LIQUID AND SOLID EFFLUENT TREATMENT PROCESS

RELATED APPLICATION

[0001] This application claims pπoπty from U S provisional patent application

61/021,147 which was filed on January 15, 2008, and U S application No 12/331 ,058 which was filed on January 9, 2009

BACKGROUND OF THE INVENTION

[0002] The present invention refers to a process for treatment of liquid and solid effluents allowing recovering metals through piecipitation of co-sulphide, enabling magnesium recovery and providing sulphate recovery as gypsum and ammonium sulphate

[0003] The main objectives of any method foi treatment of liquid and solid effluent are (i) neutralize and fit them in a pioper manner to be launched and ietumed to environment and (a) obtain recyclable byproducts to be reused in the mannei of a captive consumption and/or via commercialization to third parties

[0004] In utilization of latentic and nickeliferous ores, seveial factors affect nickel pioduction process by hydiometallurgical ioute and high pressure acid leaching (HPAL), namely

• Geological origin of beds,

• Oi e mineralogical composition,

• Oi e granulometπc distribution,

• Piocessing operation conditions,

• Configuiation of ore pieparation, leaching, piecipitation, solvent extraction and electio-iefirung systems

[0005] High piessure acid leachmg (HPAL) is iecommended foi predominantly limonitic ores presenting low contents of magnesium - usually limited to 4% at most - once oies bearing high contents of magnesium piesent a high consumption of sulphuπc acid

[0006] Processes used to produce nickel by known loutes, such as HPAL, as illustrated in figure 1, essentially comprises the following steps (i) piepaiation of nickel lateπtic ore, (n) nickel leaching under piessure with sulphuric acid, (in) nickel piecipitation, (iv) re-leachmg, (v) nickel so lvent-exti action and (vi) electro-refinmg for pioduction of cathode nickel (metallic nickel with 99 95% purity) In view of the significant piesence of cobalt in ore, the same is will be obtained as a coproduct, also in metallic form

[0007] This technology is the most indicated piocess to extract nickel and cobalt fiom limonitic lateπtes due to the following advantages

• limonitic lateπtes present low magnesium contents and, therefore, a low consumption of sulphuiic acid,

• Low operating cost due to low cost of sulphuπc acid and low specific consumption theieof,

• No drying or reduction stage is required, as raw lateπte (Run Of Mine - ROM) is used in suspension form,

• High selectivity to relevant metals,

• Sulphur dioxide emissions below environmental standaids,

• Recovery rates above 90% for nickel and cobalt contained m the oie

[0008] Leaching under pressure is usually performed in titanium-coated autoclaves, in temperatures ranging fiom 463 to 518° F (245 to 27O ⁰ C) In this process, autoclave feed suspension contains approximately 40-45% solids, when previously heated with steam In some ores, due to natuie of aigillaceous ore which are piesent, tins concentiation may be limited up to 25% to 30% Thickening level of the suspension has a significant influence in autoclave capacity, which constitutes an equipment with a high capital cost Leaching mechanism involves acid dissolution in high tempeiature of nickel and cobalt contained in the host ore matnx In these conditions, non dissolution of these oies occur, followed by formation of sulphates, which in high tempeiatuie conditions ieact with water to form hematite, theieby regenerating sulphuiic acid

2 FeOOH + 3 H ₂ SO ₄ = Fe ₂ (SO ₄ ) ₃ + 4 H ₂ O Fe ₂ Si ₄ Oi ₀ (OH) ₂ + 3 H ₂ SO ₄ = Fe ₂ (SO ₄ ) ₃ +4SiO ₂ + 4 H ₂ O Fe ₂ (SO ₄ ) ₃ + 2H ₂ O = 2 Fe(OH)SO ₄ + H ₂ SO ₄ 2 Fe(OH)SO ₄ + H ₂ O = Fe ₂ O ₃ + 2H ₂ SO ₄

[0009] Extraction levels of this piocess ieach values fiom 92% to 96% for nickel and 90 to 92% for cobalt Normally, in order to obtain this degiee of extiaction, reaction suspension aftei chemical attack should present a residual fiee acid concentration between 30 and 50 g/1

[0010] Aftei leaching, autoclave-derived suspension is depressunzed and cooled in expansion chambers (flash vessels), at approximately 212 ⁰ F (100°C), the iemammg solids being sepaiated from liquid phase Solid-liquid sepaiation is peifoπned in decanters opeiatmg m countercurrent (CCD), geneiating a liquor laden with nickel, cobalt, magnesium, manganese, zinc, coppei, iron and othei metals sulphates Then, nickel and cobalt piesent m the liquor are piecipitated in the mannei of sulphides (by using H ₂ S), carbonates (by using ammonium carbonate) oi as hydroxides, by using magnesia - MgO These intermediate products usually present contents of 55% (Ni+Co) foi sulphides (MSP - Mixed Sulphide Precipitate) and 40 to 45% (Ni+Co) in case of hydioxides (MHP - Mixed Hydroxide Precipitate) Recoveiy of these metals is also possible through solvent extraction directly applied to hquoi derived from decantation system It should be noted

that MSP process enables to obtain a product with a higher contents of valuable metals and a lowei level of contamination by manganese, magnesium and sulphates However, pioduction by MSP route involves a high capital cost foi auxiliary facilities, once hydrogen and hydrogen sulphite units aie necessary, requiimg sophisticated secuπty and handling systems foi these products

