Characterrization of gold mine tailings and heavy metals leaching and transport in lateritic soil

Abstract

This study evaluated the leaching/desorption of metals from mine tailings and investigated the movement of these heavy metals in mine lateritic soils under different pH and concentration conditions. Except for Mn2+, the concentrations of metals in the tailings were found to be within the concentration of the Thailand Soil Standards for Habitat and Agriculture. However, leaching of metals from the tailings at pH 5-6 showed that Pb2+ (18 mg L-1) exceeded the drinking water standard for Pb2+. Using soil column studies, Pb2+ had the higher sorption capacity and retardation factors than those of Mn, Ni and Zn at pH 4 and 5. Retardation factors and sorption capacity of these heavy metals (i.e., Pb, Mn, Ni and Zn) at pH 5 were higher than at pH 4. The retardation factors from largest to smallest were: Pb2+ > Zn2+ > Mn2+ > Ni2+ for pH 4 and Pb2+ > Zn2+ > Ni2+ > Mn2+ for pH 5. The breakthrough curves of the heavy metals showed asymmetrical shapes with long tailing, indicating the presence of chemical nonequilibrium process. The two-site nonequilibrium model of HYDRUS-1D described the experimental data better than the local equilibrium convection-dispersion model using linear and Langmuir sorption isotherms. The fractions of instantaneous sites were found to range from 30-58 %. In the presence of other metals, competition for sorption sites were observed as seen by the lower maximum sorption capacities of Pb2+ for increasing concentration of the secondary metals (Zn2+, Ni2+, and Mn2+). Use of local equilibrium convection-dispersion model with linear and Langmuir isotherm did not describe the rising and declining limbs of metal concentration in binary and multi-metal systems. The two-site model (TSM) described the rising limb and initial declining limb well but could not explain the extended tailing phenomenon.