凹凸棒石及其改性材料对土壤镉生物有效性的影响与机制

采用室内盆栽实验和吸附平衡实验,研究了凹凸棒石及其改性材料对土壤镉移动性和生菜吸收镉的影响,并通过X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)以及X射线光电子能谱(XPS)探讨了其机制.结果表明,凹凸棒石及其改性材料均可显著降低生菜体内的Cd含量,改性材料作用优于未改性材料,分别使生菜地上部分Cd含量最大降低41.0%和56.5%.凹凸棒石及其改性材料在投加量为1%时均可显著降低土壤CaCl_2提取态Cd含量,最大降低幅度分别为34.2%和34.3%.凹凸棒石改性后对镉的饱和吸附容量明显提高.凹凸棒石主要是通过表面的硅羟基与Cd~(2+)发生配位反应形成络合物来固定土壤镉,而改性凹凸棒石材料能够通过其表面的硅羟基和羧基与Cd~(2+)发生配位反应形成络合物,从而降低Cd~(2+)在土壤中的移动性,进而达到钝化修复Cd污染土壤的效果.因此凹凸棒石及其改性材料均可被用于镉污染农田土壤修复,但机制不同.

Effect and Mechanism of Attapulgite and Its Modified Materials on Bioavailability of Cadmium in Soil

The effect of attapulgite (magnesium aluminium phyllosilicate) and its modified materials on the extractability of soil Cd and the accumulation of Cd in lettuce (Lactuca sativa) were investigated using a pot-culture experiment, and the immobilization mechanism of attapulgite and its modified materials was explored through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results showed that attapulgite and its modified materials could significantly reduce the Cd concentration in Lactuca sativa, with maximum reductions of 41.0% and 56.5%, respectively, and attapulgite modified materials treatments appeared more efficient than attapulgite treatments in reducing Cd uptake of Lactuca sativa. The saturated adsorption capacity for the adsorption of Cd²⁺ on attapulgite rose distinctly after being modified. Attapulgite and its modified materials could significantly reduce Cd content in soil CaCl₂ extract at the dosage of 1%, with the maximum reduction rates of 34.2% and 34.3%, respectively. The attapulgite formed a complex to immobilize Cd mainly through the surface silanol and Cd²⁺ complexation reaction, while the modified attapulgite formed a complex mainly through the complexation of Cd²⁺ with carboxyl groups which existed in addition to the complexation with surface hydroxyl, thus reducing the mobility of Cd²⁺ and achieving remediation of Cd-contaminated soil. In summary, attapulgite and its modified materials can both be used for remediation of Cd-contaminated soil, and the mechanisms for this function were found to be different.