Chemical behavior of tungstate solutions. Part 1. A spectroscopic survey of the species involved

This study is focused on the composition and the evolution of tungstate ions solutions as a function of pH and increasing concentrations. The Raman analysis showed that, during the titration of the tungstate solutions, WO4(2-), HWO4- ions and probably W2O7(2-) , HW2O7(2-) and H2W2O7 solvated species could exist in aqueous solutions. For diluted solutions, additions of a strong acid does not cause any precipitation, whereas the formation of the unstable solid tungstic acid (H2WO4 or WO3.H2O) could occur in concentrated solutions.