Mi Li

Immobilization of uranium into magnetite from aqueous solution by electrodepositing approach

Immobilization of uranium into magnetite (Fe3O4), which was generated from metallic iron by electrochemical method, was proposed to rapidly remove uranium from aqueous solution. The effects of electrochemical parameters such as electrode materials, voltage, electrode gap, reaction time and pH value on the crystallization of Fe3O4 and uranium removal efficiencies were investigated. More than 90% uranium in the solution was precipitated with Fe3O4 under laboratory conditions when uranium concentration range from 0.5mg/L to 10mg/L. The Fe3O4 crystallization mechanism and immobilization of uranium was proved by XPS, XRD, TEM, FTIR and VSM methods. The results indicated that the cationic (including Fe2+, Fe3+ and U(VI)) migrate to cathode side under the electric field and the uranium was incorporated or adsorbed by Fe3O4 which was generated at cathode while the pH ranges between 2-7. The uranium-containing precipitate of Fe3O4 can exist stably at the acid concentration below 60g/L. Furthermore, the precipitate may be used as valuable resources for uranium or iron recycling, which resulted in no secondary pollution in the removal of uranium from aqueous solution.

Uranium adsorption and subsequent re-oxidation under aerobic conditions by Leifsonia sp. - Coated biochar as green trapping agent

It has generally been assumed that the immobilization of U(VI) via polyphosphate accumulating microorganisms may present a sink for uranium, but the potential mechanisms of the process and the stability of precipitated uranium under aerobic conditions remain elusive. This study seeks to explore the mechanism, capacity, and stability of uranium precipitation under aerobic conditions by a purified indigenous bacteria isolated from acidic tailings (pH 6.5) in China. The results show that over the treatment ranges investigated, maximum removal of U(VI) from aqueous solution was 99.82% when the initial concentration of U(VI) was 42 μM, pH was 3.5, and the temperature was with 30 °C much higher than that of other reported microorganisms. The adsorption mechanism was elucidated via the use of SEM-EDS, XPS and FTIR. SEM-EDS showed two peaks of uranium on the surface. A plausible explanation for this, supported by FTIR, is that uranium precipitated on the biosorbent surfaces. XPS measurements indicated that the uranium product is most likely a mixture of 13% U(VI) and 87% U(IV). Notably, the reoxidation experiment found that the uranium precipitates were stable in the presence of Ca2+ and Mg2+, however, U(IV) is oxidized to U(VI) in the presence of NO3- and Na+ ions, resulting in rapid dissolution. It implies that the synthesized Leifsonia sp. coated biochar could be utilized as a green and effective biosorbent. However, it may not a good choice for in-situ remediation due to the subsequent re-oxidation under aerobic conditions. These observations can be of some guiding significance to the application of the bioremediation technology in surface environments.

The treatment of U-containing wastewater by electro-deposition

Abstract. A new method for treating U-containing wastewater and recovering of uranium simultaneously by electro-deposition was proposed. The complexity of adsorbent preparation and difficulty in uranium recovery that existed in traditional adsorption method are solved by electrodeposition approach. The iron and graphite are used as anode electrode and cathode electrode in this experiment, respectively. The innovative view in this study is to promote the rapid generation of magnetite stemmed from iron dissolution under direct current. The uranium is incorporated or adsorbed to the magnetite through accurate controlling experimental conditions. The effects of initial U-concentration, voltage, electrode spacing, ion concentration, pH value on uranium removal efficiencies were investigated. Uranium removal efficiencies reached 83.5% under laboratory conditions that uranium concentration at 10mg/L, voltage at 30V, electrode spacing at 5 cm, ion concentration at 3 g/L, at pH 3.45. It is the advantages of U-containing magnetic is easily separated from aqueous solution and can be utilized as secondary low grade uranium deposit after treatment that making this method has a bright prospect.

Extraction of uranium from tailings by sulfuric acid leaching with oxidants

Recovery of uranium have been performed by leaching uranium-containing tailings in sulfuric acid system with the assistance of HF, HClO4, H2O2 and MnO2. The effect of reagent dosage, sulfuric acid concentration, Liquid/solid ratio, reaction temperature and particle size on the leaching of uranium were investigated. The results show that addiction of HF, HClO4, H2O2 and MnO2 significantly increased the extraction of uranium under 1M sulphuric acid condition and under the optimum reaction conditions a dissolution fraction of 85% by HClO4, 90% by HF, 95% by H2O2 can be reached respectively. The variation of technological mineralogy properites of tailings during leaching process show that the assistants can break gangue effectively. These observations suggest that optimum oxidants could potentially influence the extraction of uranium from tailings even under dilute acid condition.