The Geosciences Research Program supports research aimed at developing an understanding of fundamental Earth processes that can be used as a foundation for efficient, effective, and environmentally sound use of energy resources, and provide an improved scientific basis for advanced energy and environmental technologies.

Minerals as semiconductors: Dissolution and precipitation coupled with electron transfer in hematite crystals

Image of fulvic acid macromolecule

Precipitation of large hematite pyramids (e) on reacted (001) surface [(a) shows unreacted surface – AFM image].
Experiments conducted by Kevin Rosso and Svetlana Yanina at Pacific Northwest National Laboratory demonstrate that simultaneous precipitation and dissolution reactions occurring on distinct crystal surfaces are linked by electron transfer occurring through the bulk mineral. Natural hematite crystals (Fe2O3) were tested in several electrolyte solutions and were observed to have new crystal growth on the basal crystal face and dissolution on all other exposed crystal faces. The process was determined to require electron transport through the bulk crystal between these distinct mineral surfaces, with one face acting as an anode and another as a cathode. When either of the two types of faces was isolated from the reactive solution only dissolution was observed to occur. The definitive experiment involved two crystals that were joined with an electrical conductor, with one crystal having only basal faces exposed, and the other with only alternate sides exposed to the solution. These electrically connected crystals proved to behave as a single entity with one crystal face growing and one dissolving.  Bulk crystal conduction is likely to be important in many types of metals and semiconducting minerals or materials exposed to corrosive or even mildly reactive natural environments. For more details, see the Highlights page.

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