the precipitated solid with dilute HCI treatment This Fe removal-2 solid can be considered a saleable by-product. 11. Mn/Mg removal from Fe removal-2 final liquor

[172] The final liquor from the Fe removal-2 test was evaporated to nearly half from its initial volume to increase the Mn and Mg concentration in the liquor prior Mn/Mg removal. The evaporated liquor analysis reported -4.8 g/L Mg, 0.77 g/L Mn and 55.8 g/L Ca. The Mn/Mg removal was performed using 1 .23 L of evaporated liquor at 60 °C adding -30% lime slurry. Initially the pH of the liquor at 60 °C was raised to above 8 followed by required amount of H2O2 was added to oxidise Mn(ll) to Mn(IV) for Mn- dioxide/hydroxide/oxy-hydroxide formation. The lime slurry addition was continued to achieve an equilibrium reaction pH of 9.5 for the complete precipitation of both Mn and Mg. Air/oxygen can also be used as an oxidant for the Mn oxidation and precipitation. The analysis of the precipitated solid gave 31.1 % Mg, -5.3% Mn and -0.4% Ca. The feed and final liquor analyses are given in Table 25.

[173] Table 25. Feed and final liquor analyses of Mn/Mg removal test at 60 °C with -30% lime slurry and H2O2 addition.

[174] Even though Mn and Mg were precipitated together in this typical test, however, these metals can be precipitated separately in two different stages to obtain separate Mn-removal solid and Mg removal solid by controlling/manipulating the pH of each of the reaction stages. This will help to obtain value added by-products for the process.

12. Hydrochloric acid regeneration

[175] The Mn/Mg removed final liquor was evaporated to achieve a desired Ca concentration in the evaporated liquor that is suitable for HCI regeneration of a required acid concentration (24.5% w/w HCI). In the HCI regeneration process, CaCk is reacted with concentrate 98% H2SO4 to produce HCI solution and CaSCU solid. The CaSCU formation may possibly occur in the form of gypsum, bassanite or anhydrite. In this reaction, the aim was to produce anhydrite only. [176] Two HCI regeneration tests were performed using two different evaporated liquors at -80-84 °C with 94.4% and 88% stoichiometric addition of 98% H2SO4. The feed and final liquors analyses, and the acid concentration in the liquors are given in Table 26. In these reactions, the concentrations of regenerated acid were 24.3% and 24.9% w/w HCI. The HCI regeneration reaction produced target acid concentration (24.5% w/w HCI) that can be recycled to ore leaching stage. High Ca concentration in the regenerated HCI solution will not be an issue as lime and limestone are used in the various stages of the process. High Ca concentration in the regenerated HCI solution will give low sulphate concentration in the liquor which is important in the process to prevent gypsum scaling in the equipment and pipelines. The XRD of the solid reported only anhydrite phase formation during HCI regeneration reaction at -80-84 °C.

[177] Table 26. Feed and final liquor analysis for HCI regeneration tests at 80-84 °C with 94.4% and 88% stoichiometric addition of 98% H2SO4

[178] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[179] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.