Scanning electron microscopy with energy dispersive X-ray analysis of a uranium-bearing particle in soil from the study site, showing the uranium morphology and distribution of associated elements. Source: Nature Materials Degradation

Arsenic may be a toxic element, but it prevents uranium from an abandoned uranium production mine in the UK from migrating into rivers and groundwater. The discovery made by an international research team at the abandoned South Terras mine in Cornwall, England, could aid in the remediation of former uranium mines and other radioactively contaminated areas.

Topsoil samples from the study site were assayed by synchrotron X-ray microscopes to isolate microscopic uranium particles and determine their chemical composition and mineral species. Ore extraction operations and natural weathering of rock at the mine has led to the accumulation of other elements during degradation, particularly arsenic and beryllium, which were measured in significant concentrations. The arsenic and uranium were found to have formed the highly insoluble secondary mineral metazeunerite.

As a result of the complex environmental conditions brought about by the combined degradation of uranium ores and granitic lithologies at South Terras, arsenic contamination benefits the attenuation of uranium through direct precipitation of metazeunerite and metatorbernite, a copper uranyl phosphate in solid solution.

To identify this remediation mechanism at other sites, where arsenic and uranium are key co-contaminants, further detailed mineralogical assessments are required. These should be considered as an essential input to understand the ultimate environmental fate of degraded uranium ore.

Scientists from University of Sheffield and Atomic Weapons Establishment plc, both in the UK; Brookhaven National Laboratory in Upton, New York; and Paul Scherrer Institute in Villigen, Switzerland, participated in this research, which is published in the journal Nature Materials Degradation.