Indications that weathering of evaporite minerals affects groundwater salinity and As mobilization in aquifers of the northwestern Hetao Basin, China. (October 2019)

• Record Type: Journal Article
• Authors: Wang, Hong-Yan; Guo, Hua-Ming; Xiu, Wei; Bauer, Jonas; Sun, Guo-Xin; Tang, Xiao-Hui; Norra, Stefan
• Is Part Of: Applied geochemistry. Volume 109(2019)
• Publication Date: 2019-10
• Subjects: Salinization -- Sulphate minerals -- pH decrease -- Ca2+ release -- Sulphide -- As mobilization; Environmental geochemistry -- Periodicals; Water chemistry -- Periodicals; Geochemistry -- Social aspects -- Periodicals; Geochemistry -- Periodicals; 551.9
• DOI: 10.1016/j.apgeochem.2019.104416
• Languages: English
• ISSNs: 0883-2927

Abstract

Abstract: Elevated arsenic (As) concentration and salinity (TDS > 1000 mg/L) seriously affect the groundwater quality in the Hetao Basin, China, however, the origin of groundwater salinity and its influence for As mobilization has not been widely studied. In this study, the influence of evaporite minerals weathering on groundwater salinity and As mobilization were investigated by lithological and mineralogical analysis of sediments from two boreholes in combination with groundwater hydrogeochemical characteristics analysis in the northwestern Hetao Basin. Results from a water-leaching method suggest that Na and Ca related sulphates dominate the evaporite minerals in sediment samples. Groundwater salinization mainly results from evaporation and Na + /Ca 2+ cation exchange followed by sulphate and silicate minerals weathering. Saturated indices for calcite, dolomite and unsaturated indices for gypsum as well as negative correlation between pH and SO4 2- suggest that groundwater chemistry does not reach equilibrium with continual carbonates precipitation by an excessive Ca supply from Ca related sulphates weathering. The groundwater pH decrease and Ca 2+ release during weathering of Ca related sulphates can retard As desorption from Fe (oxyhydr)oxides and clay minerals. Furthermore, pyrite minerals were also found in the sediments induced by high sulphide flux and it can cause As sequestration. However, modeling results suggest the occurrence of thio-As species in the study area, which can potentially enhance the As mobilization. This study contributes to the ongoing research into As mobilization in the groundwater of lacustrine basins. Highlights: Silicate and sulphate minerals weathering controlled groundwater chemical composition. pH decreases and Ca 2+ release induced by Ca sulphates weathering retard As desorption. Pyrite and thio-As species formation are suggested in the aquifers.