| WO2013082614A1 | 2013-06-06 |
| US7935173B1 | 2011-05-03 |
| Claims: 1. A platinum-group metals (PGM) beneficiation process which includes the following steps: (A) obtaining from a PGM bearing ore body a PGM concentrate from which most base metals have been recovered or removed, the PGM concentrate including PGM complexes as dissolved chloride species; (B) producing from the PGM concentrate at least one refining stream rich in one or more chloride complexes or species of one of the PGM's; (C) if desired or necessary, in all or at least a portion of said refining stream, consolidating all chloride complexes or species of said one PGM so that said one PGM is present as a single chloride complex or species at the lowest common valence for said one PGM at consolidating conditions, to form a consolidated PGM complex stream; (D) optionally increasing the purity of the PGM chloride complex or species in the consolidated PGM complex stream or in the refining stream; (E) if desired or necessary, replacing the chloride ligand of said PGM chloride complex or species in the consolidated PGM complex stream or in the refining stream with a different ligand; and (F) withdrawing the consolidated PGM complex stream or the refining stream comprising the PGM complex as a saleable product with less than 1000 ppm of impurities, with the proviso that the platinum-group metals beneficiation process includes at least one of step (C) and step (E). 2. The PGM beneficiation process of claim 1, in which, in step (C), all chloride complexes or species of said one PGM are consolidated in all of said refining stream, without the process including production of said one PGM as a metal in an oxidation state of zero from said refining stream. 3. The PGM beneficiation process of claim 1, in which, in step (C), all chloride complexes or species of said one PGM are consolidated in only a portion of said refining stream, with a balance of said refining stream being processed to produce said one PGM as a metal in an oxidation state of zero. 4. The PGM beneficiation process of any of claims 1 to 3, in which, in step (B), refining streams respectively rich in Pd, Pt, Rh, Os, Ru and Ir are produced, with the refining streams having less than 50 000 ppm of impunities and in which, in step (F), the withdrawn consolidated PGM complex stream or the refining stream comprises a PGM complex of one of Pd, Pt, Rh, Os, Ru and Ir as a saleable product. 5. The PGM beneficiation process of any of claims 1 to 4, in which, in step (B), at least refining streams respectively rich in Pd, Pt and Rh are produced, with the refining streams having less than 50 000 ppm of impurities and in which, in step (F), at least three consolidated PGM complex streams or refining streams are withdrawn, the withdrawn consolidated PGM complex streams or refining streams respectively comprising a PGM complex of Pd, Pt and Rh as a saleable product. 6. The PGM beneficiation process of any of claims 1 to 5, in which, in step (E), the chloride ligand of said PGM chloride complex or species in the consolidated PGM complex stream or in the refining stream is replaced with a non-halide ligand. 7. The PGM beneficiation process of any of claims 1 to 5, in which, in step (E), the chloride ligand of said PGM chloride complex or species in the consolidated PGM complex stream or in the refining stream is replaced with a nitrate, hydroxide, iodide, sulphate, nitrite, oxide, or sulfide ligand. 8. The PGM beneficiation process of any of claims 1 to 5, in which, in step (E), the chloride ligand of said PGM chloride complex or species in the consolidated PGM complex stream or in the refining stream is replaced with a nitrate, hydroxide, or sulphate ligand. 9. The PGM beneficiation process of claim 1, in which, in step (B), said chloride complex or species is selected from the group consisting of H2PtCl6, (NH3)2PtCl6, (NFIs PdCU, H2PdCI4, H3RhCI6, Na3RhCI6, (NFUblrC and H3RuCI6. 10. The PGM beneficiation process of any of claims 1 to 4, in which the withdrawn PGM complex in step (F) is selected from the group consisting of PtCI4 (Platinum (IV) chloride), PtCI2.xH20 (Platinum (II) chloride), [H2PtCl6].nH20 (Hexachloroplatinic acid), K2PtCl6 (Potassium hexachloroplatinate), (IMFI4)2PtCl6 (Ammonium chloroplatinate (ACP)), Pt02 (Platinum black), Pt(OH)2 (Platinum hydroxide), H2Pt(OH)6 (hexahydroxy-platinic acid), Pt(N03)2 (Platinum (II) nitrate), Pt(NC>3)4 (Platinum (IV) nitrate), Na2PtCl6 (Sodium hexachloroplatinate), [Na2Pt(0H)6].nH20 (Sodium hexahydroxyplatinate), Na2PtCI4 (Sodium tetrachloroplatinate), [Pt(NH3)4]CI2.nH20 (Tetraamine platinum chloride), Pd(OH)2 (Palladium hydroxide), Pd(NC>3)2 (Palladium nitrate), [Pd(NH3)2CI2] (Palladium diamine), [Pd(NH3)4CI2] (Palladium tetramine), PdO (Palladium black), PdCI2.nH20 (Palladium chloride), PdS (Palladium sulphide), PdS04 (Palladium sulphate), K2PdCl6 (Potassium hexachloropalladate), K2PdCI4 (Potassium tetrachloropalladate), Na2PdCl6 (Sodium hexachloropalladate), Na2PdCI4 (Sodium tetrachloropalladate), PdCI2(en) ((Ethalenediamine) dichloropalladate), H2PdCI4 (dihydrogen tetrachloropalladate), H3RhCl6 (Hexachloro rhodic acid), RhCI3.SH20 (Rhodium trichloride), NasRhC (Sodium hexachlororhodate (III)), Rh(OH)3 (Rhodium hydroxide), H3Rh(OH)6 (rhodium hydroxide trihydrate), [(NH3)sRhCl]Cl2 (Claus salt), Na3Rh(N02)6 (Sodium hexanitrorhodate (III)), [(NH4)3Rh(N02)6] (Ammonium hexanitrorhodate), Rh203 (Rhodium oxide), [Rh(en)2CI2]CI (Dichlorobis(ethylenediamine) rhodium chloride), [RhCl3.3DETA] (DETA (diethylenetriamine) salt), [Rh(NH3)6]CI3 (Hexaamine rhodium chloride), Rh(N03)3 (Rhodium nitrate), Rh2(S04)3 (Rhodium suphate), H3Rh(N03)6 (Hexanitrato rhodic acid), Ru04 (Ruthenium tetroxide), Ru02 (Ruthenium black), (NH4)3RuCI3 (Ammonium trichlororuthenate), RuCI3 (Ruthenium trichloride), [(NH4)3lrCl6] (Ammonium hexachloroiridate), Na3lrCl6 (Sodium hexachloroiridate), lrCl3.3H20 (Iridium trichloride), Ir02 (Iridium oxide) and Os04 (Osmium tetroxide). 11. The PGM beneficiation process of claim 10, in which the withdrawn PGM complex in step (F) is selected from the group consisting of Pt02 (Platinum black), Pt(OH)2 (Platinum hydroxide), H2Pt(OFI)6 (hexahydroxy-platinic acid), Pt(N03)2 (Platinum (II) nitrate), Pt(N03)4 (Platinum (IV) nitrate), [Na2Pt(0FI)6].nH20 (Sodium hexahydroxyplatinate), Pd(OH)2 (Palladium hydroxide), Pd(N03)2 (Palladium nitrate), PdO (Palladium black), PdS (Palladium sulphide), PdS04 (Palladium sulphate), Rh(OFf)3 (Rhodium hydroxide), Fl3Rh(OFI)6 (rhodium hydroxide trihydrate), a3Rh(N02)6 (Sodium hexanitrorhodate (III)), [(IMH4)3 h(N02)6] (Ammonium hexanitrorhodate), Rh203 (Rhodium oxide), Rh(NOs)3 (Rhodium nitrate), Rh2(S04)3 (Rhodium suphate), H3Rh(N03)6 (Hexanitrato rhodic acid), Ru04 (Ruthenium tetroxide), Ru02 (Ruthenium black), Ir02 (Iridium oxide) and Os04 (Osmium tetroxide). 