Tracing Molybdenum Attenuation in Mining Environments Using Molybdenum Stable Isotopes

Skierszkan, E.K.; Robertson, Jared; Lindsay, Matthew B.J.; Stockwell, Justin S.; Dockrey, John W.; Das, Soumya; Weis, Dominique; Beckie, Roger; Mayer, K. Ulrich

doi:10.1021/acs.est.9b00766

Cited by 27 publications

(8 citation statements)

References 70 publications

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“…The recorded waste-rock properties are in line with previous results from work conducted at the Antamina mine site: they confirm that some of the highly variable rock types may be potentially acid generating and show that elevated trace element levels can occur in various waste-rock types. 2,[52][53][54]63 Overall, solid-phase concentrations of As, Mo, Se, and Sb in the Antamina waste rock were elevated compared to natural backgrounds but not exceptional compared to previously recorded levels at other mine sites, i.e., compared to >10 000 mg/kg As in other tailings and waste rock 21,24 or Mo levels >1000 mg/kg in other tailings 68 and waste rock. 69 3.2.…”

Section: Acs Omegamentioning

confidence: 98%

Mobilization of Metal(oid) Oxyanions through Circumneutral Mine Waste-Rock Drainage

et al. 2019

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Most studies on the weathering of mine waste rock focus on the generation of acidic drainage with high metal concentrations, whereas metal(loid) release under neutral-rock drainage (NRD) conditions has received limited attention. Here, we present geochemical and mineralogical data from a long-term (>10 years) kinetic testing program with 50 waste-rock field barrels at the polymetallic Antamina mine in Peru. The weathering of most rock lithologies in the field experiments generated circumneutral to alkaline drainage (6 < pH < 9) but with concentrations of the oxyanion-forming metal(loid)s As, Mo, Se, and Sb in the mg/L range. The mobilization of As and Sb was particularly efficient from intrusive, marble and hornfels rocks that contained labile As- and Sb-sulfides, irrespective of bulk elemental content or waste-rock reactivity. High-alkalinity drainage from these materials sustained neutral-pH conditions that are unfavorable to oxyanion adsorption onto Fe-(oxyhydr)oxides and, therefore, enhanced As and Sb leaching. The release of Mo and Se from sulfidic skarn and intrusive waste rock was more proportional to elemental content but equally enhanced by pH-inhibited adsorption and negligible secondary mineral precipitation under NRD conditions. Our results demonstrate that oxyanion concentrations of environmental concern may be conveyed by neutral- to alkaline-pH waste-rock drainage and should be a focus of mine wastewater monitoring programs.

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Section: Acs Omegamentioning

confidence: 98%

Mobilization of Metal(oid) Oxyanions through Circumneutral Mine Waste-Rock Drainage

et al. 2019

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“…Adsorbed metals, metalloids or other elements such as As, , P, − and Mo , add an additional layer of complexity to Fe(II)-induced Fe(III) (oxyhydr)oxide transformations. Our current understanding of the fate of associated Mo during this transformation process is limited, despite the abundance of Mo in some Fe(III) (oxyhydr)oxide rich environments including those impacted by mining activities. ,, Previous studies have investigated ferrihydrite transformation under alkaline conditions (pH 8 and 10) , and elevated temperatures (75 °C) . These studies were conducted both with Fe(II) and without Fe(II), and are not broadly applicable.…”

Section: Introductionmentioning

confidence: 99%

Structural Incorporation of Sorbed Molybdate during Iron(II)-Induced Transformation of Ferrihydrite and Goethite under Advective Flow Conditions

Schoepfer

Qin

Robertson³

et al. 2020

ACS Earth Space Chem.

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Aqueous Fe(II) can induce recrystallization of ferrihydrite and goethite [α-FeOOH] to their more crystalline or molecularly homogeneous counterparts. Despite common association with these and other Fe(III) (oxyhydr)oxides, relationships between Fe(II)-induced transformation and Mo mobility remain poorly constrained. We conducted laboratory column experiments to examine repartitioning of sorbed Mo during Fe(II)-induced transformation of ferrihydrite and goethite under advective flow conditions. We first pumped (∼0.25 L d–1) artificial groundwater containing 0.1 mM MoO4 2– and buffered to pH 6.5 through columns packed with ferrihydrite- and goethite-coated sand until >90% Mo breakthrough was observed. Extended X-ray absorption fine structure (EXAFS) spectroscopy shows that initial Mo attenuation resulted from inner sphere complexation of MoO4 tetrahedra at ferrihydrite and goethite surfaces. We then pumped Mo-free anoxic artificial groundwater containing 0.2 mM or 2.0 mM Fe(II) through the columns until effluent Mo concentrations remained <0.005 mM. Raman spectroscopy shows that Fe(II) introduction induced transformation of both ferrihydrite and goethite to lepidocrocite. Additionally, Fe(II) introduction mobilized 4–34% of sorbed Mo and total mass release was greater for (i) ferrihydrite compared to goethite columns and (ii) low Fe(II) compared to high Fe(II) influent. Effluent pH decreased to ∼5.8 for columns receiving the high Fe(II) influent and returned to pH 6.5 after 5–10 pore volumes. EXAFS spectroscopy indicates that structural incorporation of MoO6 octahedra into neoformed phases contributes to Mo retention during Fe(II)-induced transformation. Our results offer new insight into Mo repartitioning during Fe(II)-induced transformation of Fe(III) (oxyhydr)oxides and, more generally, controls on Mo mobility in geohydrologic systems.

