Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF COPPER AND NICKEL POWDER FROM THE ELECTROLYTIC BLEED STREAM OF A COPPER PLANT

Abstract

The present invention provides a process for the preparation of copper and nickel powder from the impurity laden copper bleed electrolyte generated from the electrolytic tank directly by hydrogen reduction under pressure. Copper powder was selectively produced first in an autoclave under certain pressure and temperature till all the copper present in the solution is reduced into metallic form. The mother liquor is then treated with sodium sulphide to precipitate out the copper present in traces. The copper free mother liquor is evaporated to form nickel sulphate crystals. This nickel sulphate is then dissolved in ammonia. A known amount of this solution is then taken in a Teflon lined vessel and pressurised with hydrogen gas to yield pure nickel Powder. The Copper powder formed was washed with distilled water followed by sodium carbonate solution and then with distilled water again. It was finally treated with sodium potassium tartarate before drying and storing. The nickel powder produced is washed with acidic water to neutralise ammonia adhering to the surface of the nickel powder formed, then with distilled water and finally with a solution of sodium potassium tartrate to restrict oxidation of the metal powder and dried at 100°C to produce a high pure powder for P/M applications.

Full Text

FIELD OF THE INVENTION The present invention relates to an improved process for the preparation of copper and nickel powder from the electrolytic bleed stream of a copper plant The invention particularly relates to selectively and directly producing copper and nickel powder by the treatment of copper bleed electrolyte generated in the electro-refining of impure copper by direct pressure reduction using hydrogen gas. Thus, under the optimised conditions copper powder is formed and the mother liquor is purified for copper, which is then evaporated to crystallize out nickel sulphate. The ammoniacal solution of nickel sulphate is then reduced under pressure with hydrogen. Copper bleed electrolyte generated in the copper smelters has substantial amount of nickel, besides a host of other impurities. Copper and nickel are the metals of strategic importance and therefore this invention will be useful for producing value added products such as powders for powder metallurgical (P/M) applications. BACKGROUND OF THE INVENTION Copper bleed electrolyte is presently purified for the removal of copper, arsenic and antimony by electrolytic stripping in the liberator cell, followed by liquor concentration to crystallise out salt of nickel and recycling of the black acid to the system. The drawbacks of this process are the liberation of the arsine gas, high operation cost, poor grade NiSO4, and loss of acid (Habashi, F., Ismail, M.I., Health hazards and pollution in the metallurgical industry due to phosphine and arsine, CIM Bull., 68(760), 99-103, 1975.)- There are reports on the processing of copper bleed streams of copper smelters in the literature. Havlik et al (Havlik, T, Skrobian, M, Kammel, R, Curilla J and Cmorejova, D, Hydrometallurgy, 41, 1996, p.79-88) and Nagai et al (Nagai, T, Zaki, NY and Kobayashi, MMIJ, L-l, 1976, p. 1-4) reported the process involving cumbersome steps such as (i) decopperisation to remove copper as poor quality nodular sheet (99.6% purity) for recharging to the smelter, (ii) evaporation / crystallisation to produce impure nickel sulphate (iii) purification of nickel sulphate by hydrometallurgical process, and (iv) crystallisation of nickel sulphate. The drawbacks are production of poor quality metal, recycling of this copper to smelter thereby reducing the productivity, high-energy requirement, production of off-grade nickel sulphate crystal, environmental problems due to evolution of abnoxious arsine gas during de-copperisation etc. Reference may be made to Toyabe, K, Segawa, C and Sato H (In Proc. Electro refining and winning of copper, 116 th Annual Meeting, Denver, Colorado, 1987, AIME Penn., p.99-116) and Shibata, T, Hashivchi, M and Kato, T,116 th Annual Meeting, Dever, Colorado, 1987, AIME Penn., p.l 17-128, Shibayama, R and Nagai, T (ISEC 1990, p.l 193-1198), wherein the processes have drawbacks of selective removal of Sb and Bi from electrolyte in lenthy and cumbersome options viz. adsorption on carbon or chelating resin and producing nickel sulphate crystals after removal of arsenic in de-copperisation-a polluting step. Togashi, R and Nagai, T (Hydrometallurgy, 11, 1983, p. 149-163) reported the production of copper powder by hydrogen reduction from copper bleed stream with above 100 g/L sulphuric acid. The drawbacks are the production of poor quality powder at higher depletion level, requiring removal of arsenic and bismuth ions. Amongst other known processes to produce copper and nickel powder from the