FIELD

[0001] The present disclosure generally relates to acid neutraliser compositions. In particular, the present disclosure particularly relates to acid neutraliser compositions comprising magnesite obtained from mined material which can be used to at least partially neutralise free acid in a leach slurry, including for example a leach slurry produced during an acid leach of a nickel laterite ore. The present disclosure also relates to processes, methods and uses comprising the acid neutraliser compositions comprising magnesite.

BACKGROUND

[0002] The acid leaching of mineralised ores is commonly practiced for metal production. To ensure desired leaching efficiency, the resulting effluent usually contains excess acid, as well as other soluble impurities that are also dissolved during the leaching step.

[0003] After leaching, the excess acid is often removed by reacting with neutralising agents such as lime, limestone, magnesia or caustic hydroxide. Removal of the excess acid renders the solution amenable to downstream solution purification and metal recovery, and may also remove some or all of the undesired metal species from the pregnant liquor solution.

[0004] In the hydrometallurgical treatment of nickel laterite ores, calcium-based neutralisers such as limestone and lime are commonly used for solution neutralisation because of their lower unit costs. Of the two reagents, limestone (CaCOs) is cheaper, but not as reactive. Hence lime (CaO) or slaked lime (Ca(OH)2) is used for processes requiring higher pH endpoints. [0005] Limestone or its derivatives (calcrete, lime sand etc.) are the most common reagents for the neutralisation of relatively acidic solutions. This reagent results in the production of gypsum (CaSO4.2H2O) or other calcium sulphate precipitates; these report to tailings streams and/or present a residue disposal issue. The gypsum-saturated waters also give rise to potential scaling issues within a hydrometallurgical circuit, particularly around heat transfer surfaces and within pumps and reaction vessels.

[0006] Additionally, for many industrial hydrometallurgical treatment processes, the amount of limestone or its derivatives required to neutralise excess acid present in various leach slurries is high (e.g. 75 tonnes or more of limestone per hour in a 3 million tonne per annum high pressure acid leach), and often exceeds local availability. As a result, the limestone needs to be imported or sourced elsewhere adding significant cost and increasing the carbon footprint through transportation.

[0007] Thus, there is a need for cost-effective alternative to limestone that is efficacious and can go some way to alleviate the drawbacks associated with the use of limestone.

[0008] It will be understood that any prior art publications referred to herein do not constitute an admission that any of these documents form part of the common general knowledge in the art, in Australia or in any other country.

SUMMARY

[0009] The present disclosure is based, in part, on the finding that compositions containing high concentrations of magnesite, which is predominantly magnesium carbonate (MgCCh), can be selectively obtained from a mined material and used for acid neutralisation, particularly for at least partially neutralising free acid in a leach slurry.

[0010] According to at least some embodiments or examples described herein, the present inventors have surprisingly identified that the magnesite-containing compositions obtained from a screened mined material, particularly those compositions that have been comminuted post-screening into smaller particles, can effectively replace limestone in post leaching acid neutralisation whilst achieving a target pH endpoint (~pH 5). Further, the magnesite-containing compositions described herein was found to react very efficiently under more acidic conditions, for example where the pH is lower than 3, where the neutralising efficacy of the magnesite is enhanced. Advantageously, when used to neutralise free acid (e.g. sulfuric acid) present in leach slurries, metal values, such as or nickel and/or cobalt values, present in iron-containing minerals such as goethite which may also be present in the neutraliser compositions can pass into solution which results in an increased metal recovery.

[0011] The present disclosure provides an acid neutraliser composition obtained from a mined material, the acid neutraliser comprising magnesite. The acid neutraliser composition comprises magnesium, and may also comprise one or more of silicon, aluminium, or iron which may be present as impurities. The acid neutraliser composition may have an Acid Neutralising Capacity (ANC) of at least about 50% of the ANC of an equivalent amount of calcium carbonate (CaCCh). The acid neutraliser composition may be obtained from mined material, such as a magnesite-containing saprock, such as a magnesite-containing saprock occurring within a nickel laterite deposit/profile.

[0012] In one aspect, there is provided an acid neutraliser composition obtained from a mined material, the acid neutraliser comprising magnesite and one or more of: a) a silicon content of less than about 25% w/w based on the total weight of the composition; b) an aluminium content of less than about 2% w/w based on the total weight of the composition; c) an iron content of less than about 15% w/w based on the total weight of the composition; d) a magnesium content of at least about 5% w/w based on the total weight of the composition; e) a carbon content of at least about 2% w/w based on the total weight of the composition; and/or f) an Acid Neutralising Capacity (ANC) of at least about 50% of the ANC of an equivalent amount of calcium carbonate (CaCCh).

[0013] In another aspect, there is provided an acid neutraliser composition obtained from a mined material, the acid neutraliser composition comprising magnesite and has an Acid Neutralising Capacity (ANC) of at least about 50% of the ANC of an equivalent amount of calcium carbonate (CaCCh).

[0014] In another aspect, there is provided an acid neutraliser composition obtained from a mine material, the acid neutraliser comprising magnesite and one or more of: a) a goethite content of between about 2 % w/w to about 25 % w/w based on the total weight of the composition; b) a magnesite content of between about 20 % w/w to about 80 % w/w based on the total weight of the composition; c) a chlorite content of between about 0.5 % w/w to about 28 % w/w based on the total weight of the composition; d) a serpentine content of between about 2 % w/w to about 10 % w/w based on the total weight of the composition; e) a silica content of between about 5 % w/w to about 30 % w/w based on the total weight of the composition; and/or f) a dolomite content of between about 1 % w/w to about 3 % w/w based on the total weight of the composition.

[0015] In another aspect, there is provided a process for recovering an acid neutraliser composition comprising magnesite from a magnesite-containing saprock, the process comprising screening crushed magnesite-containing saprock into a screened undersize fraction and a screened oversize fraction comprising magnesite as the acid neutraliser composition. [0016] In another aspect, there is provided a method of at least partially neutralising an acid comprising contacting an acid neutraliser composition as described above or an acid neutraliser composition recovered by the process as described above with the acid.

[0017] In another aspect, there is provided use of an acid neutraliser composition as described above or an acid neutraliser composition recovered by the process as described above for at least partially neutralising an acid.

[0018] In another aspect, there is provided a method of at least partially neutralising free acid in leach slurry produced during an acid leach of a nickel laterite ore, comprising contacting an acid neutraliser composition as described above or an acid neutraliser composition recovered by the process as described above with the free acid in the leach slurry.

[0019] In another aspect, there is provided use of an acid neutraliser composition as described above or an acid neutraliser composition recovered by the process as described above for at least partially neutralising free acid in leach slurry produced during an acid leach of a nickel laterite ore.

[0020] In another aspect, there is provided a method of at least partially neutralising free acid in leach slurry produced during an acid leach of a nickel laterite ore, comprising: screening crushed magnesite-containing saprock into a screened undersize fraction and a screened oversize fraction comprising magnesite as an acid neutraliser composition; optionally, comminuting (e.g. milling) the acid neutraliser composition; contacting the acid neutraliser composition with the free acid in the leach slurry to at least partially neutralise the acid; and optionally, passing the screened undersize fraction to an acid leach step to recover nickel and/or cobalt values. [0021] In another aspect, there is provided a method of recovering nickel and/or cobalt values from a nickel laterite ore, comprising: a) acid leaching a nickel laterite ore comprising heating a slurry containing a nickel laterite ore and sulfuric acid under conditions effective to produce a leached nickel-bearing slurry; b) screening crushed magnesite-containing saprock into a screened undersize fraction and a screened oversize fraction comprising magnesite as the acid neutraliser composition; and optionally, milling the acid neutraliser composition; c) optionally, passing the screened undersize fraction to the acid leach step a) to recover nickel and/or cobalt values; d) contacting the acid neutraliser composition with the leached nickel-bearing slurry to at least partially neutralise free sulfuric acid; and e) washing the neutralised nickel-bearing slurry and separating solids therefrom to produce a nickel-bearing solution.

[0022] It will be appreciated that any one or more of the embodiments and examples described herein for the acid neutraliser compositions may also apply to the processes, methods, and/or uses described herein. Any embodiment herein shall be taken to apply mutatis mutandis to any other embodiment unless specifically stated. It will also be appreciated that other aspects, embodiments and examples of the acid neutraliser compositions, processes, methods, and/or uses are described herein.

