BIOSORPTION OF FLUORIDE IONS USING ACTIVATED TAMARIND FRUIT SHELL FROM WASTEWATER

Abstract

Fluoride-related health hazards are a serious environmental problem across the globe. They can occur due to both natural as well as anthropogenic activities. Drinking water containing fluoride may be beneficial or detrimental depending upon its concentration and total amount consumed. Fluoride concentrations between 0.5-1.5 mg/L are beneficial, especially to infants for the prevention of dental caries or tooth decay, but concentrations above 1.5 mg/L cause mottling of teeth in mild cases but fluorosis (dental or skeletal) and several neurological disorders in severe cases. Defluoridation is generally carried.,out by adsorption, chemical treatment, electrochemical methods, dialysis and the ion-e-xchange process. Among them, adsorption is found to be effective, environmental friendly and economical. Under the above backdrop, the present study has been undertaken to develop suitable agro based biosorbent for defluoridation from wastewater. In the continuing search to achieve the desired objective, Tamarind Fruit Shell was selected as suitable biosorbent for defluoridation from aqueous solutions. The above stated adsorbent is activated by two different methods into two different sizes of 500μm and 600 μm which provided two adsorbents named as CaCl2 Activated Tamarind Fruit Shell (ATFS) and NInO2-coated Tamarind Fruit Shell (MTFS). Batch experiments were performed to study the adsorption of fluoride ions on MTFS and ATFS adsorbents with various sizes. Characterization of both adsorbents was carried out using various techniques such as BET Surface Area analysis, FTIR, XRD, FE-SEM and EDAX. Effects of process parameters like biosorbent concentration, contact time, pH, biosorbent particle size and temperature. on the removal of fluoride ions from wastewater have been investigated us.in'- the above biosorbents to determine the optimum process conditions for maximum removal. The fluoride concentration of 20 mg/L, is removed upto 93% by MTFS effectively. Effects of initial fluoride concentration on the removal have also been investigated. Optimum adsorbent concentration for the removal of fluoride ions at agitation period of 30 min is found to be 1 g/50 ml. To facilitate mathematical modelling adsorption kinetic models as well as adsorption isotherms have been developed. Adsorption of Fluoride ions on MTFS adsorbent has been found to follow pseudo second order kinetic model among the pseudo first order, peudo second order, Weber-Morris model and Elovich model fitted to the experimental data.. Amongst the conventional isotherms such as Langmuir, Freundlich and Temkin isotherms, the Langmuir isotherm gave better prediction of specific uptakes for Fluoride ions at equilibrium for MTFS adsorbent.