Ultra-high purification of iron by anion exchange in hydrochloric acid solutions

Promising applications in advanced electronics have created a demand for ultra-high purity iron. Anion exchange in chloride solutions may offer an efficient and practical way of purification. Examination of anion-exchange distribution functions revealed a variety of behavior patterns to be exploited. Elution tests in laboratory-scale columns suggested that virtually all the impurities can be separated from the iron chloride solution by anion exchange. The hydrochloric acid concentration and volume of the rinsing and eluent solutions determine the efficiency of the procedure. Separation of certain elements (e.g. copper and molybdenum) requires strict control of redox conditions. The designed procedure consists of two anion-exchange steps. In the first step and during solution preparation, those impurities are separated which can be precipitated by iron, or sorbed in the resin at low HCl solutions under reducing conditions determined by the addition of Fe powder. The remaining impurities are separated from iron, applying a second ion exchange step under oxidizing conditions. Performance characteristics (yield, purification ratio and volume efficiency) of the separation indicate the optimum parameters of the rinsing and eluent solutions and the suitable way of defining the collected volume fraction of the effluent.