Field of the Invention
The present invention relates to a process for the recovery of copper and nickel in the form of powder from a high iron containing waste or secondary resource. Copper and nickel are the metals of high value/strategic importance and therefore their recovery from such waste and by-product is of great importance particularly for producing value added products such as powders with specific demand in the area like powder metallurgical (P/M) applications. Copper and nickel powders can also be prepared from other copper-nickel containing secondary resource from other industries. Background of the invention and Description of the prior art
The invention particularly relates to selectively producing copper and nickel powder by the treatment of a high iron containing waste material/by-product, generated at south African mines during recovery of copper and nickel from the roasting of chalcopyrite and pendlindite and provided by Refmet Technology (P) Ltd. Raipur, through leaching-crystallisation of the copper and nickel containing solution-leaching with water followed by iron removal - separation of copper and nickel from the mixed solution by solvent extraction-reductive precipitation stripping of the loaded organic containing copper or nickel to get pure metal powder. During recovery of copper and nickel from a complex sulphide concentrate containing chalcopyrite and pentlandite by roasting in a fluidized bed, a high iron containing ferritic by-product having substantial amount of copper and nickel is generated [Opie, W.A., Coffin, L.D., Cusanelli, D.C. In J.C. Yannopoulos, J.C. Agrawal (Eds.), Extractive Metallurgy of Copper, New York, 1: 1980, pp416-426].
The conventional hydrometallurgical processing for recovery of metals from ores concentrates or wastes involve leaching, solvent extraction followed by electrowinning or H2-reduction of purified and concentrated aqueous solution. In this process metal ions from the complex leach liquor are separated by solvent extraction with suitable organic extractant. The loaded organic is then treated with acid solution to regenerate purified aqueous solution of desired metal. Fro.m the purified aqueous solution metal powder can be prepared by electrowinning or H2-reduction. The reference may be made to recent reports [A. Agrawal, S. Kumari, D. Bagchi, Vinay Kumar, B.D. Pandey Min. Engg., 20, 2007, 95-97 and A. Agrawal, D. Bagchi, S. Kumari, Vinay Kumar, B.D. Pandey, Powder
Technology, 177, 2007, 133-139] wherein high grade copper and nickel powders were produced from copper bleed electrolyte solution by electrowinning process. Krupin et al. [Krupin, S.V. and Yurev, B.S. Sov. Powder Metall. Met. Ceram.,14, 1975, 17-19] have prepared nickel powder from several solutions. Main drawback of the electrowinning process is that the composition of the solution changes during deposition so that frequent corrections are needed to maintain a constant quality and grain size of powder. Under optimum conditions current efficiency is also rather low of 30-50% [Applet, K. and Paszkiowiez, Electrochim. Acta, 13, 1968, 843-849]. Reference may also be made to [A. Agrawal, V. Kumar, B.D. Pandey, K. K. Sahu, Mat. Res. Bull., 41, 2006, 879-892] wherein preparation of metal powders by t^-reduction from the leach solutions of metals from their ores has been reviewed. The main requirements of producing metal powders are purity of individual metal sulphates, metal ion concentration, specific pH, seeding and additives, thus restricting the applicability in complex situation as encountered in the processing of wastes and secondaries.
In all the hydrometallurgical processing routes for metals such as electrowinning or H2-reduction of aqueous solution, solvent extraction technique is used to separate and prepare purified precursor solutions for the recovery of metals. Apart from purification role, there exists distinct possibility of using solvent extraction media for the in-situ preparation of high value materials. Hydrogen stripping in solvent extraction is an alternative to aqueous based stripping and electrowinning, allowing direct high purity metal powder production from the organic phase. The concept of combining stripping and metal recovery into a single step by reacting the loaded organic medium with hydrogen gas has been suggested by Burkin, US Pat. No. 3,532,490 and Van Der Zeeuw, British Pat. No-. 1,265,586. On a laboratory scale, the technique has been tested for synthetically prepared solution of copper, nickel and cobalt for extraction and precipitation by organic reagents such as tertiary monocarboxylic acids [Burkin, US Pat. No. 3,844,763; Burkin, US Pat. No. 3,532,490], alkyl phosphoric acids [Burkin, A.R., Burgess, J.E.A., Proc. 1st Annual Meeting of Canadian Hydrometallurgists, Montreal, Canada, 1971, pp 51-62], and chelating extractants [Demopolous, G.P., Distin, P.A., US Pat. No. 4,5411,861]. The major drawback of this technique is its unsuitability for direct production of value added products from ores, concentrates or secondary materials.
