Migration Characteristics of Cadmium and Lead in Soil Profiles from a Zinc Smelting Site under Simulated Rainwater Infiltration

PENG Yingxiang; TANG Bin; LIU Lingqing; ZENG Tianjing; ZOU Lin; RONG Xing; XIAO Xiyuan; YANG Aiping

doi:10.19672/j.cnki.1003-6504.0832.23.338

Abstract：The column leaching experiments were carried out under different leaching conditions of flooding water,alter-nating dry and wet(ADW),and continuous leaching with simulated acid rain of pH 4.4 for 30 days to study the release,mi-gration,and transformation characteristics of Cd and Pb in the soil profile from a zinc smelting site.The results showed that the leachate concentrations of Cd and Pb from all treatments reached a peak value on the 5th day of early leaching stage,and then gradually decreased.The peak Cd concentration ranged from 21.7 to 45.1 μg/L,which exceeded the threshold limit of Cd(10 μg/L)of Standard for Groundwater Quality(GB/T 14848-2017).Moreover,the Cd concentration from AF treatment was higher than the Cd threshold limit throughout the whole leaching period,indicating that there was Cd pollution risk of ground-water.The peak value of leachate Pb concentration ranged from 0.90 to 2.69 μg/L,which was much lower than the threshold limit for Pb(100 μg/L).Acid rain leaching promoted the release and migration of Cd and Pb in the upper layer of miscella-neous fill soil(0～10 cm),which were predominately accumulated in the plain fill soil of 15～20 cm depth,and Cd showed a higher migration depth than Pb.The results of three-step sequential extraction method formulated by the European Communi-ty Bureau of Reference showed that the residual fraction of Cd and Pb in the surface soil after leaching was decreased,and their exchangeable fraction was increased showing high mobility.The exchangeable fraction percentage of Cd and Pb in the deeper soil(10～60 cm)was decreased,and their residual fraction percentage was increased.ADW treatment promoted the transformation of Cd and Pb in soil to the exchangeable fraction,and the potential pollution risk to the surrounding soil and groundwater was increased.Rainfall,especially acid rain leaching can cause the release and migration of Cd and Pb in soil from the smelting site,then result in increasing the risk of groundwater pollution.The results can provide scientific basis for risk management and remediation of heavy metal contaminated soil from smelting sites.