leach liquors of their ores, reference may be made to US Patent 2,7976,342 wherein copper precipitation is followed with modification for other metals. Reference may also be made to US Patent 332, 679 wherein attempts had been made to the continuous preparation of metal powders by hydrogen reduction from the leach solutions of metals from their ores. Ref may also be made to an Indian patent 0419/DEL/2004,wherein the process is based on solvent extraction and electrowinning of the metal separated. However solvent extraction process for metal separation will be unsuitable for smaller units and the powder produced by electrolytic is mostly dendritic in nature and is coarser in size. Because of the drawbacks such as the purification steps , separation of metals from a solution with multi metals, and production of copper powder of coarser size and incomplete recovery, above processes are not suitable for the treatment of the copper bleed electrolytes. OBJECTIVES OF THE INVENTION The main object of the present invention is to provide a process for the preparation of copper and nickel powder by aqueous reduction from the electrolytic bleed stream of a copper plant. Yet another object is to provide a process for selectively and directly producing copper and nickel powder by the treatment of copper bleed electrolyte generated in the electro-refining of impure copper by direct pressure reduction using hydrogen gas SUMMARY OF THE INVENTION Accordingly, the present invention provides an improved process for the preparation of copper and nickel powder from the electrolytic bleed stream of a copper plant, the said process comprising the steps of: a) reducing the spent copper electrolyte containing copper and nickel bleed from a copper plant, under hydrogen pressure ranging between 10-40kg/cm2, for a period of 30 to 120 minutes, at a temperature in the range of 150 to 190°C , under stirring at a speed of 200-500rpm, in the presence of 2-30 g/L of electrolytic grade copper or nickel powder, as seed material, b) filtering the above said reaction mixture followed by washing and drying of the resultant residue by known methods to obtain the desired copper powder, c) evaporating the reduced spent liquor filtrate obtained in step (b) to crystallise out the nickel sulphate and separating the resultant crystals by known method, d) dissolving the above said nickel sulphate crystals in ammonia in concentration ranging between 30 to 40 g/L to obtain a nickel-amine complex solution, e) reducing the above said nickel-amine complex solution in hydrogen atmosphere, at a pressure in the range of 10 to 35 kg/cm2, for a period of 30 to 180 min, at a temperature in the range of 150 to 200°C, cooling down the reaction mixture to a temperature of 20-30°C, followed by filtration, washing and drying the residue product by known methods to obtain the desired nickel powder. In an embodiment of the present invention the spent copper bleed stream used has the following composition range Cu = 30-60 g/1 Ni = 7-22 g/1 Bi = 0.0-0.3 g/1 Fe = 0.1-2.0 g/1 H2SO4 = 150-200 g/1 In yet another embodiment the amount of electrolytic copper powder used as seed is in the range 2-10 g/1. In yet another embodiment the copper depleted mother liquor filtrate obtained in step (b) is treated with sodium sulphide to precipitate out the residual copper left with the purified solution having a composition as Ni in the range of 8 to 25 g/1 and sulphuric acid in the range of 150 to 240 g/1. In yet another embodiment the nickel sulphate crystals obtained by the evaporation of copper depleted mother liquor filtrate in step (c) are dried at a temperature ranging between 90tol20°C. In yet another embodiment the yield of the copper powder obtained is in the range of 83 to 100%. In yet another embodiment the yield of the nickel powder obtained is in the range of 90 to 100%. In the process of the present invention the copper depleted mother liquor is evaporated to crystallise out nickel sulphate, which is washed and dried at 100°C. This nickel sulphate crystal is dissolved in ammoniacal solution to bring the nickel as nickel amine complex. The nickel powder is prepared from the purified ammoniacal liquor containing nickel as its amine complex in the temperature range 150-200°C for stirring time varying from 30 to ISOmin and stirring speed varying from 250-450 rpm at hydrogen pressure varying from 10-50 kg/.cm2. The obtained copper and nickel powder is washed with acidic water to neutralise acid or ammonia adhering to the surface of the copper and nickel powder formed, then with distilled water and finally with a solution of sodium potassium tartrate to restrict oxidation of the metal powder and dried at 100°C to produce pure powder for P/M applications. The purity of powders prepared may be of 99.93% for copper and 99.8% for nickel. Novelty of the present invention is preparation of value added products viz high purity copper and nickel