Removal of cytotoxic tamoxifen from aqueous solutions with hydroxyapatite adsorbent

The growing problem of pharmaceutical contamination poses a significant challenge to the protection of water resources. Tamoxifen, a widely used anticarcinogenic drug, is one of the pharmaceutical residues found in wastewater and poses serious environmental risks. In this study, chemically synthesized hydroxyapatite (HAP) was used as an adsorbent to remove tamoxifen from aqueous solutions. The synthesized HAP was thoroughly characterized by BET surface area analysis, SEM-EDX imaging and FTIR spectroscopy. A systematic evaluation of key adsorption parameters was carried out to determine the most effective conditions for tamoxifen removal. Experiments were performed by varying parameters such as initial tamoxifen concentration (20-70 μg/mL), solution pH (2-10), adsorbent dosage (20-50 mg per 50 mL solution), contact time (0-240 min) and temperature (298-318 K). The equilibrium state of the adsorption process was analyzed using Langmuir and Freundlich isotherm models. Pseudo-first and pseudo-second order kinetic models were used to determine the rate of the process. Thermodynamic properties were also calculated to provide information on the nature of the process. A maximum removal efficiency of 90.85% was obtained under optimum conditions of initial concentration 40 μg/mL, adsorbent dosage 40 mg, contact time 180 min and pH 7. Notably, the pseudo-second-order kinetic model (R²: 0.9997) and the Langmuir isotherm model (R²: 0.9994) exhibited the closest alignment with the experimental data. Thermodynamic studies have shown that the adsorption was a by itself (ΔG<0), exothermic (ΔH<0) process, accompanied by an increase in system disorder (ΔS>0). Consequently, this research underscores the viability of HAP as an economical and ecologically sound approach for remediating wastewater contaminated with pharmaceuticals.