Nicholas Buchanan

Mentor

Jon Chorover, PhD

Department

Environmental Sciences

Abstract

Subsurface geochemistry dynamics investigated with specific and sequential extraction of solid phases during active phytostabilization of Iron King Mine Tailings.

Legacy mine tailings in semiarid environments present significant health risks to nearby communities from off-site wind and water transport of toxic fugitive dusts. Without remediation, tailings can remain barren, providing a point-source of toxic metal(loids).  Phytostabilization of mine tailings has been implemented as a successful mitigation strategy to reduce exposures of arsenic, zinc, and lead at the Iron King Mine Dewey-Humboldt Smelter Superfund site (IKMHSS) in central AZ, a National Priorities List Site since 2008. The site has generated significant University of Arizona Superfund Research Program (UA SRP) involvement including field and greenhouse studies. Although plant growth on the tailings has successfully decreased wind dispersion, questions remain about the subsurface mineralogical and geochemical dynamics and As, Pb, and Zn lability in response to compost-assisted phytostabilization. A mesocosm greenhouse study investigated the subsurface effects with unamended control tailings, composted amended (15 wt%), and compost amended with seeds of buffalo grass (Bouteloua dactyloide) or quail bush (Atriplex lentiformas). Core samples were collected throughout the experiment to characterize tailing geochemical dynamics by sequential extraction of specific solid-phase pools, and targeted phases were confirmed by X-ray diffraction. We show that the phytostabilization imposed disequilibrium, which alters the species, fate, and bioavailability of toxic metal(loid)s, results in a time dependent removal of efflorescent salts, an increase in crystalline iron phases, an increase in soluble (bioaccessible) zinc, and had no significant effect on contaminant pools of arsenic. This mesocosm-scale study is helping to understand the subsurface temporal changes in contaminant lability promoted by biogeochemical weathering in response to phytostabilization.