Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning, 110016, PR China; University of Chinese Academy of Sciences, Beijing, 100049, PR China.
Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning, 110016, PR China.
Chemosphere. 2022 Aug;301:134665. doi: 10.1016/j.chemosphere.2022.134665. Epub 2022 Apr 19.
Ubiquitous co-existence of arsenic (As) and cadmium (Cd) in smelting operations and mine drainage presents a major challenge to the environment. Fe(II)-induced ferrihydrite transformation into secondary, more crystalline minerals often controls the geochemical behavior of associated contaminants including arsenate (As(V)) and Cd(II) in natural and contaminated environments. However, the fate of co-existent As(V) and Cd(II) and the underlying mechanism during this transformation process remain unclear. In this contribution, ferrihydrite containing co-precipitated Cd(II) and As(V) with Fe(II) under diverse pH conditions has been investigated. Results from powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectra show that the co-existence of As(V) and Cd(II) significantly retards the transformation rates of As(V)/Cd(II)-bearing ferrihydrite to more stable iron oxides and reduces that from the newly formed lepidocrocite to goethite. Compared to Cd(II), the co-existent As(V) has stronger influence on the compositions of the transformation products. Chemical analysis shows that phosphate-unextractable As(V) and 0.4 M HCl unextractable Cd(II) both increase as the reaction proceeds during the recrystallization of As(V)/Cd(II)-bearing ferrihydrite, indicating that both As(V) and Cd(II) partially transform to a more stable phase. The co-existent Cd(II) has negligible effects on the As(V) redistribution, but the co-existent As(V) at high loadings has a significant modification in the distribution of Cd(II) during the transformation, which reduces the liberation of Cd(II) into solution, thus decreasing the mobility of Cd(II). These findings have important implications for understanding the mobility and fate of the co-existent As(V) and Cd(II) under natural anoxic environments, remediating the co-existent contaminants, and predicting the long-term behavior of As(V) and Cd(II) in natural and contaminated environments.
在冶炼作业和矿山排水中，砷（As）和镉（Cd）普遍共存，这对环境构成了重大挑战。Fe(II)诱导的水铁矿向次生、更具结晶性的矿物转化，通常控制着相关污染物（包括砷酸盐（As(V)）和 Cd(II)）在自然和污染环境中的地球化学行为。然而，共存的 As(V)和 Cd(II)在这一转化过程中的命运和潜在机制仍不清楚。在本研究中，我们研究了不同 pH 值条件下 Fe(II)共沉淀的含 co-precipitated Cd(II)和 As(V)的水铁矿。粉末 X 射线衍射（PXRD）、傅里叶变换红外光谱（FTIR）和拉曼光谱的结果表明，共存的 As(V)和 Cd(II)显著减缓了含 As(V)/Cd(II)水铁矿向更稳定的氧化铁转化的速率，并降低了由新形成的纤铁矿向针铁矿的转化速率。与 Cd(II)相比，共存的 As(V)对转化产物的组成有更强的影响。化学分析表明，在 As(V)/Cd(II)水铁矿的再结晶过程中，随着反应的进行，磷酸根不可提取的 As(V)和 0.4 M HCl 不可提取的 Cd(II)都增加，这表明 As(V)和 Cd(II)部分转化为更稳定的相。共存的 Cd(II)对 As(V)的再分配几乎没有影响，但在高负荷下共存的 As(V)在转化过程中对 Cd(II)的分布有显著的修饰作用，减少了 Cd(II)向溶液中的释放，从而降低了 Cd(II)的迁移性。这些发现对理解自然缺氧环境中共存的 As(V)和 Cd(II)的迁移性和命运、修复共存污染物以及预测自然和污染环境中 As(V)和 Cd(II)的长期行为具有重要意义。