[0011] In the next step - iefinmg - intermediate pioducts (sulphites or nickel and cobalt hydioxide) are re-leached and so, dissolved, they are submitted to purification treatments, such as (i) solvent extiaction for nickel and cobalt sepaiation and (n) electiolysis (electro-refining) aiming to ieach higher degiees of purity.

[0012] In nickel production process by HPAL route fiom oie containing silicate and magnesium carbonate, geneiation of liquid effluent m proportions from 250 to 400 m3/kg of Ni pioduced takes place, containing essentially magnesium and sulphate, and in a small quantity, cobalt, zinc, manganese, nickel, iron, chiomium, among othei elements Table 1 presents chemical composition of the effluent to be tieated and shows the significant sulphate and magnesium contents

Table 1 - Composition of effluent to be treated

Components Unit Contents

Ni ppm 2,00

Co ppm 6,00

Zn ppm 0,90

Mn ppm 40,00

Fe ppm 10,00

Cr g/i 3,45

Mg g/i 18,00

SO4 g/i 75,00

NH3 g/L 0,50

PH 7,5

[0013] Effluents treatment piocess has being exhaustively used to avoid sending- off noxious waste in the environment Most part of the final product of the effluents tieatment has being discharged when it could be reused in the main process oi for any other situation in many field In this sense, US patent 6,861,041 iefers to a method for

treating and upgiadiπg effluents containing at least a metallic sulphate This method compiises steps which consist in adding at least a base to the effluent to piecipitate the metallic ions in the form of metallic hydroxides Mea(OH)e, sepaiatmg the precipitated hydroxide calcium sulphate CaSO4, and separating the calcium sulphate CaSO4 precipitated during the preceding step Said method enables to obtain calcium sulphate (white gypsum) substantially fiee of metals and therefore capable of being upgiade and metallic oxy-hydi oxides likewise capable of being upgraded Even though this piocess allows lemoving metallic sulphate from the effluent, the final pioduct of the tieatment, the sulphate, is not reused

[0014] Further, GB patent 1346524 discloses a tieatment of polluted watei that comprises mixing the water with one or more of sulphuric acid, nitπc acid and hydiochloπc acid to lower the pH of the water to at least 2 5, maintaining this pH for a time sufficient to destroy bacteria present, then bringing the mixtuie into contact with an acid soluble form of iron for a time sufficient for the iron to react with part of the acid and then raising the pH of the mixture to 7 by the addition of an aUcaline solution Duπng the contact with the acid soluble form of iron, at least one salt selected from the sulphates and nitrates of iron and aluminium, may be piesent The mixture of acid and water is piefeiably contacted with at least 3 2 sq ft (0 3m ^" ) of iron per gallon pei minute of acid and water mixture, Ammonium, sodium and potassium hydroxides are suitable alkaline solutions for use in the neutralization step

SUMMARY OF THE INVENTION

[0015] Due to the above mentioned characteristics of the liquid effluent and ceitain limitations of the current ioutes foi nickel pioduction piocessmg related with effluent treatment methods and ieuse of treated water, the present piocess was developed to recovei (i) magnesium and (ii) sulphui The foπner, in Older to be recycled m the own nickel extiaction hydiometallurgical process, for agricultural purposes (correctives and fertilizers) and as iaw material foi industry in general The latter, in form of calcium

sulphate and/oi ammonium sulphate (SAM), used as agπcultuial collective and nitrogenous feitihzer, respectively

[0016] Additionally, this process enables to remove iemainmg metals in the liquid effluent, such as Mn, Zn, Co, Cu, among others, which allows (i) a significant improvement in quality of watei, theieby ci eating conditions foi its full recycling m industrial processes and (n) enables an additional pioduction of micionutπents for agπcultuial purposes, among otheis

