Abstract: Aiming to remediate and utilize red soil contaminated by arsenic, cadmium and lead safely, simulated incubation experiments were conducted to investigate the stabilization effect of chemical amendments on the immobility of arsenic (As), cadmium (Cd) and lead (Pb) in red soil of southern China, and the technical formula of remediation materials for the best stabilization effect were also explored. Experimental procedures are as following: using biochar(BC) and lime(SH) for immobilization materials, with 1% and 4% of the weight of soil as material application rate, biochar and lime were applied singly or mixed into contaminated soil by arsenic, cadmium and lead, and incubated at the situation with a constant temperature(25℃) and 70% field capacity in soils for 60 days, then the samples were taken on the 1st, 30th and 60th days during the incubation experiment. The changes of pH, contents of water soluble As, Cd, Pb(WSAs, WSCd, WSPb) and the speciation of As, Cd, Pb in soils were determined. and the stabilization effects of single and mixed application of biochar/lime were analyzed. The results showed that the contents of water-soluble cadmium (WSCd) and lead (WSPb) in soil were reduced to different degrees by applying biochar/lime singly or in combination, and the corresponding ranges for immobilization efficiencies were 33.51%−78.89% and 9.05%−96.24%, respectively. Under the treatment of single application of biochar/lime (1BC, 4SH) or combined application of high amount of biochar and lime (4BC4SH), the content of water soluble As (WSAs) in soils decreased obviously, and the reduced percentage of WSAs ranged from 10.25% to 55.27%. Among all the treatments, the combined treatment with a high dosage had the best synergistic immobilization effect on As, Cd and Pb in red soil. When the incubation test lasted for 60 days, the immobilization efficiency reached 55.27%, 76.39% and 96.24%, respectively. In the meanwhile, the forms of As in soils changed from non-specifically sorbed and specifically sorbed phases which can be easily absorbed by plants to residual ones, and the forms of Cd and Pb in soils changed from the most active acid-extractable to residual phases. The stabilization effect of As, Cd and Pb in soil was observed obviously, and the migration coefficient decreased simutanously. In addition, the application of biochar/lime alone and in combination resulted in a significant increase of soil pH(P<0.05), which was beneficial for the improvement of acidified soil in southern China. In general, through this investigation, the combined application of biochar/lime at a high dosage(4BC4SH) as amendments can stabilize the available As, Cd and Pb in red soils effectively and has the best immobilization effect on heavy metals.

Key words: Red soil, Heavy metal contamination, Biochar, Lime, Chemical immobilization