Solvent extraction separation of molybdenum and tungsten from ammonium solution by H2O2-complexation

Abstract

A novel process of solvent extraction for separation of molybdenum (Mo) from ammonium tungstate (W) solution containing high content of Mo was developed using a mixture of tri-alkyl phosphine oxide (TRPO) and tributyl phosphate (TBP) as extractant and hydrogen peroxide (H2O2) as complex agent. The extraction process was studied to optimize various parameters such as extractant concentration, contact time, temperature, dosage of H2O2, and initial pH of aqueous solution. The extraction isotherms for Mo were also plotted. The results indicated that the addition of TBP in organic not only improved phase separation both in extraction and stripping, but also increased the extraction of Mo and decreased the extraction of tungsten (W), and hence improved the separation properties of Mo/W. The extraction of Mo was higher than 63% and the separation coefficient βMo/W was larger than 80 under optimal conditions. The loading capacity was determined to be 12.33g/L Mo and 9.44g/L Mo at equilibrium pH of 1.58 and 2.05, respectively.The further separation of W and Mo was realized in stripping process. NH4HCO3 was the optimum stripping agent because of its good phase separation, effective stripping of Mo and high Mo/W selectivity. The effects of contact time, temperature, concentration of stripping agent and O/A ratio on the stripping were investigated with NH4HCO3. The stripping of Mo reached 89% in comparison to that of W that is less than 16% after one contact. The concentration of Mo in strip liquor was 70–90g/L and the mass ratio of Mo/WO3 in strip liquor was larger than 26 at an O/A ratio of 8:1–10:1 using 0.8–1.0mol/L NH4HCO3. The stripped organic was directly reused to extraction. A principle flowsheet of the recovery of Mo and W was developed.