RU2156819C1 - Method of purifying rhodium and iridium - Google Patents

Abstract

FIELD: technology of recovery, separation and purification of rhodium and iridium. SUBSTANCE: original solution contains rhodium and iridium total amount of which is by 20-70 times greater than total amount of platinum and palladium. Platinum and palladium are extracted with sulfoxide solution. Phase ratio is 1:(2-5). Rhodium and iridium remain in aqueous phase. They are separate by extraction with phosphoric acid tributyl ester. Method makes it possible to simplify production process, widen technological possibilities of process, increase purity of rhodium and iridium. EFFECT: more efficient purification method. 2 cl, 3 ex

Description

 The invention relates to a technology for the extraction, separation and purification of platinum metals, in particular rhodium and iridium.

 The separation of platinum metals is complex and time-consuming.

 The most promising of them are extraction processes, which allow relatively quickly and with high quality to obtain compounds of individual platinum metals. However, the separation of iridium and rhodium from solutions containing other platinum metals is a difficult task because of their ability to coextract with platinum and palladium.

 A known method of separating iridium and rhodium from solutions containing platinum and palladium by extraction of platinum and palladium with a secondary amine. Rhodium and iridium remain in the aqueous phase. To prevent their extraction in the initial solution, a potential of -425 - -650 mV is maintained.

 This method does not allow to obtain pure rhodium and iridium from solutions in which the total content of rhodium and iridium significantly exceeds the content of platinum and palladium (see US patent 4041126, C 01 G 55/00, 1977).

 There is also known a method involving the extraction of rhodium and iridium from a solution in which their total content significantly exceeds the total content of platinum and palladium.

 The solution is treated with a reducing agent to transfer iridium to the trivalent state.

 Then platinum and palladium are recovered by amino acid extraction.

 The extract is washed and sent to separate extraction of platinum and palladium.

 Rhodium and iridium remain in the aqueous phase (see US patent 4105742, C 01 G 55/00, 1978, example 3).

 The disadvantage of this method is the use of a rare and expensive extractant-amino acids, which is unacceptable on an industrial scale.

 The method also requires complex preparation of the solution for extraction - evaporation and new dissolution and a high concentration of hydrochloric acid for re-extraction of platinum and palladium.

 Closest to the claimed is a method of purification of rhodium and iridium from platinum and palladium, including the extraction of platinum and palladium sulfoxide.

 Rhodium and iridium remain in the aqueous phase (see RF patent 2121517, C 22 B 11/00, 1998).

In this method, the initial solution contains rhodium and iridium in a much smaller amount than the content of platinum and palladium:
the total content of rhodium and iridium is 5-11 g / l, and platinum and palladium 87-93.5 g / l.

 The low content of rhodium and iridium with a high content of platinum and palladium in solution leads to the fact that during extraction part of the platinum and palladium cannot be recovered from the aqueous phase (99.5% recovery of platinum and palladium).

 As a result, rhodium and iridium of high purity cannot be obtained without additional purification.

 The objective of the invention is the creation of such a method of purification of rhodium and iridium, the results of which would be to simplify the process, expand the technological capabilities of the method, increase the purity of rhodium and iridium.

 To this end, in a method for purifying rhodium and iridium from platinum and palladium, including extraction of platinum and palladium with a sulfoxide solution, separating the organic phase containing platinum and palladium from the aqueous phase containing rhodium and iridium, the extraction of platinum and palladium is carried out from a solution in which the total content platinum and palladium are less than the total content of rhodium and iridium, and rhodium and iridium in the aqueous phase are separated by extraction with phosphoric acid tributyl ether.

 The extraction of platinum and palladium is carried out from a solution in which the total content of rhodium and iridium is 20-70 times higher than the total content of platinum and palladium while maintaining the volume ratio of the organic phase to the aqueous medium equal to 1: (2-5).

 As a result of the studies, it was found that sulfoxides as extractants retain their selectivity with respect to platinum and palladium even if their content in the solution is several tens of times lower than the content of rhodium and iridium.