[0017] The mam characteristics of the present process are a) use of ammonia, an easily recyclable substance generating alkaline conditions, lecovery and lmpiovement in valuable co-products, b) use of quicklime (CaO) as a supplementary heat generator and sulphate fixation agent (CaSC^ 2H ₂ O, dihydrate gypsum), c) lemoval of metal remaining in liquid effluent (Co, Mn, Ni, Zn, Cu, etc ) and impiovement theieof as law material in pioduction of micro nutnents for agricultural puiposes, d) lemoval of soluble magnesium, deπved fiom mckeliferous lateiite acid solubilization, in the form of precipitated Mg(OH) ₂ and its change mto magnesium (MgO) for purposes of reuse m the own nickel extraction process and as iaw material for agiicultuial and industrial puiposes, e) removal of sulphate (SO ₄ ^" ) in the form of (1) ammonium sulphate (SAM) - (NH^ ₂ SO ₄ - and/or (11) calcium sulphate - CaSθ ₄ 2H ₂ O -, for agricultural and industrial puiposes as well, f) change of liquid effluent mto water with a sufficient degiee of purity for industrial purposes, thereby piovidmg operations in condition of "zeio effluent", with a significant ieduction in consumption of replacement water in industrial complex, g) this process, m addition to significantly reduce envuonmental impact of industrial opeiations, provides (1) reduction of CO ₂ emissions and (11) an increase in use of the othei nickel-related mineral resouices,

h) moieovei, this liquid effluent treatment process piesents a wide opeiatmg flexibility and can be implemented in a modular manner

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In the drawings

[0019] FIG 1 is a schematic diagram of nickel production process by the prior art

HPAL piocess,

[0020] FIG 2 is a schematic diagiam of liquid effluent tieatment piocess accoiding to Route I, and

[0021] FIG 3 is a schematic diagram of liquid effluent treatment process according to Route II

PREFERRED EMBODIMENT OF THE INVENTION

[0022] Figures 2 and 3 show the two modalities of opeiation for the effluent treatment piocess (Route I and Route II) under the present invention patent The effluent treatment umt, in view of its flexibility, contemplates the two ioutes mentioned (I and II), and may further operate by direct neutralization of the effluent, with as quicklime (CaO), thereby iesultmg in a precipitate containing CaSO ₄ 2PLO, Mg(OH) ₂ and MgCO ₃ , which can be stored foi subsequent use in the agricultural area

[0023] In Route I (Figuie 2), the liquid effluent (1) is received in agitated tanks foi equalization Then, the homogenized effluent (2) leceives additions of sulphides (3) - in the form of NaiS and/or H ₂ S - foi piecipitation of iemaining metals - Ni, Co, Mn, Zn, Cu, among otheis - in the form of metallic sulphides (4) In the subsequent step, metallic sulphides are submitted to a solid-liquid separation step, resulting m a cuπent plenty of metallic sulphides (5) Washed m a suitable manner, sulphides are oxidized in oxygen injection-agitated reactors (6) and the resulting solution (7) is submitted to crystallization

aimed towaids obtamment of the lespective salts (8), either fractioned or mixed, which aie stored and sent to shipment (9)

[0024] The liquid effluent tieated in this way and practically metal-free (10) is transferred to a reaction system, composed by agitated tanks and tray columns, where it is contacted with ieplacement ammonia (12), lecoveied ammonia gaseous current (1 1) and a weak ammoniacal solution (14) from washing of precipitated magnesium hydroxide (19), iesultmg the piecipitated magnesium hydi oxide suspension This suspension is tiansferred to a thickenei to impiove the solids contents and deciease the solid/liquid separation step and then to a solid/liquid separation m order to deciease the quantity of water foi the step of dry and calcinations with an economic consumption of eneigy

[0025] Washed magnesium hydroxide (15) is transfeπed to drying and calcination, iesultmg in the obtamment of magnesia (16) which is stoied, a part of which being recycled to the nickel extraction process and the remaining part commercialized

[0026] In the reaction system, pH of the precipitation is kept withm the iange between 9 and 11 and the ammonia concentration between 20 and 150 g/L of NH ₃ The tempeiatuie is between 60 ⁰ C and 100 ⁰ C, the solid quantity is between 1,5% and 15% w/w and the iesidence time can vary fiom 0,5 to 2 hours

[0027] Part of precipitated magnesium hydioxide suspension cuculates again to the contacting ieactois in order to promote growth of Mg (OH) ₂ crystals by means of seeds, by the iatio of 1 1 until 15 1

[0028] Gaseous current leaving piecipitation reactors (17) is tiansferred to the ammonia depletion system and, together with the addition of low pressuie steam (21) - 2 to 6 kgf/cm ² man - free ammonia contained in the effluent without magnesium (20) - liquid phase of solid-liquid separation Of Mg(OH) ₂ - is lemoved in a depletion operation that takes place m a multiple stages depletion column, countei-flow, with a low pressure

steam/air mixture, pieferably between 2 to 6 kgf/cm ² The free ammonia is lecovered and tiansfeπed to the magnesium piecipitation system The effluent so tieated (22) piesents about 0 to 1 g/L free NH ₃ and about 15 to 30 g/L total NH ₃