[0023] It will also be appreciated that some features of acid neutraliser composition may also apply to the processes, methods, and/or uses identified in some aspects, embodiments or examples as described herein may not be required in all aspects, embodiments or examples as described herein, and this specification is to be read in this context. It will also be appreciated that in the various aspects, embodiments or examples, the order of method or process steps may not be essential and may be varied. BRIEF DESCRIPTION OF FIGURES

[0024] Embodiments of the present disclosure will be further described and illustrated, by way of example only, with reference to the accompanying drawings in which:

[0025] Figure 1: Block flow diagram of an embodiment of a method of recovering nickel values from a nickel laterite ore utilising the acid neutraliser composition of the present disclosure.

DETAILED DESCRIPTION

[0026] With regards to the definitions provided herein, unless stated otherwise, or implicit from context, the defined terms and phrases include the provided meanings. Unless explicitly stated otherwise, or apparent from context, the terms and phrases below do not exclude the meaning that the term or phrase has acquired by a person skilled in the relevant art. The definitions are provided to aid in describing particular embodiments, and are not intended to limit the claimed invention, because the scope of the invention is limited only by the claims. Furthermore, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0027] All publications discussed and/or referenced herein are incorporated herein in their entirety.

[0028] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present disclosure. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application. [0029] Throughout this disclosure, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e., one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. For example, reference to “a” includes a single as well as two or more; reference to “an” includes a single as well as two or more; reference to “the” includes a single as well as two or more and so forth.

[0030] Those skilled in the art will appreciate that the disclosure herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. The disclosure also includes all of the examples, steps, features, methods, hydrogels, processes, and compositions, referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features.

[0031] The term “and/or”, e.g., “X and/or Y” shall be understood to mean either “X and Y” or “X or Y” and shall be taken to provide explicit support for both meanings or for either meaning.

[0032] As used herein, the term “about”, unless stated to the contrary, typically refers to a range of up to +/- 10% of the designated value, and includes smaller ranges therein, for example +/- 5% or +/- 1% of the designated value.

[0033] It is to be appreciated that certain features that are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. [0034] Throughout the present specification, various aspects and components of the invention can be presented in a range format. The range format is included for convenience and should not be interpreted as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range, unless specifically indicated. For example, description of a range such as from 1 to 5 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 5, from 3 to 5 etc., as well as individual and partial numbers within the recited range, for example, 1, 2, 3, 4, 4.5, 4.75, and 5, unless where integers are required or implicit from context. This applies regardless of the breadth of the disclosed range. Where specific values are required, these will be indicated in the specification.

[0035] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0036] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

[0037] The terms "composition" and “formulation” as used herein are intended to encompass a product comprising the specified ingredients in the specified amounts, as well as any product which results, directly or indirectly, from combination of the specified ingredients in the specified amounts.

[0038] The reference to “substantially free” generally refers to the absence of that compound or component in the composition, other than any trace amounts or impurities that may be present, for example this may be an amount by weight % in the composition of less than about 1%, 0.1%, 0.01%, 0.001%, or 0.0001%. An example of this may be calcium carbonate (CaCCh) in the acid neutraliser composition.

Acid neutraliser compositions

[0039] The present disclosure generally relates to acid neutraliser compositions obtained from a mined material, the acid neutraliser comprising magnesite.

Mined material

[0001] The acid neutraliser composition is obtained from a mined material. Mined material includes any material extracted from the earth. The mined material may comprise ores and/or host rock. The mined material may be obtained from a nickel laterite deposit/profile. Nickel laterite profiles/deposits include numerous zones which, generally, are observed in a predictable order based on weathering. Descending downwards away from surface there may be amongst other zones: a ferricrete zone, rich in iron; a limonite zone, being hematite dominant; an upper "perched" magnesitebearing saprock zone which can include a speleothem solution breccia region; a limonite zone, being goethite dominant; a clay rich zone; a saprolite zone, a saprock zone which can include a speleothem solution breccia region, and finally an unweathered bedrock layer. The mined material may be a selectively mined material.

[0002] In one embodiment the mined material may be a selectively mined material obtained from one or more of the aforementioned zones. Selectively mined material is distinguished from run-of-mine bulk mined material which is not actively selected to be predominately from one or more specific zones.

[0003] In a further embodiment, the mined material may comprise predominately material from the saprock zone. Saprock is a hard carbonated weathered rock. Advantageously, the hard saprock is easily distinguished from the overlying soft nickel laterite ore, so the base of ore will be readily distinguished in grade control and selective mining. [0004] In a further embodiment, the mined material comprises a magnesite-containing material. In a further embodiment, the mined material is a magnesite-containing saprock. In another further embodiment, the mined material comprises magnesite.

[0005] In some cases, the magnesite-containing saprock is a “speleothem” cave deposit formed by partial dissolution by acidic groundwaters of the carbonate within saprock within and underlying the nickel laterite mineralization. The speleothem can result in a highly variable mineralogy, comprising coarse-grained white magnesite “floating” in a fine-grained nickel-enriched matrix of goethite-chlorite-serpentine clay and variable but minor sepiolite and nontronite. Thus in one embodiment, the magnesite-containing saprock is a magnesite-goethite-chlorite-serpentine containing saprock.

[0006] The selectively mined material used as the input for the process for recovering an acid neutralizer composition may be taken from the saprock layer which underlies one or more zones containing nickel laterite ore. In one example, the overlaying one or more zones containing nickel laterite ore are mined as a feedstock for a high pressure acid leach (HP AL) or atmospheric leach (AL) for the recovery of values such as nickel and/or cobalt, leaving the pit floor comprising the underlying saprock layer accessible for mining as the selectively mined material described herein.

[0007] In one embodiment, the acid neutraliser composition is obtained from a magnesite-containing saprock (e.g. which has been selectively mined from a nickel laterite profile/deposit). In one embodiment the acid neutraliser composition is obtained from a screened mined material. In one embodiment, the acid neutraliser composition is obtained from a screened magnesite-containing saprock.

Acid neutraliser composition

[0008] The acid neutraliser composition, which can be obtained from a mined material, comprises magnesite, which is predominantly magnesium carbonate (MgCCh). Owing to the presence of magnesite, the acid neutraliser composition comprises an amount of the element magnesium. The acid neutraliser composition also comprises at least one or more of the elements carbon, silicon, aluminium and/or iron. In another further embodiment, the acid neutraliser composition further comprises one or more of nickel, cobalt, manganese or chromium.

[0009] According to some embodiments or examples described herein, selectively screening crushed magnesite-containing saprock which has been selectively mined from a nickel laterite deposit can increase the concentration of magnesite within the acid neutraliser composition whilst reducing the presence of one or more impurities, including for example lowering the overall silica content. In other words, the acid neutraliser composition is mineralised.

[0010] Accordingly in one embodiment, the acid neutraliser composition is a mineralised acid neutraliser composition. As used herein, the term “mineralised” means the accumulation or enrichment in a material of one or more minerals that have been delineated by selective mining, and in some cases subsequent selective screening. A mineralised acid neutraliser composition described herein may have an enriched magnesite content whilst a lower overall silica content which in turn can increase the Acid Neutralising Capacity (ANC) of the neutraliser composition.

[0011] In a particular embodiment, the acid neutraliser composition comprises magnesite and one or more of: a) a silicon content of less than about 25% w/w based on the total weight of the composition; b) an aluminium content of less than about 2% w/w based on the total weight of the composition; c) an iron content of less than about 15% w/w based on the total weight of the composition; d) a magnesium content of at least about 5% w/w based on the total weight of the composition; e) a carbon content of at least about 2% w/w based on the total weight of the composition; and/or f) an Acid Neutralising Capacity (ANC) of at least about 50% of the ANC of an equivalent amount of calcium carbonate (CaCCh).

[0012] The magnesium content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the magnesium content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 10 to about 20. In one embodiment, the magnesium content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 1, 2, 3, 4, 5, 8, 10, 12, 15, 20, 25 or 30. In one embodiment, the magnesium content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 30, 25, 20, 18, 15, 12, 10, 8, 5, 4, 3, 2, or 1. The magnesium content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the magnesium content in the acid neutraliser composition (in % w/w of the total composition) may be between about 1 to about 30, about 5 to about 30, or between about 10 to about 20.

[0013] If present, the silicon content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the silicon content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 5 to about 20. In one embodiment, the silicon content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 1, 2, 3, 4, 5, 8, 10, 12, 15, 20, 25 or 30. In one embodiment, the silicon content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 30, 25, 20, 18, 15, 12, 10, 8, 5, 4, 3, 2, or 1. The silicon content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the silicon content in the acid neutraliser composition (in % w/w of the total composition) may be between about 1 to about 30, between about 5 to about 25, between about 5 to about 20, or between about 10 to about 20.

