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Accueil du site → Doctorat → États-Unis → 2010 → Effects of mineral weathering and plant roots on contaminant metal speciation and lability in arid lead-zinc sulfide mine tailings at the Klondyke Superfund Site, Graham County, AZ

University of Arizona (2010)

Effects of mineral weathering and plant roots on contaminant metal speciation and lability in arid lead-zinc sulfide mine tailings at the Klondyke Superfund Site, Graham County, AZ

Hayes, Sarah M.

Titre : Effects of mineral weathering and plant roots on contaminant metal speciation and lability in arid lead-zinc sulfide mine tailings at the Klondyke Superfund Site, Graham County, AZ

Auteur : Hayes, Sarah M.

Université de soutenance : University of Arizona

Grade : Doctor of Philosophy (PhD) 2010

Résumé partiel
Historic mine tailings pose a significant health risk to surrounding ecosystems and communities because of high residual concentrations of contaminant metals. The initial tailings mineral assemblage, metal sulfides, silicates, and carbonates are unstable at earth surface conditions and undergo oxidative and proton-promoted weathering. The weathering of metal sulfides generally produces acid that, if not balanced by protonconsuming dissolution of silicates and carbonates, leads to progressive acidification. The Klondyke State Superfund Site in Graham County, Arizona contains high concentrations of Pb (up to 13 g kg⁻¹) and Zn (up to 6 g kg⁻¹), and remains unvegetated 50 years after mining cessation. Field-scale investigation revealed a wide range of pH (2.5-8.0) and plant-available (DTPA-extractable) metals in the near surface of the tailings pile. Four samples were chosen for in-depth characterization ranging in pH, as denoted by subscript, from 2.6 to 5.4. The mineral transformations occurring in these four samples were investigated using a variety of techniques and the data indicated an increase in tailings weathering extent with increasing acidification (decreasing pH). Lead speciation, studied by a combination of chemical sequential extraction and X-ray absorption fine structure (XAFS) spectroscopy, was found to vary with tailings depth. The principle lead-bearing mineral was plumbojarosite (PbFe₆(SO₄)₄(OH)₁₂), with smaller amounts of anglesite (PbSO₄) and lead-sorbed iron-oxide. Anglesite, the most bioavailable mineral form of Pb in the tailings, was found to accumulate at the tailings surface, which has important implications for health risks.

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Page publiée le 15 mai 2011, mise à jour le 11 décembre 2019