Raw laterite is treated with acid-base pair under optimized condition. Treatment parameters are optimized based on removal efficiency of targeted pollutant on treated laterite (TL). Higher surface area, pore volume and enrichment of Fe/Al oxyhydroxide phases of TL compared to raw laterite (RL) contribute much superior adsorbent efficiency for Cr(VI) removal. A batch mode adsorption of Cr(VI) ion is performed using temperature controlled mechanical shaker. Adsorption isotherm model of Langmuir, Freundlich, Temkin, Redlich-Petersen are used to analyze experimental adsorption data of Cr(VI) ion on TL. The highest adsorption capacity is obtained as 16.4 mg/g of TL for 10 mg/L initial Cr(VI) concentration in batch mode of operation at 305 K. Among all isotherm models used, best correlation with experimental data is obtained for Freundlich model. In this study, the increasing order of regression coefficient for four isotherm models is obtained as Langmuir < Temkin < Redlich-Petersen < Freundlich. The kinetic data is fitted to 1st order, pseudo-second order and intraparticle diffusion kinetic model. The pseudo-second kinetic model provides the best fit with experimental data. The batch mode of experiment reveals the 99 % Cr(VI) removal for initial Cr(VI) concentration of 7.0 mg/L with TL dosing 0.5 g/L at 305 K. The plot of adsorption capacity (mg/g) as a function (time)0.5 indicates the importance of both external mass transfer and intraparticle diffusion in overall adsorption kinetic of Cr(VI) ion on TL surface. The external mass transfer controls the first ~1.0 hr of adsorption and a later part is controlled by intraparticle diffusion.
Keywords: Chromium (VI) removal, laterite, intraparticle diffusion, adsorption mechanism
