Optimization of synthesis of a geopolymer based on laterite/beer bottles composites for adsorption of methylene blue in aqueous solution

Abstract

This study aimed to develop and optimize a geopolymer composite using laterite and recycled beer bottle glass (RBB) as precursors for the adsorption of methylene blue (MB) from aqueous solutions. The synthesis process was optimized through a Box-Behnken design by varying three key factors: laterite mass (50–60 g), RBB mass (0–5 g), and sodium silicate-to-sodium hydroxide ratio (1.5–2.5). The optimal conditions were found to be 50 g of laterite, 0.114 g of RBB, and a silicate-to-hydroxide ratio of 2.5. Under these conditions, the geopolymer achieved high iodine and methylene blue indices of 348.05 mg/g and 74.87 mg/g, respectively. Characterization (XRD, FTIR, SEM, TGA) confirmed the formation of amorphous aluminosilicate phases and a dense matrix structure favorable for adsorption. Batch adsorption experiments revealed a maximum MB adsorption capacity of 12.63 mg/g, best described by the Langmuir isotherm and pseudo-second-order kinetic model, suggesting monolayer chemisorption. These results highlight the potential of this low-cost, waste-derived geopolymer as an efficient adsorbent for dye removal, promoting both environmental sustainability and circular economy principles.