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

摘要

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 degrees 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. (C) 2019 Elsevier Ltd. All rights reserved.