Title of Invention

"AN IMPROVED PROCESS FOR RECOVERING COBALT FROM ROAST-REDUCED SEA NODULES"

Abstract

This invention provides an improved process for recovering cobalt from roast-reduced sea nodules. In the process of the present invention the additive is added in the grinding stage. The wet ground slurry is stirred and the solid-liquid ratio is maintained in the range 1:1 to 1:3 during wet grinding and stirring. The slurry thus obtained is leached, in stages, after adjusting the concentration of the leach solution and the solid-liquid ratio to the desired levels by adding suitable amount of ammonia solution and water in the presence of the air. After the first stage of leaching, solid-liquid separation is done. The residue obtained in the first stage leaching is leached again (stage II) in ammoniacal solution having similar composition to that used in the first stage of leaching to recover the high yield of cobalt.

Full Text

FIELD OF THE INVENTION This invention relates to an improved process for recovering cobalt from roast-reduced sea nodules. This invention particularly related to a process for recovering cobalt from roast-reduced sea nodules using additive in two stage ammoniacal leaching. Land based resources of the strategically important metals like copper, nickel and cobalt are fast depleting. Polymetallic sea-nodules, available in plenty in the ocean beds of Pacific, Atlantic and Indian oceans, contain these strategically important metals and will be the future source of these metals. Very good recoveries, in the range of 90-95%, of nickel and copper can be obtained in ammoniacal systems. However, it is difficult to get cobalt recoveries more than 50% in ammoniacal systems. Therefore, any improvement in cobalt extraction will enhance the economics of the process and prevents the loss of scarce and costly metal. BACKGROUND OF THE INVENTION Ammoniacal systems have good selectivity for the leaching of metals and hence ammoniacal leaching has been used for extracting valuable metals from various types of minerals and materials. Some of the examples for this are recovery of copper from tailings containing copper (Duggan, E.J., Engg. Min. J.,1928, pp. 1008-1015); nickel extraction from nickel sulphides (Forward, F.A., Samis, C.S. and Kudryk, V. Trans. Can. Inst. Min. Met.,51, 1948, p.148) and from nickel bearing materials (Shimkage, K., Okyama, H and Morioka, S., J. Min. Met. Japan, 85, 1969 p.91). Caron's process developed by M.H. Caron is essential for treating widely available lateretic type nickel ores in ammoniacal medium (Caron, M.H., Trans. Inst. Min. Met. 64,1954, p.611). Many researches have applied the Caron's process for the processing of sea nodules. The nodules were roast-reduced and leached in ammonical solutions for recovering the copper, nickel and cobalt (Brooks, P.T. and Martin D.A., U.S. Bureau of Mines Rl 7473, 1971; Redman, M.J., US patent No. 3734715, 1973). During ammoniacal leaching of the sea nodules, dissolution of copper, nickel and cobalt takes place selectively. Ammine complexes of iron and manganese are comparatively less stable and they precipitate as their hydroxide/ oxides (Han, K.N., Hoover, M and Fuerstenau, D.W., Int. J. Min. Proc. 1, 1974, pp.215-230; Wilder, T.C., U.S. Patent, 3736125, 1973). The reported recoveries of nickel and copper were higher while that of cobalt was just satisfactory (50%) in the single stage ammoniacal leaching (Lee, J.W., Osseo-Asare, K and Pickering, H.W., J.Elect. Soc. 132 (3), 1985, pp. 550-555). It was seen that the recovery of metal is affected by higher recovery of other metals. Cobalt, nickel and copper in the roast reduced sea nodules dissolve as their ammine complexes during leaching in ammoniacal solutions. Cobalt dissolution takes place at a lower oxidation potential (Eh= -0.5 to 0.0V) compared to that of nickel and copper (Eh= 0.25 to 0.75V). As the leaching progresses, concentration of the copper ammine complex [Cu (NH)3 ]2+, a more powerful oxidizing agent than oxygen, in the solution increases. So the oxidation potential of the system increases due to the oxygen continuously sparged in to system and also due to the increasing concentration of copper ammine complex [Cu (NH) 3] 2+. As the oxidation potential increases beyond a certain limit, cobalt gets precipitated as cobalt hydroxide. To overcome this, a two stage leaching was developed for the roast-reduced sea nodules wherein the bulk of the cobalt (the most affected metal) was leached out