Unveiling the combined effects of water management and lime on remediation of Cd-contaminated soils with improved soil quality

Suppression of bioavailability and toxicity of Cd is a unique strategy to weaken environmental risks and health hazards in Cd-contaminated soils. Herein, the single treatment only water management of moisture (M) and the combined treatments with moisture plus bauxite residue (M-B)/lime (M-L) were designed to investigate the influence of different treatments on the bioavailability and toxicity of Cd in contaminated soils. Compared with the M treatment, the combined treatments (M-B and M-L) increased soil pH and reduced exchangeable Cd concentration and acid-soluble Cd proportion. The exchangeable Cd concentrations in soils were 4.65, 4.02, and 3.76 mg/kg following M, M-B, and M-L treatments after 1 month, respectively. Also, the proportions of residual Cd were 52.05 %, 57.16 %, and 63.76 % following M, M-B, and M-L treatments, respectively, and the acid- soluble Cd proportions were 44.98 %, 37.62 %, and 29.99 %, respectively. Soil pH versus exchangeable Cd (acid-soluble Cd) of soils presented a negative correlation. In addition, M-B and M-L treatments enhanced the amounts of soil-associated organic functional groups and soil aggregate stability. The average particle sizes of soil aggregates increased to similar to 245 nm (M-B) and similar to 295 nm (M-L) relative to similar to 120 nm of M treatment. Specifically, ML treatment exhibited superiority in suppressing bioavailability and toxicity of Cd in soils with improved soil quality, owing to that M-L treatment is conductive to trigger neutralization reaction, immobilization effect, and soil-aggregate evolution. The findings offer an evidence that M-L treatment is a facile approach to suppress bioavailability and toxicity of Cd in soils with improved soil quality, which shows promising applications for remediation of Cd-contaminated soils.