Object of the Invention
The main objective of the present investigation is to provide a process for recovery of copper and nickel powders from a high iron containing waste or secondary resource which over rules the draw back as detailed above. Summary of the Invention
In the process of present invention a waste/by-product containing substantial amount of copper and nickel is leached with sulphuric acid. The leach solution is then evaporated to crystallize mixed sulphates of copper and nickel and recycling acid of the mother liquor for releaching. From the solution containing copper and nickel sulphates, pH is adjusted and iron is removed by precipitation. The solution is then subjected to solvent extraction to separate copper and nickel. The loaded organic containing copper or nickel is then hydrogen stripped to get pure copper and nickel powders, the copper and nickel powders thus produced possess desired purity and size for powder metallurgical (P/M) applications. Detailed description of the invention
Accordingly, the present invention provides a process for preparation of copper and nickel powders from a high iron containing waste or secondary resource, which comprises:
i. providing high iron containing, ranging between 15-40%, waste or by-product having substantial amount of copper and nickel generated during recovery of copper and nickel from a sulphide concentrate with chalcopyrite and pentlandite by roasting, ii. leaching of the said by-product (stage 1) with sulphuric acid, iii. leaching of leach residue (stage 2) obtained in step (ii) with sulphuric acid, iv. mixing the leach liquors obtained in step (ii) and step (iii), v. evaporating the mixed leach solution so obtained in step (iv) to crystallize out mixed sulphate salts of copper and nickel and generating mother liquor with high acid for recycling in leaching, vi. leaching the said mixed copper and nickel sulphate salts in aqueous media, vii. removing the precipitated iron from the mixed sulphate solution obtained in step (vi) by adjusting pH at 4.5,
viii extracting copper from the above said solution from step (vii) at pH 5 by solvent extraction with extractants selected from a group consisting of organophosphorus, organophosphonic acid, tertiary mono carboxylic acids having carbon atoms above 9,
ix extracting nickel from the raffinate of step (viii) at pH 6.8 by solvent extraction with reagents which are selected from a group consisting of organophosphorus, organophosphonic acid, tertiary mono carboxylic acids having carbon atoms above 9,
x reductive precipitation stripping of loaded organic containing copper or nickel obtained in step (viii) and (ix),
xi washing and drying of the copper and nickel powder for powder metallurgical application.
In an embodiment of the present invention the by-products containing copper oxide, nickel oxide, copper and nickel ferrites as phases is selected with composition in the range 5-30% Cu, 2-15% Ni, 15-40% Fe, 1.5-5% Si02 and 1-5% A1203 to recover copper and nickel by leaching with sulphuric acid. Leaching (stage 1) of the by-product with 20-40% (v/v) sulphuric acid solution at 368 K and 20% (w/v) pulp density may produce leach solution containing 10-55 g/L copper, 2-20 g/L nickel and 20-30 g/L iron with a recovery of 90-95% copper, 50-60% nickel and 70-75% iron.
Subsequent leaching (stage 2) of the leach residue containing 1-5% copper, 1-10% nickel and 5-15% iron with 20-40% (v/v) sulphuric acid at 368 K and 20% (w/v) pulp density may produce leach solution containing 2-10 g/L copper, 5-15 g/L nickel and 30-50 g/L iron with a recovery of 95-98% copper, 55-60% nickel and 75-80% iron. In two stage sulphuric acid leaching of the material the overall recovery may be 95-99% copper, 80-85% nickel, 90-95% iron. Mixed leach solution of stage 1 and 2 may contain 10-40 g/L copper, 5-20 g/L nickel and 20-60 g/L iron.
In another embodiment of this invention the mixed leach solution may be evaporated to its 50% volume to get mixed sulphate crystals of copper, nickel and iron. The mixed sulphate crystal may be redissolved in aqueous solution and pH may be adjusted to 4.5 to remove iron as precipitate from the leach solution. Iron free leach
solution may have the composition 5-35 g/L copper and 2-15 g/L nickel. The mother liquor from the crystallization step with 200-400 g/L sulphuric acid may be recycled for leaching.
In yet another embodiment of this invention the iron free leach solution may be treated for copper solvent extraction with organo phosphoric/phosphonic acid, tertiary mono carboxylic acids having more than 9 carbon atoms in kerosene. Along with copper some amount of nickel may also be extracted into the organic phase which can be easily scrubbed with very dilute sulphuric acid solution. Remaining copper in the raffmate may be removed by one more stage of solvent extraction. From the copper free raffmate nickel may be extracted almost quantitatively using above extraction reagents.
