Utilization of Sugar Beet Pulp as Biosorbent for Molassigenic Metal Ions: Kinetic Study of Batch Biosorption

Abstract

The sugar industry is facing problems with high amount of molassigenic metal ions remained after the purification step in sugar juice. In this investigation the application of unmodified sugar beet pulp as a weak monofunctional cation-exchange biosorbent for molassigenic metal ions (Na⁺, K⁺ and Ca²⁺) removal from the alkalized sugar juice was studied. The batch biosorption experiments were performed at temperature (70 °C) and pH (10.5) of alkalized sugar juice similar to industrial conditions. The highest removal efficiency was noticed for divalent Ca²⁺ (30.2%), while monovalent Na⁺ and K⁺ ions were removed with 10.9 and 9.1% efficiency, respectively. Biosorption equilibrium was established in 90 min for all tested metals. Sugar beet pulp characterization from the perspective of cation-exhange material was conducted. The structure of the biosorbent and an insight of the functional groups were also characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The biosorption data were analyzed using four non-linear kinetic (pseudo-first order, pseudo-second order and Elovich) and diffusion models (Weber-Morris). The time course data of biosorption processes fitted well to the pseudo-first and the pseudo-second-order kinetic models indicating ion-exchange and chemisorption as dominant mechanisms for metal ions removal from the alkalized juice. HNO₃ as a desorption reagent showed the highest average molassigenic metal ions desorption efficiency (54.4%). Utilization of sugar beet biomass as cation-exchange material imposes as a potential solution for more successful sugar juice purification.