Simulating Zn, Cd and Ni Transport in Disturbed and Undisturbed Soil Columns: Comparison of Alternative Models

Abstract

This study compared four solute transport models for three heavy metals, i.e. Zn, Cd and Ni, in two disturbed and undisturbed loamy soil columns. The models include convection–dispersion equation (CDE), mobile–immobile model (MIM), fractional advection–dispersion equation (FADE) and the continuous time random walk model (CTRW). The experiments were carried out for each metal at three initial concentrations (C0 = 50, 100 and 150 mg L−1) and three replications in both soil columns. The results indicated that CDE, MIM, FADE and CTRW, with r2 > 0.98 and RMSE Ni > Cd. The hydrodynamic dispersion coefficient (D) in the undisturbed soil was higher than the disturbed soil. The spreading parameter (β) of CTRW and the fractional differentiation orders (α) in FADE were approximately 1.0 and 1.7, respectively. Consequently, the heavy metal transport within both soil columns were anomalous or non-Fickian transport. However, CDE and MIM, which are based on Fickian diffusion law, were more appropriate for simulating heavy metal transport through two soil columns in comparison with CTRW and FADE.