Investigation of elements (U, V, Sr, Ga, Cs and Rb) leaching and mobility in uranium-enriched coal ash with thermochemical treatment

Abstract Uranium and other trace elements in coal ash have received a significant attention as the beneficial reuse of hazardous wastes. In this study, combined with X-ray diffraction, field emission scanning electron microscope-energy dispersive spectroscopy and other analyses, thermochemical treatment (sodium hydroxide) and leaching trial (water, alkaline and acid solution) were conducted to evidence that elements are selectively encapsulated in Si–Al glass, eutectic and Fe-enriched fraction during combustion leading to a low extraction efficiency. Thereinto, comparing the main host of V, Cs, Rb and Sr in Si–Al glass, there are 47%, 45% and 8% of U encapsulated with Si–Al glass, eutectic and Fe-enriched fraction, while 59% of Ga remains in Si–Fe-enriched residue. Different from the large extraction of V, Cs, Rb and Ga followed by the removal of Si–Al glass and water leaching, U and Sr remained in residue with a high mobility. Overall, the leaching efficiencies of U, V, Cs, Rb, Ga and Sr were significantly improved and up to 92%, 100%, 74%, 78%, 41% and 98% respectively at the condition of NaOH/ash = 1.5, 500 °C and 1 h. Hence, it is necessary to properly handle the leachate also residue due to their potential environmental implications when the ash is employed to synthesize advanced materials.