Fluoride Removal from Aqueous Solutions via Adsorption Using Raw, Calcined, and Chemically Treated Laterite Mineral

Abstract

Accessing safe drinking water in India faces a mounting challenge due to deteriorating water quality from industrial pollution and excessive groundwater extraction, leading to increased chemical impurities like fluoride affecting 66 million people across 20 states. Fluoride contamination, arising from natural sources like volcanic activity and mineral weathering, is compounded by industrial discharge from semiconductor, metal, glass, and fertilizer industries. Prolonged exposure to fluoride-laden water poses health risks, causing dental, skeletal, and non-skeletal fluorosis. To address these risks, the World Health Organization (WHO) set the acceptable fluoride limit in drinking water at 1.5 mg/l. Despite various available technologies like coagulation and membrane processes, adsorption remains the most cost-effective method, especially for domestic use. Materials such as alumina, zeolite, clay, coal, and ceramics have been studied as fluoride adsorbents. In present study, laterite, bauxite, hematite, and calcite minerals rich in iron, aluminum, silica, and calcium were examined for fluoride ion adsorption at 7 pH and room temperature. Laterite displayed superior adsorption capacity compared to other minerals. Parameters like stirring speed, adsorbent size, and thermal treatment were investigated for their impact on laterite’s adsorption capacity. Raw laterite was successfully modified by loading it with copper oxide using a copper sulphate solution, significantly elevating its adsorption capacity from 0.26 to 1.905 mg/g, an eight-fold increase. Freundlich isotherm analysis confirmed multilayer adsorption facilitated by electrostatic forces. Isotherm study validates that surface-modified laterite is a robust adsorbent for fluoride removal at neutral pH and room temperature, presenting a promising solution for water treatment needs.