[0014] If present, the aluminium content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the aluminium content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 0.1 to about 1. In one embodiment, the aluminium content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 2, 3, 4 or 5. In one embodiment, the aluminium content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 5, 4.5, 4, 3.5, 3, 2.5, 2, 1, 0.8, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05 or 0.01. The aluminium content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the aluminium content in the acid neutraliser composition (in % w/w of the total composition) may be between about 0.01 to about 5, between about 0.01 to about 2, or between about 0.1 to about 1.

[0015] If present, the iron content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the iron content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 1 to about 12. In one embodiment, the iron content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 8, 10, 12, 15 or 20. In one embodiment, the iron content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 20, 15, 12, 10, 8, 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.5 or 0.1. The iron content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the iron content in the acid neutraliser composition (in % w/w of the total composition) may be between about 0.1 to about 20, between about 0.1 to about 15, between about 1 to about 12.

[0016] Owing to the presence of carbonate in magnesite, the acid neutraliser composition comprises an amount of carbon. The carbon content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the carbon content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 1 to about 20. In one embodiment, the carbon content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 8, 10, 12, 15, 20, or 30. In one embodiment, the carbon content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 30, 20, 15, 12, 10, 8, 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, or 1. The carbon content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the carbon content in the acid neutraliser composition (in % w/w of the total composition) may be between about 1 to about 20, or between about 2 to about 15.

[0017] If present, the nickel content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the nickel content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 0.2 to about 0.8. In one embodiment, the nickel content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 2, 3, 4 or 5. In one embodiment, the nickel content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1.2, 1, 0.8, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05 or 0.01. The nickel content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the nickel content in the acid neutraliser composition (in % w/w of the total composition) may be between about 0.2 to about 1.5, or between about 0.2 to about 1.0, between about 0.2 to 0.8, for example about 0.6.

[0018] If present, the manganese content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the manganese content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 0.01 to about 0.3. In one embodiment, the manganese content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 0.01, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3. In one embodiment, the manganese content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 0.3, 0.25, 0.2, 0.15, 0.1, 0.05 or 0.01. The manganese content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the manganese content in the acid neutraliser composition (in % w/w of the total composition) may be between about 0.01 to about 0.3.

[0019] If present, the chromium content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the chromium content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 0.1 to about 1. In one embodiment, the chromium content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 2, 3, 4 or 5. In one embodiment, the chromium content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1.2, 1, 0.8, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05 or 0.01. The chromium content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the chromium content in the acid neutraliser composition (in % w/w of the total composition) may be between about 0.1 to about 1.

[0020] If present, the cobalt content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the cobalt content in the acid neutraliser composition (in ppm) is between about 10 to about 500. In one embodiment, the cobalt content in the acid neutraliser composition (in ppm) is at least about 10, 50, 100, 200, 300, 400, 500. In one embodiment, the cobalt content in the acid neutraliser composition (in ppm) is less than about 500, 400, 300, 200, 100, 50 or 10. The cobalt content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the cobalt content in the acid neutraliser composition (in ppm) may be between about 10 to about 500.

[0021] In one embodiment, the acid neutraliser composition has a calcium content (in % w/w of the total weight of the composition) of less than about 5, 2, 1, 0.8, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05 or 0.01. The calcium content may be range provided by any two of these values, for example between about 0.01 to about 1. [0022] In addition to the elemental make-up, of the acid neutraliser composition may also comprise one or more minerals, including one or more of goethite, magnesite, chlorite, serpentine, silica, or dolomite.

[0023] In one embodiment, the acid neutraliser composition has one or more of: a) a goethite content of between about 2 % w/w to about 25 % w/w based on the total weight of the composition; b) a magnesite content of between about 20 % w/w to about 80 % w/w based on the total weight of the composition; c) a chlorite content of between about 0.5 % w/w to about 28 % w/w based on the total weight of the composition; c) a serpentine content of between about 2 % w/w to about 10 % w/w based on the total weight of the composition; d) a silica content of between about 5 % w/w to about 30 % w/w based on the total weight of the composition; and/or f) a dolomite content of between about 1 % w/w to about 3 % w/w based on the total weight of the composition.

[0024] If present, the goethite content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the goethite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 2 to about 25. In one embodiment, the goethite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 1, 2, 3, 4, 5, 8, 10, 12, 15, 20, 25 or 30. In one embodiment, the goethite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 30, 25, 20, 18, 15, 12, 10, 8, 5, 4, 3, 2, or 1. The goethite content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the goethite content in the acid neutraliser composition (in % w/w of the total composition) may be between about 1 to about 30, between about 2 to about 25. [0025] The magnesite content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the magnesite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 20 to about 80. In one embodiment, the magnesite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, or 90. In one embodiment, the magnesite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 90, 80, 70, 60, 50, 40, 30, 20, 15, 10 or 5. The magnesite content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the magnesite content in the acid neutraliser composition (in % w/w of the total composition) may be between about 5 to about 90, between about 10 to about 80, or between about 20 to about 80.

[0026] If present, the chlorite content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the chlorite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 0.5 to about 28. In one embodiment, the chlorite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 0.1, 0.5, 1, 2, 3, 4, 5, 8, 10, 12, 15, 20, 25, 28 or 30. In one embodiment, the chlorite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 30, 28, 25, 20, 18, 15, 12, 10, 8, 5, 4, 3, 2, 1, 0.5 or 0.1. The chlorite content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the chlorite content in the acid neutraliser composition (in % w/w of the total composition) may be between about 0.1 to about 30, between about 0.5 to about 28.

[0027] If present, the serpentine content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the serpentine content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 2 to about 10. In one embodiment, the serpentine content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 1, 2, 3, 4, 5, 8, 10, 12, 15. In one embodiment, the serpentine content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 15, 12, 10, 8, 5, 4, 3, 2 or 1. The serpentine content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the serpentine content in the acid neutraliser composition (in % w/w of the total composition) may be between about 1 to about 20, between about 1 to about 15, between about 2 to about 10.

[0028] If present, the silica content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the silica content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 5 to about 30. In one embodiment, the silica content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 1, 2, 3, 4, 5, 8, 10, 12, 15, 20, 25, 30, 35 or 40. In one embodiment, the silica content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 40, 35, 30, 25, 20, 18, 15, 12, 10, 8, 5, 4, 3, 2, or 1. The silica content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the silica content in the acid neutraliser composition (in % w/w of the total composition) may be between about 1 to about 35, or between about 5 to about 30.

[0029] If present, the dolomite content in the acid neutraliser composition may be provided as a % w/w of the total weight of the composition. In one embodiment, the dolomite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is between about 1 to about 3. In one embodiment, the dolomite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is at least about 0.1, 0.5, 1, 2, 3, 4, 5. In one embodiment, the dolomite content in the acid neutraliser composition (in % w/w of the total weight of the composition) is less than about 5, 4, 3, 2, 1, 0.5 or 0.1. The dolomite content in the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the chlorite content in the acid neutraliser composition (in % w/w of the total composition) may be between about 0.1 to about 4, or between about 1 to about 3.

[0030] In one embodiment, the acid neutraliser composition has a calcium carbonate (CaCCh - also called calcite) content (in % w/w of the total weight of the composition) of less than about 10, 8, 5, 4, 3, 2, 1, 0.1 or 0.01. In one embodiment, the acid neutraliser composition is substantially free of calcium carbonate. In a related embodiment, the acid neutraliser composition has a limestone content in % w/w of the total weight of the composition) of less than about 10, 8, 5, 4, 3, 2, 1, 0.1 or 0.01. In one embodiment, the acid neutraliser composition is substantially free of limestone.

Acid Neutralising Capacity

[0031] The present inventors have surprisingly identified that magnesite of the acid neutraliser composition as described herein can effectively neutralise free acid in a leach slurry, including a leach slurry produced during an acid leach of a nickel laterite ore. According to some embodiments or examples described herein, the acid neutraliser composition described herein is a cost effective, readily available within the mining site, substitute for outsourced/imported acid neutralisers known in the art, such as limestone.

[0032] The acid neutraliser composition has an Acid Neutralising Capacity (ANC). As used herein, the term “Acid Neutralising Capacity” or “ANC” refers to a measure of the amount of base needed to change the pH of an acid containing solution from one value to a chosen different value.

