Comparative Adsorbent Studies using Pyrolyzed Materials Prepared from Custard Apple (Annona squamosa) Leaves in Removal of Fluoride from Wastewater

Abstract

Pyrolyzed materials (biochar) obtained from the leaves of custard apple (Annona squamosa) at 800 ºC in open air (OPA) and in presence of inert gas (IGPA) were used as adsorbent materials. The effect of different parameters such as particle size, agitation speed, pH, contact time, adsorbent dosage, initial fluoride concentration and temperature on fluorine adsorption on Annona squamosa as the adsorbent has been investigated. At pH 7, the optimized factors were contact period (30 min), the agitation speed (500 rpm) and the adsorbent dosage (1.5 g per 50 mL of fluoride water). A maximum fluoride removal efficiency of 93% in the case of OPA and 96% in the case of IGPA was achieved. Adsorption isotherm modeling studies show that the adsorption onto OPA followed Dubinin-Raudskevitch isotherm model,whereas IGPA followed Langmuir isotherm model, respectively. Thermodynamic parameters such as ΔHº, ΔGº and ΔSº were also estimated to ascertain the reaction is endothermic. In case of kinetics, pseudo-second order is the best fit for both OPA and IGPA. The SEM, FTIR and XRD patterns of the adsorbents were also recorded to have a greater comprehension of the adsorption process mechanism.