Simultaneous reduction of available arsenic and cadmium in contaminated soil by iron-modified fly ash

Arsenic (As) and cadmium (Cd) co-contamination in the soil is a serious global health concern. Three iron-modified fly ash (FA) composites were synthesised, including FA-supported nanoscale zero-valent iron (FA-nZVI), FA-supported FeCl3 (FA-FeCl3) and FA-supported Fe-oxyhydroxide sulphate (FA-FeOS) for remediation of As and Cd co-contaminated soil. Soil incubation experiments were conducted to evaluate the effects of iron-modified FA on the soil pH, availability and geochemical fractions of As and Cd. The results showed that FA and FA-nZVI significantly (P < 0.05) increased the soil pH, but FA-FeCl3 and FA-FeOS decreased the soil pH in general. FA, FA-nZVI, FA-FeCl3 and FA-FeOS decreased the concentration of available As by 15.13∼21.22%, 46.20∼46.66%, 30.02∼38.09% and 12.05∼30.50%, respectively. However, only FA and FA-nZVI decreased the concentration of available Cd by 4.85∼26.09% and 37.74∼52.18%, respectively. The results showed that FA-nZVI was the most effective amendment for simultaneous immobilisation of As and Cd. Besides, FA-nZVI stimulated the transformation of As and Cd from reactive states to less reachable states to decrease the toxicity of As and Cd in soil. In conclusion, FA-nZVI is a potential amendment for soil remediation in As and Cd co-contaminated soil.