Dynamic Adsorption Characteristics of Cr(VI) in Red-Mud Leachate onto a Red Clay Anti-Seepage Layer

Red-mud leachate from tailings ponds contains Cr(VI), which can pollute groundwater via infiltration through anti-seepage layers. This paper investigates leachate from a red-mud tailings pond in southwest China and the red clay in the surrounding area to simulate the adsorption of Cr(VI) onto clay at different pHs, using geochemical equilibrium software (Visual MINTEQ). We also performed dynamic adsorption testing of Cr(VI) on a clay anti-seepage layer. The dynamic adsorption behaviors and patterns in the dynamic column were predicted using the Thomas and Yoon–Nelson models. Visual MINTEQ predicted that Cr(VI) adsorption in red-mud leachate onto clay was 69.91%, increasing gradually with pH, i.e., adsorption increased under alkaline conditions. Cr(VI) concentration in the effluent was measured using the permeability test through a flexible permeameter when the adsorption saturation time reached 146 days. At a low seepage rate, Cr(VI) adsorption onto the clay anti-seepage layer took longer. Saturation adsorption capacity, q(0), and adsorption rate constant, K(th), were determined using the Thomas model; the Yoon–Nelson model was used to determine when the effluent Cr(VI) concentration reached 50% of the initial concentration. The results provide parameters for the design and pollution prediction of the clay anti-seepage layer of red-mud tailings ponds.