The Changes of Heavy Metals Solubility with Time under Different Chelants in Contaminated Soil

Heavy metals contamination of soil is a widespread global problem. Chelants assisted phytoextraction has been proposed to improve the efficiency of phytoextraction. To study the effects of different chelants on the solubility of heavy metals with time, a batch of soil incubation experiment was conducted. EDTA, EDDS, AES and IDSA of 5 mmol·kg-1 were singly added to the contaminated soil with no chelants addition as control. After 7 days of incubation, the concentrations of water-soluble Pb, Zn, Cu and Cd increased significantly compared to the control. Pb was increased by 158.6, 3.9, 42.2 and 5.3 times respectively, Cu was increased by 45.0, 162.0, 40.0 and 53.6 times respectively, Zn was increased by 6.2, 5.6, 9.4 and 1.5 times respectively, and Cd was increased by 33.5, 3.3, 126.5 and 38.0 times respectively. The results showed that EDDS was more effective for Cu desorption, EDTA was more effective for Pb desorption, and AES was more effective for Zn and Cd desorption, IDSA was more effective for Cd desorption, which was our interesting findings. With the time increasing, the soluble metals with EDTA treatment was increased or not changed, while the water-soluble metals with EDDS, AES and IDSA treatments were decreased significantly. The underlying reason for the results may be the different chemical characteristics of the chelants. EDTA, a persistent chelant, can’t be degraded in the environment, while EDDS, AES and IDSA are biodegradable chelants which were degraded with time increasing and the metals were absorbed to the bulk soil again, resulting in water-soluble metals reduced.