An alternative way to separating Ir(IV) and Rh(III) ions from a mixed chloride solution with added stannous chloride

Abstract

An alternative way was put forward to separate Ir(IV) and Rh(III) ions from a mixed chloride solution by extraction of rhodium with tri-butyl phosphate (TBP). Stannous chloride was added to the original solution containing RhCl 6 3− and IrCl 6 2− ions before extraction; IrCl 6 2− was reduced to IrCl 6 3−, which cannot be extracted by TBP, and RhCl 6 3− was reduced to Rh(I), which was further complexed with SnCl 3 −, forming a bi-nuclei bridged complex anions of the form [Rh 2Cl 6− n (SnCl 3) n ] 4− ( n=2–4) and were extracted by TBP simultaneously. A mixed solution of HCl and NaClO 3 in which the strong oxidant chlorine was produced, was used for stripping the rhodium. During the stripping process, both Rh(I) and SnCl 3 − in the complex anions were oxidized to Rh(III) and Sn(IV) destroying the structure of the [Rh 2Cl 6− n (SnCl 3) n ] 4− ( n=2–4) anions; Rh(III) was stripped into the aqueous solution while IrCl 6 2− remained in the organic phase experiencing no change in the strong oxidative environment. Because of their high percent extraction by TBP, the SnCl 3 − and SnCl 6 2− anions are always kept in the organic phase whether in the process of extraction or stripping the rhodium. The rhodium was selectively stripped with iridium and tin. Finally, all of the tin was stripped by sodium hydroxide and reclaimed, meanwhile, the TBP was regenerated. The effect of Sn/Rh and Sn/Ir molar ratios on the percent extraction was studied. The results show that separation of the two ions can be realized only when the two molar ratios are both at least equal to 4. Two groups of separation tests were conducted: one with the solution containing identical quantities of Rh(III) and Ir(IV), the other with the solution containing very low Rh(III)/Ir(IV) ionic concentration ratio. Both of the separation results proved to be very effective.