Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Platinum group metal
Patent
1992-10-16
1994-03-08
Langel, Wayne
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Platinum group metal
C01G 5500
Patent
active
052924912
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the solvent extraction of palladium from aqueous solutions which contain nitrate ions, pyridine-3,5-dicarboxylic diesters being used as the extraction medium.
It is known that palladium can be removed and recovered from aqueous solutions by solvent extraction. The solvent extraction media conventionally used according to the prior art, for example dialkyl sulfides, are lacking in resistance to oxidation and can therefore not be used in an oxidizing environment (for example in nitric acid solutions); dialkyl sulfides further suffer from poor extraction kinetics.
EP-A-0,332,314 describes the solvent extraction of palladium from aqueous solutions of palladium salts which obligatorily contain halide or pseudohalide anions, using a solution of a heterocyclic compound in a water-immiscible solvent, which has at least one ring substituent of the type -COX, where X is an alkoxy group having at least 5 carbon atoms. The heterocyclic ring compound in this case can be a pyridine mono-, pyridine di- or pyridine tricarboxylic ester, for example a diester of pyridine-3,5-dicarboxylic acid. Palladium is extracted in this case from the aqueous solution containing halide or pseudohalide anions into the water-immiscible solvent, whereas the majority of the other metals remain in the aqueous solution. If copper is present, it is coextracted to a great extent and must be separated off in a separate step. The palladium is extracted from the water-immiscible solvent using an aqueous solution (strip solution).
It has now surprisingly been found that it is possible to extract palladium from solutions which are essentially free from halide and psuedohalide anions, using these heterocyclic compounds. In contrast to the teaching given in EP-A-0,332,314 "the process of the present invention is believed to proceed by the formation of a complex, for example a halogeno complex, between the palladium, or copper, salt and the substituted heterocyclic compound", with the aid of the process according to the invention, the procedure can therefore be carried out even in the absence of halide or pseudohalide anions. The extraction rate is high in this case, the palladium extraction proceeds almost quantitatively and with high selectivity over the majority of other metals; copper is not coextracted or is coextracted only in very small amounts.
The solvent extraction media used for this are described in EP-B-0 057 797.
It has been further shown that the pyridine-3,5-dicarboxylic diesters described in EP-B-0,057,797 are distinguished by a high oxidation stability and are thus suitable for use in an oxidizing environment, such as for example nitrate solutions acidified by nitric acid.
The invention thus relates to a process for the solvent extraction of palladium from aqueous solutions of palladium salts which are essentially free of halide and pseudohalide ions, comprising the following steps: with a solution of the extraction medium in a water-immiscible organic solvent; medium in the water-immiscible organic solvent into which the palladium has been extracted; acids to remove accompanying metals possibly coextracted in small amounts; the palladium transferring into the aqueous strip solution; transferred, from the solution of the extraction medium in the water-immiscible organic solvent; dilute aqueous solutions or dilute acids prior to reuse, formula (1) ##STR1## in which n=1 to 3 and R is a identical or different hydrocarbon radicals having 5-36 C atoms and where the sum of the carbon atoms of all the Rs is between 16 and 36.
The invention further relates to a process for the solvent extraction from aqueous nitrate ion-containing and halide ion-free solutions, the extraction medium used being pyridine-3,5-dicarboxylic diesters of the general formula (2) ##STR2## in which R.sup.1 and R.sup.2 are identical or different unbranched or branched-chain or mixed isomeric alkyl groups having 5 to 36 carbon atoms.
Further subjects of the invention are characterized by the claims.
The range of variation of the chai
REFERENCES:
patent: 4961856 (1990-10-01), Dalton et al.
Langel Wayne
Schering Aktiengesellschaft
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