Immobilization of copper in contaminated sandy soils using calcium water treatment residue.

Chemical remediation has attracted increasing attention for heavy metal contaminated soils because of its relatively low cost and high efficiency. In this study laboratory incubation and column leaching experiments were conducted to understand the mechanisms of copper (Cu) immobilization by calcium water treatment residue (Ca-WTR) and to estimate the optimal rate for remediating Cu-contaminated soils. The results showed that Ca-WTR amendment significantly raised soil pH and decreased water soluble and exchangeable Cu by 62-90% in the contaminated soils. Most of the bioavailable Cu was converted into more stable Cu fractions, i.e. oxides-bound and residual Cu. The cumulative amount of Cu in the leachate after 10 leaching events was reduced by 80% and 73%, respectively for the two tested soils at the Ca-WTR rate of 20 g kg(-1) for Alfisol and 100 g kg(-1) for Spodosol. These results indicate that Ca-WTR is effective in raising soil pH and converting labile Cu to more stable forms in the contaminated soils. A pH value of 6.5 was found to be critical for lowering Cu availability in the soils. Based on this criterion and pH response curve to Ca-WTR application, the optimal rates of Ca-WTR can be estimated for different Cu-contaminated soils.