Metal separation by supercritical carbon dioxide extraction method. Application in nuclear technology

Principle, characteristics and application in nuclear technology of a supercritical CO2 leaching method are explained. This method is able to separate metals from solid using supercritical CO2 with reactant. Mixed fluid of reactant and supercritical CO2 is admitted into a reactor containing sample with metal compounds. The metal compounds react with the reactant to form metal complexes, which are dissolved into the supercritical CO2. The supercritical CO2 with metal complexes leads to recovery container, where the supercritical CO2 becomes carbon dioxide gas and the metal complexes precipitate and are collected under atmosphere pressure. The characteristics of the method are 1) a small amount of waste are produced in order not to use any acid solution at pretreatment and separation solvent, 2) metals are taken out rapidly and with high efficiency of solid, because supercritical CO2 can diffuse and penetrate into pore of sample, 3) clean and dry solid is obtained after removing the metals, 4) metals can be easily collected and CO2 can be recycled. As an application of the method, for example, uranium oxides (UO2 and U3O8) are separated from sand, HNO3-TBP complex is used as reactant and all procedures are repeated two times. Almost uranium was separated from sand. However, in the case of mixture of uranium oxides and sea sand, the uranium complexes can not be solved into supercritical CO2 under the condition of the pressure of less than 15 MPa. (S.Y.)