Comparison of trace element pollution, sequential extraction, and risk level in different depths of tailings with different accumulation age from a rare earth mine in Jiangxi Province, China

Abstract

The main objective of this study was to conduct a preliminary comparison on the trace element pollution, sequential extraction, and risk level in different depths of tailings with different accumulation age from a rare earth mine in Jiangxi Province, China. We collected samples at different depths of rare earth tailings with 1- and 5-year accumulation age in the same rare earth mine. The total concentrations of six potentially toxic elements (Pb, Cd, Cr, Cu, Ni, and As) were determined by acid digestion and the chemical fractionation of Pb and Cd were analyzed using the modified sequential extraction procedure (SEP) proposed by the Community Bureau of Reference (BCR) in combination with inductively coupled plasma mass spectrometry (ICP-MS). A preliminary comparison on the trace element pollution, sequential extraction, and risk level in different depths of rare earth tailings with diverse accumulation age was then conducted. High pollution levels were observed for Pb and Cd, with total concentrations in the range 79.33~134.54 and 0.83~1.83 mg kg−1, respectively. However, low pollution levels were found for Cr, Cu, Ni, and As. For the concentrations of total Pb and Cd, Pb and Cd associated with the Fe–Mn oxides and the residual fraction from top to bottom layers decreased predominantly. Overall, for the concentrations of total Pb and Cd, Pb and Cd associated with the residual fraction in all depths of the mine tailings with 5-year accumulation age were much higher than those in the mine tailings with 1-year accumulation age. The rare earth tailings showed low risk for Pb with risk assessment code (RAC) values less than 10%, but medium risk for Cd showed in the rare earth tailings with 5-year accumulation age at all depths and in the rare earth tailings with 1-year accumulation age at 10~20- and 20~30-cm depths. Advances made in our understanding of trace element pollution, sequential extraction, and risk level in different depths of tailings with different accumulation age are providing new evidences for the transportation of contaminants that derive from mining activities.