Removal of fluoride in groundwater by adsorption using hydroxyapatite modified Corbula trigona shell powder
N’Zébo Sylvestre Yapo, Sadat Aw, Bi Gouessé Henri Briton, Patrick Drogui, Kouassi Benjamin Yao, Kopoin Adouby
Abstract
Corbula trigona shell powder (CTSP) was modified by a hydrothermal method using phosphoric acid to remove fluoride ions from groundwater. This method was performed by keeping the Ca/P molar ratio constant at 1.67. Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD) and scanning electronic microscopy (SEM) analysis confirmed the formation of hydroxyapatite (HAP) after CTSP pre-treatment. Batch adsorption experiments were conducted in beakers containing modified-CTSP. Moreover, the modified-CTSP dose variated from 0.1 to 0.8 g, in the presence of 100 mL of groundwater. This groundwater was contaminated by 2.20 mg/L of fluoride. Adsorption kinetics indicated that the adsorption process was governed by pseudo-second-order kinetics. Furthermore, the reaction rate constant for fluoride removal was 0.161 g mg−1 min−1. Also, adsorption isotherms showed that fluoride removal was mainly controlled by physical adsorption with 4.517 mg g−1 maximum adsorption capacity. But the relatively low enthalpy value (∆adH0 < 200 kJ.mol−1) indicated that during the adsorption process, very low interactions occurred between fluoride and modified-CTSP. The adsorption process was spontaneous, endothermic, and irreversible in nature. The best results with 89% fluoride removal were recorded at pH 7.5 ± 0.1 in 175 min with 5 g/L modified-CTSP. These results showed that HAP derived from Corbula trigona shell waste can be a promising sorbent for groundwater fluoride removal in developing countries.