Removal of Th(IV) ions from aqueous solution using newly developed bicomponent bio-based adsorbents

An immobilized hybrid biosorbent (IHB) was prepared by hybridizing two biosorbents and evaluated for its ability to remove thorium ions from an aqueous solution. The combined effect of the initial pH of the solution (2 to 6), initial Th(IV) ion solution concentration (50 to 300 mg.L−1), IHB dose (0.5 to 5 g.L−1), and sorption duration (10-180 min) were investigated using central composite design (CCD). Experimental data were analyzed using Design Expert 8.0.6 software and fitted to a second order polynomial model with logarithm transform function. The adequacy of the model was verified using three indices, model analysis, coefficient of determination (R2), and the lack-of-fit test. The initial pH of the solution was determined as the most effectual factor on Th(IV) ions biosorption removal by using the analysis of variance (ANOVA). According to the obtained results, pH value of 4.5, initial metal ion concentration of 210 mg.L−1, IHB dose of 5 g.L−1, and sorption duration of 95 minutes were proven to be the optimum conditions, for maximum biosorption removal of Th(IV) ions from aqueous solutions. Thermodynamic parameters have been evaluated, and it has been determined that the sorption process is feasible in going forward with more products than reactants, exothermic in nature and the reaction is entropy-driven. The equilibrium data were analyzed by the Langmuir, Freundlich, and Temkin sorption isotherms. The maximum monolayer sorption capacity of the IHB was found to be 142.86 mg.g−1. Pseudo-second-order kinetics model provided a better fit for all the biosorption processes which let suppose a physical rate-limiting step for the process.