Adsorption Of Uranium (Ⅵ) By Immobilized Fungi Beads

Uranium mining and metallurgical waste waters are considered to be the majorsources of uranium contamination. Uranium (VI) is soluble and mobile and itsaccumulation in water will have tremendous impact on environment. Furthermore, theuranium compounds can enter into human bodies through food chain and cause severedamage to their kidney and even cause them to die. Studies have shown that thebiosorption is one of the economic and effective methods in treating the uranium pollutionand microbial biomass can serve as efficient and safe biosorbent.In the present research, the immobilized Aspergillus niger powder beads wereobtained by entrapping nonviable A. niger powder into Ca-alginate gel. The effects of pH,contact time, initial uranium (VI) concentration and biomass dosage on the biosorption ofuranium (VI) onto the immobilized A. niger powder beads from aqueous solutions wereinvestigated in a batch system. In order to determine the adsorption characteristics,Langmuir, Freundlich and Redlich-Peterson adsorption isotherms were applied to theadsorption data. Lagergren pseudo-first, pseudo-second order models and intraparticlediffusion equation were used to test the experimental data involved in the biosorption ofuranium (VI) onto the immobilized A. niger powder beads at30℃. The thermodynamicparameters such as variations of enthalpy ΔH~o, entropy ΔS~o and variation of Gibbs freeenergy ΔG~o were calculated from the slope and intercept of ln Kdvs.1/T plots. Scanningelectron microscopy (SEM) coupled with EDX was used to analyze the immobilized A.niger powder beads before and after biosorption treatment.The results suggested that Ca-alginate immobilization has clearly improved uraniumbiosorption capacity. The biosorption process was highly pH dependent, the optimal pHwas5.0and reached equilibrium in9h. Biosorption equilibrium data were agreeable with Langmuir isotherm model and the maximum biosorption capacity of the beads for uranium(VI) was estimated to be649.4mg/g at30°C. The biosorption kinetics followed thepseudo-second order model and intraparticle diffusion equation. The variations in enthalpy(26.45kJ/mol), entropy (0.167kJ/mol K) and Gibbs free energy were calculated from theexperimental data. SEM and EDS analysis indicated that the beads have strong adsorptioncapability for uranium (VI). The adsorbed uranium (VI) on the beads could be releasedwith HNO3or HCl. The results showed that the immobilized A. niger powder beads hadgreat potential for removing and recovering uranium (VI) from aqueous solutions. And theimmobilized A. niger powder beads could be suitable as a sorbent material for adsorptionand removal of uranium from aqueous solution.