Estimation of arsenic leaching from Zn–Pb mine tailings under environmental conditions

Abstract

This research aimed to study the leaching characteristics of arsenic from the Zn–Pb mine tailings under different conditions. The parameters and factors controlling the arsenic concentration of leachate were also determined. In order to estimate the concentrations of arsenic leached in different environmental conditions, four leaching protocols were used. These protocols included toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), field leach test (FLT) and leachate extraction procedure (LEP) which was performed on two samples (S1 and S2) of the Zn–Pb mine tailings from Zanjan province, Iran. Also, the effects of various factors such as the pH of leaching water, the contact time of tailings with water, liquid to solid ratio and the particle size of tailings on the concentration of arsenic released from the Zn–Pb mine tailings were assessed using batch leaching tests. The results showed that in both samples, the highest concentration of arsenic was in the residual fraction that was relatively stable under natural environmental situations. The highest arsenic concentration occurred in the LEP test performed on the S1 sample. According to the SPLP protocol, the Zn–Pb tailings had a high potential for contamination of surface and underground water. The mobility of arsenic in the tailings was entirely affected by the pH of leaching water, the contact time of the tailings with water, the particle size of the tailings and solid to liquid ratio. The leaching of arsenic enhanced in acidic and alkaline conditions and the concentrations of arsenic leached in acidic conditions were much higher than the concentrations of arsenic leached in alkaline conditions. The pH-dependent leaching behavior of arsenic from the Zn–Pb mine tailings was amphoteric. In both S1 and S2 samples, a larger fraction of arsenic released from the Zn–Pb mine tailings as the liquid to solid ratio and the contact time of the tailings with the water increased. In the S1 sample, the highest concentration of arsenic released was observed in particles with a size of 500–600 μm, while for the S2 sample, it was observed in particles with a size of 150–250 μm. According to the results of this experiment, important factors in preventing the release of arsenic from the Zn–Pb mine tailings into the environment are 1) controlling the pH of leaching water, 2) reducing the amount of pore water, and 3) reducing the contact time of the tailings with the water.