[0033] The acid neutraliser compositions described herein demonstrate good ANC compared to the ANC of calcium carbonate (CaCCh) which limestone is primarily composed of. The acid neutraliser composition may have an ANC of at least about 50% of the ANC of an equivalent amount of CaCCh. The ANC of the acid neutraliser composition may be provided in terms of the equivalent amount of CaCCh. [0034] In one embodiment, the ANC of the acid neutraliser composition (% in terms of the equivalent amount of CaCCh) is between about 60 to about 90. In one embodiment, the ANC of the acid neutraliser composition (% in terms of the equivalent amount of CaCCh) is at least about 50, 55, 60, 70, 80, 90, or 95. In one embodiment, the ANC of the acid neutraliser composition (% in terms of the equivalent amount of CaCCh) is less than about 95, 90, 80, 70, 65, 60, 55, or 50. The ANC of the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the ANC of the acid neutraliser composition (% in terms of the equivalent amount of CaCCh) may be between about 50 to about 95, between about 60 to about 90. In one embodiment, the ANC of the acid neutraliser composition (% in terms of the equivalent amount of CaCCh) may be about 80%.

[0035] The ANC of the acid neutraliser composition may be provided in terms of neutralising sulfuric acid to pH 2.5 at 95°C (in kg of sulfuric acid per tonne of composition; kg H2SO4/t). In one embodiment, the composition has an ANC of sulfuric acid to pH 2.5 at 95°C (in kg of sulfuric acid per tonne of composition; kg H2SO4/t) of between about 500 to about 900. In one embodiment, the composition has an ANC of sulfuric acid to pH 2.5 at 95°C (in kg of sulfuric acid per tonne of composition; kg H ₂ SO ₄ /t) of at least about 500, 550, 600, 650, 700, 800, or 900. In one embodiment, the composition has an ANC of sulfuric acid to pH 2.5 at 95°C (in kg of sulfuric acid per tonne of composition; kg H2SO4/t) of less than about 900, 800, 700, 650, 600, 550 or 500. The ANC of the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the composition may have an ANC of sulfuric acid to pH 2.5 at 95°C (in kg of sulfuric acid per tonne of composition; kg H ₂ SO ₄ /t) of between about 500 to about 900, or between about 600 to about 800.

[0036] According to some embodiments or examples described herein, an acid neutraliser composition having an ANC of sulfuric acid to pH 2.5 at 95°C (in kg of sulfuric acid per tonne of composition; kg H2SO4/t) of between about 500 to about 900 can effectively neutralise free sulfuric acid present in leached nickel-bearing slurries produced by an atmospheric leach (AL) and/or a high pressure acid leach (HP AL) of a nickel laterite ore (e.g. at a primary neutralisation stage). During this neutralisation, any metal values, such as nickel or cobalt, present in the neutraliser can pass into solution which yields a production bonus due to the extra metal recovery.

[0037] The ANC of the acid neutraliser composition may be provided in terms of neutralising sulfuric acid from pH 2.5 to pH 5 at 75°C (in kg of sulfuric acid per tonne of composition; kg H2SO4/t). In one embodiment, the composition has an ANC of sulfuric acid from pH 2.5 to pH 5 at 75°C (in kg of sulfuric acid per tonne of composition; kg H2SO4/t) is between about 50 to about 300. In one embodiment, the composition has an ANC of sulfuric acid from pH 2.5 to pH 5 at 75°C (in kg of sulfuric acid per tonne of composition; kg H2SO4/t) is at least about 50, 75, 100, 150, 200, 250, or 300. In one embodiment, the ANC of the acid neutraliser composition (in kg of sulfuric acid per tonne of composition; kg H2SO4/t) is less than about 300, 250, 200, 150, 100, 75 or 50. The ANC of the acid neutraliser composition may be in a range provided by any two of these upper and/or lower values, for example the composition may have an ANC of sulfuric acid from pH 2.5 to pH 5 at 75°C (in kg of sulfuric acid per tonne of composition; kg H2SO4/t) may be between about 50 to about 300, or between about 100 to about 200.

[0038] According to some embodiments or examples described herein, despite the need for a comparatively larger volume of acid neutraliser compositions described to neutralise free sulfuric acid present after the acid leaching of mineralised ores (owing to the lower ANC), the resulting MgSO4.2H2O produced is readily soluble and therefore lowers the tailings solid volume and flow on costs associated with tailings storage. In contrast, limestone produces gypsum when used to neutralise sulfuric acid which reports to tailings streams as a solid presenting a significant disposal issue. Furthermore, nickel or cobalt values present in the neutraliser can be pass into solution during neutralization, which yields a production bonus due to the extra metal recovery.

Particle size

[0039] The acid neutraliser composition may contain a magnesite-containing particulate. The term “particulate” refers to the form of discrete solid units. The units may take the form of flakes, fibres, agglomerates, granules, powders, spheres, dust, pulverized materials or the like, as well as combinations thereof. The particulate may have any desired shape including, but not limited to, cubic, rod like, polyhedral, spherical or semi-spherical, rounded or semi-rounded, angular, irregular, and so forth. The particulate morphology can be determined by any suitable means such as optical microscopy. The particulate comprises swellable support particles as described herein.

[0040] In one embodiment, the acid neutraliser composition comprises a magnesitecontaining particulate having a particle size (in pm) of between about 10 to about 5,000. In one embodiment, the acid neutraliser composition comprises a magnesitecontaining particulate having a particle size (in pm) of at least about 1, 5, 10, 15, 20, 25, 50, 75, 100, 150, 200, 500, 1,000, 2,000 or 5,000. In one embodiment, the acid neutraliser composition comprises a magnesite-containing particulate having a particle size (in pm) of less than about 5,000, 2,000, 1,000, 500, 200, 150, 100, 75, 50, 25, 20, 15, 10, 5 or 1. The particle size may be a range provided by any two of these upper and/or lower values, for example between about 10 to about 1000, between about 10 to about 100 to between about 10 to about 75.

[0041] In one embodiment, the acid neutraliser composition comprises a magnesitecontaining particulate having a median average particle size (Dso in pm) of between about 10 to about 5,000. In one embodiment, the acid neutraliser composition comprises a magnesite-containing particulate having a Dso particle size (in pm) of at least about 1, 5, 10, 15, 20, 25, 50, 75, 100, 150, 200, 500, 1,000, 2,000 or 5,000. In one embodiment, the acid neutraliser composition comprises a magnesite-containing particulate having a Dso particle size (in pm) of less than about 5,000, 2,000, 1,000, 500, 200, 150, 100, 75, 50, 25, 20, 15, 10, 5 or 1. The Dso particle size may be a range provided by any two of these upper and/or lower values, for example between about 10 to about 1000, between about 10 to about 100 to between about 10 to about 75. The Dso particle size defines the size value where 50% of the particles in a given sample are smaller than that value. [0042] In one embodiment, the acid neutraliser composition comprises a magnesitecontaining particulate having a D90 particle size (in pm) of at least about 1, 5, 10, 15, 20, 25, 50, 75, 100, 150, 200, or 500. In one embodiment, the acid neutraliser composition comprises a magnesite-containing particulate having a D90 particle size (in pm) of less than about 500, 200, 150, 100, 75, 50, 25, 20, 15, 10, 5 or 1. The D90 particle size may be a range provided by any two of these upper and/or lower values, for example between about 10 to about 500, between about 10 to about 100 to between about 10 to about 75. The D90 particle size defines the size value where 90% of the particles in a given sample are smaller than that value.

[0043] In a preferred embodiment, the acid neutraliser composition comprises a magnesite-containing particulate having a particle size (in pm) of less than about 75 (e.g. sub 75 micron). It was found that magnesite-containing particulates of this size or less could neutralise acid more effectively than comparably larger particles owing to the increase in reactive surface area. The particle size is taken to be the longest cross- sectional diameter across a magnesite-containing particulate. For non-spherical particulates, the particle size is taken to be the distance corresponding to the longest cross-section dimension across the particle. The particle size or size distribution can be determined by any standard method, including for example using graduated mesh filters, sieves or screens.

Process for recovering the acid neutraliser composition

[0044] In another aspect or embodiment, there is provided a process for recovering the acid neutraliser composition. In one embodiment, the process for recovering an acid neutraliser composition comprising magnesite from a magnesite-containing saprock, the process comprising screening crushed magnesite-containing saprock into a screened undersize fraction and a screened oversize fraction comprising an enrichment of magnesite as the acid neutraliser composition. Compared to the pre-screened crushed saprock, the screened undersize fraction may be enriched in one or more metal values such as nickel and/or cobalt, and the screened oversize fraction may be enriched in magnesite (e.g. a mineralised acid neutraliser composition), as described herein according to at least some embodiments or examples.

[0045] As described above, saprock either perched or at base of nickel laterite is one of zones found in nickel laterite deposits. Saprock is a hard carbonated weathered rock. Advantageously, the hard saprock is easily distinguished from the overlying soft ore, so the base of ore will be readily distinguished in grade control and selective mining.

[0046] The magnesite-containing saprock comprises magnesite. The magnesitecontaining saprock also comprises one or more of goethite, magnesite, chlorite, serpentine, and silica.