[0029] Liquid effluent resulting from ammonia depletion (22) contains appioximately 90 to 140 g/L ammonium sulphate (SAM) - (NH ₄ )ISCU - in solution In these conditions, the liquid effluent is submitted to clarification foi lemoval of suspended solids remaining in the supernatant phase (23), resulting in a claiified (24) After the claiification the solution is concentrated through membianes - opeiations of microfiltering, ultiafiltenng, nanofiltenng, and reverse osmosis - oi electiodialysis, iesulting in a lecovered water current (25) and anothei saline solution cuπent (26), containing about 200 to 450 g/L of dissolved (NH ₄ ) ₂ SO ₄

[0030] This saline solution (26) is then fed in an evapoiation-crystalhzation system, with a number of steps ranging fiom 3 to 6, receiving low pressme steam (27) Removal of watei denved from evapoiation process promotes crystallization of ammonium sulphate (30), which is centπfuged, dπed, stoied and shipped (31) at the end Crystallized ammonium sulphate presents a purity ranging from 94 to 97%, which leads to products with medium nitrogen and sulphur contents of the older from 20% and 23%, lespectively

[0031] Recovered water (28) in evapoiation-crystalhzation unit is sent to recoveied water storage tank, together with recovered water current (25) of the membiane tteatment umt, to be ieused duπng nickel industrial piocessmg (13, 29)

[0032] Oscillations in ammonium sulphate demand caused by vaπations in the fertihzei maiket can be compensated with vaπations m stoiage of this product

[0033] However, should that condition become more evident, Route II (Figure 3), together with the magnesium precipitation process, allow fixation of sulphate with

quicklime (32), thus generating a suspension of dihydrate calcium sulphate (33) - CaSθ ₄ 2H ₂ O - which is densified in a thickenei and pumped (35) to the gypsum stoiage stack (Stack I) This route II should be used when there is a πgoious i eduction in the ammonium sulphate demand m the maiket In this case, the lime is added aftei the magnesium hydroxy piecipitation for converting of ammonium sulphate in calcium sulphate and consequently liberating the ammonia and its return to the piocess The densification of the calcium sulphate is necessary to deci ease the period of solid/liquid step

[0034] Should the precipitation system of magnesium hydroxide with ammonia be out of operation, neutralization of effluent, as well as sulphate and magnesium piecipitation can be performed by adding quicklime and carbon dioxide (34), resulting in a mixed gypsum precipitate, magnesium and calcium hydioxides and caibonates (35'), which should be stoied apart (Stack II) In this case, the thickenei supernatant (36) goes to a mam tank and therefrom (37) to the softening unit with ionic exchange iesins - IX, regeneialed with salts oi alkalis (38) and acids (39) Resulting softened watei (40) is transferred to a recoveied watei tank and iecycled therefrom m the nickel extiaction piocess (41)

[0035] Thus, by coupling Routes I and II, a flexibility is cieated to absoib variations (i) in generation of liquid effluent, due to pluviometπc system in industrial complex, and (ii) seasonality of demand of bypioducts resulting fiom tieatment ammonium sulphate, agricultural gypsum and micronutπents

EXAMPLE

[0036] Simulation tests of the process under the present patent performed in laboratory scale showed the possibility to obtain byproducts (solids, recyclable) with business value and recoveied water with propel quality foi reuse m industiial process, which allows to reach the condition of zeio effluent as to liquid effluent emissions Table

2 shows evolution of quality of liquid effluent in the course of treatment piocess under the present patent

Table 2 - Evolution of quality of the effluent along the treatment process

Effluent After Me ⁺ " After Mg After SAM

Components Unit Just as precipitated precipitated crystallized

Ni mg/L 2,00 <0,5 <0,5 <0,5

Co mg/L 6,00 <0,5 <0,5 <0,5

Zn mg/L 0,90 0,90 0,90 0,90

Mn mg/L 40,00 9,00 9 00 0,10

Fe mg/L 10,00 0,30 0,30 0,30

Cr mg/L 3 450,00 0,05 0,05 0,05

Mg mg/L 18 000,00 18 000,00 1 555,20 62,50

SO4 mg/L 75 000,00 75 000,00 75 000,00 250,00

NH3 mg/L 500,00 500,00 120 000,00 nd

PH 7,5 - 10,6 7,0

[0037] As byproducts, the following have been obtained (i) magnesium oxide

(MgO), with a proper quality foi reuse in nickel extiaction process, (ii) metallic sulphides, as iaw material for obtarnment of agricultural micronutnents, (in) dihydrate gypsum, also foi agricultural purposes and (iv) saline solution containing ammonia sulphate in solution, proper for evaporation and crystallization purposes

[0038] While in accordance with the provisions of the statute, there is illustiated and descπbed herein specific embodiments of the invention Those skilled in the art will understand that changes may be made m the form of the invention coveied by the claims and that certain featuies of the invention may sometimes be used to advantage without a corresponding use of the other features