Surface modification of pumice enhancing its fluoride adsorption capacity: An insight into kinetic and thermodynamic studies

The present research contribution is pertaining to the surface modification of natural pumice (NP) using aqueous solution of magnesium chloride (MgCl2) and hydrogen peroxide (H2O2) and exploring the fluoride uptake capacity between the natural and modified pumice materials. The effect due to hydrogen peroxide, an oxidant, towards modification of pumice surface was greater than the magnesium chloride solution and showed a substantial increase in the specific surface area of 53.11 m(2) g(-1), and 41.63 m(2) g(-1), respectively for hydrogen peroxide modified pumice (HMP) and magnesium chloride modified pumice (MGMP) as compared to that of NP of 2.34 m(2) g(-1). The extent of surface modification with enhanced porosity in MGMP and HMP was apparent from the recorded SEM patterns. XRD and FTIR studies of surface modified pumice did not show any structural distortion. In this contribution, the fluoride uptake capacity of NP was initially studied and then compared with the modified pumice adsorbents, MGMP and HMP. From the results of various kinetic models, pseudo-second-order fit well with the fluoride sorption kinetics conducted at different initial fluoride concentrations. The experimental adsorption isotherm complied with Freundlich type with K-F less than 1 ascertains the dominance of multisite adsorption on the surfaces of NP, HMP and MGMP. Thermodynamic parameters viz., Delta G degrees, Delta H degrees and Delta S degrees reveal that the fluoride adsorption process was feasible and endothermic nature associated with increased randomness. Desorption potential of NP of 88% was improved to 98% and 100% for the modified MGMP and HMP adsorbents respectively. (C) 2013 Elsevier B.V. All rights reserved.