The Immobilization Effect of Oxalic Acid Activated Phosphate Rocks Applied to the Cd Contaminated Farmland Soil in Mining Area

A pot experiment was conducted to study the Cd immobilization effect of oxalic acid activated phosphate rocks on a contaminated soil in mining area,using lettuce as a test crop.The results showed that when applied Nanzhang phosphate rock,the content of exchangeable Cd in the soil was reduced by 12.5%～20.3%.Application of oxalic acid activated Nanzhang phosphate rock at different levels,decreased the content of exchangeable Cd up to 39.5%,compared with the control treatment.The change in the content of exchangeable Cd as the amount of applied Baokang phosphate rock increased was slightly significant.The maximum reduction of 21.5% exchangeable Cd was obtained after applying Baokang activated phosphate rock to the soil.At the same time,the maximum content of residual Cd was 2.03 times higher than the control of the treatments with Nanzhang phosphate rock,while it was 2.61 times higher than the control of the treatments with Nanzhang activated phosphate rock.The contents of residual Cd among the treatments with Baokang phosphate rock and activated phosphate rock were significantly higher than the control.Application of phosphate rocks and activated phosphate rocks to the soil could significantly reduce the Cd uptake and accumulation in various parts of lettuce.However,the low-grade phosphate rocks activated by oxalic acid had a better effect than raw phosphate rocks on immobilization of Cd when applied to the contaminated soil.