Tungsten speciation and its geochemical behavior in geothermal water: A review

Tungsten and most of its compounds remain one of the least regulated substances. As the potential toxicity of tungsten has been reported, the stereotypes about tungsten are gradually being broken. Areas with intense magmatic hydrothermal activity are likely threatened by geothermal tungsten (up to 1037 mu g/L of tungsten was detected in the geothermal waters from a magmatic hydrothermal system in Tibet, Daggyai), and the geothermal developers should be cautious during the utilization of geothermal resource. This paper reviews the studies on transformation of aqueous tungsten species, distribution of tungsten in geothermal waters, and critical geochemical processes (or parameters) controlling geothermal tungsten concentrations. The mobility of aqueous tungsten depends on environmental pH, its complexation with sulfide, and its sorption onto Fe(III) oxides/oxyhydroxides. More attention still needs to be paid to environmental geochemistry of tungsten, in view that there are limited literatures reporting the thermodynamic properties of tungsten compounds at high temperatures and the models delineating the geochemical behavior of tungsten.