Zinc Alginate Beads as an Effective Biosorbent for the Removal of Eosin-B from Aquatic Solutions: Equilibrium, Kinetics, and Thermodynamic Behaviors

Spherical alginate-based hydrogels have been applied for environmental pollutants removal from aqueous solutions. In this study, zinc alginate beads were prepared using an ionotropic gelation process. The wet hydrogels prepared in various operational conditions were studied to remove eosin-B dye. The effect of operational variables such as pH, initial concentration of eosin-B, contact time, dose of synthesized hydrogel beads, and environmental temperature on the eosin-B removal process was evaluated. The maximum dye removal efficiency was obtained by zinc alginate biosorbent at pH = 3, contact time of 40 min, and 35 mg of biosorbent dose. The maximum adsorption capacity of zinc alginate beads for eosin-B uptake was 53.48 mg/g of biosorbent. The mechanism, kinetics, isotherms, and thermodynamic studies of eosin-B sorption by zinc alginate hydrogels were investigated. Based on the results, the biosorption process follows pseudo-second-order kinetics. The experimental data of the biosorption process are matched with the Langmuir isotherm model, suggesting that monolayer adsorption plays a vital role in the analyte biosorption. According to the thermodynamic studies, the parameters ∆H° (+4679.12 J.mol-1), ∆G° (from -173.45 to -499.13 J.mol-1), and ΔS° (+16.284 J.mol-1.K-1) confirmed the endothermic, spontaneity and randomness of the biosorption process, respectively. This study shows that zinc alginate can be a suitable biosorbent for removing eosin-B from aqueous solutions.