 Moreover, the completeness of the extraction of platinum and palladium in the organic phase increases.

 With a decrease in the total content of rhodium and iridium with respect to the total content of platinum and palladium below 20, the degree of purification of rhodium and iridium decreases.

 If the total content of rhodium and iridium is more than 70 times higher than the content of platinum and palladium, then the extraction of rhodium and iridium decreases, which are coextracted with platinum and palladium. As a result, a second stage of purification of platinum and palladium from rhodium and iridium is required.

If the ratio of the volumes of the organic and aqueous phases V _о : V _is less than 1: 2, then the extraction of rhodium and iridium, which are coextracted with platinum and palladium, decreases.

 If the ratio of the volumes of the organic and aqueous phases is more than 1: 5, the degree of purification of rhodium and iridium decreases.

 Separation of rhodium and iridium is carried out with TBP phosphoric acid tributyl ester.

 The method is illustrated by the following examples.

Example 1
The initial solution contains platinum 5 g / l, palladium 1 g / l, iridium 90 g / l, rhodium 30 g / l, hydrochloric acid acidity 4,5N.

Platinum and palladium are extracted from the solution with sulfoxide at V _about : V _in = 1: 2.

 Platinum and palladium pass into the organic phase.

 The aqueous phase (raffinate) contains platinum and palladium less than 10 mg / l, rhodium 27 g / l, iridium 80 g / l.

 The aqueous phase containing rhodium and iridium is directed to separation by extraction of TBP.

 Before extraction, iridium (III) is oxidized to iridium (IV) with chlorine.

Extraction of TBP is carried out with a ratio of V _about : V _in = 1: 1.

 Iridium goes into the organic phase, and rhodium remains in the aqueous phase.

 The rhodium content in the organic phase is less than 5 mg / L, and the iridium content in the aqueous phase is less than 15 mg / L.

Example 2
The initial solution contains platinum 1 g / l, palladium 0.2 g / l, iridium 75 g / l, rhodium 9 g / l, hydrochloric acid 4.0 N.

Extraction of platinum and palladium is carried out by sulfoxide while maintaining V _about : V _in = 1: 5.

 The residual content of platinum and palladium in the aqueous phase is <10 mg / L. The iridium content in the raffinate is 70 g / l, rhodium 8.9 g / l.

 Iridium in an aqueous solution is oxidized with chlorine and the solution is sent to the extraction of TBP to separate rhodium and iridium. Iridium is extracted into the organic phase, and rhodium remains in the aqueous phase.

 The rhodium content in the organic phase is less than 5 mg / L, and the iridium content in the aqueous phase is less than 15 mg / L.

Example 3
The initial solution contains platinum 2 g / l, palladium 0.5 g / l, iridium 100 g / l, rhodium 25 g / l.

Extraction of platinum and palladium sulfoxide is carried out at V _about : V _in = 1: 3,5.

 Platinum and palladium <10 mg / l, iridium 96 g / l, rhodium 24 g / l remain in the aqueous phase.

The separation of rhodium and iridium is carried out as in example 1, maintaining V _about : V _in = 1,2: 1.

 The purity of rhodium and iridium (the content of rhodium and iridium in the organic phase and iridium in water) is the same as in example 1.

 The presented examples confirm that the purification method of rhodium and iridium allows you to get pure rhodium and iridium in a simple way from various solutions.

Claims (2)

 1. The method of purification of rhodium and iridium from platinum and palladium, including the extraction of platinum and palladium with a solution of sulfoxide, the separation of the organic phase containing platinum and palladium from the aqueous phase containing rhodium and iridium, characterized in that the extraction of platinum and palladium is carried out from solution, in which the total content of platinum and palladium is 20–70 times lower than the total content of rhodium and iridium, and the rhodium and iridium in the aqueous phase are separated by extraction with phosphoric acid tributyl ether.  2. The method according to claim 1, characterized in that the extraction of platinum and palladium is carried out while maintaining the volumetric ratio of the organic phase to the aqueous phase equal to 1: (2 - 5).