in the first stage. Reference may be drawn to Patent No. 184162 wherein most of the nickel and a part of copper are also leached in the first stage. The first stage leaching was stopped prior to the precipitation of cobalt. In the second stage, remaining nickel and bulk of copper are recovered. The two-stage process increased the cobalt recovery to 60-70%. Cobalt being the costliest metal in the sea nodule system, lower recovery of cobalt, in the hitherto known processes, not only results in the loss of costly and scarce material but also leads to increased cost of production and hence affects the overall economy of the process. In the hitherto known processes, be it single stage or two stage leaching, cobalt recovery never exceeded 70%. This is due to the co-precipitation of cobalt with iron and manganese hydroxides during leaching. Some metallic iron, formed during the roasting, forms ammine complexes, which are unstable in the leaching conditions and it transforms to the more stable goethite phase. However, this transformation takes place slowly. Slower the precipitation rate, more will be the cobalt adsorption on iron precipitate. Therefore, in order to enhance the cobalt recovery, the goethite precipitation process needs to be accelerated. Thus, some additives have been used to ensure faster precipitation of goethite during the leaching. Therefore, this invention is to improve the cobalt recovery from roast-reduced sea nodules without affecting the recoveries of copper and nickel using certain additives in ammoniacal leaching. OBJECTIVES OF THE INVENTION The main objective of the present invention is to provide an improved process for recovering cobalt from roast-reduced sea nodules which obviates the drawbacks detailed above. Another objective of the present invention is to enhance the economics of the process through prevention/minimization of cobalt loss during the two stage ammoniacal leaching of roast reduced sea nodules with the help of certain additives. SUMMARY OF THE INVENTION Accordingly, the present invention provides An improved process for recovering cobalt from roast-reduced sea nodules, the said process comprising the steps of: (i) wet grinding of roast-reduced sea nodules and additive in ammoniacal solution with a solid to liquid ratio in the range of 1:1 to 1:3 and stirring the above said slurry for a period ranging between 15 to 45 min, (ii) leaching the above said slurry obtained in step (i) in ammoniacal solution, in the first stage of leaching, in presence of air sparging, at a flow rate of 0.5 to 2.0 liter per minute, (iii) separating the solids and liquids of the above said leach slurry by known methods, (iv) leaching the residue obtained in step (iii) in ammoniacal solution, in the second stage of leaching , in the presence of air sparging, at a flow rate in the range of 0.5 to 2.0 liter per minute, (v) separating the solid and liquid of the slurry and in-situ washing of the resultant residue by known method and (vi) recovering cobalt from the leach solutions by known processes. In an embodiment of the present invention the roast-reduced sea nodules used have the following compositional range: Cu = 0.9-1.4 %, Ni = 1.0-1.5 %, Co = 0.15 - 0.25 % In yet another embodiment the ammonia solution used contains NH3 and CO2 in the range of 180 to 250 gm./liter and 80 to130 gm./liter, respectively. In yet another embodiment the additive used is selected from salts of alkali or alkaline earth metals In yet another embodiment the yield of cobalt recovered is in the range of 75-82%. The present invention provides the recoveries of copper 90-95%, nickel 90-95% and cobalt 75-82%. Novelty of the present invention is the use of additive for recovery of cobalt. The additive used in the two stage ammoniacal leaching process enhanced the cobalt recovery to ~ 80%, This improvement in cobalt recovery is achieved without affecting the copper and nickel recoveries. DETAILED DESCRIPTION OF THE INVENTION In the process of the present invention the additive may be added in the grinding stage. The wet ground slurry is stirred and the solid-liquid ratio may be maintained in the range 1:1 to 1:3 during wet grinding and stirring. The slurry thus obtained may be leached (in stages) after adjusting the concentration of the leach solution and the solid-liquid ratio to the desired levels by adding suitable amount of ammonia solution and water in the presence of the air. After the first stage of leaching, solid-liquid separation may