Studies on fluoride adsorption by apatitic tricalcium phosphate (ATCP) from aqueous solution

ABSTRACT

The present study was conducted to evaluate the feasibility of apatitic tricalcium phosphate (ATCP) for fluoride adsorption from aqueous solutions. The adsorbent was characterized using X-ray diffraction and scanning electron microscope with energy dispersive X-ray analysis. Batch adsorption studies were performed as function of contact time, initial fluoride concentration, temperature, adsorbent dose, pH, and influence of competing anions. Fluoride adsorption kinetics was well fitted by pseudo-second-order model. The maximum sorption capacity of ATCP for fluoride removal was found to be 15.42 mg g⁻¹ at 313 K. Thermodynamic parameters viz. ΔG°, ΔH°, and ΔS° were calculated indicating that the adsorption process was spontaneous and endothermic. The fluoride adsorption was well explained using Langmuir Freundlich, Temkin and Dubinin–Radushkevick models. Fluoride adsorption was influenced by the presence of HCO₃⁻ ions. It was observed that at pH = 12.75 around 88% desorption efficiency was found. Results from this study demonstrated potential utility of ATCP that could be developed into a viable technology for fluoride removal from aqueous solution.

Keywords:

• Apatitic tricalcium phosphate
• Fluoride
• Adsorption isotherms
• Adsorption kinetics