Biosorption Mechanisms Of Uranium(?) By Saccharomyces Cerevisiae And Aspergillus Niger

Uranium is one of the most important radioactive elements in the developing nuclear industry.In order to prevent it diffusion, it is imminent to explore an effective method to deal with the increasing of the radioactive uranium pollution in the environment. Compared with the traditional disposal methods, biosorption takes the advantage of low cost and high efficiency has received widespread attention. Using the waste mycelium of the fermentation industry to adsorption the radioactive uranium pollution, it will not only reduce the production cost of the adsorbent, but also can better realize the industrial application, achieving the purpose of using waste to treat waste.Based on the two kinds of fungi (Saccharomyces cerevisiae and Aspergillus niger), the study focuses on the following two parts.1.The biosorption capacity and mechanisms of uranium(VI) by live and heat-killed Saccharomyces cerevisiae were investigated in this part. The results indicated that the optimal uranium adsorption pH was observed at 5.5 and 4.5 for live and heat-killed cells, respectively.Compared with the heat-killed cells, the live cells were affected by temperature changes significantly, and the optimal biosorption temperature for live cells was 26 ?. Under the same adsorption condition, the biosorption capacity of heat-killed cells was almost one order of magnitude higher than the live one under the acidic pH conditions. The adsorption process of heat-killed cells was fast and stable, while the live one was a relatively slow process which including the metabolism of complex life process.The kinetic investigations showed the biosorption process were well described by the Pseudo-second order model (with the linear correlation more than 0.99) at different temperatures for both live and heat-killed cells, indicating that the shared electronic or electron transfer were involved in the biosorption process. The SEM-EDS (Scanning electron microscopy- X-ray energy dispersive spectrum) results showed that the live cells were sunken and the surfaces were unevenly covered with little uranium precipitation after the biosorption. While the heat-killed cells which had gone through the high temperature and pressure, the surface of heat-killed cells had increased, and plenty of nano-particle of uranium precipitated on it. The FTIR spectrum (Fourier transform infrared) illustrated that the -OH?C=O?N-H?C-N played important roles in the interaction process between live cells and uranium ions, while the ketone carbonyl and HPO42-were important for heat-killed cells.2?The "CMCC(F)-98003" Aspergillus niger was used as biosobent in this part to investigate the adsorption behavior and mechanisms between the adsorbent and uranium ions. The optimal uranium adsorption pH by A.niger was observed at 5.5. When the initial uranium concentration was 0.75 mg/L, the maximum uranium adsorption capacity reached 12.5 mg/g. Under different concentration of biomass,the experimental data was well-fitted with the Freundlich model. The Dubinin-Radushkevish model showed that the adsorption free energy E were all less than 8 kJ/mol,indicating that the A.niger-uranium interaction was closely related to the physical adsorption process. Pseudo-second order model under different temperature fitted the kinetic results very well(R2>0.99), indicating that the chemical adsorption process was also related to the A.niger-uranium interaction. It could be comprehended that the chemisorption occupied the predominant process,and the physical effects enhanced the chemisorption.The biosorption process of uranium(VI) by A.niger was fast and stable, within 60 min the adsorption can reach the dynamic equilibrium under different temperature. The calculated thermodynamic parameters showed that the biosorption of uranium ions was endothermic and spontaneous (?H°>0, ?G°<0). The SEM results showed that the A.niger cells surface were uniformity covered with nano-particles of uranium precipitation after biosorption. The FTIR spectrum indicated the functional groups of -OH?-COOH?N-H?P043- were take part in the adsorption process. With the increasing of contact time between A.niger and uranium ions, X-ray diffraction spectrometry (XRD) results showed that the crystalline precipitation had been formed.