Removal of Fluoride by Effective Utilization of Activated Red Mud-Bentonite as a Reactive Material for Permeable Reactive Barrier

Abstract

The direct consumption of fluoride-contaminated groundwater is increasing day by day without our knowledge escalating health risks. Therefore, it is imperative to carry out in-situ fluoride treatment where fluoride exposure is higher, rather than confining to small or large-scale industries. This necessitates of choosing appropriate purification methods and materials for effective treatment. The main objective of this research is to determine the adsorption/removal capacity of different proportions of activated red mud and bentonite mixture (RM:BEN) to remove fluoride from water. The characteristics of adsorption materials such as Red Mud (RM) and Bentonite (BEN) have been studied using Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray diffractometer (XRD). These techniques reveal the morphological changes and a loss of crystalline nature, indicating the adsorption of fluoride on the RM:BEN mixture. Different mix proportions of activated red mud and bentonite such as 95%:05% (Mix-A), 90%:10% (Mix-B), 85%:15% (Mix-C), 80%:20% (Mix-D) was analysed to determine its fluoride adsorption characteristics. The results revealed that RM:BEN (Mix-C) mixture demonstrated a higher adsorption capacity of 2.65 mg/g than other mixtures. The adsorption isotherm and kinetics model, fitting the Langmuir and Pseudo-first-order models, suggest that monolayer physical adsorption occurs during fluoride removal. In-situ experiments showed that the maximum removal efficacy of RM:BEN (Mix-C) reached 89.52% on the 7th day under lateral flow conditions and 93.81% on the 10th day under longitudinal flow conditions.