12. The PGM beneficiation process of any of claims 1 to 11, in which, in step (C), the consolidation of all chloride species includes boiling down all or at least a portion of said refining stream until solids start forming a thick slurry but not to dryness to force all metals into fully chlorinated species rather than aquated species, and redissolving of the solids in water to aquate base metals present and to form base metal hydroxides that are precipitated and removed in step (D). 13. The PGM beneficiation process of claim 12, in which said refining stream includes ligands containing IM, the process including, in step (C), boiling down all or at least a portion of said refining stream until solids start forming a thick slurry but not to dryness a second time, and again redissolving the solids in water, to destroy any ligands containing N and to remove the N in the form of NOX. 14. The PGM beneficiation process of any of claims 1 to 13, in which step (D) includes adjusting the pH of the consolidated PGM complex stream or the refining stream to precipitate any base metal hydroxides present in the consolidated PGM complex stream or in the refining stream, followed by filtration to remove precipitated base metal hydroxides. 15. The PGM beneficiation process of any of claims 1 to 14, in which in step (B), a refining stream rich in Pt is produced, in step (D), metals in the consolidated PGM complex stream or in the refining stream rich in Pt are oxidised to higher valences, hydrolysed to metal hydroxides, and the metal hydroxides are precipitated and removed, and in step (E) the Pt chloride species is converted to a Pt hydroxide species or to a Pt nitrate species or to PtO. 16. The PGM beneficiation process of any of claims 1 to 14, in which in step (B), a refining stream rich in Pd, in the form of (NH3)2PdCl4 is produced, and in step (E), the (NH3)2PdCI4 is converted by heating and reaction with sodium hydroxide in the presence of a reductant to form PdO, which is optionally converted by reaction with HN03 to Pd(N03)2.2H20 or by reaction with H2S04 to PdS04.2H20. 17. The PGM beneficiation process of any of claims 1 to 14, in which in step (B), a refining stream rich in Pd, in the form of H2PdCI4 is produced, in step (C), the consolidation of all chloride species includes boiling down all or at least a portion of said refining stream until solids start forming a thick slurry but not to dryness to force all metals into fully chlorinated species rather than aquated species and to destroy any ammonium ions that may be present, in step (D), metals in the consolidated PGM complex stream or in the refining stream rich in Pd are oxidised to higher valences, hydrolysed to metal hydroxides, and base metal hydroxides and amphoteric metals are precipitated and removed, and in step (E) the Pd is hydrolysed at a pH below 10 to form Pd(OH)2, which is optionally converted by reaction with HNO3 to Pd(N03)2. 18. The PGM beneficiation process of claim 17, which includes producing the Pd(OH)2 as a filter cake, redissolving the Pd(OH)2 in HCI to form a solution, re-oxidising the Pd(OH)2 in solution, and again hydrolysing, precipitating and filtering at a pH below 10 to form a Pd(OH)2 filter cake, and optionally converting the Pd(OH)2 by reaction with HN03 to Pd(N03)2. 19. The PGM beneficiation process of any of claims 1 to 14, in which in step (B), a refining stream rich in Rh, in the form of H3RhCl6 is produced, in step (C), the consolidation of all chloride species includes boiling down all or at least a portion of said refining stream until solids start forming a thick slurry but not to dryness to force all metals into fully chlorinated species rather than aquated species, in step (D), the solids are redissolved or diluted in water and filtered to remove base metals as base metal hydroxides and to provide a filtrate, and in step(E), metals in the filtrate are oxidised to higher valences, and the Rh is hydrolysed to form H3Rh(OH)6, precipitated and removed by filtration. 20. The PGM beneficiation process of claim 19, in which the H3Rh(OH)6 is reacted with HNO3 and optionally evaporated to dryness to produce Rh(N03)3.2H20 or is reacted with H2SO4 and optionally evaporated to dryness to produce h2(S04)3· 21. The PGM beneficiation process of any of claims 1 to 4, in which the withdrawn PGM complex in step (F) is selected from the group consisting of H2PtCI6, H2Pt(OH)6, Na2Pt(OH)6, Pt(N03)4, Pd(OH)2, Pd(N03)2.xH20, PdS04.xH20, H3Rh(OH)6, H3Rh{N03)6, Rh(N03)3.xH20, Rh2(S04)3 and PdO. 22. The PGM beneficiation process of claim 21, in which the withdrawn PGM complex in step (F) is selected from the group consisting of H2Rί(OH)6, Na2Pt(OH)6, Pt(N03)4, Pd(OH)2, Pd(N03)2.xH20, PdS04.xH20, H3Rh(OH)6, H3Rh(N03)6, Rh(N03)3.xH20, Rh2(S04)3 and PdO. 23. A product that includes a PGM complex with less than 1000 ppm of impurities when produced by the PGM beneficiation process of any of claims 1 to 22. |
THIS INVENTION relates to the beneficiation of platinum-group metals. In particular, the invention relates to a platinum-group metals beneficiation process and the products of such a process.
Generally, platinum-group metal refineries receive a mixed metal concentrate feedstock having a platinum-group metal (PGM) content ranging between 55 to 75 % by mass, and produce through various processes, including a hydrochloric acid/chlorine leach, a variety of saleable PGMs, typically in sponge or ingot format with the platinum-group metals being in oxidation state zero, having purities of more than 99.95%, e.g. 99.99% or 99.999%. These pure PGMs are then disposed to downstream industries where they are used in a variety of applications ranging from electronic, electrical, glass, refining, automotive, medical and numerous fine chemical applications.
Since PGMs are particularly suited for catalysing a myriad of reactions, one application that has received and still is receiving a considerable amount of attention, is the use of PGM salts and metal as catalysts. These catalysts are often coated or impregnated onto inert substances. In the case of automobile exhaust gas catalysts, the PGMs are supported on inert substrates which are often coated with a high surface area alumina prior to impregnation with an active PGM catalytic component.
The process of impregnation can generally be described as dipping the inert substrate into a solution or solutions of water-soluble PGM salts or compounds, i.e. catalytic PGM precursor salts or compounds. Examples of such PGM salts or compounds are sodium hexachloroplatinate, chloroplatinic acid, palladium nitrate, rhodium nitrate and palladium oxide. The salts or compounds are then typically precipitated by pH adjustment on the surface of the substrate as hydroxides. Hydroxides are reduced to PGM 'blacks' and /or metal, i.e. pure metal or oxide with a small particle size, by chemical or thermal reduction. There are many variations in catalyst preparation and these are often typically tailor-made to suit the needs of a particular industry. This invention provides a process for the production of saleable PGM salts or complexes that can be used, inter alia, in these catalyst-manufacturing processes.