be done. The residue obtained in the first stage leaching may be leached again (stage II) in ammoniacal solution having similar composition to that used in the first stage of leaching. Solid-liquid ratio also may be kept similar to that in the first stage. Second stage leaching, with air sparging, may be carried out for a period of 1-3 hours. At the completion of the second stage leaching, solid-liquid separation is done. After that, the residue may be washed in situ with dilute ammonia solution. Recovery of metals from the leach liquors can be achieved by any known Solvent Extraction and Electro winning process. The following examples are given by way of illustration and should not be construed to limit the scope of invention. Example-1 The roast-reduced sea nodules used having composition Cu =1.1%, Ni = 1.3 %, Co = 0.24 %, Fe = 10 % and Mn = 18 %. 15 g of roast-reduced sea nodules and 7.5 g of the additive were wet ground with 40 ml of ammonia solution containing 220 gpl of ammonia and 120 gpl of CO2 for 15 minutes. The wet ground slurry was transferred in a glass reaction vessel and agitated for half an hour without any aeration. In the same reaction vessel containing the above slurry, 35 ml of ammonia solution having 220 gpl NH3 & 120 gpl CO2 and 75 ml of distilled water were added to maintain the NH3 and CO2 concentrations 110 gpl and 60 gpl respectively. The solid: liquid ratio thus becomes 1: 10. Keeping an oxygen flow rate of 1 lit/min in to the slurry, the slurry was agitated for 15 minutes. After leaching, the slurry was filtered and the filtrate volume was measured and anlysed. The leach recoveries at this stage for cobalt, copper and nickel were 61.87%, 66.25% and 71.08% respectively. The material used for the second stage leaching was the residue obtained in the first stage leaching. The residue was made in to a slurry by thoroughly mixing it with 75 ml of ammonia solution having 220 gpl NH3 & 120 gpl CO2 and 75ml of distilled water so that the leachant volume and concentration were maintained at 150 ml and 110 gpl NH3 & 60 gpl CO2 respectively. The slurry was agitated for two hours while keeping the oxygen flow rate 1 lit/min. On completion of the leach—II, the slurry was filtered. The residue was washed, in situ with 25 ml solution containing 50 gpl ammonia and 25 gpl CO2. The wash solution and the filtrate of leach-ll were mixed together and analyzed. The leach-ll recoveries in this stage for cobalt, copper and nickel were 19.77%, 30.59% and 24.04% respectively. Thus the total recovery of the metals in leach-l and Leach-ll cum washing stage was 81.64%, 96.84% and 95.12% for cobalt, copper and nickel respectively. Example-2 The roast-reduced sea nodules used having composition Cu =1.1%, Ni = 1.3%, Co =0.24%, Fe =10% and Mn = 18%. 100 g of roast-reduced sea nodule and 30 g of the additive were ground in a pot mill with 250 ml of ammonia solution containing 220 gpl of ammonia and 120 gpl of CO2 for 15 minutes. The wet ground slurry was transferred to a glass reaction vessel and stirred for half an hour without any aeration. To the above slurry, 250 ml of ammonia solution having 220 gpl NH3 and 120 gpl CO2 and 500 ml of distilled water were added so as to make 1000 ml of leach solution having 110 gpl NH3 and 60 gpl CO2. The slurry was agitated for 30 minutes. During the leach-l stage oxygen was sparged in to the slurry continuously at the rate of 1 lit/min. After the leaching, the slurry was filtered and the filtrate volume was measured and anlysed. The leach recoveries at this stage for cobalt, copper and nickel were 54.91%, 61.85% and 70.64% respectively. The residue obtained in the first stage leaching was leached again. The residue was pulped with 500 ml of ammonia solution having 220 gpl NH3 and 120 gpl CO2 and 500 ml of distilled water such that the leachant volume and concentration is maintained at 1000 ml and 110 gpl NH3 & 60 gpl CO2 respectively. The slurry was agitated for two hours while keeping the oxygen flow rate 1 lit/min. On completion of the leach -II, the slurry was filtered. The residue was washed in situ with 100 ml of ammonia solution (50 gpl NH3 and 30 gpl CO2). The wash solution and the filtrate of leach-l I are mixed and analyzed. The leach-l I recoveries in this stage for cobalt, copper and nickel were 20.82%, 35.59% and 19.51% respectively. Thus the total recovery of the metals in leach-l and Leach-l I cum washing is 75.73%, 97.44% and 90.15% for cobalt, copper and nickel respectively. Example-3 The roast-reduced sea nodules used having composition Cu =1.1% Ni = 1.3%, Co =0.24%, Fe =10% and Mn = 18%. 