薄层油膜层流萃取分离浓盐酸介质中的铂钯铁

Separation of Pd(Ⅱ),Pt(Ⅳ)and Fe(Ⅲ)in concentrated hydrochloric acid using thin-layer oil membrane based laminar flow extraction

本文提出一种采用中性膦类萃取剂Cyanex 301分离浓盐酸中Pd(Ⅱ)、Pt(Ⅳ)、Fe(Ⅲ)阴离子的薄层油膜层流萃取新方法。利用PdCl^(2-)_(4)、PtCl^(2-)_(6)、FeCl^(-)_(4)在浓盐酸表面与Cyanex 301分子竞争相互作用的差异,实现了传统油滴分散搅拌萃取方式难以实现的Pd(Ⅱ)、Pt(Ⅳ)、Fe(Ⅲ)强化分离。考察了Fe(Ⅲ)浓度、盐酸浓度、H^(+)和Cl−浓度等对Pd(Ⅱ)、Pt(Ⅳ)、Fe(Ⅲ)萃取率及其相互间分离系数的影响规律。结果表明:由于浓盐酸表面Cl−富集、游离H^(+)浓度较低,Fe(Ⅲ)主要以H^(+)·FeCl^(-)_(4)离子对形式被Cyanex 301溶剂化萃取,而PdCl^(2-)_(4)以取代机理被萃取,PtCl^(2-)_(6)几乎无萃取。随浓盐酸体相中Fe(Ⅲ)浓度的增加,Pd(Ⅱ)和Fe(Ⅲ)的分离增强。Pd(Ⅱ)和Fe(Ⅲ)之间的分离系数随Cl−浓度增加而下降,但H^(+)浓度增加对二者的分离几乎无影响。

A new thin-layer oil membrane extraction strategy based upon laminar flow was proposed in this paper,using neutral organophosphorus Cyanex 301 as extractant to separate Pd(Ⅱ),Pt(Ⅳ)and Fe(Ⅲ)anions in concentrated hydrochloric acid.It exhibited an obvious advantage over conventional stirring extraction in promoting the separation of Pd(Ⅱ),Pt(Ⅳ)and Fe(Ⅲ)in concentrated aqueous hydrochloric acid solutions though the difference of the interaction between PdCl^(2-)_(4),PtCl^(2-)_(6),FeCl^(-)_(4)and phosphoric acid extractant Cyanex 301 on the surface of concentrated hydrochloric acid.The effects of Fe(Ⅲ)ions concentration,hydrochloric acid concentration,H^(+)and Cl−concentrations on the extraction rates of Pd(Ⅱ),Pt(Ⅳ)and Fe(Ⅲ)and their mutual separation coefficients were investigated.The results indicate that,due to Cl−enrichment and the low concentration of free H^(+)ions on the surface of concentrated hydrochloric acid,Fe(Ⅲ)is mainly extracted by Cyanex 301 through the solvation of ion pairs in the form of H^(+)·FeCl^(-)_(4),while PdCl^(2-)_(4)ions are still extracted with substitution mechanism and PtCl^(2-)_(6) ions are hardly extracted.With the increase of Fe(Ⅲ)ions concentration in the concentrated hydrochloric acid bulk phase,the separation of Pd(Ⅱ)and Fe(Ⅲ)is enhanced.The separation coefficient between Pd(Ⅱ)and Fe(Ⅲ)decreases with the increase of Cl−concentration,but the increase of H^(+)concentration has little effect on it.