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Guo, Qinghai ; Planer-Friedrich, Britta ; Yan, Ketao:
Tungstate thiolation promoting the formation of high-tungsten geothermal waters and its environmental implications.
In: Journal of Hydrology.
Bd. 603, Part B
(2021)
.
- 127016.
ISSN 0022-1694
DOI: https://doi.org/10.1016/j.jhydrol.2021.127016
Abstract
Tungsten is a toxic trace element that poses a threat to the environment and human health, especially in places where it occurs in high concentrations, such as geothermal areas. In the present study, hydrochemical processes controlling tungsten concentrations in various types of geothermal waters and the effects of thiolation on tungsten geochemistry were investigated in the Tengchong-Longling geothermal region, China. Neutral-to-alkaline hot springs, which are the majority of springs in Tengchong-Longling (and globally), exhibited much higher tungsten concentrations than acidic hot springs. Within the neutral-to-alkaline springs, total tungsten concentration correlated with reservoir temperatures, and springs rich in sulphide exhibited higher total tungsten concentrations than those with low or no detectable sulphide. The formation of thiotungstates apparently increased total tungsten solubility. Results from thermodynamic equilibrium modelling did not match measured data, and the extent of thiolation was over- and under-predicted at low and high pH, respectively. Cooccurring arsenic substantially inhibited the thiolation of tungsten at sulphide concentrations and S(-II)/(W+As) ratios of less than 5 mg/L and 50, respectively. Above these limits, however, tungsten and arsenic had comparable tendencies of being thiolated. The present study suggests that consideration of thiotungstates, which is seldom done, is necessary when studying tungsten hydrochemistry of sulphidic natural waters, and current thermodynamic constants are not suitable for predictions in dynamic systems, including hydrothermal systems.