Application of synthesized Fe/Al/Ca based adsorbent for defluoridation of drinking Water and its significant parameters optimization using response surface methodology

Abstract

Present work was mainly focused on to adopt a mixed metal oxide adsorbent for efficient fluoride treatment in drinking water with parametric optimization of the adsorption process. Mixed Al/Fe/Ca metallic oxide adsorbent was synthesized using co-precipitation technique of Al (III), Fe (III) and Ca(OH)2 salt solutions at molar proportion of 1:1:1. Fluoride adsorption process was optimized using Box-Bhekhen methodology by planning design of experiments with respect to various process parameters, such as, initial fluoride concentration, adsorbent dose, pH and contact time. Maximum fluoride removal of 91.1% was observed at an optimum operating condition of 7 mg L−1 initial fluoride concentration, 3 g L−1 adsorbent dosage, pH of 7 and 3 h of contact time. Freundlich isotherm model described the present adsorption experimental data with best fitting, which demonstrate the mechanism of multilayer adsorption with a pseudo second order reaction kinetics. Continuous column adsorption study was dissected utilizing Thomas model, Adams-Bohart model and Yoon Nelson model. Column breakthrough performance was best described by Thomas model. Likewise, an attempt was made to examine the synthesized adsorbent reusability. It was discovered to be minute loss in adsorption capability after 5 recycle; 92.1% fluoride removal for fresh adsorbent and 90.6% removal after 5 time use. The treated water was analysed for remaining aluminium at optimum condition and noted to have < 0.2 mg L−1 which is within the desirable limits set by WHO standards. Finally, the synthesized adsorbent was tested for ground water samples of Nagaur district of Rajasthan, India containing high fluoride content.