Surface mining for rare earth elements used in smartphones and wind turbines is difficult and rarely done in the United States. Scientists wanted to know if they could pull the metals, present at trace levels, from geothermal brines using magnetic particles. The particles, wrapped in a molecular framework shell known as a metal-organic framework, or MOF, should easily trap the metals and let the rest flow past. However, the team led by Pete McGrail at Pacific Northwest National Laboratory found the magnetic strength dropped by 70 percent after the MOF shell was formed.
The use of MOFs may allow for the separation of yttrium, scandium, and other elements from saline water from geothermal sources, produced waters from oil and gas fields, or wastes such as fly ash.
The team showed that the chromium penetrated into the pores in the iron particles and was reduced by capturing an electron from the iron thus oxidizing it. The magnetic strength of magnetite is strongly determined by the amount of ferrous versus ferric (oxidized) iron in the material. The iron oxidation thus degraded the magnetic properties. These fundamental insights will allow materials science researchers to adjust the MOF chemistry to prevent the unwanted oxidation-reduction reactions and better retain the core-shell material's magnetic properties.
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Sameh K. Elsaidi et al. Reduced Magnetism in Core–Shell Magnetite@MOF Composites, Nano Letters (2017). DOI: 10.1021/acs.nanolett.7b03451
Sameh K. Elsaidi et al. Reduced Magnetism in Core–Shell Magnetite@MOF Composites, Nano Letters (2017). DOI: 10.1021/acs.nanolett.7b03451