powder from copper bleed electrolyte generated during the electro-refining of the impure copper produced in a copper plant The main novelty of the invention is production of high purity P/M grade metal powders by direct reduction of the spent copper electrolyte under pressure in a controlled hydrogen atmosphere without going into cumbersome intermediate steps. DETAILED DESCRIPTION OF THE INVENTION In the process of the present invention, the impurity laden copper bleed electrolyte generated from the electrolytic tank is directly used for the purpose of copper and nickel powder synthesis by hydrogen reduction under pressure. Copper powder was selectively produced first in an autoclave under certain pressure and temperature till all the copper present in the solution is reduced into metallic form. The mother liquor is then treated with sodium sulphide to precipitate out the copper present in traces. The copper free mother liquor is evaporated to form nickel sulphate crystals. This nickel sulphate is then dissolved in ammonia. A known amount of this solution is then taken in a Teflon lined vessel and pressurised with hydrogen gas to yield pure nickel Powder. The Copper powder formed was washed with distilled water followed by sodium carbonate solution and then with distilled water again. It was finally treated with sodium potassium tartarate before drying and storing. The nickel powder produced is washed with acidic water to neutralise ammonia adhering to the surface of the nickel powder formed, then with distilled water and finally with a solution of sodium potassium tartrate to restrict oxidation of the metal powder and dried at 100°C to produce a high pure powder for P/M applications. The following examples are given by the way of illustration and therefore should not be construed to limit the scope of the invention. Exam pie-1 600mL of copper bleed solution containing Cu : 39.85 g/1, Ni : 9.58 g/1, Fe : 0.255 g/1, Bi : 0.108 g/1 and 194.0 t^SC^ g/1 was transferred to an autoclave (a titanium vessel) of 1L capacity and copper was reduced under hydrogen pressure of 15kg/cm2 at 180°C for 120min in presence of 5g of -100 mesh electrolytic copper powder added as seed. Copper powder formed was filtered after cooling the solution in the autoclave up to 50°C. The Copper powder formed was washed with distilled water followed by sodium carbonate solution and then with distilled water again. It was finally treated with sodium potassium tartarate before drying and storing. The copper powder recovery was 95%. After recovering copper from the CBS the filtrate or the spent mother liquor was further treated with sodium sulphide to remove the remaining copper and was evaporated to crystallise out nickel sulphate. These crystals were dissolved in ammoniacal solution to bring the nickel as nickel amine complex with final pH of 10.6 and chemical composition as Ni 17.6 g/1, NH3 37.6 g/1. 500ml of this ammoniacal nickel solution was put in a Teflon lined titanium vessel (autoclave). Hydrogen gas was passed at a pressure of 20kg/cm2 at 150°C temperature with stirring at 400rpm. The experiment was conducted for 90min, then the solution was cooled to room temperature and the metal thus formed was filtered out. Nickel powder recovery was 91.83%. Example-2 600mL of copper bleed solution containing Cu : 39.85 g/1, Ni : 9.58 g/1, Fe : 0.255 g/1, Bi: 0.108 g/1 and HaSCU : 194.0 g/1 was transferred to titanium autoclave of 1L capacity and reduced at hydrogen pressure of 20kg/cm2 at 160°C for 120min in presence of 5g of-100 mesh electrolytic copper powder added as seed. Copper powder formed was filtered after cooling the solution in the autoclave up to 50°C. The Copper powder formed was washed with distilled water followed by sodium carbonate solution and then with distilled water again. It was finally treated with sodium potassium tartarate before drying and storing. The copper powder recovery was 84.38%. After the complete recovery of copper from the CBS the filtrate or the spent mother liquor was further treated with sodium sulphide to remove the remaining copper and was evaporated to crystallise out nickel sulphate crystals. These crystals were dissolved in ammoniacal solution to bring the nickel as nickel amine complex with final pH of the solution of 10.66 and composition as Ni 17.6 g/1, NHa 37.6 g/1 and pH 10.66. 