[0047] In one embodiment, the magnesite-containing saprock has one or more of: a) a goethite content of between about 2 % w/w to about 25 % w/w based on the total weight of the saprock; b) a magnesite content of between about 20 % w/w to about 80 % w/w based on the total weight of the saprock; c) a chlorite content of between about 5 % w/w to about 28 % w/w based on the total weight of the saprock; d) a serpentine content of between about 2 % w/w to about 10 % w/w based on the total weight of the saprock; and/or e) a silica content of between about 5 % w/w to about 30 % w/w based on the total weight of the saprock.

[0048] If present, the goethite content in the saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the goethite content in the saprock (in % w/w of the total weight of the saprock) is between about 2 to about 25. In one embodiment, the goethite content in the saprock (in % w/w of the total weight of the saprock) is at least about 1, 2, 3, 4, 5, 8, 10, 12, 15, 20, 25 or 30. In one embodiment, the goethite content in the saprock (in % w/w of the total weight of the saprock) is less than about 30, 25, 20, 18, 15, 12, 10, 8, 5, 4, 3, 2, or 1. The goethite content in the saprock may be in a range provided by any two of these upper and/or lower values, for example the goethite content in the saprock (in % w/w of the total saprock) may be between about 1 to about 30, between about 2 to about 25.

[0049] The magnesite content in the saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the magnesite content in the saprock (in % w/w of the total weight of the saprock) is between about 20 to about 80. In one embodiment, the magnesite content in the saprock (in % w/w of the total weight of the saprock) is at least about 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, or 90. In one embodiment, the magnesite content in the saprock (in % w/w of the total weight of the saprock) is less than about 90, 80, 70, 60, 50, 40, 30, 20, 15, 10 or 5. The magnesite content in the saprock may be in a range provided by any two of these upper and/or lower values, for example the magnesite content in the saprock (in % w/w of the total saprock) may be between about 5 to about 90, between about 10 to about 80, or between about 20 to about 80.

[0050] If present, the chlorite content in the saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the chlorite content in the saprock (in % w/w of the total weight of the saprock) is between about 0.5 to about 28. In one embodiment, the chlorite content in the saprock (in % w/w of the total weight of the saprock) is at least about 0.1, 0.5, 1, 2, 3, 4, 5, 8, 10, 12, 15, 20, 25, 28 or 30. In one embodiment, the chlorite content in the saprock (in % w/w of the total weight of the saprock) is less than about 30, 28, 25, 20, 18, 15, 12, 10, 8, 5, 4, 3, 2, 1, 0.5 or 0.1. The chlorite content in the saprock may be in a range provided by any two of these upper and/or lower values, for example the chlorite content in the saprock (in % w/w of the total saprock) may be between about 0.1 to about 30, between about 0.5 to about 28.

[0051] If present, the serpentine content in the saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the serpentine content in the saprock (in % w/w of the total weight of the saprock) is between about 2 to about 10. In one embodiment, the serpentine content in the saprock (in % w/w of the total weight of the saprock) is at least about 1, 2, 3, 4, 5, 8, 10, 12, 15. In one embodiment, the serpentine content in the saprock (in % w/w of the total weight of the saprock) is less than about 15, 12, 10, 8, 5, 4, 3, 2 or 1. The serpentine content in the saprock may be in a range provided by any two of these upper and/or lower values, for example the serpentine content in the saprock (in % w/w of the total saprock) may be between about 1 to about 20, between about 1 to about 15, between about 2 to about 10.

[0052] If present, the silica content in the saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the silica content in the saprock (in % w/w of the total weight of the saprock) is between about 5 to about 30. In one embodiment, the silica content in the saprock (in % w/w of the total weight of the saprock) is at least about 1, 2, 3, 4, 5, 8, 10, 12, 15, 20, 25, 30, 35 or 40. In one embodiment, the silica content in the saprock (in % w/w of the total weight of the saprock) is less than about 40, 35, 30, 25, 20, 18, 15, 12, 10, 8, 5, 4, 3, 2, or 1. The silica content in the saprock may be in a range provided by any two of these upper and/or lower values, for example the silica content in the saprock (in % w/w of the total saprock) may be between about 1 to about 35, or between about 5 to about 30.

[0053] The magnesite-containing saprock also comprises one or more of silicon, aluminium, magnesium and iron.

[0054] In one embodiment, the magnesite-containing saprock has one or more of: a) a silicon content of less than about 20% w/w based on the total weight of the saprock; b) an aluminium content of less than about 2% w/w based on the total weight of the saprock; c) an iron content of less than about 15% w/w based on the total weight of the saprock; d) a carbon content of at least about 2% w/w based on the total weight of the saprock; and /or d) a magnesium content of at least about 5% w/w based on the total weight of the saprock. [0055] The magnesium content in the magnesite-containing saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the magnesium content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is between about 10 to about 30. In one embodiment, the magnesium content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is at least about 5, 8, 10, 12, 15, 20, 25, 30, 35 or 40. In one embodiment, the magnesium content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is less than about 40, 35, 30, 25, 20, 18, 15, 12, 10, 8 or 5. The magnesium content in the magnesite-containing saprock may be in a range provided by any two of these upper and/or lower values, for example the magnesium content in the magnesitecontaining saprock (in % w/w of the total composition) may be between about 1 to about 30, between about 10 to about 30.

[0056] The carbon content in the magnesite-containing saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the carbon content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is between about 1 to about 20. In one embodiment, the carbon content in the magnesitecontaining saprock (in % w/w of the total weight of the saprock)is at least about 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 8, 10, 12, 15, 20 or 30. In one embodiment, the carbon content in the magnesite-containing saprock (in % w/w of the total weight of the saprock)is less than about 30, 20, 15, 12, 10, 8, 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, or 1. The carbon content in the magnesite-containing saprock may be in a range provided by any two of these upper and/or lower values, for example the carbon content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) may be between about 1 to about 20, or between about 2 to about 15.

[0057] If present, the silicon content in the magnesite-containing saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the silicon content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is between about 5 to about 20. In one embodiment, the silicon content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is at least about 1, 2, 3, 4, 5, 8, 10, 12, 15, 20, 25 or 30. In one embodiment, the silicon content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is less than about 30, 25, 20, 18, 15, 12, 10, 8, 5, 4, 3, 2, or 1. The silicon content in the magnesite-containing saprock may be in a range provided by any two of these upper and/or lower values, for example the silicon content in the magnesite-containing saprock (in % w/w of the total composition) may be between about 1 to about 30, between about 5 to about 20.

[0058] If present, the aluminium content in the magnesite-containing saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the aluminium content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is between about 0.1 to about 1. In one embodiment, the aluminium content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is at least about 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 2, 3, 4 or 5. In one embodiment, the aluminium content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is less than about 5, 4.5, 4, 3.5, 3, 2.5, 2, 1, 0.8, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05 or 0.01. The aluminium content in the magnesitecontaining saprock may be in a range provided by any two of these upper and/or lower values, for example the aluminium content in the magnesite-containing saprock (in % w/w of the total composition) may be between about 0.01 to about 5, between about 0.1 to about 1.

[0059] If present, the iron content in the magnesite-containing saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the iron content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is between about 1 to about 12. In one embodiment, the iron content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is at least about 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 8, 10, 12, 15 or 20. In one embodiment, the iron content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is less than about 20, 15, 12, 10, 8, 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.5 or 0.1. The iron content in the magnesite-containing saprock may be in a range provided by any two of these upper and/or lower values, for example the iron content in the magnesite-containing saprock (in % w/w of the total composition) may be between about 0.1 to about 20, between about 1 to about 12.

[0060] The magnesite-containing saprock contains may further comprise one or more of nickel, cobalt, manganese or chromium.

[0061] If present, the nickel content in the magnesite-containing saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the nickel content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is between about 0.2 to about 0.8. In one embodiment, the nickel content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is at least about 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 2 or 3. In one embodiment, the nickel content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is less than about 3, 2.5, 2, 1.5, 1.2, 1, 0.8, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05 or 0.01. The nickel content in the magnesite-containing saprock may be in a range provided by any two of these upper and/or lower values, for example the nickel content in the magnesite-containing saprock (in % w/w of the total composition) may be between about 0.2 to about 1.5, or between about 0.2 to about 0.8, for example about 0.6.

