Application of response surface methodological approach to optimize removal of Cr ions from industrial wastewater

In the present study, the adsorption of chromium (Cr) onto clay using response surface methodology (RSM) was investigated as an efficient approach for examining predictive model building and optimization. To optimize experimental variables and predictive regression models, statistical design models were carried out. A five-level four-fac-tor central composite design (CCD) combined with RSM was performed with synthetic aqueous solutions on natural clay. The experimental variables included pH and agitation speed and were selected for optimization. The Cr ions ideal removal conditions were obtained using pH 5.0, contact time 23.0 minutes, adsorbent dosage of 69.4 mg, and agitation speed of 135 rpm. Chromium removal efficiency was found at 23.16 mg g-1. The independent variables significance and their interactions were verified by means of the analysis of variance (ANOVA). These results were justified by the relatively high correlation coefficients (R2 = 0.9902) of the statistical prediction. Clay and Cr loaded clay were characterized by X-ray dif-fractometer (XRD) and energy dispersive spectroscopy (EDS). The proposed adsorption process efficiently removed the Cr ions present in various aqueous media and was also applied to various industrial wastewaters.