Many different PGM salts or complexes have been employed as impregnating agents, from compounds comprising hexachloroplatinate to bis cyclooctadiene ruthenium chloride (i.e. 1,5-cyclooctadiene ruthenium(ll) chloride). These salts or complexes are usually manufactured by the catalyst industry from the pure PGMs (i.e. the pure metals) sourced from primary PGM refiners, i.e. the refiners producing PGM's from PGM bearing ore bodies, or sourced from secondary producers. The performance of a PGM catalyst is greatly affected by surface contaminants and defects, as well as various chemical contaminations. The chemical contamination can result from poisoning of the catalyst by the reductants and products within a catalysed reaction or from poor catalyst preparation. Pure PGMs are the preferred feedstock for catalyst production processes as the use of a high-quality feedstock avoids the possibility of spurious chemical contamination.
It has also been found that PGM halide salts used as impregnating agents in the automotive catalyst manufacturing industry, to some extent, corrode inert supports or substrates and therefore are not always the most suitable catalytic impregnating agents. This has also been observed in fuel cell catalysts.
PGM refining methods for producing pure PGMs are typically chlorine-based and it is this chlorine which, in the form of a PGM chloride salt or complex, is typically a contaminant the catalyst industry wishes to avoid.
The primary producers of PGMs are the platinum mines. The value in mining is, however, in ore extraction and not metal refining. Hence, the goal of the primary producers of PGMs typically is to process the PGM bearing ore only as far as its simplest, saleable form, namely pure platinum-group metals, and not to produce pure, saleable PGM salts or complexes. In short, the primary producers consider themselves to be miners, not chemical manufacturers. Platinum metal refining deals with the process of separating and extracting PGMs from a crude feed or concentrate obtained from a PGM bearing ore body. The PGMs are very similar chemically and so this process is far more complex than in comparison to the refining of gold. The emphasis in this process is around separating the PGMs from each other, rather than avoiding possible contamination with, for example, chloride complexes. As a result, the mining industry has historically focused on the production of pure metals and they have not focused on the production of PGM salts or complexes of a high purity as saleable products.
A PGM beneficiation process for the production of saleable PGM complexes or salts, which has the potential to shorten the manufacturing process and to lower processing costs, would be desirable. If such a process can avoid or lessen the need to dissolve a pure platinum-group metal of zero valency, it would be an added advantage.
According to one aspect of the invention, there is provided a platinum-group metals (PGM) beneficiation process which includes the following steps:
(A) obtaining from a PGM bearing ore body a PGM concentrate from which most base metals have been recovered or removed, the PGM concentrate including PGM complexes as dissolved chloride species;
(B) producing from the PGM concentrate at least one refining stream rich in one or more chloride complexes or species of one of the PGM's;
(C) if desired or necessary, in all or at least a portion of said refining stream, consolidating all chloride complexes or species of said one PGM so that said one PGM is present as a single chloride complex or species at the lowest common valence for said one PGM at consolidating conditions, to form a consolidated PGM complex stream;
(D) optionally increasing the purity of the PGM chloride complex or species in the consolidated PGM complex stream or in the refining stream;
(E) if desired or necessary, replacing the chloride ligand of said PGM chloride complex or species in the consolidated PGM complex stream or in the refining stream with a different ligand; and
(F) withdrawing the consolidated PGM complex stream or the refining stream comprising the PGM complex as a saleable product with less than 1000 ppm of impurities,
with the proviso that the platinum-group metals beneficiation process includes at least one of step (C) and step (E).
Said different ligand is typically a non-chloride ligand. Preferably, the saleable product, comprising a PGM complex or salt, has less than 500 ppm of impurities. Advantageously, such a saleable product may be suitable for use directly as a catalytic precursor salt which can be impregnated onto a substrate.
The PGM concentrate is thus typically a precious metals refinery feed, processed to remove most of the base metals that are typically present in a concentrate obtained from a PGM bearing ore body, such as the UG2 chromitite ore body, the Merensky Reef or the Platreef of the Bushveld Igneous Complex in South Africa. Typically, primary PGM refiners use such a PGM concentrate in a PGM refining process to produce PGM's as sponge metal. The PGM refining process employed by a primary PGM refiner may be the classical PMR process, which is well known to those skilled in the art, or a more modern PMR process. Irrespective of whether the classical or a more modern PMR process is used, the PMR process typically involves an initial hydrochloric acid/chlorine leach of a PGM concentrate from which most base metals have been recovered or removed, so that the PGM concentrate contains PGM complexes as dissolved chloride species. Subsequently, the PGM concentrate is processed or separated into various refining streams for the separate production of Pd, Pt, Rh, Os, Ru and Ir typically as sponge metal. The process of the invention thus advantageously proposes using one or more of these refining streams to produce one or more valuable high purity saleable products comprising a PGM complex or salt, without going to the trouble and expense of producing said PGM as a metal in oxidation state zero, and then redissolving the metal in order to produce a PGM complex or salt of high purity.
The process may include, in step (C), consolidating all chloride complexes or species of said one PGM in all of said refining stream, without the process including production of said one PGM as a metal in an oxidation state of zero from said refining stream. In other words, the process may represent a drastic shortening of a conventional PGM refining process, at least in respect of one of the PGM's or in respect of one of the refining streams.
Instead, the process may include, in step (C), consolidating all chloride complexes or species of said one PGM in only a portion of said refining stream, with a balance of said refining stream being processed to produce said one PGM as a metal in an oxidation state of zero. In such a process, only a portion of a refining stream is thus diverted for production of a saleable PGM complex, with at least some PGM as a metal in an oxidation state of zero also being produced from said refining stream, typically in conventional fashion, e.g. using the classical PMR process.
The process may include, in step (B), producing refining streams respectively rich in Pd, Pt, Rh, Os, Ru and Ir, with the refining streams having less than 50 000 ppm of impurities and in step (F), withdrawing the consolidated PGM complex stream or the refining stream comprising a PGM complex of one of Pd, Pt, Rh, Os, Ru and Ir as a saleable product.
In one embodiment of the invention, the process includes, in step (B), producing at least refining streams respectively rich in Pd, Pt and Rh, with the refining streams having less than 50 000 ppm of impurities and in step (F), withdrawing at least three consolidated PGM complex streams or refining streams, the withdrawn consolidated PGM complex streams or refining streams respectively comprising a PGM complex of Pd, Pt and Rh as a saleable product.
Preferably, the refining stream(s) has/have less than 25 000 ppm of impurities, more preferably less than 20 000 ppm of impurities, most preferably less than 10 000 ppm of impurities, e.g. less than 5 000 ppm of impurities in the case of a refining stream rich in Pt or Rh or Ir or less than 10 000 ppm of impurities in the case of a refining stream rich in Pd or less than 500 ppm in the case of a refining stream rich in Ru.