[0062] If present, the cobalt content in the magnesite-containing saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the cobalt content in the magnesite-containing saprock (in ppm) is between about 10 to about 500. In one embodiment, the cobalt content in the magnesite-containing saprock (in ppm) is at least about 10, 50, 100, 200, 300, 400, or 500. In one embodiment, the cobalt content in the magnesite-containing saprock (in ppm) is less than about 500, 400, 300, 200, 100, 50 or 10. The cobalt content in the magnesite-containing saprock may be in a range provided by any two of these upper and/or lower values, for example the cobalt content in the magnesite-containing saprock (in ppm) may be between about 10 to about 400. [0063] If present, the manganese content in the magnesite-containing saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the manganese content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is between about 0.01 to about 0.15. In one embodiment, the manganese content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is at least about 0.01, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3. In one embodiment, the manganese content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is less than about 0.3, 0.25, 0.2, 0.15, 0.1, 0.05 or 0.01. The manganese content in the magnesite-containing saprock may be in a range provided by any two of these upper and/or lower values, for example the manganese content in the magnesitecontaining saprock (in % w/w of the total composition) may be between about 0.01 to about 0.15.

[0064] If present, the chromium content in the magnesite-containing saprock may be provided as a % w/w of the total weight of the saprock. In one embodiment, the chromium content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is between about 0.1 to about 1. In one embodiment, the chromium content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is at least about 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5 or 2. In one embodiment, the chromium content in the magnesite-containing saprock (in % w/w of the total weight of the saprock) is less than about 2, 1.5, 1.2, 1, 0.8, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05 or 0.01. The chromium content in the magnesite-containing saprock may be in a range provided by any two of these upper and/or lower values, for example the chromium content in the magnesite-containing saprock (in % w/w of the total composition) may be between about 0.1 to about 0.8.

Screening crushed saprock

[0065] The magnesite-containing saprock is crushed to produce a particulate with a desired distribution of particle sizes prior to screening. The crushing may be performed by any suitable method known in the art, such as jaw crusher, impact crusher, roll crusher, cone crusher, or gyratory crusher. The crushing may also comprise one or more stages, for example one or more coarser crushing stages and one or more finer crushing stages.

[0066] In one embodiment, the crushed saprock prior to screening has a particle size (in mm) of between about 0.001 to about 500 mm. In one embodiment, the crushed saprock prior to screening has a particle size (in mm) of at least about 0.001, 0.01, 0.1, 1, 5, 10, 15, 20, 25, 50, 75, 100, 150, 200, 500, 1,000, 2,000 or 5,000. In one embodiment, the crushed saprock prior to screening has a particle size (in mm) of less than about 5,000, 2,000, 1,000, 500, 200, 150, 100, 75, 50, 25, 20, 15, 10, 5, 1, 0.1, 0.01 or 0.001. The particle size may be a range provided by any two of these upper and/or lower values, for example between about 10 to about 5000.

[0067] In one embodiment, the crushed saprock prior to screening has a Dso particle size (in mm) of between about 0.001 to about 500 mm. In one embodiment, the crushed saprock prior to screening has a Dso particle size (in mm) of at least about 0.01, 0.1, 1, 5, 10, 15, 20, 25, 50, 75, 100, 150, 200, 500, 1,000, 2,000 or 5,000. In one embodiment, the crushed saprock prior to screening has a Dso particle size (in mm) of less than about 5,000, 2,000, 1,000, 500, 200, 150, 100, 75, 50, 25, 20, 15, 10, 5, 1, 0.1, 0.01. The Dso particle size may be a range provided by any two of these upper and/or lower values, for example between about 10 to about 5000.

[0068] The crushed magnesite-containing saprock is screened into a screened undersize fraction and a screened oversize fraction comprising magnesite. The screened oversize fraction is then recovered as the acid neutraliser composition. Screening is a mechanical process which accomplishes a division of particles on the basis of size and their acceptance or rejection by a screening surface.

[0069] The crushed saprock may be screened by any suitable technique such as wet or dry screening. In one embodiment, the crushed magnesite-containing saprock is wet- screened. Wet-screening involves the physical sizing using openings through which a slurry comprising the crushed saprock will either pass through or not., where particles larger than the screen size form the majority of the oversize fraction and particles smaller than the screen size form the majority of the undersize fraction. Examples of suitable screens (for both wet and dry screening) may include sieves, vibrating screens, multideck screens, sieve bends, static screens, grizzly screens and trommel screens as well as cyclones, Wilfley tables or similar to help separate mineral types on the basis of their specific gravity.

[0070] In one embodiment, the crushed magnesite-containing saprock is wet-screened into a slurry stream comprising the screened undersize fraction and a solids stream comprising the screened oversize fraction comprising magnesite.

[0071] The crushed saprock may be passed through multiple screening steps, for example screens or sieves, of different sizes such that the screened oversize fraction comprising magnesite has well defined lower and upper particle size limits. The lower and upper particle size limits may be varied depending on the desired composition of the screened undersize fraction and the screened oversize fraction.

[0072] Advantageously, passing the crushed saprock through multiple screening steps can reduce the silicon content in the oversized fraction, for example by removing larger silica particles. Decreasing the silica content in the oversized fraction can increase the ANC of the acid neutraliser composition relative to an equivalent amount of CaCCh, and in turn reduces the amount of acid neutraliser composition required during a neutralising process and therefore operating costs are reduced, as for example less mass is required to transported throughout the process. Further, inventors have discovered that the screened undersize fraction may have an increased nickel content relative to the saprock. The screened undersize fraction can, therefore, be utilised as an additional source of nickel and/or cobalt to improve valuables recovery within an acid leaching circuit.

[0073] The crushed saprock may be screened at between 10 pm to about 5,000 pm (that is the size of the openings in a suitable screen described herein). In one embodiment, the crushed saprock is screened (in pm) at about 10, 25, 50, 75, 100, 125, 150, 175, 200, 250, 300, 350, 400, 500, 600, 700, 1,000, 2,000, 4,000 or 5,000. In one embodiment, the crushed saprock is screened (in pm) at less than about 5,000, 4,000, 2,000, 1,000, 700, 600, 500, 400, 350, 300, 250, 200, 175, 150, 125, 100, 75, 50, 25 or 10. The screen size may be in a range provided by any two of these upper and/or lower values, for example between about 10 to about 100, e.g. about 75 pm.

[0074] In one embodiment, the crushed magnesite-containing saprock is passed through two or more screening steps. In one embodiment, there is provided a process for recovering an acid neutraliser composition comprising magnesite from a magnesitecontaining saprock, the process comprising subjecting the crushed magnesitecontaining saprock to two or more screening steps to obtain a screened undersize fraction and a screened oversize fraction comprising magnesite as the acid neutraliser composition.

[0075] In one embodiment, the crushed saprock is passed through at least two screening steps, one of which screens at a smaller size compared to the other. It will be appreciated that the order of screening is not material to the present disclosure. For example, if the crushed saprock is passed through the smaller screen first, the particles retained by the smaller screen can then subsequently be passed through the larger screen. Alternatively, if the crushed saprock is first passed through the larger screen, particles passing through the larger screen can then be subsequently passed through the smaller screen. In such embodiments, crushed saprock particles which pass through both screens form the screened undersize fraction, crushed saprock particles which pass through the larger screen but not the smaller screen form the screened oversized fraction, and crushed saprock particles that do not pass through either of the screens can be discarded as waste due unsatisfactory silica and other impurity content having limited potential as a neutraliser.

[0076] In one embodiment, the smaller screen has a size (in pm) of between about 10 to about 500, and the larger screen has a size (in pm) of between about 200 to about 5,000. In one embodiment, the smaller screen has a size (in pm) of about 10, 25, 50, 75, 100, 125, 150, 175, 200, 250, 300, 350, 400 or 500. In one embodiment, the larger screen has a size (in pm) at about 200, 250, 300, 350, 400, 500, 600, 700, 1,000, 2,000, 4,000 or 5,000. In one embodiment, the smaller screen has a size (in pm) of between about 10 to about 200, and larger screen has a size (in gm) of between about 500 to about 2,000.

[0077] According to some embodiments or examples described herein, screening the crushed saprock at least 75 pm generates a magnesite-containing oversize fraction having low silica and comparatively low nickel content and a nickel-rich undersize fraction which can be feed to an acid leach (such as an atmospheric leach with sulfuric acid) increasing overall nickel recovery.

Screened oversize fraction and acid neutralisation

[0078] The screened oversize fraction has been surprisingly found to contain higher amounts of magnesite and lower levels of nickel compared to the screened undersize fraction. It will be appreciated that screening the crushed saprock ore generates a screened oversize fraction having a particle size distribution which is larger than the screened undersize fraction.

