SORPTIVE REMOVAL OF ARSENIC FROM DRINKING WATER

Abstract

Consumption of arsenic and its compounds present in the drinking water causes many health problems. High arsenic concentrations have been reported in USA, China, Chile, Bangladesh, Taiwan, Mexico, Argentina, Poland, Canada, Hungary, Japan and India. Epidemiological studies suggest that there are significant health risks, including cancer, associated with prolonged exposure to elevated arsenic concentrations in drinking water even at quite low concentrations. Many removal processes have been in practice for the removal of arsenic from the aqueous solutions viz. adsorption, oxidation, microfiltration, coagulation, etc. In the present study, iron-coated bagasse fly ash (BFA-Fe) and rice husk ash (RHA-Fe) have been used for the removal of arsenic from synthetic drinking water. The physico-chemical characterization of the adsorbents have been carried out using standard methods e.g. sieving, scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA), FTIR spectroscopy, etc. Batch experiments were carried out to determine the effect of various factors such as contact time (t), initial concentration (C.), pH, adsorbent dose (m) and temperature (T) on adsorption process. Results obtained from these studies have been analyzed by various kinetic and isotherm models. The removal efficiency of BFA-Fe was found to be more than that of RHA-Fe at its natural pH (6.3-6.5). Pseudo-first-order, pseudo-second-order, intraparticle diffusion models and Bangham models have been used to represent the kinetics of the sorption process. The sorption kinetics was best approximated by pseudo-second-order kinetic model. An increase in temperature induced a negative effect on the sorption process. Experimental equilibrium isotherm data have been analyzed using Langmuir, Freundlich, Temkin and Redlich—Peterson (R—P) isotherms, and their parameters have been determined by non-linear regression analysis. Error analysis has been carried out using various error functions. Freundlich isotherms, generally, well-represented the equilibrium adsorption of As onto BFA-Fe and RHA-Fe. Thermal degradation kinetics of spent adsorbents were carried out and found that the they are stable upto 400 °C.