As will be appreciated, the level of impurities in the refining stream and the required purity of the saleable product will determine whether it is necessary to effect step (D), i.e. to increase the purity of the PGM chloride complex or species in the consolidated PGM complex stream or in the refining stream. When step (D) is present, it typically involves the removal of impurities such as base metals and/or noble metals.
The process may include, in step (E), replacing the chloride ligand of said PGM chloride complex or species in the consolidated PGM complex stream or in the refining stream with a nitrate, hydroxide, iodide, sulphate, nitrite, oxide, or sulfide ligand. The presence of a halide ligand may be undesirable in some downstream uses of the saleable product. The PGM beneficiation process may thus include, in step (E), replacing the chloride ligand of said PGM chloride complex or species in the consolidated PGM complex stream or in the refining stream with a non-halide ligand.
In one embodiment of the invention, in step (E), the chloride ligand of said PGM chloride complex or species in the consolidated PGM complex stream or in the refining stream is replaced with a nitrate, hydroxide, or sulphate ligand.
The chloride complex or species in step (B) may be selected from the group consisting of H 2 PtCI 6 , (NH 3 ) 2 PtCI 6 , (NH 3 ) 4 PdCl 4 , H 2 PdCI 4 , H 3 RhCI 6 , Na 3 RhCI 6 , (NH 4 ) 2 lrCI 6 and H 3 RUCI 6 .
The process of the invention may include the step of removal of Au from the PGM concentrate prior to step (B) and/or removal of Au from said refining stream in step (C). The Au removed from the PGM concentrate and/or the Au removed from said refining stream may be converted to a saleable Au complex or salt.
The withdrawn PGM complex in step (F) may be selected from the group consisting of but not necessarily limited to PtCU (Platinum (IV) chloride), PtCh.xPhO (Platinum (II) chloride), [H 2 PtCl 6 ].nH 2 0 (Hexachloroplatinic acid), K 2 PtCl 6 (Potassium hexachloroplatinate), (NH 4 ) 2 PtCI 6 (Ammonium chloroplatinate (ACP)), Pt0 2 (Platinum black), Pt(OH) 2 (Platinum hydroxide), H 2 Pt(OH) 6 (hexahydroxy-platinic acid), Pt(NC>3)2 (Platinum (II) nitrate), Pt(N0 3 ) 4 (Platinum (IV) nitrate), a2PtCI 6 (Sodium hexachloroplatinate), [Na 2 Pt(0H) 6 ].nH 2 0 (Sodium hexahydroxyplatinate), l\la 2 PtCl 4 (Sodium tetrachloroplatinate), [Pt(l\IH 3 ) 4 ]CI 2 .nH 2 0 (Tetraamine platinum chloride), Pd(OH)2 (Palladium hydroxide), Pd(N0 3 ) 2 (Palladium nitrate), [Pd(NH3) 2 CI 2 ] (Palladium diamine), [Pd(NH 3 ) 4 CI 2 ] (Palladium tetramine), PdO (Palladium black), PdCI 2 .nH 2 0 (Palladium chloride), PdS (Palladium sulphide), PdS0 4 (Palladium sulphate), K2PdCl6 (Potassium hexachloropalladate), K 2 PdCI 4 (Potassium tetrachloropalladate), Na2PdCl6 (Sodium hexachloropalladate), Na 2 PdCl 4 (Sodium tetrachloropalladate), PdCl 2 (en) ((Ethalenediamine) dichloropalladate), PhPdCU (dihydrogen tetrachloropalladate), H 3 RhCl 6 (Hexachloro rhodic acid), RhCI 3 .3H 2 0 (Rhodium trichloride), Na 3 RhCl 6 (Sodium hexachlororhodate (III)), Rh(OH)3 (Rhodium hydroxide), H 3 Rh(OH)6 (rhodium hydroxide trihydrate), [(NH 3 )5RhCl]CI 2 (Claus salt), Na 3 Rh(N0 2 ) 6 (Sodium hexanitrorhodate (III)), [(NH 4 ) 3 Rh(N0 2 ) 6 ] (Ammonium hexanitrorhodate), Rh 2 0 3 (Rhodium oxide), [Rh(en) 2 Cl2]Cl (Dichlorobis(ethylenediamine) rhodium chloride), [RhCI 3 .3DETA] (DETA (diethylenetriamine) salt), [Rh(NH 3 ) 6 ]CI 3 (Hexaamine rhodium chloride), Rh(N0 3 ) 3 (Rhodium nitrate), Rh 2 (S0 4 ) 3 (Rhodium suphate), H 3 Rh(N0 3 ) 6 (Hexanitrato rhodic acid), Ru0 4 (Ruthenium tetroxide), Ru0 2 (Ruthenium black), (NH 4 ) 3 RuCl 3 (Ammonium trichlororuthenate), RuCis (Ruthenium trichloride), [(NH 4 ) 3 lrCl 6 ] (Ammonium hexachloroiridate), l\la 3 lrCl 6 (Sodium hexachloroiridate), lrCI 3 .3H 2 0 (Iridium trichloride), Ir0 2 (Iridium oxide) and 0s0 4 (Osmium tetroxide).
In one embodiment of the invention, the withdrawn PGM complex in step (F) is selected from the group consisting of Pt0 2 (Platinum black), Rΐ(OH) 2 (Platinum hydroxide), H 2 Pt(OH) 6 (hexahydroxy-platinic acid), Pt(N0 3 ) 2 (Platinum (II) nitrate), Pt(N0 3 ) 4 (Platinum (IV) nitrate), [Na 2 Pt(0H) 6 ].nH 2 0 (Sodium hexahydroxyplatinate), Pd(OH) 2 (Palladium hydroxide), Pd(N0 3 ) 2 (Palladium nitrate), PdO (Palladium black), PdS (Palladium sulphide), PdS0 4 (Palladium sulphate), Rh(OH) 3 (Rhodium hydroxide), H 3 Rh(OH) 6 (rhodium hydroxide trihydrate), Na 3 Rh(N0 2 ) 6 (Sodium hexanitrorhodate (III)), [(NH 4 ) 3 Rh(N0 2 ) 6 ] (Ammonium hexanitrorhodate), Rh 2 0 3 (Rhodium oxide), Rh(N0 3 ) 3 (Rhodium nitrate), Rh 2 (S0 4 ) 3 (Rhodium suphate), H 3 Rh(N0 3 ) 6 (Hexanitrato rhodic acid), Ru0 4 (Ruthenium tetroxide), Ru0 2 (Ruthenium black), Ir0 2 (Iridium oxide) and Os0 4 (Osmium tetroxide).
In another embodiment of the invention, the withdrawn PGM complex in step (F) is selected from the group consisting of H 2 PtCI 6 , H 2 Pt(OH) 6 , Na 2 Pt(OH) 6 , Pt(N0 3 ) 4 , Pd(OH) 2 , Pd(N0 3 ) 2 .xH 2 0, PdS0 .xH 2 0, H 3 Rh(OH) 6 , H 3 Rh(N0 3 ) 6 , Rh(N0 3 ) 3 .xH 2 0, Rh 2 (S0 4 ) 3 and PdO.
