Selective recovery of aluminium, cobalt and platinum values from a spent catalyst composition

Abstract

The invention provides a process for the selective recovery of aluminium, cobalt and platinum, and compounds thereof, from a catalyst composition including aluminium, cobalt and platinum, said proscess including the steps of treating the catalyst composition to selectively get ions of substantially only one of the aluminium. cobalt and platinum into solution, recovering, in separate process steps, the thus treated aluminium, cobalt, or platinum in salt or metal form, and repeating the treating and recovering steps for each of the aluminium, cobalt and platinum. The treating steps may include process steps such as leaching, washing, dissolving, stripping, and the like. The recovery steps may include filtration, precipitation, separation, flocculation, and the like.

1 . A process for the selective recovery of aluminium, cobalt and platinum, and compounds thereof, from a catalyst composition including aluminium, cobalt and platinum, said process including the steps of: 
 treating the catalyst composition to selectively get ions of substantially only one of the aluminium, cobalt and platinum into solution;    recovering, in separate process steps, the thus treated aluminium, cobalt, or platinum in salt or metal form; and    repeating the treating and recovering steps for each of the aluminium, cobalt and platinum.    
     
     
         2 . A process for the selective recovery of aluminium, cobalt and platinum, and compounds thereof, from a catalyst composition including aluminium, cobalt and platinum, said process including the steps of: 
 oxidising substantially all organic material present with the catalyst composition;    leaching the aluminium and/or compounds thereof from the oxidised catalyst composition with a strong or weak base to form an aluminium containing product and a filtrate;    filtering of alkali insoluble residue from the filtrate;    washing of the alkali insoluble residue with water to remove the residual alkali aluminate solution;    precipitating of silica from alkali aluminate with slaked lime or quicklime;    filtering of insoluble silicate from alkali aluminate;    crystalising aluminium trihydrate from the alkali aluminate solution;    filtering aluminium trihydrate crystals from the alkali aluminate solution    recycling of the alkali solution to the leaching step;    dissolving the cobalt and compounds thereof present in the water washed-insoluble residue composition with an inorganic acid;    separating a substantial portion of the cobalt rich solution from a solid component present after the dissolving step;    precipitating substantially all non-cobalt and/or non-cobalt compound impurities from the cobalt rich solution;    crystallizing the cobalt and/or cobalt compounds out of the cobalt rich solution to form impure cobalt nitrate salt; or    as an alternative to the crystallizing step, selectively loading substantially all cobalt ions from the impure cobalt rich solution into an organic phase by solvent extraction;    subsequently stripping the cobalt-containing organic phase with a solution of nitric acid to form a pure cobalt nitrate salt;    dissolving the platinum and compounds thereof and non-cobalt and/or non-cobalt compound impurities from the cobalt rich solution out of the water washed solid component to obtain a platinum rich solution; and    recovering platinum and/or platinum salts from the platinum rich solution.    
     
     
         3 . A process as claimed in  claim 2 , wherein after the aluminium leaching step and prior the alkali insoluble residue filtration step, a flocculation step is included to remove ultra fine solids which inhibit efficient filtration.  
     
     
         4 . A process as claimed in  claim 2  or  claim 3 , wherein after the cobalt dissolution step and prior to the separation of a substantial portion of the cobalt rich solution, a flocculation step is included to remove ultra fine solids which may inhibit efficient separation.  
     
     
         5 . A process as claimed in  claim 3 , wherein the flocculation is carried out with th aid of flocculating agents selected from a group including modified anionic polyacrylamides.  
     
     
         6 . A process as claimed in  claim 3  or  claim 5 , wherein the flocculation is carried out at a pH of about 12.  
     
     
         7 . A process as claimed in any one of  claims 2  to  6 , wherein for the oxidising step, the catalyst composition is heated to a temperature of between 600° C. and 1400° C., generally between 700° C. and 1000° C.  
     
     
         8 . A process as claimed in any one of  claims 2  to  7 , wherein where the catalyst composition is Co/Pt/Al 2 O 3 /SiO 2 , then the oxidised spent catalyst composition contains about 0.0125 g Pt per 100 g Al 2 O 3  to 0.175 g Pt per 100 g Al 2 O 3  and from 5 g Co per 100 g Al 2 O 3  to 70 g Co per 100 g Al 2 O 3 .  
     
     
         9 . A process as claimed in any one of  claims 2  to  8 , wherein the leaching of the aluminium and/or the aluminium compounds from the oxidised spent catalyst composition is carried out with a solution of sodium hydroxide of about 20% to 50% w/w NaOH, generally 25%, at a temperature ranging from 110° C. to 250° C., typically 200° C., and at a high pressure ranging from 5 to 20 bar, typically 15 bar, with substantially no dissolution of cobalt and platinum from the spent catalyst composition.  
     
     
         10 . A process as claimed in  claim 9 , wherein the leachate is in the form of a slurry.  
     
