Optimization of a Binary Dye Mixture Adsorption by Moroccan Clay Using the Box-Behnken Experimental Design

In this work the Removal of the basic blue 41 and crystal violet mixture was studied using Moroccan clay as an adsorbent. The morphology and structure of this local adsorbent were examined using different analysis techniques and physicochemical measures, including X-Ray diffraction (XRD), Fourier transform spectroscopy (FTIR), scanning electron microscopy (SEM), surface area (BET) and point of zero charge (pH(pzc)). The effects of three operating variables on removal efficiency of dye mixture were investigated and analyzed using Response surface methodology based on Box-Behnken design, namely: initial concentration of the dye mixture, adsorbent dose and solution pH. The proposed model (quadratic) was approved with high correlation coefficients (R-2 = 0.9964), (R-adj(2) = 0.9919), and a value of the percentage absolute error of deviation (AED) equal to 0.792. Furthermore, the p-value of the model was < 0.0001 and F-value of 217.37 implies the model is highly significant. The linear effects of dye mixture concentration and clay dose were the principal determining factors that affected the dye removal efficiency on local clay According to the analysis of variance (ANOVA). A significant dye removal rate (approximately 99% after only 50 min) was achieved under the following optimized conditions: dye concentration of 78.14 mg/L, adsorbent dose of 1.3 g/L and pH = 8.12. Practically, the removal rate was found to range from 55 to 99%. The isotherms and kinetics studies show that the adsorption process follows the Langmuir isotherm model (R-2 = 0.98), and the adsorption is well described by the pseudo second order kinetic (R-2 = 0.99), the calculated thermodynamic parameters revealed that the adsorption was endothermic. The present study showed that the tested local clay has significant adsorbing characteristics displaying high efficiency in removing basic blue 41 and crystal violet mixture. Thus, the germination test was initiated to confirm the low toxicity of the treated water after the adsorption process. The regeneration experiments were also carried out and it was found that the tested clay was regenerable.