Synthesis and characterization of a multifunctional Fe3O4@Mn-MOF@Bentonite nanocomposite for efficient Ca2+ removal from clarified sugar beet juice

Abstract Residual Ca 2+ in clarified sugar beet juice can interfere with downstream processing by promoting scale formation and adversely affecting heat transfer, evaporation, and crystallization. In this study, a magnetic Fe 3 O 4 @Mn-MOF@bentonite nanocomposite was synthesized, characterized, and evaluated for Ca 2+ removal from clarified sugar beet juice. FTIR, XRD, SEM, and TGA analyses confirmed the formation of the hybrid material and its constituent phases. Batch adsorption experiments were conducted to investigate the effects of pH, temperature, adsorbent dosage, contact time, and initial Ca 2+ concentration. Under the optimized conditions, a Ca 2+ removal efficiency of 74.40% was obtained at pH 8.0 and 80 °C after 30 min. The adsorption proceeded rapidly during the initial stage, reaching 64.0% removal within 5 min and 74.40% after 30 min, with an experimental adsorption capacity of 471.4 mg/g at 40 min. Kinetic analysis showed that the pseudo-second-order model provided the best fit to the experimental data, with a calculated equilibrium capacity of 485.437 mg/g. The equilibrium data were better represented by the Langmuir model than by the Freundlich model, yielding a calculated maximum adsorption capacity of 699.301 mg/g. The R L values of 0.0571–0.1587 and 1/ n = 0.169 indicated favorable Ca 2+ adsorption. Thermodynamic analysis revealed an endothermic and spontaneous process, with ∆H of 73.33 kJ/mol, ∆S of 243.45 J/mol.K, and ∆G values ranging from − 78.60 to − 85.90 kJ/mol. The porous surface observed by SEM, together with the complementary functionalities of bentonite and Mn-MOF and the magnetic responsiveness imparted by Fe 3 O 4 , contributed to the overall adsorption performance. These results demonstrate the potential of Fe 3 O 4 @Mn-MOF@bentonite as an effective and magnetically recoverable adsorbent for Ca 2+ removal from clarified sugar beet juice.