Abatement of chromium by adsorption on nanocrystalline zirconia using response surface methodology

Abstract

Application of nanocrystalline zirconia was investigated for the removal of chromium from aqueous solutions. The nanozirconia was synthesized by ‘precipitation method’. The parameters namely initial concentration (5–65ppm), pH (0.5 to 10.5), adsorbent dose (2 to 10g/l) and temperature (298K to 318K) were optimized employing central composite design of response surface methodology. The removal of Cr was most affected by pH, followed by an initial concentration and adsorbent dose. Maximum removal (%) was achieved at an initial concentration of 20ppm, pH=3, adsorbent dose=4g/l and temperature 313K. The experimental data were best fitted in Langmuir's isotherm equation and the removal followed pseudo second order kinetics. The mechanism of removal was explained by boundary layer diffusion via intraparticle diffusion and was further confirmed by Boyd plot. Thermodynamic parameters revealed that the removal process was spontaneous, endothermic and physiosorptive in nature. Adsorbent was regenerated with hydroxides (0.1N NaOH, KOH and NH4OH) for further reuse.