Enhanced adsorption of heavy metals in groundwater using sand columns enriched with graphene oxide: Lab-scale experiments and process modeling

Abstract

In this study, sand enriched with graphene oxide (GO) was applied as the medium to prevent heavy metals migration to groundwater. The retention of heavy metals including Cr(VI), As(III), Cd(II), and Pb(II) in the prepared medium was investigated. Batch experiments results revealed that the adsorption capacities of GO were 530.85, 170.1, 49.78, and 14.41 mg g−1 for Pb(II), Cd(II), As(III), and Cr(VI). The adsorption characteristics of GO were investigated by four linear and nonlinear isotherm models. Nonlinear Freundlich was the best model fitting the experimental observations in equilibrium reactions. The presence of GO enhanced adsorption capacity of the sand column to 92, 87, 88, and 94 % for Pb(II), Cd(II), As(III), and Cr(VI), respectively. The retention of single component and a mixture of heavy metals in the prepared medium was studied, showing that in the mixture of metals, the adsorption capacity of GO reduced by 14, 21, and 39 % for Pb(II), Cd(II), and As(III), respectively. A longer breakthrough time for GO was achieved for Pb(II) (10.83 h) and Cd(II) (4.23 h), indicating higher efficiency of the reactive medium in the retention of Pb(II) and Cd(II). Thomas and Adam’s–Bohart kinetic models were applied to express the dynamic characteristics of the proposed medium. Breakthrough curves of Cr(VI), Cd(II), and Pb(II)were successfully predicted by Thomas model, while that of As(III) was described better by Adam’s–Bohart model. This can be associated with the fact that the Thomas model assumes Langmuir isotherm, while adsorption behavior of As(III) was well-depicted by Freundlich isotherm.