[Effect and mechanism of immobilization of cadmium and lead compound contaminated soil using new hybrid material].

The effect of new hybrid material and its compound treatments with phosphate on immobilization of cadmium and lead in contaminated soil was investigated using a pot-culture experiment, and the immobilization mechanism of hybrid material was clarified through analysis of heavy metal fractions, sorption equilibration experiment and X-ray photoelectron spectroscopy (XPS). The single treatments of hybrid material could not significantly promote growth of Brassica chinensis, while the compound treatments of hybrid material and phosphate markedly increased dry biomass of shoots and roots, with maximal increases of 75.53% and 151.22%, respectively. Different hybrid material treatments could significantly reduce Cd and Pb concentrations in shoots, with maximal reductions of 66.79% and 48.62%, respectively, and the compound amendment treatments appeared more efficient than the single amendment treatments in reducing Cd and Pb uptake of B. chinensis. Different hybrid material treatments could significantly decrease concentrations of toxicity characteristic leaching procedure (TCLP) extractable Cd and Pb, and the compound hybrid material treatments appeared more efficient than the single treatments in reducing TCLP extractable Cd and Pb. Through the formation of bidentate ligand between metal ions and surface sulfhydryl by complexing reaction, the hybrid material could absorb and fix mobile fractions of Cd and Pb in soil, and promote transformation of acid extractable Cd and Pb into residual fraction, resulting in significant reduction of heavy metals bioavailability and mobility and then fixing remediation of contaminated soil. In summary, the compound treatment of hybrid material and phosphate is the most effective treatment for immobilization of Cd and Pb in contaminated soils, and the hybrid material inactivates Cd and Pb in soil mainly through special chemical adsorption.