Research And Application Of Combined Amendment For Remediation Of Paddy Soil Complexly Contaminated With Pb,Cd And As

In this paper, limestone, sepiolite, titanium dioxide and ferric sulfate were combinated in different proportion of single-phase, two-phase and three-phase, then added each of them to soil and cured at room temperature for 30 days. After screening and matching from above materials, two three-phane combined amendments with better stabilization effects for soil heavy metals were prepared:limestone+sepiolite+ titanium dioxide (LST) and limestone+sepiolite+ferric sulfate (LSF). Pot experiments of rice planting were conducted to study the stabilization effects of soil Pb, Cd, and As in complexly contaminated paddy soil system, and to study the adsorption and accumulation of these elements in various rice organs, with LST and LSF applying of 0,1,2,4,8,16 g-kg-1. The main results were as follows:(1) The stabilization effects of multiphase combined amendments were superior to any single amendment. LST and LSF were better than other combined amendments. Compared with the control, when adding L8S4T2 (2,4,8 indicated the added amount-g·kg-1, the same below), soil pH increased by 1.02; contents of soil Ex-Pb, Ex-Cd, Ex-As decreased by 97.0%,42.7% and 42.9%, respectively; and contents of soil TCLP-Pb and TCLP-Cd, TCLP-As decreased by 51.7%,40.5% and 32.5%, respectively. When adding L8S4F2, soil pH increased by 0.61; contents of soil Ex-Pb, Ex-Cd, Ex-As decreased by 95.2%,43.8% and 52.4%, respectively; and contents of soil TCLP-Pb and TCLP-Cd, TCLP-As decreased by 46.3%,42.7% and 54.5%, respectively.(2) In the pot experiments of rice planting, compared with the control, LSF and LSF both made soil pH and cation exchange capacity (CEC) increase, and showed that there were significant differences between the control and the treatments. LST increased soil pH values higher than LSF, while LST increased soil CEC values lower than LSF. Applying LST with the amount of 1-16 g-kg"1 decreased Ex-Pb and Ex-Cd of SH (before rice planting) soil significantly by 76.0%-100.0%,43.1%-94.9%, decreased TCLP-Pb and TCLP-Cd of SH soil by 21.0%-51.0%,7.9%-17.4%, but increased Ex-As of SH soil by 23.6%-172.4%, increased TCLP-As of SH soil by 41.7%-105.4%. Meanwhille, Ex-Pb, Ex-Cd and Ex-As of CS (after rice harvesting) soil significantly decreased by 16.8%-88.3%,22.4%-73.7% and 2.25%-43.8%, TCLP-Pb, TCLP-Cd and TCLP-As of CS soil decreased by 14.4%-34.0%, 10.8%-23.5% and 14.3%-48.3%, respectively. With increase in the amounts of LSF applying (1-16 g·kg-1), Ex-Pb and Ex-Cd of SH soil decreased significantly by 72.3%-99.5% and 41.9%-94.1%, TCLP-Pb and TCLP-Cd of SH soil decreased by 30.6%-64.0% and 13.5%-25.1%, but Ex-As of SH soil increased by 24.4%-90.2%, TCLP-As of SH soil increased by 25.4%-91.1%; Ex-Pb, Ex-Cd and Ex-As of CS soil significantly decreased by 20.2%-86.9%,20.7%-51.2% and 18.0%-55.1%, TCLP-Pb, TCLP-Cd and TCLP-As of CS soil decreased by 4.3%-42.6%,10.8%-32.7% and 8.1%-35.9%, respectively.(3) In the pot experiments of rice planting, LST and LSF significantly decreased contents of Pb, Cd and As of rice root, shoot, husk and brown rice. When applying 16 g·kg-1 of LST and LSF, contents of Pb, Cd and As in brown rice decreased 50.7%, 64.7%,34.1%, and 40.7%,40.7%,36.2%, respectively. The ability of rice organs transferring Pb and As was husk> rice straw> root, and that transferring Cd was husk > root> rice straw. The ability to transfer Pb, Cd and As from rice straw to brown rice was Cd> As> Pb. After applying LST and LSF, a significant positive relationship was observed between contents of Pb, Cd and As in brown rice and exchangeable concentrations of Pb, Cd and As in soil. Between contents of Pb, Cd and As in brown rice and soil pH values, there was a significant negative relationship.