Precious Metals Rhodium, Iridium Separation And Enrichment

Aqueous two-phase extraction technique,a new separation technology,has been paid more and more attention. Compared with the traditional extraction methods,it has some unique advantage.This paper has chosen alcohol-ammonium sulphate-water aqueous two-phase extraction system and the separation and concentration of two elements of precious metals-rhodium and iridium were investigated. And then it tested the separation effect, explored the mechanism of the extraction and found appropriate methods for their determinations. The finished work as follows:(1)According to the stability difference between rhodium and iridium chlorine matches ion, activating agent(SnCl₂) and extractant(MBT) were chosen for the separation of rhodium and iridium .The factors which affected the formation of the complex such as acidity,reaction time,activating agent volume,extractant volume ,etc. were analyzed through many experiments,and then the best conditions was established for the formation of the complex.(2)Using SnCl₂ as the activating agent and MBT as the extractant,alcohol was chosen as the extraction and ammonium sulphate as the salting-out agent,then alcohol-ammonium sulphate-water aqueous two-phase extraction system was established.(3)Through the conditional experiments of alcohol-ammonium sulphate-water aqueous two-phase system,its best experiment conditions were decided. That is:the volume ratio of alcohol in solution is 30% or 40%, ammonium sulphate volume is 15.0 g,and the 2.0 mol/L chlorhydric acid volume is 0.4～1ml.(4)In the best conditions,the extraction maximum and the extraction rate were studied both in the rhodium solution and in the iridium solution. In the mixed solution, the extraction maximum of rhodium and the content of iridium in raffinate were investigated too. The results are:in the rhodium solution,the extraction maximum is about 400ug/25ml and the extraction rate is nearly above 95%; in the iridium solution , the extraction maximum is about 450ug/25ml. When the volume of iridium is less than 1000ug/25ml,the extraction rate is 20%～30%; When the volume of iridium is more than 1000ug/25ml,the extraction rate is smaller than 10%.In the mixed solution,theresults are similar with the one which are in the rhodium and the iridium solution.(5)The composition of the Rh-SnCl₂-MBT in alcohol phase was determinated by continuous variation method and equilibrium shift method. Mechanism of extraction in this aqueous two-phase system was studied on the basis of the results and combined theory.(6)In the spectrometry determination,the rhodium extractive was studied in the present of alcohol and ammonium sulphate. It was found that alcohol and ammonium sulphate had no effect. Therefore,the direct determination for the extractive was decided. The iridium determination used the classic method of SnBr₂ and was analyzed in this system. So the iridium determination method was chosen.