Distribution and mode of occurrence of uranium in bottom ash derived from high-germanium coals

The radioactivity of uranium in radioactive coal bottom ash (CBA) may be a potential danger to the ambient environment and human health. Concerning the limited research on the distribution and mode of occurrence of uranium in CBA, we herein report our investigations into this topic using a number of techniques including a five-step Tessier sequential extraction, hydrogen fluoride (HF) leaching, Siroquant (Rietveld) quantification, magnetic separation, and electron probe microanalysis (EPMA). The Tessier sequential extraction showed that the uranium in the residual and Fe–Mn oxide fractions was dominant (59.1% and 34.9%, respectively). The former was mainly incorporated into aluminosilicates, retained with glass and cristobalite, whereas the latter was especially enriched in the magnetic fraction, of which about 50% was present with magnetite (Fe3O4) and the rest in other iron oxides. In addition, the uranium in the magnetic fraction was 2.6 times that in the non-magnetic fraction. The experimental findings in this work may be important for establishing an effective strategy to reduce radioactivity from CBA for the protection of our local environment.

Graphic abstractEPMA image of the residual fraction and BSE images showing the distribution of related elements.The graphic abstract of this paper is the EPMA image of the residual fraction in the Tessier procedure, which can represent the distribution of uranium and related elements. It can be seen from this image that the distribution of uranium is consistent with Si, Al, Fe and O, which verifies that uranium exits with the Fe/Al/Si/O-rich phases in residual fraction. A statistical analysis with SPSS also shows that uranium in the residual fraction mainly has a high coefficient with Si, Al and Fe.Figure optionsDownload full-size imageDownload as PowerPoint slide