In still another embodiment of the present invention the high grade copper or nickel powder may be prepared by reductive precipitation/stripping of the loaded organic solution containing 20-25 g/L copper or nickel, using carbon monoxide or hydrogen gas as reductant in autoclave at pressure 5-60 bar, temperature 390-500 K and 150-700 rpm for 10-180 min. In the process of present invention copper and nickel powders (of very close size range: 10-100 urn for Cu and 0.5-5 um for Ni) prepared by reductive precipitation stripping of respective loaded organic is washed with acetone. The metal powders prepared may be of 99.9% purity with a stripping efficiency of 90-99.9%.
Novelty of the present invention is development of a simplified and selective extraction process for recovery and preparation of value added products viz. high grade copper and nickel powder from ferritic waste/by-product generated during the recovery of copper and nickel from a complex sulphide concentrate by roasting. The main novelty of the invention is production of high purity P/M grade metal powders by leaching-crystallisation-solvent extraction-reductive precipitation/stripping, which is nowhere cited in the literature.
Flow Chart
(Flow Chart Removed)
The following example is given by way of illustration and should not be construed to limit the scope of the invention.
Example-1
A by-product/waste material containing 22.4% Cu, 7.9% Ni and 36.3% Fe 3.05 % Si02 and 2.72 % A1203 was leached with 20% (v/v) sulphuric acid solution at 368 K and 20% (w/v) pulp density. The leach residue containing 4.7% Cu, 10.7% Ni and 29.6% Fe was further leached with 30% sulphuric acid solution at 368 K and 20% (w/v) pulp density. The leach solutions obtained from the two stages of leaching were mixed together and evaporated to its 50% volume to get mixed sulphate crystals of copper, nickel and iron. The mixed crystals were filtered, redissolved in water, and then pH was adjusted to 4.5 to remove iron as precipitate. The iron free leach solution contained 26 g/L Cu and 6 g/L Ni. The mother liquor containing 350 g/L sulphuric acid was reused for leaching the waste material in stage 2.
A 500 mL of 1.5 M Versatic acid (with 10 carbon atoms) in kerosene was pre-equilibrated with 35 mL of ammonia solution. The said pre-equilibrated solvent was then contacted with 500 mL of the said iron free leach solution at equilibrium pH 5.0 to extract copper from the aqueous phase to the organic phase. At this pH only trace amount of nickel is extracted into the organic phase. The organic phase was separated from the aqueous phase and scrubbed with 0.001 M sulphuric acid solution to remove trace amount of nickel extracted into the organic phase. The organic phase contained 25.6 g/L Cu. Fresh organic solvent was contacted with the raffinate to extract residual copper.
When 500 mL of copper loaded solvent was autoclaved for 2h under hydrogen atmosphere of 16 bar at 413 K and 700 rpm copper was stripped out as metal powder. After 25 min the reaction vessel was allowed to cool and copper powder was filtered and washed with acetone, dried and weighed. Copper recovery as powder was found as 99.9%. The copper powder produced was annealed under hydrogen atmosphere at 973 K for 2h. The purity of the copper powder was found to be 99.9%, and particle size of the powder ranged between 50-100 µm.
A 2 L solution of copper free leach solution containing 5.7 g/L Ni was produced as stated above and contacted with 500 mL 1.5 molar pre-ammoniated Versatic acid to extract nickel from the aqueous phase to the organic phase. The organic phase was separated from the aqueous phase and stored. The organic phase contained 21.6 g/L Ni. A
500 mL of the said nickel containing Versatic 10 was autoclaved for 35 min under hydrogen atmosphere of 38 bar at 473 K to produce nickel powder. The nickel powder produced was filtered from the organic solution, washed with acetone, dried and weighed. The weight of the nickel powder produced was 10.1 g, while initial nickel content of the organic phase was 10.8 g with a recovery of 94%. The nickel powder produced was annealed under hydrogen atmosphere at 973 K for 2h. the purity of the nickel powder was 99.9%, and particle size of the powder ranged between 1-2 |am.
Example 2
From a by-product/waste containing 22.4% Cu, 7.9% Ni and 36.3% Fe 3.05 % Si02 and 2.72 % AI2O3, copper and nickel were recovered by 2-stage sulphuric acid leaching-crystallisation-redissolution in water-iron removal by precipitation as described in example 1. The purified leach solution contained 20 g/L Cu and 4.5 g/L Ni. A 1.5M Versatic acid (with 10 carbon atoms) solution was loaded with 16.3 g/L Cu by contacting with the above purified leach solution at equilibrium pH 4.8 as described in example 1. The loaded solvent after scrubbing with 0.001 M sulphuric acid was autoclaved for lh under hydrogen atmosphere of 20 bar at 403 K and 400 rpm to produce copper powder, which was then annealed as described in example 1. Copper powder recovery was 95%. The purity of the copper powder was 99.5% and particle size ranged between 50-100 urn.
