Adsorption of fluoride ions from aqueous solution by rice husk based nanocellulose

Synthesis of nanocellulose using crop residue rice husk is an innovative method. Morphological and structural characterizations of nanocellulose were analyzed. The rice husk based nanocellulose had a particle height of 5.7 nm and a crystallinity index of 70%. Raw rice husk comprises 35% cellulose, 22% hemicellulose, 19.1% lignin, and 20% ash. Defluoridation of water samples is an imperious provocation for the advancement of society. According to World Health Organisation (WHO) guidelines, a fluoride concentration of more than 1.5 milligrams per litre leads to dental problems and bone deficiency. The appropriate defluoridation practice was selected to avoid these problems. Cost-effective nanocellulose from rice husk was used as an adsorbent to purify a fluoride-rich aqueous solution in batch experiments on a lab scale. Response of dose, temperature, time, pH, and initial ion concentration on adsorption capacity and removal efficiency were deliberated. In batch experiments, the highest removal efficiency of fluoride from aqueous solution was 74% at a 120 min time, 2 mg/l initial ion concentration, 30 ˚C temp, 0.9 g adsorbent dose at pH 2. According to WHO standards, fluoride concentrations above 1.5 mg/l cause tooth and bone insufficiency. Regeneration showed that the adsorbent was cost-effective and reusable. Two, three, and four-parameter isotherm models were applied to the experimental data. The Freundlich, Langmuir, Temkin, Redlich-Peterson, and Baudu isotherm models and the pseudo-second-order kinetic and intra-particle diffusion models best fit the data. The studied thermodynamic constraints showed the physical adsorption of fluoride.