Boron adsorption from aqueous solutions using chemically activated kaolin clay adsorbents kinetics isotherm and...

Boron contamination in water is a global concern due to its narrow threshold between beneficial and toxic levels for humans, crops, and ecosystems. Long-term exposure to elevated boron concentrations can cause serious health risks and reduce agricultural productivity, making its removal from water an urgent priority. Conventional treatment methods often fail to achieve efficient and sustainable boron removal, creating a need for low-cost and effective adsorbents. In this study, kaolin clay was chemically activated with hydrochloric acid (HCl) and phosphoric acid (H₃PO₄) to improve its adsorption capacity and surface reactivity. Structural and surface modifications were confirmed through FTIR, XRF, and BET analyses, which showed increased porosity, higher surface area, and the formation of functional groups favorable for boron binding. Batch adsorption experiments were performed to investigate the effect of pH, adsorbent dosage, initial boron concentration, contact time, and temperature. Raw kaolin exhibited negligible adsorption efficiency and was excluded from further tests. In contrast, activated kaolin achieved significantly higher capacities, with maximum adsorption of 2.39 mg/g for HCl-treated kaolin and 2.18 mg/g for H₃PO₄-treated kaolin at an initial concentration of 16.5 mg/L. Adsorption was most favorable at pH 4. Isotherm studies indicated that equilibrium data fitted well to Freundlich and Sips models, suggesting multilayer adsorption on heterogeneous surfaces. Kinetic analysis revealed excellent agreement with the pseudo-second-order model, while thermodynamic evaluation confirmed the exothermic and spontaneous nature of the process. Tests on groundwater samples from Gaza City showed performance consistent with laboratory results, confirming the reliability and scalability of the method. This study demonstrates that chemically activated kaolin is a promising, low-cost, and environmentally friendly adsorbent for boron removal, offering a practical solution for water treatment systems in regions facing boron contamination challenges.