Clay minerals are ubiquitous in subsurface environments and have long been recognized as having a limited or negligible impact on the fate of arsenic (As) due to their negatively charged surfaces. Here, we demonstrate the significant role of kaolinite (Kln), a pervasive clay mineral, in enhancing As(V) immobilization during ferrous iron (Fe(II)) oxidation at near-neutral pH. Our results showed that Fe(II) oxidation alone was not capable of immobilizing As(V) at relatively low Fe/As molar ratios (≤2) due to the generation of Fe(III)–As(V) nanocolloids that could still migrate easily as truly dissolved As did. In the presence of kaolinite, dissolved As(V) was significantly immobilized on the kaolinite surfaces via forming Kln–Fe(III)–As(V) ternary precipitates, which had large sizes (at micrometer levels) to reduce the As mobility. The kaolinite-induced heterogeneous pathways for As(V) immobilization involved Fe(II) adsorption, heterogeneous oxidation of adsorbed Fe(II), and finally heterogeneous nucleation/precipitation of Fe(III)–As(V) phases on the edge surfaces of kaolinite. The surface precipitates were mixtures of amorphous basic Fe(III)–arsenate and As-rich hydrous ferric oxide. Our findings provide new insights into the role of clay minerals in As transformation, which is significant for the fate of As in natural and engineered systems.

中文翻译：

---

高岭石在亚铁氧化过程中通过非均相途径增强砷酸盐固定化


粘土矿物在地下环境中无处不在，长期以来，由于其表面带负电荷，人们一直认为它们对砷 (As) 的去向影响有限或可以忽略不计。在这里，我们证明了高岭石 (Kln)（一种普遍存在的粘土矿物）在接近中性 pH 值的亚铁 (Fe(II)) 氧化过程中增强 As(V) 固定的重要作用。我们的结果表明，单独的 Fe(II) 氧化不能在相对较低的 Fe/As 摩尔比 (≤2) 下固定 As(V)，因为会生成仍然可以迁移的 Fe(III)-As(V) 纳米胶体就像以前那样容易真正溶解。在高岭石存在下，溶解的 As(V) 通过形成 Kln-Fe(III)-As(V) 三元沉淀物而显着固定在高岭石表面，该沉淀物具有大尺寸（微米级）以降低 As 迁移率。高岭石诱导的 As(V) 固定非均相途径涉及 Fe(II) 吸附、吸附的 Fe(II) 的非均相氧化，以及最终 Fe(III)-As(V) 相在边缘表面的非均相成核/沉淀。高岭石。表面沉淀物是无定形碱性砷酸铁和富砷水合氧化铁的混合物。我们的研究结果为粘土矿物在砷转化中的作用提供了新的见解，这对于砷在自然和工程系统中的命运具有重要意义。