Competitive modeling of sorption and transport of Pb2 +, Ni2 +, Mn2 + AND Zn2 + under binary and multi-metal systems in lateritic soil columns

Transport of heavy metals from acid mine drainage through soils can impact valuable water resources and have a deleterious effect on their associated ecosystems. The movement of single, binary and multi-metal systems through lateritic soil columns were experimentally determined and then modeled with the HYDRUS-1D using a local equilibrium convection–dispersion (CDeq) model, or chemical nonequilibrium two-site model (TSM) with first order kinetics. The TSM model described the breakthrough curves better than the CDeq model in both binary and multi-metal systems. The (Qmax)/(Qmax⁎) ratios were generally greater than unity suggesting that the presence of other metals reduced sorption through competition for sorption sites . Ratios of (Qmax)Pb2 +/(Qmax)secondary metals (Mn2 +, Zn2 +, Ni2 +) (ranging from 0.92 to 1.09) were lower than ratios of (Qmax⁎)Pb2 +/(Qmax⁎)secondary metals (Mn2 +, Zn2 +, Ni2 +) (ranging from 0.94 to 2.80), which indicated the highest sorption affinity of Pb2 + was under both binary and multi-metal systems. Furthermore, the fraction of the instantaneous equilibrium site (f) of all metals, particularly for secondary metals, tended to increase with increasing metal concentrations in the system, suggesting that diffusion probably dominates the sorption and transport of heavy metals in the system.

► We modeled the mechanisms of competitive metal systems in lateritic soil. ► We explained the mechanisms under single, binary and multi-metal systems. ► The chemical nonequilibrium two-site model well described the breakthrough curves. ► Competition for sorption site promoted the retention of 2nd metal on sorption site. ► Sorption mechanism changes to more equilibrium condition under competitive system.