[0079] In one embodiment, the screened oversize fraction has a Dio particle size of at least about 10, 20, 30, 40, 50, 75, 100, 200, 300, 400, 500, 1000 or 2000. In one embodiment, the screened oversize fraction has a Dio particle size of less than about 5000, 2000, 1000, 500, 400, 300, 200, 100, 75, 50, 40, 30, 20 or 10. The Dio particle size of the screened oversize fraction may be in a range provided by any two of these upper and/or lower values, for example the Dio particle size of the screened oversize fraction (in pm) may be between about 10 to about 5000, or between about 75 to about 1000. The D io particle size defines the size value where 10% of the particles in a given sample are smaller than that value.

[0080] In one embodiment, the screened oversize fraction has a D90 particle size (in pm ) of at least about 200, 300, 400 500, 1000, 2000 or 5000. In one embodiment, the screened oversize fraction has a D90 particle size (in pm ) of less than about 5000, 2000, 1000, 500, 400, 300 or 200. The D90 particle size of the screened oversize fraction may be in a range provided by any two of these upper and/or lower values, for example the D90 particle size of the screened oversize fraction (in pm) may be between about 200 to about 5000, between about 500 to about 2000, for example about 1000.

[0081] The screened oversize fraction comprising magnesite may be comminuted (e.g. milled). The comminution can reduce the particle size, which can increase the efficacy of the acid neutraliser composition, for example by increasing the reactive surface area of the neutraliser particulate for contact with acid. Any suitable method known in the art can be used to comminute the oversized fraction, including for example, crushing or milling.

[0082] In one embodiment, the comminuted screened oversize fraction has a particle size (in pm ) of at least about 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 75, 100, 200, 300, 400 500, 1000, 2000 or 5000. In one embodiment, the comminuted screened oversize fraction has a particle size (in pm ) of less than about 5000, 2000, 1000, 500, 400, 300, 200, 100, 75, 50, 40, 30, 20, 10, 5, 4, 3, 2 or 1. The particle size of the comminuted screened oversize fraction may be in a range provided by any two of these upper and/or lower values, for example the particle size of the comminuted screened oversize fraction (in pm) may be between about 1 to about 1000, between about 1 to about 100, or between about 1 to about 75.

[0083] In one embodiment, the comminuted screened oversize fraction has a D90 particle size (in pm ) of at least about 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 75, 100, 200, 300, 400 500, 1000, 2000 or 5000. In one embodiment, the comminuted screened oversize fraction has a D90 particle size (in pm ) of less than about 5000, 2000, 1000, 500, 400, 300, 200, 100, 75, 50, 40, 30, 20, 10, 5, 4, 3, 2 or 1. The D90 particle size of the comminuted screened oversize fraction may be in a range provided by any two of these upper and/or lower values, for example the D90 particle size of the comminuted screened oversize fraction (in pm) may be between about 1 to about 1000, between about 1 to about 100, or between about 1 to about 75. [0084] In one embodiment, the comminuted screened oversize fraction has a particle size of less than 75 pm (e.g. sub 75 micron). In one embodiment, the comminuted screened oversize fraction has a D90 particle size of less than 75 pm. According to this embodiment, a high ANC can be obtained.

[0085] In one embodiment, the process described herein further comprises contacting the screened oversize fraction comprising magnesite with an acid to at least partially neutralise the acid. For example, the magnesite (MgCCh) in the screened oversize fraction can react with an acid to form a magnesium salt, water and carbon dioxide.

[0086] The acid may be any acid that requires neutralisation. The acid may be any acid used in extractive metallurgy to recover one or more metal values from a mined material. In one embodiment, the acid is hydrochloric acid (HC1), nitric acid (HNO3), hydrofluoric acid (HF) or sulfuric acid (H2SO4), preferably H2SO4.

[0087] In a further embodiment, the acid is a free acid in a leach slurry. For example, the leach slurry may be produced during an acid leach of a nickel laterite ore. The nickel laterite ores may be one or more of goethite/limonite, saprolite/serpentine, nontronite/smectite, asbolite, or other commonly found lateritic minerals, or combinations thereof. The ore feed may include alumina, silica and other minerals that are incidental to the leaching process.

[0088] In another further embodiment, the screened oversize fraction comprising magnesite is mixed counter-currently with the leach slurry. In another embodiment, the leach slurry is produced by an atmospheric leach (AL) and/or a high pressure acid leach (HP AL) of the nickel laterite ore.

Screened undersize fraction

[0089] Screening the crushed magnesite-containing saprock generates a screened undersize fraction having a smaller particle size to the screened oversize fraction comprising magnesite prior to any comminution. [0090] In one embodiment, the screened undersize fraction has a D90 particle size of at least about 10, 20, 30, 40, 50, 75, 100, 200, 300, 400 500, 1000 or 2000. In one embodiment, the screened undersize fraction has a D90 particle size of less than about 5000, 2000, 1000, 500, 400, 300, 200, 100, 75, 50, 40, 30, 20 or 10. The D90 particle size of the screened undersize fraction may be in a range provided by any two of these upper and/or lower values, for example the D90 particle size of the screened undersize fraction (in pm) may be between about 10 to about 5000, or between about 75 to about 1000. The D90 particle size defines the size value where 10% of the particles in a given sample are smaller than that value. The D90 particle size defines the size value where 90% of the particles in a given sample are smaller than that value.

[0091] The inventors have discovered that the screened undersize fraction may have an increased nickel and/or cobalt content relative to the saprock and the screened oversize fraction. The screened undersize fraction can, therefore, be utilised as an additional source of nickel to improve valuables recovery. In one embodiment, the nickel content in the screened undersize fraction (in % w/w of the total weight of the screened undersize fraction) is between about 0.8 to about 2.0, for example between about 1.0 to about 1.5, e.g. about 1.2. In one embodiment, the nickel content in the screened undersize fraction (in % w/w of the total weight of the screened undersize fraction) is at least about 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5 or 2. In one embodiment, the nickel content in the screened undersize fraction (in % w/w of the total weight of the screened undersize fraction) is less than about 2, 1.5, 1.2, 1, 0.8, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05 or 0.01. The nickel content in the screened undersize fraction may be in a range provided by any two of these upper and/or lower values, for example the nickel content in the screened undersize fraction (in % w/w of the total weight of the screened undersize fraction) between about 0.8 to about 2.0, for example between about 1.0 to about 1.5.

[0092] In a further embodiment, the process described above further comprises passing the screened undersize fraction to one or more acid leach steps to recover nickel values. According to some embodiments or examples described herein, utilising the nickel concentrated undersize fraction as an additional feed into an acid leach circuit (e.g. atmospheric leach (AL) circuit) can potentially provide in a 3,500 ktpa nickel laterite operation some 200 ktpa of feed exceeding 1% nickel.

Methods and uses

[0093] The present inventors have discovered a method of at least partially neutralising an acid comprising contacting an acid neutraliser composition as described herein or an acid neutraliser composition recovered by the as described herein with the acid.

[0094] The present inventors have discovered a use of an acid neutraliser composition as described herein or an acid neutraliser composition recovered by the process as described herein for at least partially neutralising an acid. In one embodiment, the acid is a free acid in a leach slurry.

[0095] In another aspect or embodiment, there is provided method of at least partially neutralising an acid with an acid neutraliser composition, comprising: screening crushed magnesite-containing saprock into a screened undersize fraction and a screened oversize fraction comprising magnesite as the acid neutraliser composition; optionally, milling the acid neutraliser composition; contacting the acid neutraliser composition with an acid to at least partially neutralise the acid; and optionally, passing the screened undersize fraction to an acid leach step to recover nickel values.

[0096] In another aspect or embodiment, there is provided a method of recovering nickel values from a nickel laterite ore, comprising: a) acid leaching a nickel laterite ore comprising heating a slurry containing a nickel laterite ore and sulfuric acid under conditions effective to produce a leached nickel-bearing slurry; b) screening crushed magnesite-containing saprock into a screened undersize fraction and a screened oversize fraction comprising magnesite as the acid neutraliser composition; and optionally, milling the acid neutraliser composition; c) optionally, passing the screened undersize fraction to the acid leach step a) to recover nickel values; d) contacting the acid neutraliser composition with the leached nickel-bearing slurry to at least partially neutralise free sulfuric acid; and e) washing the neutralised nickel-bearing slurry and separating solids therefrom to produce a nickel-bearing solution.

