Extraction of phosphorus, arsenic and/or silica from sodium tungstate and molybdate solutions with primary amine and tributyl phosphate as solvents. I — Synergistic extraction and separation of phosphorus, arsenic and/or silica from tungstate and molybdate solutions

Abstract

Studies on the synergistic extraction of phosphorus, arsenic and silica as impurities from sodium tungstate and molybdate solutions with a solvent mixture of primary amine and tributyl phosphate (TBP) were made. The experimental results indicate that phosphorus, arsenic and silica can be extracted and separated very effectively from weakly alkaline sodium tungstate and neutral molybdate solutions. The extraction behavior of phosphorus and arsenic for molybdate systems is quite different from that for tungstate systems. For molybdenum systems, the optimum separation of phosphorus and arsenic can only be obtained in a narrow range of equilibrium pH values of about 6–7; outside this pH range the extraction of these two elements decreases sharply. However, the extraction of phosphorus, arsenic and silica for tungsten systems and silica for molybdenum system increases with decreasing pH. Phosphorus, arsenic and silica cannot be extracted without the presence of tungsten and molybdenum in the aqueous phase. The loaded organic phase can be stripped with dilute sodium hydroxide solution quantitatively. The alkaline crude leaching solutions of sodium tungstate and ammonium molybdate were tested and the results were in agreement with those obtained from solutions prepared by mixing sodium salts of the elements concerned.