System Of Topo Extraction Separation Of Rhodium And Iridium

The separation and purification of rhodium from the other precious metals is one of the more difficult areas in precious metal refining, due mainly to the complex solution chemistry of rhodium in chloride solution.In this paper ,Tin (II) chloride was used as labilizing reagent, and the results of a systematic study on the solvent extraction of rhodium with tri-n-octylphosphine oxide(TOPO) in aqueous solution of Rh(III)-Sn(II)-Cr system by activation-solvent extraction technology are given. The effects of the molar ratio of Sn to Rh , TOPO concentration, acidity, aging time ect. were inspected. The optimum extraction conditions are as follows: the amount of added stannous chloride is four times that of Rh according to the molar ratio of Sn to Rh, the temperature of complex reaction 60℃, aging time 1 h, phase ratio 1:1, the Rh percentage extraction was over 98% .The percentage of stripping may reach to 95% through one stage with 4 mol·L^-1 hydrochloric acid containing potassium chlorate. The results of this study show that the extraction of rhodium can be improved observably by the labilizing progress with SnCLl₂ and indicate the feasibility of recovery and purification of rhodium by activation-solvent extraction technology.In the TOPO system , activation-solvent extraction technology was put forward to separate Ir(IV) and Rh(III) ions from a mixed chloride solution by extraction of rhodium .Stannous chloride was added to the original solution containing IrCl₆^2- and RhCl₆^3- ions before extraction. IrCl₆^2- was reduced to IrCl₆^3- , which cannot be extracted by TOPO, and RhCl₆^3- was reduced to Rh(I), which was further complexed with SnCl₃^- forming a bi —nuclei bridged complex anions of the form[Rh₂Cl_6-n(SnCl₃)_n]^4-(n=2—4) and were extracted by TOPO simultaneously.A mixed solution of HC1 and KClO3 in which the strong oxidant chlorine was produced was used for stripping the rhodium. During the stripping process, both Rh(I) and SnCl₃^- in the complex anions were oxidized to Rh(III) and Sn(IV) destroying the structure of the [Rh₂Cl_6-n(SnCl₃)_n]^4-(n=2 — 4) anions; Rh(III)was stripped into the aqueous solution . The process was affected only slightly by the characteristic hing frequency of between IrCl₆^2- and IrCl₆^3- ions;a little amount of IrCl₆^2- might be extracted by TOPO in the course of extracting rhodium . IrCl₆^2- remained in the organic phase experiencing no change in the strong oxidative environment can be stripped with nitric acid. Because of their high percent extraction by TOPO, the SnCl3"" and SnCl₆^2- anions are always kept in the organic phase whether in the process of extraction or stripping the rhodium. Finally, all of the tin was stripped by sodium hydroxide and reclaimed. Meanwhile the TOPO was...