水铝钙石对不同镉污染农田重金属的钝化效果及机制

水铝钙石(Ca-Al-LDHs)是一种新型的层状复合金属氢氧化物,具有较大的比表面积、良好的阴离子交换性能和高稳定性的优点.本研究选择高Cd污染农田、中Cd污染农田和低Cd污染农田3种不同Cd污染水平的自然农田土壤作为研究对象.通过室内钝化实验,探讨水铝钙石对3种Cd污染农田土壤Cd、Pb、Zn有效态的变化规律以及形态转换的影响,进一步采用X射线衍射仪(XRD)和傅里叶变换红外光谱仪(FTIR)初步探讨其钝化机制.结果表明,在高中低这3种Cd污染土壤中,水铝钙石均能够增加土壤pH,降低Cd、Pb和Zn的有效态含量,其中Cd有效态含量最大降幅分别为97. 7%、96. 3%和91. 8%.水铝钙石促使高Cd污染土壤中Cd、Pb和Zn的可交换态转化成活性低的碳酸盐结合态、铁锰氧化态和残渣态,高Cd污染土壤的钝化效果优于中低污染土壤.水铝钙石的吸附作用、层间离子交换作用以及表面羟基和羧基等活性官能团的配位反应,在很大程度上降低了土壤重金属的生物有效性.因此,水铝钙石可有效应用于Cd、Pb、Zn等重金属污染农田的钝化修复.

Hydrocalumite Passivation Effect and Mechanism on Heavy Metals in Different Cd-Contaminated Farmland Soils

Hydrocalumite (Ca-Al-LDHs) is a new type of layered composite metal hydroxide that has a large specific surface area, high anion exchange performance, and high stability. This study focuses on the application of hydrocalumite to remediate different Cd-contaminated farmland soils. These were collected from the Lanping County in the Yunnan Province (highly polluted), Kunshan City in the Jiangsu Province (medium polluted), and Nanjing City in the Jiangsu Province (lowly polluted). Changes in the available Cd, Pb, Zn, and the morphological transformations of these heavy metals in the three soils were investigated through a passivation experiment; moreover, the immobilization mechanism of hydrocalumite was explored by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results showed that hydrocalumite could increase the soil pH and reduce the content of available Cd, Pb, and Zn:the maximum reduction in the available Cd reached 97.7%, 96.3%, and 91.8% in each of the three polluted soils, respectively. The easily exchangeable heavy metals were converted into carbonates, as well as into Fe-Mn oxide organic and residual forms following the addition of hydrocalumite:the passivation effect was more evident in the highly Cd-polluted soil than in the low and medium Cd-polluted soils. Since hydrocalumite possess several adsorption sites, the presence of carbonate impurities and reactive groups (e.g., hydroxyl and carboxyl groups) easily coordinated with Cd, Pb, and Zn can lead to a considerable reduction of heavy metal availability in the soils. Therefore, we conclude that hydrocalumite can be effectively applied to the remediation of farmland soils characterized by different Cd pollution levels.