Separation of molybdenum and tungsten from iron in hydrochloric-phosphoric acid solutions using solvent extraction with TBP and P507

Abstract

A mixture of TBP and P507 was proposed for the separation of molybdenum (Mo) and tungsten (W) from iron (Fe) in a hydrochloric-phosphoric acid (HCl-H3PO4) solution that was obtained from the hydrochloric acid preleaching of low-grade scheelite. Various extractants with TBP were investigated, and P507 showed synergistic effects on Mo and W extraction and a strong antagonistic effect on Fe extraction. Then, the effects of various conditions on the separation of Mo and W from Fe with the mixture of TBP and P507 were investigated. Using 24% (v/v) TBP, 16% (v/v) P507 and 60% (v/v) kerosene as extractants, 90% Mo and 88% W were extracted with only 8% Fe co-extraction, and the separation factors of Mo/Fe and W/Fe were 153 and 118, respectively, through one-stage extraction under the following conditions: 1.7 mol/L H+, A/O ratio of 3:1, contact time of 10 min, and temperature of 15 °C. After two-stage batch continuous extraction, 99% Mo, 94% W and 10% Fe were extracted. By washing with 2 mol/L hydrochloric acid, most of the Fe and other impurities were removed with negligible losses of Mo and W. Upon stripping with 5 mol/L ammonia at a 1:1 organic-to-aqueous phase ratio, almost 100% of the Mo and W were recovered from the washed organic phase. Other impurities, such as P, Si, Ca, Al, and Mn, minimally affected the extraction of Mo and W.