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“…Despite its critical role in biological systems, high Mo concentrations in drinking water and food can adversely affect human and animal health, respectively. , Excessive Mo exposure can trigger various responses in humans and ruminants, many of which are linked to Mo–S–Cu interactions that can lead to Cu deficiency. − The World Health Organization (WHO) in 1993 established a health-based guideline of 70 μg L –1 for drinking water based on health effects related to chronic Mo exposure, but later withdrew this formal guideline on the basis that Mo concentrations are generally low in drinking water supplies . Nevertheless, contamination by anthropogenic activities including mining and metallurgy, petroleum upgrading and refining, and fossil fuel combustion can produce dissolved Mo concentrations greatly exceeding the informal WHO health-based guideline for drinking water. − …”

Section: Introductionmentioning

confidence: 99%

“…Although biological uptake can influence dissolved Mo concentrations, interactions with inorganic and organic solids are principal controls on Mo mobility and bioavailability in geohydrologic systems. , Aqueous Mo concentrations are strongly controlled by pH- and redox-dependent reactions with Fe(III) (oxyhydr)oxides . Under oxic conditions, adsorption and coprecipitation reactions with Fe(III) (oxyhydr)oxides often limit MoO 4 2– concentrations in surface and groundwater systems. ,− Molybdate exhibits a strong affinity for ferrihydrite and goethite surfaces under acidic to neutral pH conditions and can readily displace PO 4 3– below pH 5. , Coprecipitation with ferrihydrite is highly effective at dissolved MoO 4 2– incorporation, with reported uptake capacities several times that of adsorption . Thermal transformation of ferrihydrite furthermore promotes incorporation of adsorbed and coprecipitated Mo(VI) into octahedral sites of neoformed hematite [α-Fe 2 O 3(s) ]. ,, …”

Section: Introductionmentioning

confidence: 99%

Molybdenum(VI) Sequestration Mechanisms During Iron(II)-Induced Ferrihydrite Transformation

Schoepfer

Lum

Lindsay

2021

ACS Earth Space Chem.

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Adsorption and coprecipitation reactions with Fe(III) (oxyhydr)oxides contribute to Mo(VI) attenuation within geohydrologic systems. Redox transitions within these systems can promote transformation of metastable phases, including ferrihydrite, and repartitioning of associated Mo(VI). Recent studies show that Mo(VI) coordination shifts from tetrahedral to octahedral during Fe(II)-induced ferrihydrite transformation. However, effects of initial conditions including solution pH, the Mo(VI) uptake mechanism, and Mo(VI) loading on repartitioning are not known. We performed batch experiments using ferrihydrite suspensions prepared with adsorbed or coprecipitated Mo(VI) (0, 25, and 100 μmol g–1) at two initial pH values (pH0; 5.0 and 6.5). We catalyzed ferrihydrite transformation under anoxic conditions by adding Fe(II)(aq) (0.5 mM) and monitored pH, [Mo]T, and [Fe]T over time. After 168 h, we collected reacted solids for analysis by powder X-ray diffraction (XRD), transmission electron microscopy-selected area electron diffraction (TEM-SAED), and Mo K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. XRD data indicate that bulk ferrihydrite transformation was limited in all but the pH0 6.5 coprecipitated Mo(VI) experiments. The TEM-SAED results reveal that nanoscale lepidocrocite and goethite formed at ferrihydrite surfaces in all experiments, whereas nanoscale bamfordite [FeMo2O6(OH)3·H2O] crystallites were observed in pH0 6.5 experiments. EXAFS models reveal changes in Mo(VI) coordination and bonding consistent with bamfordite precipitation combined with structural incorporation into neoformed goethite and lepidocrocite. Our results improve the understanding of Mo(VI) retention pathways in geohydrologic systems.

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Tracing Molybdenum Attenuation in Mining Environments Using Molybdenum Stable Isotopes

Cited by 27 publications

References 70 publications

Mobilization of Metal(oid) Oxyanions through Circumneutral Mine Waste-Rock Drainage

Mobilization of Metal(oid) Oxyanions through Circumneutral Mine Waste-Rock Drainage

Structural Incorporation of Sorbed Molybdate during Iron(II)-Induced Transformation of Ferrihydrite and Goethite under Advective Flow Conditions

Molybdenum(VI) Sequestration Mechanisms During Iron(II)-Induced Ferrihydrite Transformation

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