     
         11 . A process as claimed in any one of  claims 4  to  10 , wherein the flocculation of the slurry prior to filtration is carried out using a flocculant solution prepared from approximately 2% w/w of flocculant which in turn is prepared using a solution of sodium hydroxide of about 2% w/w NaOH, whereafter the flocculant solution is conditioned at ambient temperature for one hour to form homogeneous solution, whereafter it is diluted with a solution of sodium hydroxide of 2% w/w NaOH to produce a final solution containing about 0.25% w/w of the flocculent.  
     
     
         12 . A process as claimed in any one of the preceding claims, wherein water leaching is used to selectively solubilize sodium aluminate formed during the oxidising of the spent catalyst in the presence of either sodium carbonate or sodium chloride.  
     
     
         13 . A process as claimed in  claim 12 , wherein the water leaching is carried out at 50° C. at atmospheric pressure.  
     
     
         14 . A process as claimed in  claim 12  or  claim 13 , wherein a solution of sodium aluminate from the water leaching step is reserved for the precipitation of aluminium hydroxide.  
     
     
         15 . A process as claimed in any one of  claims 12  to  14 , wherein the water-washed base insoluble residue is used in the strong or weak inorganic acid cobalt dissolving step.  
     
     
         16 . A process as claimed in any one  claims 2  to  15 , wherein the leached residue recovered from the aluminium leaching step contains 51% w/w cobalt, 0.124% w/w platinum and 4.9% w/w aluminium.  
     
     
         17 . A process as claimed in any one of the preceding claims, wherein cobalt recovery is initiated by dissolving the cobalt and compounds thereof present in the water-washed leached residue of the oxidised catalyst composition with a strong acid.  
     
     
         18 . A process as claimed in  claim 17 , wherein the water washed-leached residue is contacted with a solution of nitric acid of about 55% w/v HNO 3  at a temperature of between 80° C. and 200° C. and at a pressure of between 1 bar and 20 bar, in order to selectively dissolve cobalt.  
     
     
         19 . A proc ss as claimed in  claim 18 , wherein the cobalt dissolution step is carried out at 100° and 1 atmospheric pressure.  
     
     
         20 . A process as claimed in  claim 17 , wherein including the separating of a substantial portion of the impure cobalt nitrate as the cobalt rich solution, from the strong acid insoluble residue in the form of the solid component present after the dissolving step.  
     
     
         21 . A process as claimed in  claim 20 , wherein the separation includes a precipitation step during which impurities are precipitated out of the cobalt rich solution.  
     
     
         22 . A process as claimed in  claim 20  or  claim 21 , wherein the separation is aided by flocculating using a suitable flocculant used as 0.1% w/w solution.  
     
     
         23 . A process as claimed in any one of  claims 17  to  22 , wherein the cobalt rich solution is purified by selectivley removing substantially only cobalt ions from the cobalt rich solution by solvent extraction so that the cobalt rich solution from the precipitation step typically contains Co, Pt, Al, Fe, N 3   −  and NH 4   +  ions.  
     
     
         24 . A process as claimed in  claim 23 , wherein a suitable type of an acidic extractant is used.  
     
     
         25 . A process as claimed in  claim 24 , wherein the acidic extractant is di-(2-ethylhexyl) phosphoric acid (DEHPA) and tributylphosphate (TBP) as a modifier in illuminating paraffin for extracting Co ions from the cobalt rich solution.  
     
     
         26 . A process as claimed in  claim 24  or  claim 25 , wherein the solvent extractant is used as an ammonium salt which assists in keeping the pH of the mixture relatively constant after contacting the acidic cobalt rich solution with the organic extractant phase.  
     
     
         27 . A process as claimed in any one of  claims 23  to  26 , wherein the aqueous phase recovered from the solvent extraction is used in the precipitation of Fe and Al ions step, while the loaded organic phase containing mainly Co ions is reserved for a stripping step.  
     
     
         28 . A process as claimed in  claim 27 , wherein the Co loaded organic phase is contacted with a solution of the stripping agent to remove the extracted species.  
     
     
         29 . A process as claimed in any one  claims 2  to  28 , wherein the purified cobalt rich solution is crystallised to form a red-brown crystalline cobalt nitrate salt, Co(NO 3 ) 2 .6H 2 O or Co(NO 3 ) 2 .4H2O depending on the retention time when heating the crystals at 55° C.  
     
     
         30 . A process as claimed in any one of  claims 2  to  29 , wherein platinum is recovered from the nitric acid insoluble solid component from the cobalt dissolution step by dissolving the platinum and compounds thereof and non-cobalt and/or non-cobalt compound impurities from the cobalt rich solution out of the solid component to obtain a platinum rich solution.  
     
     
         31 . A process as claimed in  claim 30 , wherein the dissolved platinum is precipitated out of the platinum rich solution by to form platinum salts complex which can be recovered by a liquid: solid separation process.  
     
     
         32 . A process substantially as hereinbefore described and illustrated.  
     
     
         33 . A new process substantially as hereinbefore described.