Optimization of chromium (VI) adsorption by novel nano-pumice modified by cationic surfactant from aqueous media using the response surface method: Isotherm and kinetic studies

Abstract

The present study focused on the evaluation of modified nano-pumice with hexadecyl trimethyl ammonium bromide (HDTM.Br) surfactant in adsorption of Cr(VI) from aqueous environments. The effects of pH (3–9), contact time (30–120 min), Cr(VI) concentration (0.05–1 mg/L) and adsorbent dose (0.1–1 g) on the adsorption rate were designed, modeled and optimized according to central composite design-response surface methodology (CCD-RSM). Considering ANOVA and regression analyses, the adsorption process better follows the quadratic polynomial model with p-value < 0.005, R2 = 0.9906. The model adequacy established based on CCD-RSM is quite clear with regard to the value of lack of fit test, which is 0.75. The optimum conditions were obtained at pH 3, Cr(VI) concentration 0.05 mg/L, adsorbent dose 1 g/L and contact time 120 min, respectively. The maximum adsorption capacity of Cr(VI) was found to be 0.24 mg/g. Kinetic and isotherm studies showed that the adsorption process is better described with pseudo-second kinetics with R2 = 0.9983 and Freundlich isotherm with R2 = 0.9971. Given to the highest efficiency of Cr(VI) adsorption (about 96%) by pumice/HDTM.Br nano composite, the composite can be proposed as a promising adsorbent for the removal of Cr(VI) in water under specific conditions.