Lamont-Doherty Earth Observatory, Columbia University , Palisades, New York 10964, United States.
School of Earth Sciences, University of Western Australia , 35 Stirling Highway, Perth, West Australia 6009, Australia.
Environ Sci Technol. 2018 Feb 6;52(3):1045-1053. doi: 10.1021/acs.est.7b05406. Epub 2018 Jan 19.
Considerable questions persist regarding tungsten geochemistry in natural systems, including which forms of tungsten are found in soils and how adsorption regulates dissolved tungsten concentrations. In this study, we examine tungsten speciation and solubility in a series of soils at firing ranges in which tungsten rounds were used. The metallic, mineral, and adsorbed forms of tungsten were characterized using X-ray absorption spectroscopy and X-ray microprobe, and desorption isotherms for tungsten in these soils were used to characterize its solid-solution partitioning behavior. Data revealed the complete and rapid oxidation of tungsten metal to hexavalent tungsten(VI) and the prevalence of adsorbed polymeric tungstates in the soils rather than discrete mineral phases. These polymeric complexes were only weakly retained in the soils, and porewaters in equilibrium with contaminated soils had 850 mg L tungsten, considerably in excess of predicted solubility. We attribute the high solubility and limited adsorption of tungsten to the formation of polyoxometalates such as WSiO, an α-Keggin cluster, in soil solutions. Although more research is needed to confirm which of such polyoxometalates are present in soils, their formation may not only increase the solubility of tungsten but also facilitate its transport and influence its toxicity.
关于自然界中钨的地球化学，仍存在许多问题，包括土壤中存在哪些形式的钨以及吸附作用如何调节溶解态钨的浓度。在这项研究中，我们研究了在使用钨合金弹丸的射击场中的一系列土壤中的钨形态和溶解度。采用 X 射线吸收光谱和 X 射线微探针对钨的金属、矿物和吸附形态进行了表征，并通过对这些土壤中钨的解吸等温线来描述其固溶分配行为。研究结果表明，钨金属会迅速完全氧化为六价钨(VI)，而且土壤中存在的是吸附态的聚合钨酸盐，而非离散的矿物相。这些聚合复合物在土壤中保留性较弱，与污染土壤相平衡的孔隙水中含有 850mg/L 的钨，远超过预测的溶解度。我们认为，钨具有高溶解度和有限的吸附性，这归因于土壤溶液中形成了多金属氧酸盐，如 WSiO，一种 α-Keggin 簇。尽管需要进一步研究来确认土壤中存在哪些多金属氧酸盐，但它们的形成不仅会增加钨的溶解度，还会促进其迁移并影响其毒性。
