Competitive sorption and transport of Pb2+, Ni2+, Mn2+, and Zn2+ in lateritic soil columns

Knowledge of sorption and transport of heavy metals in soils in the presence of other metals is crucial for assessing the environmental risk of these metals. Competitive sorption and transport of four metals, Pb2+, Ni2+, Zn2+, and Mn2+, were investigated using multi-metal column experiments with lateritic soils obtained from a gold mine impacted by acid mine drainage. Based on Pb2+ breakthrough time for single-metal system at a pH of approximately 5, the sorption capacity of Pb2+ was estimated to be higher in lateritic soil than the other metals. For multi-metal systems, the estimated retardation factors for the metals from highest to lowest were: Pb2+ > Zn2+ ∼ Ni2+ > Mn2+, suggesting the mobility of metals through lateritic soil for a multi-metal system would be in the order of Mn2+ > Ni2+ ∼ Zn2+ > Pb2+. For binary and multi-metal systems, the estimated sorption capacities of individual metals were found to be lower than the sorption capacities in single metal system - indicating possible competition for sorption sites. Mass recoveries estimates showed that the sorption of metals was more reversible under competitive multi-metal systems than in single metal systems.