[0097] As exemplified in Figure 1, in another aspect or embodiment, there is provided a method of recovering nickel values from a nickel laterite ore (100), comprising: a) acid leaching (101) a nickel laterite ore (100) comprising heating a slurry containing a nickel laterite ore and sulfuric acid under conditions effective to produce a leached nickel -bearing slurry (102); b) screening (103) crushed magnesite-containing saprock (104) into a screened undersize fraction (105) and a screened oversize fraction comprising magnesite as the acid neutraliser composition (106); d) milling (107) the acid neutraliser composition (106) to obtain a comminuted acid neutraliser composition (108); e) passing the screened undersize fraction (105) to the acid leach step (101) at step a) to recover nickel values; f) contacting the comminuted acid neutraliser composition (108) with the leached nickel -bearing slurry (102) to at least partially neutralise free sulfuric acid (109) to produce a neutralised nickel-bearing slurry (110); and e) washing (111) the neutralised nickel-bearing slurry (110) and separating solids (112) therefrom to produce a nickel-bearing solution (113).

[0098] It will be appreciated that in some embodiments, the solids obtained from the washing step (112) according to any aspects or embodiments described herein may undergo further processing. For example, the solids may be subjected to a further neutralisation step to make them suitable for storage (e.g. a tailings neutralisation step and subsequent tailings storage).

[0099] It will also be appreciated that in some embodiments, the nickel-bearing solution (113) obtained from the washing step according to any aspects or embodiments described herein may be further processed to obtain one or more desirable products. For example, the nickel-bearing solution may undergo one or more purification steps to remove one or more undesirable impurities and/or recover the desirable products. For example, the nickel -bearing solution may be subjected to a neutralisation step and/or one or more precipitation steps. For example, magnesium oxide may be added to the nickel bearing solution to precipitate a mixed hydroxide product from which nickel and cobalt containing products can be obtained. Other processing steps are also envisaged as required. In some embodiments, in addition to the recovery of nickel containing products, processing of the nickel-bearing solution obtained from the washing step may allow for the recovery of other desirable products including, but not limited to, soluble salts of scandium, rare earths, aluminium and other metals.

[0100] The embodiments and examples described above for the acid neutraliser composition, saprock, screened fractions, free acid and leach slurry etc., and any applicable process steps, equally apply to the methods and uses described herein.

[0101] The present application claims priority from AU2022903389 filed on 11 November 2022, the entire contents of which are incorporated herein by reference.

EXAMPLES

[0102] In order that the disclosure may be more clearly understood, particular embodiments of the invention are described in further detail below by reference to the following non-limiting experimental materials, methodologies and examples.

Example 1: Selectively extracting magnesite-containing saprock [0103] Five magnesite-containing saprock samples were selectively extracted from the regolith and/or saprock regions of a nickel laterite deposit/profile. These samples were taken to provide a representative sample of the composition of the magnesitecontaining saprock from the total nickel laterite deposit/profile. Each sample was analysed to determine its composition and these are shown in Table 1.

[0104] The overall composition of the magnesite-containing saprock extracted from the nickel laterite deposit/profile for crushing and subsequent screening to obtain the acid neutraliser composition is then calculated as the weight average of these samples. This is also shown in Table 1.

[0105] It will be appreciated that the composition of the magnesite-containing saprock being crushed and screened to obtain the acid neutraliser composition in this example will have a % w/w composition that generally reflects the weighted average shown in Table 1.

Table 1: Composition of magnesite-containing saprock

Example 2: Preparation of acid neutraliser composition

[0106] The five samples of magnesite-containing saprock were combined to provide a total of 60.5 kg. The 60.5 kg magnesite-containing saprock was then crushed. The crushed magnesite-containing saprock was then wet-screened at 75 microns to obtain an undersize fraction (e.g. fines) and oversize fraction (e.g. scats). The oversize fraction was subsequently milled to sub 75 microns to enhance its neutralisation potential.

[0107] The composition of the undersize and milled oversize fraction (i.e. acid neutraliser composition) is shown in Table 2. The undersize fraction has an increased nickel content relative to the oversize fraction.

Table 2: Screened fraction compositions

Example 3: Acid neutralising capacity (ANC) test procedure

[0108] The neutraliser test procedure was as follows:

(1) The neutralisation tests were conducted in a 5 litre baffled glass vessel, with agitation provided by an overhead stirrer driving a pitch bladed Teflon impellor.

(2) The test commenced with the addition of solid sample to sulphuric acid solution that had been heated to 95°C using a temperature-controlled hotplate. The pH of the slurry was measured using a pH probe (calibrated at 95°C using heated pH buffers). (3) The initial slurry consisted of a pre-determined mass of 50 g/L sulphuric acid solution prepared using the synthetic process water and the required mass of solids. The initial mass of 50 g/L sulphuric acid solution was based on the calculated ANC (acid neutralising capacity) of the solids. Further small incremental amounts of solids were added to achieve the target slurry pH or just over.

(4) Once the initial slurry had been prepared, manual additions of 100 g/L sulphuric acid solution were required to maintain the target pH value. The test was conducted for 4 hours with regular sampling of the slurry to provide solution and residue solids for analysis.

(5) The tests were conducted in two stages:

Stage 1 : pH 2.5 at 95°C for 4 hours

Stage 2: pH 5.0 at 80°C for 6 hours

(6) After the first stage had been completed the slurry was cooled to 80°C and further solids carefully introduced into the slurry to achieve the second stage pH target. Again the pH was controlled using small additions of 100 g/L sulphuric acid solution. The second stage was conducted for 6 hours with regular sampling of the slurry to provide solution and residue solids for analysis.

(7) Slurry samples taken during the test were weighed and centrifuged to recover solution which was filtered for analysis. The solids were washed three times by dilution with pH and calcium adjusted wash water and centrifuging/decanting. The final thickened washed slurry was filtered and the solids dried for analysis.

(8) Solution samples were analysed for Al, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, S, Si and Zn by ICP. Free acid titrations were also conducted.

(9) Solid samples were analysed for the same element suite as the solutions using XRF. (10) The bulk slurry at the end of the test was weighed and filtered to recover the final solid residue.

Example 4: Neutralisation results

[0109] The neutralisation test results are presented in the tables below:

[0110] The acid neutralisation test on the “Milled” <75 pm Neutraliser determined that 1298 kg of dry solids is required to neutralise 1000 kg of sulphuric acid to pH 2.5 at 95°C. Expressed as kilograms of acid per tonne of solids the neutralising capacity is 771 kg H ₂ SO ₄ /t. [0111] To raise the slurry pH from 2.5 to 5.0 it was determined that 5,627 kg of solids is required to neutralise 1000 kg of sulphuric acid at 75°C. Expressed as kilograms of acid per tonne of solids the neutralising capacity is 178 kg H2SO4/t.

[0112] During acid neutralisation to pH 2.5 it was determined that the dissolution of the sample was 52.4% by mass (i.e. 47.6% of the initial sample mass remained at the end of Stage 1). The additional solids added to raise the slurry pH from 2.5 to 5.0 lost approximately 21% by mass. The calculated combined solids mass loss for Stage 1 and Stage 2 was 39.5% (i.e. 60.5% of the total sample mass added in Stage 1 and Stage 2 remained at the end of Stage 2).

[0113] Metal extractions calculated from metal in solution versus metal in sub-sample (metal in solution plus metal in solids) compared well with extractions calculated using the silica tie method. For example nickel leached in Stage 1 was calculated at 82.7% (metal in solution method) versus 85.0% using the Si tie method. Similarly overall nickel extraction at the end of Stage 2 was calculated at 51.7% (metal in solution method) versus 55.7% using the Si tie method. For cobalt extractions, the metal in solution method obtained 71.9% versus 75.1% for Si tie method. Overall cobalt extraction was 56.3% by metal in solution method versus 63.0% by Si tie method. Iron and aluminium leached during Stage 1 neutralisation at pH 2.5 but precipitated during Stage 2 neutralisation at pH 5. Solution assay data shows 10 mg/L Al at pH 2.5 and <2 mg/L at pH 5. For Fe solution assay was 388 mg/L at pH 2.5 and <1 mg/L at pH 5.

[0114] The acid neutralisation tests indicated that, while the milled acid neutraliser composition comprising magnesite could produce the target pH endpoint (~pH 5) under simulated process conditions, its ANC value was relatively low, at less than 200 kg acid/tonne reagent. However, the milled neutraliser was found to react very efficiently under more acidic conditions, such as a primary neutralisation of leach slurries, where the pH is expected to be lower than pH 3. As demonstrated above, a further benefit of this procedure is that the nickel and cobalt values present in the magnesite can pass into solution, which yields a production bonus due to the extra metal recovery. [0115] Based on these results, the mineralized acid neutraliser composition and associated processes described herein may provide one or more benefits, including:

• Reduced mining and operating costs due to in-house reagent supply;

• Lower tailings solid volume and tailings storage costs with consequent environmental benefit; and/or

• Increased metal recovery.