Adsorption of hexavalent chromium from aqueous solution using cationic modified rice husk: Parametric optimization via Taguchi design approach

Abstract

The current work study the adsorption capacity of modified rice husk for the removal of Cr(VI) from aqueous solution. The rice husk was prepared and modified cationicaly. The cationic modified risk husk (cRH) was characterized by scanning electron microscopy (SEM) and fourier transform infrared (FTIR) spectroscopy. Also, point-of-zero pH (pHzero), specific surface area (m2/g) and bulk density (g/cm3) of the cRH were determined. The adsorption process was optimized by considering four independent process parameter at three variation levels using Taguchi design approach. The results showed the bulk density (0.392 g/cm3) and surface area (192 m2/g) which revealed the presence of numerous sorption sites on the cRH. Also the SEM micrograph showed the pores of different sizes which favoured the adsorption of Cr(VI). Taguchi experimental design predicted initial Cr (VI) concentration of 25 mg/L, contact time of 90 min, 2 g cRH dosage and pH of 2 as the optimum conditions to achieve 91.48% removal efficiency. The optimized condition was verified and 91.13% removal efficiency was achieved. The experiment data fitted well to Langmuir model indicating anion species monolayer adsorption on the cRH homogeneous surface. Also, the process is in better agreement with pseudo-second-order kinetic model, indicating a chemisorption controlled process. Thus, the study revealed that cationic modified rice-husk is suitable for the removal of Cr(VI) from aqueous solution.