Extraction of tungsten as polyoxometalate anion using a layered double hydroxide: Selectivity and regeneration

Extraction of tungstate species as highly charged polyoxometalates has been performed with hydrotalcite. An optimum pH around 5 has been determined, correlated with the stability domain of heptatungstate species. Two mechanisms have been shown from in situ infrared spectroscopy and zeta potential measurements: exchange of carbonate ions by heptatungstate species and adsorption as inner-sphere surface complexes. The presence of nitrate, chloride, and sulfate has no effect on the extracted fraction and it was concluded that the extraction is selective toward these anions. The regeneration of the solid was performed with a solution of carbonate sodium at pH 10.