Description:
<jats:p>Transport of heavy metals such as Cd is affected by several rate‐limiting processes including adsorption and release reactions in soils. In this study, column transport and batch kinetic experiments were performed to assess Cd mobility in an acidic (Windsor) and an alkaline (Bustan) soil. Adsorption and desorption isotherms exhibited strong nonlinearity in both soils. A nonlinear multireaction and transport model (MRTM) successfully described adsorption with time as well as adsorption–desorption hysteresis. Breakthrough curves (BTCs) from column experiments indicated strong Cd retardation accompanied by slow release during leaching. The Cd was nearly immobile in the calcareous Bustan surface soil, whereas 20 and 30% of the applied Cd was mobile in the Windsor and Bustan subsurface soil columns. Sequential extractions of soils from the batch and column transport experiments indicated that Cd was associated with carbonates for the alkaline soil and with exchangeable and oxide fractions for the acidic Windsor soil. The MRTM was capable of describing the Cd arrival time in effluent and its concentration during leaching from the soil columns. When the CXTFIT model, which accounts for linear adsorption, was used, adequate overall predictions of the BTCs were obtained including the magnitude and time of peak arrival; however, effluent concentrations at advanced stages of leaching were underestimated. Sorbed Cd based on soil extractions vs. depth at the termination of column experiments were adequately described by the MRTM and CXTFIT.</jats:p>