Distinguishing secondary uranium mineralizations in uranium ore using LIBS imaging

The main aim of this work is to demonstrate the potential of LIBS as a complementary technique to electron probe microanalysis (EPMA) for distinguishing and characterizing uranium mineralizations. Combining both methods can help estimate uranium oxidation states and monitor the possible mobilization of uranium in the environment by detecting oxygen and hydrogen using LIBS. It was confirmed that the LIBS signal of oxygen is proportional to oxygen content and that the strength of the oxygen signal is closely related to the oxidation state of uranium. The second assumption that the hydrogen signal is closely related to water (or hydroxyl group) content was also confirmed by detecting a stronger hydrogen signal from the presumed secondary mineralization. In contrast, hydrogen was not found in uraninite and quartz. When superimposed, images obtained with LIBS and EPMA show a clearly visible contrast between primary and secondary uranium mineralizations. Images of uranium obtained with the two techniques match perfectly, while the LIBS image of oxygen confirms the presence of an oxidized form of secondary uranium minerals (uranophane). The LIBS image of hydrogen clearly shows mineral phases containing water or a hydroxyl group, confirming that uranophane and other associated minerals contain greater amounts of hydrogen (water).