Transport and adsorption-desorption of heavy metals in different soils
Understanding the reactivity and mobility of heavy metals in soils is indispensable for assessing their potential risk to the environment. In this study, column transport and batch kinetic experiments were performed to assess the sorption-desorption and mobility of Cd, Cu, Pb, and Sn in alkaline and acidic soils. Furthermore, sequential extractions were accomplished to examine their behavior in soils. Also, the competitive reactivity of Sn and Pb in two acidic soils was quantified. Additionally, the effect of introducing Cd and Cu after a Pb pulse in calcareous soil was presented. Modeling of these heavy metals retention and transport was carried out using different models; multireaction and transport model, CXTFIT model, kinetic ion exchange formulation, and second-order two-site model. The results revealed that: 1) the studied heavy metals exhibited strong nonlinear and kinetic retention behavior; 2) Cd was nearly immobile in alkaline soil with 2.8% CaCO3, whereas 20 and 30% of the applied Cd was mobile in the acidic soil and the subsurface layer of the alkaline soil with 1.2% CaCO3, respectively; 3) for a short Cu pulse, the recoveries were <1 and 11% for alkaline and acidic soils, respectively, whereas, for the long Cu pulse, the recoveries ranged from 27 to 85% for the studied soils; 4) tin was highly sorbed in acidic soils where more than 99% of applied Sn was retained in the acidic soils columns; 5) the presence of Sn in solution reduced Pb retention in soils since the Pb recovery in the effluent solution ranged from 37.4 to 96.4%; and 6) the multireaction approach was capable of describing heavy metals retention and transport in soil columns. Moreover, a field study of the spatial distributions and the accumulation of Pb, Cd, Cu, and Ni among soil depth as consequence of irrigation with domestic wastewater were studied. The results of this research showed that Pb, Cu, and Ni had high affinity for retention in the surface soil layer whereas Cd results showed homogeneous distribution within soil depth. The impact of time scale effect on accumulation and spatial distribution of heavy metals indicated the urgent need for remediation and rational management.
Heavy metals, Solute transport, Modeling, Sorption, Kinetics
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Plant, Environmental Management and Soil Sciences