In California, the mining and processing of mineral resources such as gold and silver ore deposits has resulted in large volumes of metal(loid)-bearing mine wastes, including arsenic, which remain largely untreated and exposed, threatening the health of humans and the environment. Determining the chemical speciation and bioaccessibility of arsenic in mine wastes is critical to assessing the potential toxicity. Bioaccessibility is dependent on physical and chemical properties of the waste materials, such as particle size, surface area, initial arsenic concentration, arsenic speciation, and arsenic spatial distribution; however, the relative contribution of each of these factors is insufficiently understood. This study examines the spatial distribution and speciation of arsenic on mine tailing particles and their relationships with particle size and resulting bioaccessibility with the hypothesis that more bioaccessible arsenic species may be found more commonly as surface-bound and as low-concentration, homogenous distribution forms, in smaller particle size fractions. Also, the prediction that the less bioaccessible species may be found more commonly in encapsulated form, in larger particle size fractions. X-Ray absorption spectroscopy and X-Ray fluorescence techniques that target arsenic species were applied to analyze size-sorted mine-tailing samples collected from several sites of the Empire Gold Mine, Grass Valley, CA, USA. 30 µm thin sections of selected size-sorted samples were prepared for µXRF analysis at Stanford Synchrotron Radiation Lightsource. XRF maps of the thin sections, contrasting As and Fe, were produced to study the relationships between arsenic’s spatial distribution and its chemical speciation. EXAFS analysis was also conducted on bulk ground and unground tailing samples before and after leach extraction tests with simulated gastric fluid. Linear combination fitting of EXAFS data was employed to characterize the arsenic species existing in these mine tailings. Analysis of µXANES data visualized in XRF maps reveals the arsenic species present as encapsulated, homogenous, or surface bound with respect to particle distribution. Insights in these relationships should enable us to produce more comprehensive assessments of short- and long-term potential health hazards caused by the various arsenic species and their potential toxicity, which can help inform the remediation of arsenic-contaminated environments.

EXAFS and µXRF analysis of arsenic speciation and spatial distribution in mine tailings: Implications for physical weathering, bioaccessibility, and remediation

255th National Meeting (2018)

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