100 g of roast-reduced sea nodule and 30 g of the additive were ground in a pot mill with 250 ml of ammonia solution containing 220 gpl of ammonia and 120 gpl of CO2 for 15 minutes. The wet ground slurry was transferred to a glass reaction vessel and agitated for half an hour without aeration. To the above slurry, 250 ml of ammonia solution having 220 gpl NH3 and 120 gpl CO2 and 500 ml of distilled water were added so as to make 1000 ml of leach 80 solution having 110 gpl NH3 and 60 gpl CO2. The slurry was agitated for 30 minutes. During the leach-l stage oxygen was sparged in to the slurry continuously at the rate of 1 lit/min. After the leaching, the slurry was filtered and the filtrate volume was measured and anlysed. The leach recoveries at this stage for cobalt, copper and nickel were 55.91%, 62.15% and 71.44% respectively.The residue obtained in the first stage leaching was leached again. The residue was pulped with 500 ml of ammonia solution having 220 gpl NH3 and 120 gpl CO2 and 500 ml of distilled water such that the leachant volume and concentration is maintained at 1000 ml and 110 gpl NH3 & 60 gpl CO2 respectively. The slurry was agitated for two hours while keeping the oxygen flow rate 1 lit/min. On completion of the leach -II the slurry was filtered. The residue was washed in situ with 100 ml of ammonia solution (50 gpl NH3 and 30 gpl CO2). The wash solution and the filtrate of leach-ll are mixed and analyzed. The leach-ll recoveries in this stage for cobalt, copper and nickel were 21.02%, 35.16% and 19.81% respectively. Thus the total recovery of the metals in leach-l and Leach-ll cum washing is 75.93%, 97.31% and 91.25% for cobalt, copper and nickel respectively. The main advantages of the present inventions are: 1. The invention has the potential of achieving 75-80% cobalt recovery whereas the two-stage leaching without additive cannot extract more than 70%. 2. Additional cobalt recovery does not affect the high copper and nickel recovery obtained in the earlier process cited above. 3. The improved recovery of cobalt, costly element in the sea nodule, enhances the economics of the sea nodules processing. 4. The conservation of costly and scarcely available cobalt during processing of sea nodules has been made possible, which otherwise would have gone to the waste. We claim 1. An improved process for recovering cobalt from roast-reduced sea nodules, the said process comprising the steps of: (i) wet grinding of roast-reduced sea nodules and additive in ammoniacal solution with a solid to liquid ratio in the range of 1:1 to 1:3 and stirring the above said slurry for a period ranging between 15 to 45 min, (ii) leaching the above said slurry obtained in step (i) in ammoniacal solution, in the first stage of leaching, in presence of air sparging, at a flow rate of 0.5 to 2.0 liter per minute, (iii) separating the solids and liquids of the above said leach slurry by known methods, (iv) leaching the residue obtained in step (iii) in ammoniacal solution, in the second stage of leaching , in the presence of air spraying, at a flow rate in the range of 0.5 to 2.0 liter per minute, (v) separating the solid and liquid of the slurry and in-situ washing of the resultant residue by known method and (vi) recovering cobalt from the leach solutions by known processes. 2. An improved process as claimed in claims 1-2 wherein the ammonia solution used contains NH3 and CO2 in the range of 180 to 250 gm./liter and 80 to130 gm./liter, respectively. 3. An improved process as claimed in claims 1-3 wherein the additive used is selected from salts of alkali or alkaline earth metals. 4. An improved process as claimed in claims 1-4 wherein the yield of cobalt recovered is in the range of 75-82%. 5. An improved process for recovering cobalt from roast-reduced sea nodules, substantially as herein described with reference to the examples.

Documents:

2720-DEL-2005-Abstract-(28-05-2012).pdf

2720-del-2005-abstract.pdf

2720-DEL-2005-Claims-(11-04-2012).pdf

2720-DEL-2005-Claims-(28-05-2012).pdf

2720-del-2005-claims.pdf

2720-DEL-2005-Correspondence Others-(11-04-2012).pdf

2720-DEL-2005-Correspondence Others-(28-05-2012).pdf

2720-del-2005-correspondence-others.pdf

2720-del-2005-description (complete).pdf

2720-del-2005-form-1.pdf

2720-del-2005-form-18.pdf

2720-del-2005-form-2.pdf

2720-del-2005-form-3.pdf

2720-del-2005-form-5.pdf