U.S. Department of Energy

Pacific Northwest National Laboratory

Journal Article Shares New Insights into Stability, Dissolution of Aluminium Minerals

A PNNL research team’s work could inform better methods for metal processing and the nuclear fuel cycle, including strategies for treating radioactive waste on the Hanford Site. Specifically, the research, recently published, examined stability and dissolution mechanisms of boehmite and gibbsite, two layered aluminium oxyhydroxide minerals present in Hanford tank waste that pose processing challenges.

The team’s findings, outlined in the article “Importance of Interlayer H Bonding Structure to the Stability of Layered Minerals,” were published October 16 in Scientific Reports. The work was funded through PNNL’s Nuclear Process Science Initiative.

The researchers used electron irradiation, via liquid cell electron microscopy (LCEM), to probe the importance of interlayer hydrogen bond ordering to two-dimensional layered mineral stability and dissolution mechanisms in the minerals. LCEM can reveal dissolution mechanisms in a way that the traditional electron microscopy methods cannot, but to date the tool has been used largely to study nucleation and crystal growth.

The team exploited the often-undesirable effects of electron beam irradiation to drive dissolution in the mineral boehmite, which doesn’t readily dissolve. The effort provided unprecedented insight into the mineral’s dissolution mechanism, showing that dissolution proceeds via a three-step process. Further, experiments controlling radiation intensity and concentration of radiolytic species found that direct irradiation drives dissolution.

The team also compared boehmite with the non-dissolving gibbsite, as well as iron-doped boehmite, to consider whether slight changes in ordering of interlayer oxyhydoxide terminal groups affect the capacity to accommodate hydrogen loss without structural destabilization and dissolution.

The multi-directorate team included Michele Conroy (former PNNL staff member); Jennifer Soltis, Xin Zhang and Eugene Ilton, all of the Physical and Computational Sciences Directorate; Rick Wittman, National Security Directorate; and Frannie Smith, Dev Chatterjee and Edgar Buck, all of the Energy and Environment Directorate.

Photo on front page: LCEM imaging showing Boehmite particles.

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