Efficient Removal of Tetracycline Hydrochloride via Adsorption onto Modified Bentonite: Kinetics and Equilibrium Studies

Pharmaceutical contamination of water sources has become a critical environmental challenge. Bentonite (BN), a natural clay mineral, has gained attention due to its high surface area, cation exchange capacity, and cost-effectiveness, making it a promising adsorbent for removing contaminants. This study explores the potential of BN and its acid-treated form (BA1) as effective adsorbents for the removal of tetracycline hydrochloride (TC) from aqueous solutions. Comprehensive characterization was performed using analytical techniques, including XRF, XRD, SEM/TEM, XPS, TG/DTG, and CO2 and N2 adsorption–desorption isotherms. The results indicate that BA1 is a mesoporous material with a surface area exceeding 165 m2·g−1. The adsorption process was fitted to a pseudo-second-order kinetic model. BA1 achieved a maximum adsorption capacity of 40.98 mg·g−1 and removal efficiency of up to 99% within only 30 min at an optimal pH of 5. Equilibrium isotherm calculations for BA1 show the best fit for the Freundlich model R2 > 0.9923, indicating a favorable adsorption process. The material was reused over seven consecutive cycles to evaluate the regeneration capacity of the clay mineral materials. BN stands out for its effectiveness, cost-effectiveness, and environmental sustainability as a promising material for water treatment applications.