Biosorption of Fluoride from Aqueous Solution Using Lichen and Its Ca-Pretreated Biomass

Abstract

One of the major ground water contaminants is fluoride; hence, numerous procedures for its removal are reported. In this study, adsorption of fluoride was investigated by lichen and its Ca-pretreated lichen biomass from aqueous solution. The entire study was done by batch adsorption mode. The operating parameters such as pH, adsorbent dose, stirring rate, contact time, particle size, initial fluoride solution, and temperature in such solution influence the degree of fluoride ions adsorption. The kinetics of the fluoride adsorption was calculated by pseudo-first order and pseudo-second order and intraparticle diffusion rate laws. The surface morphology was evaluated by scanning electron micrograph (SEM). In this biosorption study, results revealed that Ca-pretreated lichen showed higher removal at pH 6. The fluoride adsorption isotherms, D-R and Langmuir isotherms are well fitted for both the biomasses and pseudo-second-order kinetic model showed high regression coefficient. The Langmuir adsorption capacity of lichen and Ca-pretreated lichen are 0.81 mg/g and 1.72 mg/g, respectively. The FTIR study showed active functional groups associated with biomass. Thermodynamic parameters such as Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) change of sorption were also evaluated which indicated that the adsorption process was spontaneous, feasible, and exothermic in nature. The present findings suggest that lichen biomass may be used as an inexpensive and effective adsorbent.