500ml of this ammoniacal nickel solution was put in a Teflon lined titanium vessel (autoclave). Hydrogen gas was passed at a pressure of 30kg/cm2 at 160°C temperature and stirring at 400rpm. The experiment was conducted for SOmin after which the solution was cooled to room temperatures and the metal thus formed was filtered out. Nickel powder recovery was 94.67%. Example-3 600mL of copper bleed solution containing Cu : 39.85 g/1, Ni : 9.58 g/1, Fe : 0.255 g/1, Bi : 0.108 g/1 and H2SO4 :194.0 g/1 was taken in an autoclave as mentioned above and reduced at a hydrogen pressure of 20kg/cm2 at 180°C for 120min in presence of 5g of -100 mesh electrolytic copper powder added as seed. Copper powder formed was filtered after cooling the solution in the autoclave up to 50°C. The copper powder formed was washed and treated as detailed above before drying and storing. The copper powder recovery was 99.85%. After the complete recovery of copper from the CBS the filtrate or the spent mother liquor was further treated with sodium sulphide to remove the remaining copper and was evaporated to crystallise out nickel sulphate crystals. These crystals were dissolved in ammoniacal solution with the final pH of the solution of 10.7 and containing Ni 17.6 g/1 and NH3 37.6 g/1. 500ml of this ammoniacal nickel solution was put in a Teflon lined titanium vessel Ni was reduced at a hydrogen gas pressure of 30kg/cm2 at 160°C temperature and stirring at 400rpm. The experiment was conducted for 90min after which the solution was cooled to room temperatures and the metal thus formed was filtered out. Nickel powder recovery was 99.1 %. The main advantages of the present invention are: 1. Direct recovery of high pure copper and nickel powders with a yield of 99.85% and 99.1% respectively in a single step without any pre-treatment of the spent copper electrolyte. 2. The mother liquor obtained after copper recovery is then purified for the removal of residual copper and crystallised for nickel sulphate recovery. 3. The nickel sulphate crystal is dissolved easily in ammonia and the nickel ammine complex is treated with hydrogen under pressure to give high purity nickel powder. 4. In the present invention the purity of the copper and nickel powders produced is suitable to meet the P/M applications. 5. The process is ecofriendly and cost-effective as high value metal powders are produced as compared to other conventional processes. We claim: 1. An improved process for the preparation of copper and nickel powder from the electrolytic bleed stream of a copper plant, the said process comprising the steps of: a) reducing the spent copper electrolyte containing copper and nickel bleed from a copper plant, under hydrogen pressure ranging between 10-40kg/cm2, for a period of 30 to 120 minutes, at a temperature in the range of 150 to 190°C , under stirring at a speed of 200-500rpm, in the presence of 2-30 g/L of electrolytic grade copper or nickel powder, as seed material, b) filtering the above said reaction mixture followed by washing and drying of the resultant residue by known methods to obtain the desired copper powder, c) evaporating the reduced spent liquor filtrate obtained in step (b) to crystallise out the nickel sulphate and separating the resultant crystals by known method, d) dissolving the above said nickel sulphate crystals in ammonia in concentration ranging between 30 to 40 g/L to obtain a nickel-amine complex solution, e) reducing the above said nickel-amine complex solution in hydrogen atmosphere, at a pressure in the range of 10 to 35 kg/cm2, for a period of 30 to 180 min, at a temperature in the range of 150 to 200°C, cooling down the reaction mixture to a temperature of 20-30°C, followed by filtration, washing and drying the residue product by known methods to obtain the desired nickel powder. 2. An improved process as claimed in claim 1, wherein, the spent copper bleed stream used has the following composition range: Cu = 30-60 g/1 Ni = 7-22 g/1 Bi = 0.0-0.3 g/1 Fe = 0.1- 2.0 g/1 H2SO4= 150-200 g/1 3. An improved process as claimed in claim 1, wherein the amount of electrolytic copper powder used as seed is in the range 2-10 g/1. 4. An improved process as claimed in claim 1, wherein the copper depleted mother liquor filtrate obtained in step (b) is treated with sodium sulphide to precipitate out the residual copper left with the purified solution having a composition as Ni in the range of 8 to 25 g/1 and sulphuric acid in the range of 150 to 240 g/1. 5. An improved process as claimed in claim 1, wherein the nickel sulphate crystals obtained by the evaporation of copper depleted mother liquor filtrate in step (c) are dried at a temperature ranging between 90 to 120°C. 6. An improved process as claimed in claim 1, wherein the yield of the copper powder obtained is in the range of 83 to 100%. 7. An improved process as claimed in claim 1, wherein the yield of the nickel powder obtained is in the range of 90 to 100%.

Documents:

658-DEL-2006-Abstract-(19-07-2012).pdf

658-del-2006-abstract.pdf

658-DEL-2006-Claims-(19-07-2012).pdf

658-del-2006-claims.pdf

658-DEL-2006-Correspondence Others-(19-07-2012).pdf

658-del-2006-correspondence-others 1.pdf

658-del-2006-correspondence-others.pdf

658-del-2006-description (complete).pdf

658-del-2006-form-1.pdf

658-del-2006-form-18.pdf

658-del-2006-form-2.pdf

658-DEL-2006-Form-3-(19-07-2012).pdf

658-del-2006-form-3.pdf

658-del-2006-form-5.pdf

658-del-2006-pct-237.pdf

658-del-2006-pct-326.pdf

658-del-2006-pct-373.pdf