Swapnila Roy

Thermodynamics and kinetics study of defluoridation using Ca-SiO2-TiO2 as adsorbent: Column studies and statistical approach

Fluoride contamination of water is a potential health and environmental hazard worldwide. This study focuses on defluoridation efficiency in aqueous system by novel adsorbents, i.e., calcium impregnated silica (Ca-SiO2) and calcium impregnated silica combined with titanium dioxide (Ca-SiO2-TiO2). Comparative batch study was carried out using both adsorbents Ca-SiO2 and Ca-SiO2-TiO2 for fluoride removal efficiency in different experimental conditions where it was observed that chemically modified Ca-SiO2-TiO2 acted as a better adsorbent for defluoridation than Ca-SiO2. Thus, further batch isotherm and kinetics studies were performed using Ca-SiO2-TiO2. The phenomenon of fluoride ion uptake is realized by Langmuir and Freundlich isotherm model. Langmuir isotherm shows satisfactory fit to the experimental data. The rate of adsorption shows that the pseudo-second-order rate fitted the adsorption kinetics better than the pseudo-first-order rate equation. The mechanism of adsorption process was illustrated by calculating Gibbs free energy, enthalpy and entropy from thermodynamic studies. To further confirm the applicability of the adsorbent, a fixed bed study was carried out in column mode. Thomas and bed-depth-service-time (BDST) model were well-fitted to the experimental results. The optimal operating conditions of defluoridation were found by using response surface methodology (RSM) with the help of Design Expert Software. The maximum percentage of fluoride removal was 92.41% in case of calcium impregnated silica combined with titanium dioxide (Ca-SiO2-TiO2). Thus, it may be concluded that chemically synthesized Ca-SiO2-TiO2 could be used as an environmentally and economically safe adsorbent for defluoridation of waste water.

Assessment of De-fluoridation in Waste Water Using Activated Biochar: Thermodynamic and Kinetic Study

Thermally treated domestic food waste is utilized to prepare biochar, followed by chemical activation to obtain activated bio-char (Biochar-act) which is used as de-fluoridating agent in contaminated water. The structural property of the synthesized activated bio-char is studied in detail. From continuous batch process , it is shown that efficiency of bio-char with lower degree of carbonization has remarkable properties of de-fluoridation. Here temperature, contact time and adsorbent dose , used as process parameters, have strong influence on fluoride uptake process. The adsorption equilibrium data are well fitted to the Langmuir isotherm model. Comparatively the data provided by pseudo-second-order kinetic model correlated better experimentally than pseudo-first-order kinetic model. From thermodynamic point of view, it is experimentally proved that de-fluoridation onto activated bio-char is spontaneous and endothermic in nature. Here, a low-cost process is suggested using low-cost starting materials to convert bio-char upon heat treatment at 350˚C and then activated chemically by acid. The prepared adsorbent has higher de-fluoridation efficiency such as 91.24%. So it may be concluded that activated bio-char is economically and environmentally safe for de-fluoridation in waste water.