Investigation of dye removal from wastewaters with metakaolin-based geopolymer by experimental design method

In this study, the removal of Bismarck Brown Y (BBY) dye (Basic Brown 1) from aqueous solutions using metakaolin-based geopolymer (MKEJ) was investigated. Adsorption conditions were optimized in batch and continuous systems by Box-Behnken experimental design (BBD). ANOVA results showed that the critical parameters affecting adsorption efficiency in the batch system were contact time and adsorbent amount and flow rate and adsorbent amount in the continuous system. The adsorption efficiency and the adsorption capacity were 96.71% and 40.28 mg/g, respectively in the batch system while these values were found to be 96.14% and 34.07 mg/g, respectively in the continuous system. During the adsorption process, it was found that the pseudo-second-order kinetic model best explained the time-dependent data. The equilibrium data were evaluated with Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models and determined to fit the D-R model. Various analysis methods were used to determine the structural properties of the adsorbent. Brunauer-Emmett-Teller (BET) method was used for surface area measurement, Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) were preferred for thermal stability and degradation analysis. X-ray Diffraction (XRD), Scanning Electron Microscopy, and Energy Dispersive X-ray Spectroscopy (SEM-EDX) methods were used to analyze the crystal structures, surface morphology, and elemental composition. Fourier Transform Infrared Spectroscopy (FTIR) method was applied to analyze the chemical bonds and functional groups. The results showed that the metakaolin-based geopolymer (MKEJ) in the modified form with MnO2 can effectively remove BBY dyestuff from aqueous solutions. These findings support the feasibility of the proposed material as a low-cost and environmentally friendly adsorbent.