Arsenic and antimony speciation of historical roaster waste samples from the Giant Mine, Yellowknife, Canada

Lum, Jullieta; McBeth, Joyce; Lindsay, Matthew B.J.; Jamieson, Heather E.; Walls, Mary; Schoepfer, Valerie A.; Radková, Anežka Borčinová

doi:10.7185/gold2021.6595

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“…65 Linear-combination fitting of the XANES spectra (XANES-LCF) was conducted in ATHENA from 20 eV below to 30 eV above the As K-edge. 66 Arsenate and arsenite adsorbed to ferrihydrite were considered as references in XANES-LCF because ferrihydrite is a common sorbent of As in soils and is likely a dominant Fe-(oxyhydr)oxide phase in organic-rich permafrost terranes where active Fe-redox recycling occurs. 16 Arsenite and arsenite adsorbed on sphagnum moss were also considered in XANES-LCF, but ultimately not retained in the models because (1) they did not appreciably improve the quality of fits; (2) they did not change the overall apportioning of As oxidation states with the typical LCF error (∼10%); and (3) μ-XRF analyses revealed that the majority of As was spatially associated with Fe.…”

Section: Laboratory Analysesmentioning

confidence: 99%

Arsenic Mobilization from Thawing Permafrost

Skierszkan,

Schoepfer,

Fellwock

et al. 2024

ACS Earth Space Chem.

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Thawing permafrost releases labile organic carbon and alters groundwater geochemistry and hydrology with uncertain outcomes for the mobility of hazardous metal(loid)s. Managing water quality in thawing permafrost regions is predicated on a detailed understanding of the speciation and abundance of metal(loid)s in permafrost soils and porewaters produced during thaw, which remains limited at present. This study contributes new knowledge on the sources and fate of arsenic during the thaw of organic-rich permafrost using samples collected from a subarctic permafrost region associated with geogenic arsenic (Dawson Range, Yukon, Canada). Several permafrost cores and active-layer samples from this region were analyzed for their solid-phase and aqueous geochemical characteristics and their arsenic speciation. Porewaters were extracted from permafrost cores after thaw under anaerobic conditions for aqueous geochemical analyses. Bedrock samples from the field site were also analyzed for arsenic speciation and mineralogy. X-ray diffraction and X-ray near-edge spectroscopy (XANES) analyses of weathered bedrock upgradient of soil sampling locations contained arsenic(V) hosted in iron-(oxyhydr)oxides and scorodite. XANES and micro X-ray fluorescence analyses of permafrost soils indicated a mixture of arsenic(III) and arsenic(V), indicating redox recycling of arsenic. Soil-bound arsenic was colocated with iron, likely as arseniferous iron-(oxyhydr)oxides that have been encapsulated by aggrading permafrost over geologic time. However, permafrost thaw produced porewater containing elevated dissolved arsenic (median 40 μg L −1 , range 2−96 μg L −1 ). Thawed permafrost porewater also contained elevated dissolved iron (median 5.5 mg L −1 , range 0.5−40 mg L −1 ) and dissolved organic carbon (median 423 mg L −1 , range 72−3240 mg L −1 ), indicative of reducing conditions. This study highlights that arsenic can be found in reactive forms in permafrost soil, and that its thaw can release arsenic and iron to porewater and produce poor water quality.

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Section: Laboratory Analysesmentioning

confidence: 99%