Empirical kinetic models for the electrochemical extraction of arsenic and heavy metals from clay containing tailings

Abstract Three empirical kinetic models for the arsenic, iron and manganese electrochemical extraction from clay containing tailings highly contaminated were analysed: the intraparticle diffusion model, the Elovich model and the two first-order reactions model. Models were chosen regarding their relative simplicity and accuracy of fitting experimental data. Elovich model was the best fitted model for the As extraction data with the lowest average relative error (ARE = 0.320) and the highest coefficient of determination (R2 = 0.986). The intraparticle diffusion model was the most adequate to describe the Fe and Mn extraction (ARE = 0.142, R2 = 0.942 for Fe, and ARE = 0.112, R2 = 0.926 for Mn). The influence of the current intensity, extractant concentration and liquid/solid ratio on the coefficients of the extraction kinetic models was also determined. Arsenic extraction Elovich model coefficients showed a direct linear relationship with the process variables while iron and manganese extraction diffusion model coefficients showed a direct linear relationship with the current intensity and the extractant concentration but an inverse relationship with the liquid/solid ratio. Response surface plots were used for estimating the interactive effect of the four independent variables studied (current intensity, extractant concentration, liquid/solid ratio and time) on the electrochemical extraction.