Biosorption of fluoride using Anogeissus dhofarica – effect of process variables and kinetic studies

Abstract

In this experimental study, a novel biosorbent was synthesized from Anogeissus dhofarica and applied for defluoridation under batch-shaking conditions. The influence of process variables, namely initial pH (3.0–11.0), fluoride concentration (50–200 mg/L), biosorbent dosage (0.25–8.0 g/L) and agitation speed (0–600 rpm), on the fluoride uptake was studied. Fluoride uptakes increased with increase in fluoride concentration due to enhanced driving force and decreased with increase in biosorbent dose. An empirical relationship, exponential in nature, was proposed between fluoride uptake and biosorbent dose. The pseudo-second-order rate constant (k2) was determined as 0.00474 g/ (mg.min) at 303 K with an initial fluoride concentration of 100 mg/L and the rate constant increased with increase in temperature. The activation energy was determined as 6.023 kJ/mol. The chemisorptive nature of fluoride removal was proven through kinetic modeling. The findings of this research proved the feasibility of industrial application of this novel biosorbent for fluoride removal over a wide range of environmental conditions.