Fractionation of Zn and Pb in Bulk Soil and Size Fractions of Water-Stable Micro-Aggregates of Lead/Zinc Tailing Soil Under Simulated Acid Rain

Abstract

A typical lead/zinc tailing soil was collected from in Qixia Mountain located in the east of Nanjing City, China, and separated into four size fractions of water-stable micro-aggregates. Bulk soil and each size fractions of micro- aggregates were leached using the simulated acid rain made of a H2SO4 to HNO3 mole ratio of 4:1 with pH 4.5 under the ratio for liquid to solid (5/1, 10/1 and 50/1) and the treatment time (6h, 12h, 24h and 48h). After the leaching of the simulated acid rain, modified BCR sequential extraction procedure was used to gain information on potential mobility of heavy metals in bulk samples and size fractions of water-stable micro-aggregates of tailing soil. The extractable contents decreased with the increase of leaching time, but increased significantly with the increase of ratio of liquid to solid. The extractable contents of Cu, Pb and Zn in the 250-50μm and the <2μm fraction were significant lower than them in the fraction of the >200μm and the 50-2μm fraction. Zn was found to be predominantly associated with the acid extractable and the residual fraction; Pb was predominantly associated with the reducible fraction; Cu was dominant in the reducible and the oxidizable fraction. The treatment time has no significant effects on the fractionation of Zn, Pb and Cu, but the increase of the ratio of liquid to solid increased the acid extractable fraction of Zn, Pb and Cu. The fractionation pattern of the metals (Zn, Pb and Cu) differed with the size fractions of water-stable micro-aggregates