As described in example 1, the copper free raffinate produced above was contacted with Versatic acid(with 10 carbon atoms) solution at equilibrium pH 6.8, and the loaded solvent was autoclaved for lh under hydrogen atmosphere of 20 bar at 423 K and 200 rpm producing nickel powder with 90% recovery. The nickel powder was then annealed as described in example 1. The purity of the nickel powder was 99.8% and particle size of the powder ranged between 1-2 urn.
The main advantages of the present invention are:
1. Two stage leaching of a ferritic waste/by-product with sulphuric acid recovers 99.9%Cuand85%Ni.
2. The mother liquor obtained in the crystallization step containing sulphuric acid can be recycled to the leaching step (second stage) after acid make up.
3. The mixed metal sulphate crystal can be dissolved easily and metals can be recovered by solvent extraction
4. The preparation of copper and nickel powders by solvent extraction-reductive precipitation/stripping route has advantages such as clear separation of two metals with high recovery.
5. The process ensures production of metal powder of very close size range.
6. Flowsheet simplification, eliminating the aqueous based stripping from loaded organic.
7. In the present invention the purity of the copper and nickel powders produced is suitable to meet the P/M applications
8. The process is cost effective as high value metal powders are produced as compared to other conventional processes.

We claim:
1. A process for recovery of copper and nickel powders from a high iron containing
waste or secondary resource, which comprises:
i. providing high iron containing, ranging between 15-40%, waste material or
by-product having substantial amount of copper and nickel generated during
recovery of copper and nickel from a sulphide concentrate with chalcopyrite
and pentlandite by roasting, ii. leaching of the said by-product (stage 1) with sulphuric acid, iii. leaching of leach residue (stage 2) obtained in step (ii) with sulphuric acid, iv. mixing the leach liquors obtained in step (ii) and step (iii), v. evaporating the mixed leach solution so obtained in step (iv) to crystallize out
mixed sulphate salts of copper and nickel and generating mother liquor with
high acid for recycling in leaching, vi. leaching the said mixed copper and nickel sulphate salts in aqueous media, vii. removing the precipitated iron from the mixed sulphate solution obtained in
step (vi) by adjusting pH at 4.5, viii. viii extracting copper from the above said solution from step (vii) at pH 5 by
solvent extraction with extractants selected from a group consisting of
organophosphorus, organophosphonic acid, tertiary mono carboxylic acids
having carbon atoms above 9, ix. ix extracting nickel from the raffinate of step (viii) at pH 6.8 by solvent
extraction with reagents which are selected from a group consisting of
organophosphorus, organophosphonic acid, tertiary mono carboxylic acids
having carbon atoms above 9, x. reductive precipitation stripping of loaded organic containing copper or nickel
obtained in step (viii) and (ix), xi. washing and drying of the copper and nickel powder for powder metallurgical
application.
2. A process as claimed in claim 1, wherein the by-product is selected from the
mining industry having composition range: Cu: 5-30%; Ni: 2-15%; Fe: 15-40%;
Si02: 1.5-5%; A1203: 1-5%.
3. A process as claimed in claim 1, wherein the leach solution have the composition:
Cu: 10-40 g/L; Ni: 5-20 g/L; Fe: 20-60 g/L.
4. A process as claimed in claim 1, wherein the iron free leach solution obtained by
crystallization, redissolution and iron precipitation have the composition: Cu: 5-
35 g/L; Ni: 2-15 g/L.
5. A process as claimed in claim 1, wherein iron free leach liquor is employed for
extraction and separation of copper and nickel using organic reagents which are
selected from a group containing organophosphorous and organophosphonic acid,
tertiary monocarboxylic acids containing more than 9 carbon atoms.
6. A process as claimed in claim 1, wherein loaded organic containing copper or
nickel is employed for preparation of copper or nickel powder by reductive
precipitation/stripping using hydrogen or carbon monoxide as reductant at
pressure 5-60 bar, temperature 390-500K in 10-180 min.
7. A process as claimed in claim 1, wherein copper and nickel powder is prepared by
reductive precipitation/stripping are washed with acetone and dried.
8. A process as claimed in claim 1, wherein metal powders produced is recovered in
the range of 90-99.9% with purity of 99.9% Cu and Ni.
9. A process for recovery of copper and nickel powders from a high iron containing
waste or secondary resource is substantially described with reference to the
examples.