Optimizing the removal of color and impurities from sugar beet syrup using bentonite/iron oxide nanocomposite

Abstract Efficient removal of colorants and impurities is a crucial step in the sugar industry to ensure high-quality final products and to minimize operational costs. This study investigates the performance of a magnetic bentonite/iron oxide nanocomposite for removing color-forming compounds from beet sugar syrup under laboratory conditions. Iron oxide nanoparticles were synthesized using the co-precipitation method and subsequently immobilized onto bentonite. The main operating parameters, including contact time, adsorbent dosage, pH, and temperature, were optimized using response surface methodology (RSM). Characterization by FTIR, XRD, and SEM analyses confirmed the successful formation of the magnetic nanocomposite and its suitable surface properties for adsorption. The results showed that acidic conditions (around pH 5) significantly improved both decolorization efficiency and syrup clarity. Optimization results indicated that the optimal conditions were pH 5, a temperature of 80 °C, a contact time of 200 min, and an adsorbent dosage of 2.36 g L⁻¹. Under these conditions, the process followed the pseudo-second order kinetic model (R² = 0.981) and the Freundlich isotherm model (R² = 0.949), indicating a chemisorption-dominated process on a heterogeneous surface. Increasing the adsorbent dosage enhanced decolorization efficiency; however, exceeding the optimal dosage slightly reduced syrup clarity due to particle aggregation. Overall, the results indicate that the magnetic bentonite/iron oxide nanocomposite has considerable potential as a magnetically recoverable adsorbent for the sustainable purification of sugar beet syrup, although further pilot-scale and industrial-scale investigations are recommended to evaluate its long-term applicability.