Instead, the withdrawn PGM complex in step (F) may be selected from the group consisting of H 2 Pt(OH) 6 , IMa 2 Pt(OH) 6 , Pt(N0 3 ) 4 , Pd(OH) 2 , Pd(N0 3 ) 2 .xH 2 0, PdS0 4 .xH 2 0, H 3 Rh(OH) 6 , H 3 Rh(N0 3 ) 6 , Rh(N0 3 ) 3 .xH 2 0, Rh 2 (S0 ) 3 and PdO.
The consolidation of all chloride species in step (C) may include boiling down all or at least a portion of said refining stream until solids start forming but not to dryness to force all metals into fully chlorinated species rather than aquated species, and redissolving of the solids in water or an aqueous solvent to aquate base metals present and to form base metal hydroxides that are precipitated and removed in step (D).
The refining stream may include ligands containing N. The process may then include, in step (C), boiling down all or at least a portion of said refining stream until solids start forming but not to dryness a second time, and again redissolving the solids in water or an aqueous solvent, to destroy any ligands containing N and to remove the N in the form of NOX.
The process may include, in step (D), adjusting the pH of the consolidated PGM complex stream or the refining stream to precipitate any base metal hydroxides present in the consolidated PGM complex stream or in the refining stream, followed by filtration to remove precipitated base metal hydroxides. Said precipitation thus may involve careful pH control to achieve precipitation of different hydroxides at different pH levels.
In one embodiment of the invention, the process is characterised in that, in step (B), a refining stream rich in Pt is produced,
in step (D), metals (i.e. other than Pt) in the consolidated PGM complex stream or in the refining stream rich in Pt are oxidised to higher valences, hydrolysed to metal hydroxides, and the metal hydroxides are precipitated and removed, and
in step (E) the Pt chloride species is converted to a Pt hydroxide species or to a Pt nitrate species or to PtO.
In another embodiment of the invention, the process is characterised in that in step (B), a refining stream rich in Pd, in the form of (NH 3 )2PdCI 4 is produced, and in step (E), the (NH3hPdCI 4 is converted by heating and reaction with sodium hydroxide in the presence of a reductant to form PdO, which is optionally converted by reaction with HN0 3 to Pd(N03)2.2H 2 0 or by reaction with H2SO4 to PdS0 4 .2H 2 0.
In a further embodiment of the invention, the process is characterised in that in step (B), a refining stream rich in Pd, in the form of H 2 PdCl 4 is produced,
in step (C), the consolidation of all chloride species includes boiling down all or at least a portion of said refining stream until solids start forming but not to dryness to force all metals into fully chlorinated species rather than aquated species and to destroy any ammonium ions that may be present,
in step (D), metals (i.e. other than Pd) in the consolidated PGM complex stream or in the refining stream rich in Pd are oxidised to higher valences, hydrolysed to metal hydroxides, and base metal hydroxides and amphoteric metals are precipitated and removed, and
in step (E) the Pd is hydrolysed at a pH below 10 to form Pd(OH) 2 , which is optionally converted by reaction with HNO 3 to Pd(N0 3 ) 2 .
The Pd(OH) 2 may be produced as a filter cake. The process may then include redissolving the Pd(OH) 2 in HC1 to form a solution, re-oxidising the Pd(OH) 2 in solution, and again hydrolysing, precipitating and filtering at a pH below 10 to form a Pd(OH) 2 filter cake, and optionally converting the Pd(OH) 2 by reaction with HNO 3 to Pd(N0 3 ) 2 .
In yet another embodiment of the invention, the process of the invention is characterised in that
in step (B), a refining stream rich in Rh, in the form of H 3 RhCl 6 is produced,
in step (C), the consolidation of all chloride species includes boiling down all or at least a portion of said refining stream until solids start forming but not to dryness to force all metals into fully chlorinated species rather than aquated species,
in step (D), the solids are redissolved or diluted in water or an aqueous solvent and filtered to remove base metals as base metal hydroxides and to provide a filtrate, and
in step(E), metals in the filtrate are oxidised to higher valences, and the Rh is hydrolysed to form H 3 Rh(OH) 6 , precipitated and removed by filtration.
The H 3 Rh(OH) 6 may be reacted with HN0 3 and optionally evaporated to dryness to produce Rh(N0 3 ) 3 .2H 2 0. Instead, the H 3 Rh(OH) 6 may be reacted with H 2 S0 4 and optionally evaporated to dryness to produce Rh 2 (S0 4 ) 3 ·
The invention extends to a product that includes a PGM complex or salt with less than 1000 ppm of impurities when produced by the PGM beneficiation process hereinbefore described. The invention is now described with reference to the following examples and the accompanying diagrammatic drawings in which
Figure 1 shows a portion of a flow sheet of a classical PMR process for extraction of platinum from a PGM concentrate from which most of the base metals have been recovered or removed in a base metals refinery;
Figure 2 shows a portion of a flow sheet of a classical PMR process for extraction of palladium from a PGM concentrate from which most of the base metals have been recovered or removed in a base metals refinery; and
Figure 3 shows a portion of a flow sheet of a classical PMR process for extraction of ruthenium, iridium, osmium and rhodium from a PGM concentrate from which most of the base metals have been recovered or removed in a base metals refinery.
Example 1
Figure 1 shows a flow sheet of a portion of a classical PMR process for extraction of platinum from a PGM concentrate from which most of the base metals have been recovered or removed in a base metals refinery.
Some of the PGM salts used in downstream industries can be extracted directly from conventional PMR processes such as the process of Figure 1 as they are part of the standard process flows. Examples are the 'final metal' salts - namely the salts that would normally proceed to thermal/chemical reduction to saleable metal in a conventional PMR process. In the case of platinum this would be an ammonium chloroplatinate (ACP) salt, such as the ammonium hexachloroplatinate shown in Figure 1 at point 7. These final salts are generally of sufficient purity to meet the purity specifications required by downstream industries. If not, recrystallisation is usually sufficient to remove unwanted contamination. Final salts can also be washed free of entrained chlorides or recrystalised from an alternative organic solvent.
Figure 2 shows a flow sheet of a portion of a classical PMR process for extraction of palladium from a PGM concentrate from which most of the base metals have been recovered or removed in a base metals refinery. PGM blacks / oxides can simply be generated by the chemical reduction of final metal solutions. For example the reduction of palladium at point 20 in Figure 2 can be effected with organic reductants such as formic acid. These chemical reductions lend themselves neatly to the production of nanoparticles for the fuel cell industry.
As will be appreciated, both the final metal salts and the blacks can be utilized as starting materials for a conventional salt producing process.
Figure 3 shows a flow sheet of a portion of a classical PMR process for extraction of ruthenium, iridium, osmium and rhodium from a PGM concentrate from which most of the base metals have been recovered or removed in a base metals refinery. When Figures 1 to 3 are read together, they provide a flow sheet of a typical classical PMR process, which is well known to those skilled in the art.
