College of Resources and Environment , Huazhong Agricultural University , Wuhan 430070 , China.
GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam , Germany.
Environ Sci Technol. 2019 Jan 2;53(1):194-202. doi: 10.1021/acs.est.8b05584. Epub 2018 Dec 14.
Bioavailability and mobility of cadmium (Cd) and arsenate (As) in soils can be effectively lowered through the dissolution of brushite (dicalcium phosphate dihydrate, CaHPO·2HO) coupled with the precipitation of a more stable mineral phase containing both Cd and As. Due to the ubiquitous presence of humic acid (HA) in soil environments, it is more complex to predict the fate of dissolved Cd and As during such sequestration. Here, we used in situ atomic force microscopy (AFM) to image the kinetics of simultaneous precipitation of Cd and As at the brushite-fluid interface in the presence of HA. Results show that HA inhibits the formation of both amorphous and crystalline CdCa (PO)(AsO) (OH) on the (010) face of brushite. A combination of X-ray photoelectron spectroscopy (XPS) and real-time surface-enhanced Raman spectroscopy (SERS) reveals that part of As reduction into As with HA and [HA-Cd] complexation occurs, modulating the concentrations of free Cd and As ions to inhibit subsequent precipitation of a CdCa (PO)(AsO) (OH) phase on the dissolving brushite surface. A combination of AFM imaging, SERS analyses, and PhreeqC simulations suggests that environmentally relevant humic substances can limit the precipitation of Cd and As at mineral surfaces through a mechanism of oxidation/reduction and aqueous/surface complexation. This may exacerbate the transportation of these contaminants into waters by subsurface fluid flow, and research attempts to weaken the negative effect of HA are needed.
通过溶解磷酸氢钙（二水合磷酸二钙，CaHPO·2HO）并同时沉淀出更稳定的含有 Cd 和 As 的矿物相，可以有效降低土壤中 Cd 和砷酸盐（As）的生物有效性和迁移性。由于在土壤环境中普遍存在腐殖酸（HA），因此更难以预测在这种固定化过程中溶解的 Cd 和 As 的命运。在这里，我们使用原位原子力显微镜（AFM）来成像在 HA 存在下，Cd 和 As 同时在磷酸氢钙-流体界面上沉淀的动力学。结果表明，HA 抑制了无定形和晶体 CdCa（PO）（AsO）（OH）在磷酸氢钙（010）面上的形成。X 射线光电子能谱（XPS）和实时表面增强拉曼光谱（SERS）的组合表明，部分 As 与 HA 发生还原反应并与[HA-Cd]络合，调节游离 Cd 和 As 离子的浓度，从而抑制溶解的磷酸氢钙表面上 CdCa（PO）（AsO）（OH）相的后续沉淀。AFM 成像、SERS 分析和 PhreeqC 模拟的组合表明，环境相关的腐殖质物质可以通过氧化/还原和水/表面络合的机制，限制 Cd 和 As 在矿物表面的沉淀。这可能会加剧这些污染物通过地下水流向水体的迁移，因此需要研究尝试削弱 HA 的负面影响。
