腐殖质纳米颗粒对镉污染土壤的修复

外源腐殖质可改变土壤镉（Cd）的含量和状态。以风化煤为原料制备的不溶性胡敏酸为吸附剂，对比研究了其对冶炼厂周边污染土壤及人工模拟污染土壤中Cd的钝化效果。再以泥炭为原料，制备富里酸钾为主的水溶性腐殖酸钾为淋洗剂，用于活化、去除上述2种土壤中的Cd。结果表明，胡敏酸在砂质的人工模拟污染土壤中钝化效果更好，2%的剂量可使土壤中CaCl2提取态Cd的浓度（0.103 mg·L-1）降低19.7%。腐殖酸钾去除土壤Cd的效率随淋洗剂浓度增加而提高，在10 g·L-1的浓度时，单次淋洗可去除高达38.1%的Cd。傅里叶变换红外光谱分析表明，腐殖质与Cd反应后形成了羧酸盐。因此，腐殖质纳米颗粒既可以钝化土壤中的Cd，也可以活化土壤中的Cd，从而达到修复Cd污染土壤的目的。其关键在于根据钝化或活化的目标，选择溶解度适当的腐殖质材料。

Humic nanoparticles for remediation of Cd- contaminated soils

Extraneous humic substances could alter the dynamics of Cd in soils. An insoluble humic acid, produced from a leonardite, was used in laboratory experiment as an adsorbent to immobilize Cd in a silt-loam soil near a smelting plant and a Cd-spiked and aged sandy-loam soil, whereas a soluble peat-derived potassium humate was employed as a washing agent to mobilize Cd in, and remove it out of, the contaminated soils. Addition of 2% humic acid could reduce CaCl2 extractable Cd in a soil (0.103 mg·L-1) by 19.7%. This immobilization effect was greater in sandy-loam soil than in silt-loam soil. Similarly, Cd removed from the contaminated soils increased with washing agent dosage. A single washing at 10 g·L-1 of potassium humate removed up to 38.1% of the total Cd in soils. Fourier transform infrared spectroscopic analysis indicated the formation of Cd-carboxyl complex. This study suggests that Cd-contaminated soils can be remediated by humic substances through either an immobilization or mobilization process. The key to the success is to select humic substances with a suitable solubility: water insoluble humic acid for Cd immobilization and water soluble potassium humate for effective removal of Cd out of soils.