Insights on Immobilization of Cd Contamination in Soil: Synergic Impacts of Water Management and Bauxite Residue.

To immobilize the activity and bioavailability of soil Cd, the single treatment only flooding (F) and the combined treatments with flooding plus bauxite residue (F-B) or lime (F-L) were designed to investigate the impacts of different treatments on the toxicity and bioavailability of Cd in contaminated soil. Compared with the single treatment (F), the combined treatments (F-B and F-L) improved soil-associated organic functional groups and aggregated stability in soil. The average particle sizes of soil aggregates increased from 126 nm (F-treated soil) to 256 and 270 nm following F-B and F-L treatments, respectively. Relative to F treatment, the combined treatments (F-B and F-L) increased soil pH, soil EC, and residual Cd content in soil and reduced exchangeable Cd and acid-soluble Cd content in soil. The exchangeable Cd contents in soils were decreased to 3.17 and 3.42 mg/kg following F-B and F-L treatments in comparison with F-treated soils (4.31 mg/kg), respectively. For the soils with F-B and F-L treatments, soil residual Cd contents increased from 54% (F treatment) to 57 and 56%, respectively, and soil acid-soluble Cd contents decreased from 46% (F treatment) to 37 and 43%, respectively. A negative correlation was found in soil pH versus soil exchangeable Cd and soil acid-soluble Cd. In addition, the F-B treatment exhibited superiority in suppressing toxicity and bioavailability of soil Cd, owing to that F-B treatment is easy to induce neutralization reaction and immobilization effect in contaminated soil. The findings offer evidences that F-B treatment is a facile approach to suppress toxicity and bioavailability of soil Cd, which shows potential for immobilization of Cd in soil.