In this example, the invention is particularly described with reference to platinum and rhodium nitrate production, based on the classical PMR process represented by Figures 1 - 3, but it is to be understood that it may equally apply to the production of other PGM salts and to other PMR processes. There are many varying PMR processes used by primary producers most of which are based on the classical process as represented by Figures 1 - 3. Modern modifications involve processes which include unit operations such as solvent extraction and ion exchange unit operations. One modification, for example, to the portion of the classical process shown in Figure 1 is to use a one-step hydrolysis after the crude platinum dissolve and filtration, straight to pH 8, combining the Au removal, pH 1 hydrolysis, pH 5.5 hydrolysis and pH 10 hydrolysis shown in Figure 1 in one reactor, using NaOH for pH 1 hydrolysis, NaBr0 3 for oxidation and NaC0 3 to adjust the pH to 8. For simplicity the invention will be discussed from the perspective of the classical PMR process, but it is to be understood that the invention can equally apply to other more modern PMR processes. In fact, modern PMR processes, which are more efficient than the classical PMR process, would lend themselves more readily to salt production, as the feed sources available for salt production would be more stable and purer than those from the classical PMR process. The standard preparations of halide free platinum nitrate solution from pure platinum metal for use in the catalytic salt industry calls, in the process of the invention, for the substitution of chloride ligands, resulting from the metal dissolution step for hydroxide ligands. This allows for the precipitation of platinum (II) hydroxide, which can be washed free of chlorides before redissolution in nitric acid.
A process of selective hydrolysis is commonly used to separate and purify PGMs, as shown by the hydrolysis steps of Figure 1, between the Au removal step and the addition of DMG. This invention utilizes a ligand substitution step to achieve a salt purity upgrade.
The required feedstock can be from any source and is conveniently PMR refinery liquor just after the primary separation process as shown by point 10 in Figure 1. This could be a hexachloroplatinate solution with a platinum content equal or greater to 95.0% by mass. In Figure 1, the refining stream withdrawn for production of a saleable PGM complex is a crude platinum dissolve. A typical composition of the crude platinum dissolve stream is shown in Table
1.
Table 1: Composition of a typical crude platinum dissolve in a classic PMR process.
The crude platinum dissolve is produced by the following reaction: Pt+HCI/CI 2 ® [ H 2 PtCI 6 .xH 2 0 ]
The crude platinum dissolve is a mixture of chloride species of the formula [PtCIe- n H 2 On]. Some of these may also be polymeric.
Contaminating metals will also be present in a variety of chloride forms. Any base metals present will typically be simple chlorides, whereas the PGMs are present as complexes.
The crude platinum dissolve solution is best thought of as a dynamic soup of elements present in a variety of speciations. These species vary between states until equilibrium is reached. Equilibrium, in the case of the PGMs can take time, days even. In an effort to speed this up the solution is boiled down reducing the metal valences and forcing speciation consolidation by dehyroxylation, i.e. forcing the metal to be in one speciation state. Importantly, it is to be noted that this step is not used in a HCI/CI 2 dissolve of typical downstream catalyst preparation processes as those processes are not trying to purify the metal but to remove chloride ions.
As the solution is boiled down the metals are reduced to their lower valences. Typically, for example, Fe III is converted to Fe II, Pt is converted from IV to II and Au is reduced to metal.
The solution is initially evaporated to a thick slurry, close to near dryness. This thus consolidates the metal chloride species and removes gold and selenium as well as excess acid. Solids that start forming are then redissolved in water to a total acidity (TA) of about <0.4% and filtered. A total acidity to less than 0.4% is equivalent to a pH of about 1. Any base metals still present are precipitated as hydroxides:
MX(2-4) H 2° ( M (OH)(2-4)
FeCI 2 h 2 ° f Fe(OH) 2 NiCh H 2° f Ni(OH) 2
The solution is then oxidized at a redox potential of >970mv, with sodium bromate. This re-oxidises metals to higher valance states. The solution is then hydrolysed using NaOH and or NaHC0 3 to a final pH of 9. The hydrolysis of contaminating metals in their higher oxidation states produces clear-cut precipitation end points with a good filter cake rather than a gelatinous cake experienced with the hydroxides of metals in lower oxidation states. Most importantly the platinum will be in the IV oxidation state and this does not start to hydrolyse until pH 10.
[PtCI 6 ] 2 + 6[OH] -► [Pt (OH)e] 2 - +6CI
There will thus be a number of different, metal-dependent hydrolysis products from this raise in pH. For example, Pd, Ru, Rh, Ir and Pb will precipitate as hydroxides. Palladium for example will precipitate as H 2 Pd(OH) 4 .
It is to be noted that in this example a process is described that employs hydrolysis straight to pH 9. This is possible, because the refining stream rich in platinum chloride complexes (i.e. the crude platinum dissolve) is already quite pure. In other embodiments of the invention, where a dirtier refining stream is used, hydrolysis is effected stepwise in a series of stages, with oxidation being effected between each stage. This is because some of the metals present in the refining stream may precipitate at one pH and then re-dissolve at a higher pH. Thus, if one has higher inventories of a contaminant you need to avoid the re-dissolution of the hydroxides by removing them at the appropriate stage.
The contaminating hydroxides are filtered off and a platinum filtrate is neutralized, cold, with acetic acid to precipitate the pale-yellow platinum hexahydroxide [H 2 Pt(OH) 6 ]. The hydroxide can be converted into a number of useful catalytic salts. For example, a prolonged boiling in water will result in the formation of platinum black (i.e. PtO). This is essentially a reduction and a hydration which decomposes to give the oxide.
To generate [Pt ( 0 3 )2] the fresh hydroxide is dissolved in dilute nitric acid and evaporated to dryness.
H 2 Pt(OH) 6 +6HNO3— ► H 2 Pt(N0 3 ) 6 +12 H 2 0
The concept of ligand substitution iri a down-stream PGM salt preparation process as potential purification steps can be expanded to accommodate other ligands from differing salt preparation methods. This is illustrated for rhodium below.
There are two methods for the preparation of halide free rhodium nitrate. One uses the hydroxide ligand and this can be utilized as set out hereinbefore for platinum. The other uses iodine as a ligand. PGM iodide salts are less soluble than their chloride equivalents and the conversion rates of reaction from the chloride to the iodide ligands are relatively fast compared to the hydroxylation reaction rates.
The main contaminants in rhodium liquors from primary sources will be iridium and to lesser degrees the base metals. Comparison of the lower oxidation metal iodides indicates a marked difference in solubilities of the salts. The base metal (II) iodides are all water-soluble whilst the rhodium and iridium (III) iodides are insoluble in comparison. The iridium (III) iodide also has the advantageous property of being soluble in hot water. By precipitating the rhodium iodide, a clean-up step is therefore possible.
A typical refining stream rich in rhodium would be a rhodium chloride stream after primary separation, base metals and iridium removal, shown at point 21 in Figure 3. The rhodium should be in the PfaRhC xF O form or alternatively the Na3RhCl6.xF) 2 0 form. Table 2 shows typical compositions for potential refining streams rich in rhodium that can be considered for the production of saleable rhodium salts using the process of the invention. Table 2: Composition of typical Rh-rich refining streams
If a rhodium-rich refining stream is taken after primary separation only, e.g. a pH cake dissolve taken at point 17 in Figure 3, then the base metals and iridium will have to be removed before the production of a nitrate. There are several different methods well known in the art to accomplish this. The best removal processes would be the ion exchange processes.
