Adsorption efficiency of red mud and steel slag for as, cd, and pb: implication to understanding the chemistry of immobilization in soils

Abstract

PurposeThe contamination of potentially toxic elements (PTEs) in soil is a significant concern, posing risks to the environment and public health. This study evaluated the sorption efficiencies of two industrial by-products such as red mud (RM) and steel slag (SS) as adsorbents for use in PTEs immobilization.Materials and methodsThe characteristics of adsorbents were analyzed using SEM and BET. Batch adsorption experiments were conducted to study the adsorption of arsenic (As), cadmium (Cd), and lead (Pb) onto the selected adsorbents including RM, neutralized red mud (NRM), and SS at initial metal concentrations of 20, 50, 100, 200, 500, and 1000 mg L-1. Adsorption isotherms of As, Cd, and Pb were simultaneously investigated using from adsorption experimental data.Results and discussionResults showed that equilibrium sorption efficiencies of RM and NRM were greatly increased compared to SS since the characterization of RM and NRM have larger specific surface area and pore volumes and diameter than SS. The highest sorption efficiencies of RM, NRM, and SS were seen at 20 mg L-1, with 32.59%, 30.21%, and 23.81% for As; 99.51%, 94.55%, and 11.43% for Cd; and 99.46%, 99.29%, and 30.22% for Pb, respectively. The data were fitted to the Langmuir and Freundlich isotherm models, showing that RM, while not much different from NRM, had the highest maximum adsorption capacity with larger sorption energy and surface intensity for metal ions, especially Cd and Pb.ConclusionsThis study suggests that RM could be a cost-effective alternative adsorbent for the retention of PTEs, making it suitable for on-site metal immobilization. Finally, since NRM demonstrated good adsorption properties like RM, it can be an effective alternative for application in alkaline soils instead of RM.