A novel method for preparing tungsten and molybdenum peroxy complex solution and its application to tungsten - molybdenum separation

Aiming at the shortcomings of existing separation technology of tungsten (W) and molybdenum (Mo) by hydrogen peroxide (H2O2) complexation, the chemical behaviors of W(VI) and Mo(VI) in aqueous solutions were studied and a new method for preparing W(VI)-Mo(VI)-H2O2 solution was proposed. By using trialkyl phosphine oxide-tributyl phosphate (TRPO-TBP) as a mixed extractant system, the applications of this new method on separation of W and Mo were conducted, including the effect on third phase formation and elimination, satisfactory removal of Mo, and separation efficiency of Mo and W. The results show that the formation and depolymerization of isopoly and heteropoly compounds of W and Mo have an important influence on their separation. The core of the new method lies in the control of pH value when W and Mo begin to complex with H2O2. The formation of metatungstate and heteropoly compounds with high Mo/W atomic ratio could be avoided by adding H2O2 into the mixed solution of tungsten and molybdenum in a high pH range of 5.3–6.5 for complexation. Based on this principle, this method could not only avoid the third phase formation at the source but also effectively improve the satisfactory removal of molybdenum. As the complexation pH value increased from 3.51 to 5.51, after six-stage countercurrent extraction of feed solution containing about 127.8 g/L WO3 and 16.10 g/L Mo, the mass ratio of Mo/WO3 in raffinate decreased from 5.94 × 10−4 to 2.71 × 10−5 and the molybdenum content decreased from 77.50 mg/L to 3.54 mg/L. This study provides a relevant theoretical foundation and feasible improvement for the satisfactory separation of W and Mo from peroxy complex solution system, and is expected to facilitate the industrialization of this technology. •This work proposes a weakly acidic complexation method for preparing W(VI)-Mo(VI)-H2O2 solution.•Achieving third phase elimination and reducing Mo content to below 3.54 mg/L by controlling pH of stage 1 in range 5.3–6.5.•The new method reduces the Mo content and Mo/WO3 mass ratio in raffinate to 1.19 mg/L and 0.985 × 10−5, respectively.•The third phase is a coordination compound of uncomplexed metatungstate and TRPO.•Formation of heteropoly compounds of high Mo/W atomic ratio leads to inefficient removal of Mo.