Once a clean feed has been obtained, it should be boiled down to a thick slurry cl near to but to dryness. It is important not to bake this material. The solution is oxidized during the boil down. Na 3 RhCl 6 .xH 2 0 is precipitated, leaving Na 2 lrCl 6 .H 2 0 in solution. If the feed is sodium free some sodium is added to the reaction in the form of sodium hydroxide. The solution is filtered. The solids are re-dissolved in hydrochloric acid, boiled down and back diluted to half its volume with water. It is then boiled for an hour. This is to consolidate the chloride species of the metals that are present and to ensure that they are all in their common lower oxidation states. A stoichiometric quantity of potassium iodide is dissolved in the minimum of water and added to the rhodium chloride solution. The solution is then refluxed. The rhodium iodide is precipitated during the reflux and cooling. The precipitate is filtered and re-slurried in hot water. The slurry is filtered and washed with hot water until no iridium or chloride ions are detected in the filtrate. The black rhodium iodide is dissolved in concentrated nitric acid and hydrogen peroxide. This will produce a rhodium nitrate solution that can be crystallized by evaporation..
For the current PMR processes worldwide, the hydroxide routes although not quantitative in yield are the preferred routes as they match the current PMR process flows. As primary producers are not as restricted by the metal prices a yield of 80% is quite acceptable as resulting residues from a PGM salt production can easily be re-routed within the current refining circuits and the PGMs extracted. Both potassium and iodine are generally avoided in primary extraction circuits as they alter the solubilities of some of the metal complexes formed during the extraction processes.
The preparations, instrumentation and analytical methods employed in the following worked examples are all standard to the art and hence are not described in detail.
Example 2. Preparation of platinum hexahydroxide
An 850ml sample of impure [H 2 PtCl 6 ] liquor at 120-130g/l Pt was taken after the primary separation of PGMs in a classical PMR process. This feed liquor was boiled down to a thick slurry, near but not to dryness and back diluted with 300ml of distilled water. The solution was again boiled down and then back diluted with water to a total acidity (TA) of <0.4%. The resultant solution was filtered hot to produce a filtrate.
During the boiling down, the [H 2 PtCl 6 ] was dehydroxylated and consolidated.
Other metals presented as consolidated chloride species. This is also a reduction step dropping the metals to their respective lower common valences.
MX 3 + heat -► MX 2
AuC + heat -► Au + [Cl]
The pH adjustment was essentially to remove base metals, e.g.
20 ml of a 250g/l sodium bromate solution was then added to the filtrate. The resultant solution was refluxed for 30 mins. The redox potential was kept above 970mv.
Sodium bromate is an oxidant. The metals were thus re-oxidised to their preferred higher valences. Sodium bromate also retards Pt reaction with hydroxide groups. Sodium bicarbonate was added slowly to the solution, at the boil, until a pH of 6.5.
This solution was cooled to ambient temperature and filtered. The resulting filtrate was re- oxidised with sodium bromate and refluxed for 30 minutes whilst the redox potential was kept above 970 mv.
The addition of sodium bicarbonate to a pH of 6.5 was part of a selected hydrolysis route. The following metal hydroxides precipitate at pH 6.5: Ir, Rh, Fe, Ru, Al, Se, Te, As, Hg and Sn.
A 50% sodium bicarbonate solution was added to a pH of 8. The solution was once again cooled and filtered to produce a cold filtrate. During this second hydrolysis step, the metals were re-oxidised. This was a precaution to keep the metals in their higher valence states. The second hydrolysis was taken to pH 8, thus removing Bi, Pb, Cd and Pd.
A 50% solution of sodium hydroxide was added to the cold filtrate to a final pH of 10 over a period of four hours. The total acidity of the resulting filtrate was adjusted to 5.5% by the addition of 6M HCI. This was then refluxed until the redox potential was 720mv. The solution was then cooled and filtered.
At a pH of 10, a platinum hexahydroxide was formed
H 2 PtCI 6 +8NaOH —► Na 2 Pt(OH) 6 + 6NaCI + 2H 2 0
The pH of the filtrate was then adjusted to pH 7 with dilute acetic acid, resulting in the precipitation of the pale-yellow platinum hexahydroxide.
Na 2 Pt(OH) 6 + 2H + —► H 2 Pt(OH) 6 +2 Na +
The platinum hexahydroxide was filtered and washed with water and 5% acetic acid until the wash liquors were chloride free. This hydroxide once it is chloride free is a saleable salt.
The solid was dried on the filter, and dissolved in 300 ml of 4M nitric acid, with the resultant solution evaporated to dryness. H 2 Pt(OH) 6 +4 H O3 —► Pt(N0 3 ) 4
The compositions of various streams or solutions at different places in the process as set out in Example 2, are shown in Table 3.
Table 3 Typical results for Example 2, normalised for direct comparison.
Example 3. Preparation of platinum hexahydroxide
50g of pure final 99.95% platinum ACP salt was taken from the platinum refining stream of the classical PMR process of Figure 1 at point 7.
This was dissolved in 300ml of 6M HCI and refluxed for 1 hour. This converted the platinum species in a resultant solution to a chloride.
[(NH 4 ) 2 PtCI 6 ]+2HCl - ► H 2 PtCI 6 +2(NH 4 )CI
The solution was boiled down to 100 ml and back diluted with distilled water to
300 ml. This was an ammonium destruction step. A 30% solution of sodium hydroxide was added very slowly over a period of 2 hours to a pH of 12. As will be noted, this is a little higher pH than the method set out in Example 2 to compensate for any residual ammonium ions that may still be present.
H 2 PtCI 6 +8 NaOH -► Na 2 Pt(OH) 6 + NaCI + 2H 2 0
This resultant solution was filtered, and the pH adjusted to 7 with acetic acid to produce a hydroxide cake, where after the hydroxide cake was washed with 100ml aliquots of distilled water until no free chloride and sodium ions could be detected in the wash liquors.
The hydroxide cake was finally dried under vacuum to produce a saleable, dry salt.
Example 4. Preparation of palladium nitrate and palladium sulphate.
300 ml of a 99.95% pure palladium liquor or solution (i.e. a solution of [(NH 3 ) 4 Pd]CI 2 ) was taken from the palladium refining stream of the classical PMR process of Figure 2, just before the final salt precipitation at point 20 in Figure 2.
The palladium solution was heated to 80°C and the solution was neutralized with a 20% sodium hydroxide solution.
120 ml of 2.6% formic acid was added to the solution whilst the solution was vigorously stirred. This was to prevent coating of palladium on the walls of the vessel containing the solution. The pH of the solution was then adjusted to 12 with 20% sodium hydroxide.
A further 250ml of formic acid was added to the solution. This was then boiled for 2 hours, producing palladium oxide solids. The palladium oxide solids were filtered and washed with water until the wash water was clear of sodium and chloride ions.
