PNNL

Abstract

Chemical behavior at mineral-water interfaces is of fundamental importance to geochemistry, but for minerals that are natural semiconductors the pursuit of mechanistic understanding is uniquely challenging. We show that surface specific charge density accumulation reactions combined with bulk charge carrier diffusivity create conditions at which interfacial electron transfer reactions at one surface couple with those at another by a current through the crystal bulk. Using iron oxide as the example, we present measurements showing that chemically induced surface potential gradient across hematite (a-Fe2O3) crystals is sufficiently high and the bulk electrical resistivity is sufficiently low during reductive dissolution to link dissolution of edge surfaces to simultaneous growth of the basal plane. The finding defines a new characteristic of mineral-water interface behavior that is immediately generalizable to a host of naturally abundant semiconducting minerals playing varied key roles in soils, sediments, and the atmosphere.