Selective precipitation of tungstate from molybdate-containing solution using divalent ions

Given the differences in mineralization behavior between Mo and W, an assumption was made that W might be removed from Mo by the divalent ions whose tungstates have wolframite-like monoclinic structures rather than scheelite-like tetragonal structures. Through analyzing crystal behaviors of ABO4-type molybdates and tungstates, it was revealed that Mn2+, Fe2+, Co2+, Ni2+ and Zn2+ could combine with WO42− to form monoclinic crystals and thus might be used as separation reagents. Experiments were carried out to investigate the precipitation behaviors of Mo and W with different divalent ions. The results indicated that the separation effects were in accordance with the predictions. Namely, the separation factors obtained with Ba2+, Pb2+, Sr2+, Ca2+ or Cd2+ did not exceed 8, while those obtained with Mn2+, Fe2+, Co2+, Ni2+ or Zn2+ were more than 45. The XRD analysis showed that the former precipitates were the expected tetragonal structures. But the latter, with broad and low-intensity diffraction peaks, could not be confirmed as the expected monoclinic structures. The TGA data showed that the dehydrations of the latter were significantly higher, about 7–20% at below 400 °C, indicating they may have not only adsorption water but also crystallization water. Even so, based on this study, more available reagents, such as Ni2+ and Zn2+, were found to be effective in separating Mo and W.

► An assumption was made that W might be removed by cations whose tungstates have wolframite-like structures. ► Experiments were carried out to verify the reliability of the assumption. ► Separation factors obtained with Ba2+, Pb2+, Sr2+, Ca2+ or Cd2+ did not exceed 8. ► Separation factors obtained with Mn2+, Fe2+, Co2+, Ni2+ or Zn2+ were more than 45. ► More available reagents were found to be effective in separating Mo and W.