The formic acid works as a reductant. If the pH is less than 7, for example 3 - 4, Pd metal is produced. If the pH is 7 or higher, PdO (palladium black) is produced. The palladium black can advantageously be produced with a nanoparticle size, rendering it suitable for the fuel cell industry. Any reductant can be used for this process, e.g. N 2 H 2 , H 2 or sugar. The exact precipitation conditions can be varied to control the size of particles of Pd metal or palladium oxide produced. This would enable saleable nanoparticles to be generated in this way.
H 2 Pd CU + [reductant] -► PdO
The solids were air-dried and the air-dried solids were dissolved in 500 ml of 1.5M nitric acid. The nitric acid solution was then evaporated to dryness, producing brown/yellow deliquescent crystals of [Pd (N0 3 ) 2 . 2H 2 0].
PdO +2 HNO 3 -►Pd(N0 3 ) 2 .2H 2 0
The sulphate equivalent is simply made by dissolution and evaporation with sulphuric acid, instead of nitric acid.
Pd0+H 2 S0 4 -► PdS0 4 .2H 2 0
Example 5. Preparation of palladium nitrate solution
500ml of a solution of impure tetrachloropallidic acid [H 2 PdCI 4 ], with and average palladium content of 88% by mass or greater was taken from the palladium refining stream of the classical PMR process of Figure 2, at point 16 in Figure 2, just before palladium diamine precipitation.
The solution was boiled down to 70ml and back diluted to 550ml with distilled water. This step consolidates the metal chloride species. It also destroys any residual ammonium ions from the previous Pt precipitation in the classical PMR process. lg of sodium bromate was added to the solution. This was boiled for 10 minutes. This was an oxidation push to push all the metals to their higher common valences to facilitate clean hydrolysis and precipitation. Sodium bromate also retards the rate at which Pt reacts with the hydroxide ions. The solution was cooled to 80°C and the pH adjusted to 6.7 with sodium bicarbonate. The solution was then cooled to room temperature and filtered, to remove base metals and amphoteric metals hydrolytically and to produce a filtrate.
The filtrate was reheated to 80°C and a further lg of sodium bromate was added to the filtrate. The redox should be >970mv. This was a precautionary re-oxidation step.
The pH of the filtrate was adjusted to 8.5 and the filtrate was then boiled for 10 minutes, to effect hydrolysis of the Pd and to form a yellow precipitate. This was in effect a Pd/Pt separation step as Pt does not hydrolyse at a pH below 10.
H 2 PdCI 4 + OH -► Pd(OH) 2
The resultant yellow precipitate was filtered and washed with 100 ml of distilled water, producing a hydrolysis cake.
The yellow hydrolysis cake was dissolved in 100ml of 2M hydrochloric acid. This again dissolved the Pd to form a solution. Hydrogen peroxide was added to the palladium solution at 80°C, until a redox of > 970mv was reached. This was an oxidation step.
The pH of the solution was then again adjusted to 8.5 and the solution was boiled for 10 minutes, to effect hydrolysis of the Pd and to form a yellow precipitate. The resultant yellow precipitate was again filtered and washed with 100 ml of distilled water. In this way, any residual Pt is removed.
The resultant palladium hydroxide solids were further washed with several aliquots of distilled water, until the wash liquors were free of sodium and chloride ions. The palladium hydroxide was air-dried and the air-dried palladium hydroxide solids were then dissolved in 300 ml of 2M nitric acid. The resultant nitrate solution was evaporated to dryness to produce yellow/ brown crystals of [Pd (NC>3) 2 . 2H 2 0]. Pd(OH) 2 +2 HN0 3 - ► Pd(N0 3 )2 +2H 2 0
The compositions of various streams or solutions at different places in the process as set out in Example 5, are shown in Table 4.
Table 4: Typical results for Example 5
Example 6. Preparation of rhodium nitrate
A 1L sample of impure of [H 3 RhCl 6 ] solution with an approximate rhodium concentration of 2.8-2% was taken from the rhodium refining stream of the classical PMR process of Figure 3, at point 21 in Figure 3. This was boiled down to about 200 ml, to the point just where wine red crystals formed in a thick slurry. It is essential not to bake this material. This consolidates the chloride speciation of all the contained metals.
The boiled down solution was back diluted to 400ml with distilled water and filtered to produce a filtrate. This was a hydrolysis step to removes base metals. This filtrate was heated to 80 °C and 0.5g of NaBr0 3 was added to a redox potential of >950 mv. This ensured oxidation of Irto oxidation state IV, as well as oxidation of other metals. The pH of the solution was adjusted to 6.7 by the addition of sodium bicarbonate.
This hydrolysed the Rh.
[HsRhCle] +60H — ► [H 3 Rh(OH) 6 ] +6CI
The resultant solution was boiled for 10 minutes, cooled to ambient temperature and filtered, producing a yellow hydroxide.
The resulting yellow rhodium hydroxide was washed with 400ml of distilled water. The washings were repeated until the wash water was clean of Na + and Cl .
The washed rhodium hydroxide was dissolved in 300ml of 4M nitric acid to form a nitric solution, which was then evaporated to dryness to produce dark yellow Rh(N0 3 ) 3 .2H 2 0.
[H 3 Rh(OH) 6 ] + 6H NO3 — * [H 3 Rh(N0 3 ) 6 ] +6H2O
The compositions of various streams or solutions at different places in the process as set out in Example 6, are shown in Table 5 Table 5: Typical results for Example 6
Example 7: Preparation of rhodium sulphate Rhodium hydroxide was produced as above in Example 6.
The rhodium hydroxide was dissolved in 300 ml of 3M sulphuric acid and evaporated to dryness.
The process of the invention, as illustrated, advantageously allows production of valuable, pure PGM complexes or salts directly from standard refinery liquors holding PGM's in an oxidation state other than zero. This avoids having to deal with the problem of dissolution of a PGM to produce a PGM salt or complex, which may be quite difficult to achieve, e.g. in the case of Rh.
The use of the final metal salts from the PMR process is a simple and effective way to extract PGM salts or complexes for catalytic use, and to produce non-halide or non-chloride salts or complexes if desired.
The process of the invention, as illustrated, is more cost effective than the standard salt production methods based on using the pure metal directly. If a less pure starting material were used, i.e. further up the refining chain in a PMR process, it would allow for a greater cost saving in the process of salt production as it would eliminate many of the interim processes required in a conventional PMR process to reach the final metal stage.
Extraction of PGM salts of the required purity, in a non-chloride form, at an intermediate stage from a PGM refining or primary metal-producing process, for use, for example, as catalytic precursor salts advantageously lowers the processing costs for both the primary PGM refiner and the downstream catalyst manufacturing industry by respectively shortening both manufacturing pipelines. The nobility and hence market price of the PGM's rather than the use of optimised process configurations are dominant considerations in the manufacture of PGM catalyst precursors and catalysts. These factors expose the catalyst producers to large cost risks as a direct result of metal price fluctuations, particularly when holding large PGM stock. The process of the invention, as illustrated, should allow primary PGM refiners and catalyst manufacturers to lower the level of expensive metal stock tied up in their respective manufacturing pipelines, as well as contribute to reducing the commonly encountered metal price fluctuation risks.