Adsorption property of direct red brown onto acid-thermal-modified sepiolite and optimization of adsorption conditions using Box-Behnken response surface methodology

The chemical properties of the acid-thermal-modified sepiolite were investigated. At the same time, the adsorption behaviors of direct red brown onto modified sepiolite were studied. The pH(ZPC) of the raw sepiolite and the acid-thermal-modified sepiolite was 7.32 +/- 0.1 and 6.44 +/- 0.1, respectively. The results indicated that the acid-thermal modification increased the surface acidity of the sepiolite and the available surface sites for adsorption. According to the X-ray powder diffraction and Fourier transform infrared spectra, the results showed that the modification improved the purity of the sepiolite. The amount of the direct red brown adsorbed increased from 15.34 to 62.42mg/g onto the modified sepiolite, as initial dye concentration increased from 50 to 200mg/L. The amount of direct red brown adsorbed decreased from 18.96 to 13.76mg/g, as the initial pH of the dye solution increased from 2 to 8. The direct red brown onto modified sepiolite was best described by the pseudo-second-order kinetic model. The experiment data were calculated by the Box-Behnken, and the optimum adsorption conditions were following: the adsorbent dosage 2.53g/L, pH 4.70, and reaction time 4.46h. The decolorization rate performed in the optimum adsorption conditions was 91.5%. The initial pH, adsorbent dosage, reaction time, the interaction of adsorbent dosage and reaction time were significant factors for the adsorption.