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To investigate the heavy metal enrichment mechanisms and release characteristics of typical deposits in karst areas, the Sb tailing pond of Dachang, Qinglong, Guizhou Province, China, one of the three largest Sb mines in the word, was selected as the study area. In this study, samples were collected from tailings (0~120 cm) and analyzed for changes in Sb and As content at different pH values by simulated acid rain static release experiments, and solid waste materials (fly ash, quicklime, and zeolite powder) were selected to design an orthogonal test to explore the optimal stabilization effect of Sb and As. The results showed that the average contents of Sb and As exceeded background values of Guizhou soil to different degrees. The content of As leaching revealed slight differences in the leachate. Sb was sensitive to more acidic conditions, and its release content can pose an ecological risk. Further, the best stabilization effect of Sb and As was observed after adding different ratios of fly ash, quicklime, and zeolite powder for a period of maintenance, which can be used as promising stabilizing materials for mine tailings remediation. This study provides comprehensive theoretical support for enhancing source control and risk management of heavy metals. [ABSTRACT FROM AUTHOR]

• Sb concentrations varied with aquifers, whereas As differed seasonally. • Sb and As co-pollution types were identified by cluster analysis. • Mine activities have significant impacts on karst groundwater geochemistry. • Elevated SO 4 2− was related to Sb pollution indicated by tracing sulfate sources. The elevated levels of antimony (Sb) and arsenic (As) in groundwater caused by mine activities is of particular global concern. Understanding pollution mechanism of Sb and As related to mine activities and their influence on karst groundwater geochemistry is of great significance. However, it is still unclear. To address such questions, Sb and As and major ions, δ34S and δ18O of dissolved sulfate as well as δD and δ18O of water were analyzed for groundwater sampled from three main karst aquifers at the Xikuangshan (XKS) antimony mine from 2013 to 2017. Spatial and temporal variations of Sb and As of the three main karst aquifers were characterized as that, (1) Sb concentrations, rather than As, varied with aquifers, with high Sb (1–50 mg/L) of the D 3 s2 and C 1 y3 aquifers and low Sb (0.01–1.0 mg/L) of the D 3 x4 aquifer; (2) As concentrations had significant seasonal effect that was higher in winter and lower in summer, whereas Sb concentrations did not differ seasonally. Here we applied a recently developed cluster analysis method as well as geochemical indicators to identify pollution types of Sb and As in groundwater related to complex mine activities, and further to reveal main effects on karst groundwater geochemistry. The cluster analysis yielded a classification of four clusters, which was confirmed by principal component analysis. The groundwater of cluster 3 is of weakly alkaline HCO 3 -Ca type with low Sb (<0.015 mg/L) and low As (<0.005 mg/L), which is typical karst groundwater controlled by limestone dissolution. Whereas the other three clusters with high concentrations of Sb and As were identified to represent three pollution patterns dominated by oxidative dissolution of stibnite, leaching of mine wastes, and mixed pollution, respectively. Moreover, the effects of long-term mine activities on karst groundwater geochemistry are revealed, including: (1) Hydrogeochemical compositions of groundwater changed from HCO 3 -Ca type to SO 4 -Ca type. (2) Sulfuric acid significantly participated in carbonate weathering. (3) Weathering of silicate (main as silicified limestone) by H 2 CO 3 and H 2 SO 4 was accelerated. (4) Cation-exchange was enhanced to dominate groundwater geochemistry. Another striking finding is that sulfur and oxygen isotopes of sulfate can effectively distinguish sulfate sources related to mine activities and to trace Sb sources in karst groundwater. [ABSTRACT FROM AUTHOR]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.