Stabilization of Cd and Zn in soil using pairwise mixed amendments of three raw materials: nanohydroxyapatite, nanoiron and nanoalumina

摘要

Cadmium (Cd) has been identified as a very toxic heavy metal, which is widely present in the environment due to natural and anthropogenic emissions. Currently, in China, slight pollution of cultivated land is widespread and Cd is one of the top ranked inorganic pollutants in soils, which results in a great impact on the development of the economy and society. Therefore, there is an urgent need to develop an efficient and economical method to remediate Cd-polluted soil. This study focused on the development of new kinds of immobilizing soil amendments for the remediation of Cd-polluted soil. In addition, the immobilization capability of zinc (Zn) which may lead to increased toxicity of Cd was also investigated. The amendments, nanoiron-nanohydroxyapatite, nanoalumina-nanoiron and nanohydroxyapatite-nanoalumina, were prepared by the pairwise mixing of three raw materials: nanohydroxyapatite (nHAP), nanoiron (nFe) and nanoalumina (nAl(2)O(3)). The application rate, mixing ratio and pH of the amendments were studied to determine the optimal application conditions of the amendments. The results showed that, compared with the single materials of nHAP, nFe and nAl(2)O(3), the immobilized efficiencies of Cd and Zn in soils by the pairwise mixed amendments were both significantly (p 0.05) increased. Optimal immobilization rates of both Cd and Zn of water-soluble and available fractions were above 97.0%. Scanning electron microscopy illustrated a more uniform mixture can be obtained by wet-mixing compared with a dry-mixing method for nFe-nHAP and nHAP-nAl(2)O(3), and the uniform mixture of nAl(2)O(3)-nFe can be obtained by both dry- and wet-mixing methods. Fourier-transform infrared analysis demonstrated that the mixed amendments retained the good capability of nHAP, nFe and nAl(2)O(3) for the stabilization of Cd and Zn in soil. Generally, 4-8% application amount, 4:1 mixing ratio of nFe/nHAP, nAl(2)O(3)/nFe and nHAP/nAl(2)O(3), respectively, and neutral or slightly acid