Effect of Addition of Tin (II) Chloride on Extraction of Rhodium from Hydrochloric Acid Solution with LIX 26

Abstract

Solvent extraction applied to refining process for platinum group metals (PGMs) offers several advantages over the traditional precipitation methods.
Chloride is the only effective medium in which PGMs can be brought into a solution, thus chlorocomplexes are particularly important in the process chemistry of PGMs separations. Rh (III) chlorocomplex is poorly extracted into organic solvents, which is due to the charge of the complex as well as its labile character in a solution, that is, formation of RhCl₆-_n(H₂O)_n^(3-n)-(n=1-6). The problem of solvent extraction of Rh from chloride solutions has not yet been solved and there is no effective extractant for Rh.
In the present study, the extraction of Rh from hydrochloric acid solutions with substituted 8-hydroxyquinoline (LIX 26) was tested to clarify the effect of addition of SnCl₂ on the extraction and stripping of Rh.The results obtained in this study are summarised as follows:
(1) The extraction efficiency of Rh increased with an increase in the molar ratio of [Sn]:[Rh] and when the molar ratio of [Sn]:[Rh] was more than 10: 1, high extraction efficiency was obtained.
(2) The extraction mechanism of Rh from hydrochloric acid solutions containing SnCl₂ with LIX 26 was discussed and the following extraction reaction was considered.
3HL_o+4H⁺_a+Rh(SnCl₃)₅^4-, a=(H₂L)₃RhH(SnCl₃)_{5, o}
(3) The stripping efficiency of Rh from the organic phase by nitric acid solution was better than that by sulfuric acid solution.