改性赤泥-沸石修复材料对土壤中镉的稳定化研究

Stabilization of cadmium in soil using modified red mud-zeolite composite material

为探讨改性赤泥和沸石混合材料在镉污染土壤修复中的应用,通过连续提取测定重金属镉形态变化,分析修复土壤中有效硅含量、土壤p H值等对镉的稳定化影响。结果表明：土壤p H值受沸石的影响较大,添加5%沸石时土壤p H值最高（8.36）;添加改性赤泥-沸石混合材料增加了土壤有效硅含量,添加量为10%时,增幅高达359.1%,而对土壤p H值基本无影响（6.92~7.35）;添加量5%且改性赤泥、沸石配比3∶1时对镉的转化促进效果最明显,有效降低离子交换态镉79.31%和碳酸盐结合态镉45.17%,残渣态镉则显著增加,增幅高达170.84%。混合材料以改性赤泥为主,赤泥与沸石添加比例控制在3∶1内,铁锰氧化态镉含量和残渣态镉含量呈显著线性负相关（R=-0.975 1）。施用该混合材料在增加土壤中有效硅的同时能促进镉向稳定的残渣态转化。

A composite material of modified red mud and zeolite was used to stabilize cadmium in soil.Different fractions of soil Cd were extracted by sequential extraction.Available silicon and p H values in soil were also measured to analyze their effects on Cd stabilization.Results showed that zeolite had a great influence on soil p H,with the largest p H value of 8.36 observed at 5% zeolite.But modified red mud had little effect on soil p H even combined with zeolite,with p H ranging from 6.92 to 7.21.Adding modified red mud and zeolite composite material obviously increased available silicon in soil.As high as 359.1% increase was found at 10% application rate of the composite mate-rials（red mud：zeolite=3∶1）.At 5% composite material,the greatest stabilization of soil Cd occurred,and exchangeable and carbonate Cd decreased by 79.31% and 45.17%,respectively,while residual Cd fraction increased by 170.84%.The increases in residual Cd were significantly correlated with the decreases in iron manganese oxides-bound Cd（R=-0.975 1）.The present results suggest that the ratios of modified red mud and zeolite should be no more than 3∶1,and that applying this composite material not only increases soil available silicon but also promotes the transformation of exchangeable-,carbonates-,and iron manganese oxides-Cd to residual Cd.