(Micro)spectroscopic Analyses of Particle Size Dependence on Arsenic Distribution and Speciation in Mine Wastes

The risk of the mobilization of coal ash into the environment has highlighted the need for the assessment of the environmental behavior of coal ash, particularly with respect to toxic trace elements such as arsenic (As). Here, we examined As speciation in coal fly ash samples and transformations in response to aquatic redox conditions. X-ray absorption spectroscopy indicated that 92-97% of total As occurred as As(V), with the remainder present as As(III). Major As-bearing hosts in unamended ashes were glass, iron (oxyhydr)oxides, and calcium arsenate. Oxic leaching resulted in immediate As mobilization to the aqueous phase, reprecipitation of As-iron ferrihydrite, and As adsorption to mineral surfaces. Under anoxic conditions, the (reductive) dissolution of As-bearing phases such as iron ferrihydrite resulted in increased dissolved As compared to oxic conditions and reprecipitation of iron arsenate. Overall, As in coal ash is not environmentally stable and can participate in local biogeochemical cycles.

Section: Environmental Science and Technologymentioning

confidence: 80%

“…Reference spectra were accepted only with a 10% decrease in the residual variance (R) of the fit. 29 Further details are provided in the Supporting Information.…”

Section: ■ Introductionmentioning

confidence: 99%

Arsenic Speciation in Bituminous Coal Fly Ash and Transformations in Response to Redox Conditions

Deonarine

Kolker

Foster

et al. 2016

“…For instance, the results from this study have implications for other abandoned uranium mines in the Colorado Plateau, South Dakota (Black Hills), southwest China, southern Jordan, and the calcreted drainages of arid and semiarid western and southern Australia where carnotite, tyuyamunite and other U–V bearing minerals are commonly found. 24, 46, 60–65 …”

Section: Resultsmentioning

confidence: 99%

Reactive Transport of U and V from Abandoned Uranium Mine Wastes

Avasarala¹,

Lichtner

Ali³

et al. 2017

The reactive transport of uranium (U) and vanadium(V) from abandoned mine wastes collected from the Blue Gap/Tachee Claim-28 mine site in Arizona was investigated by integrating flow-through column experiments with reactive transport modeling, and electron microscopy. The mine wastes were sequentially reacted in flow-through columns at pH 7.9 (10 mM HCO3−) and pH 3.4 (10 mM CH3COOH) to evaluate the effect of environmentally relevant conditions encountered at Blue Gap/Tachee on the release of U and V. The reaction rate constants (km) for the dissolution of uranyl–vanadate (U–V) minerals predominant at Blue Gap/Tachee were obtained from simulations with the reactive transport software, PFLOTRAN. The estimated reaction rate constants were within 1 order of magnitude for pH 7.9 (km = 4.8 × 10−13 mol cm−2 s−1) and pH 3.4 (km = 3.2 × 10−13 mol cm−2 s−1). However, the estimated equilibrium constants (Keq) for U–V bearing minerals were more than 6 orders of magnitude different for reaction at circumneutral pH (Keq = 10−38.65) compared to acidic pH (Keq = 10−44.81). These results coupled with electron microscopy data suggest that the release of U and V is affected by water pH and the crystalline structure of U–V bearing minerals. The findings from this investigation have important implications for risk exposure assessment, remediation, and resource recovery of U and V in locations where U–V-bearing minerals are abundant.

“…These results are consistent with the findings reported in other studies. 42,51 For instance, when arsenopyrite reacted with waters from a waste rock pile, reduced arsenic was still present in the surface of oxidized arsenopyrite due to diffusion of reduced As from the unoxidized interior of the mineral. 41,43,44 While our XPS analyses suggest that reduced As(−I) is present in mine waste sample MW1, additional research is needed to identify arsenopyrite or As-bearing Feoxide mineral phases.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Elevated Concentrations of U and Co-occurring Metals in Abandoned Mine Wastes in a Northeastern Arizona Native American Community

Blake

Avasarala

Artyushkova

et al. 2015

115

The chemical interactions of U and co-occurring metals in abandoned mine wastes in a Native American community in northeastern Arizona were investigated using spectroscopy, microscopy and aqueous chemistry. The concentrations of U (67-169 μg L(-1)) in spring water samples exceed the EPA maximum contaminant limit of 30 μg L(-1). Elevated U (6,614 mg kg(-1)), V (15,814 mg kg(-1)), and As (40 mg kg(-1)) concentrations were detected in mine waste solids. Spectroscopy (XPS and XANES) solid analyses identified U (VI), As (-I and III) and Fe (II, III). Linear correlations for the release of U vs V and As vs Fe were observed for batch experiments when reacting mine waste solids with 10 mM ascorbic acid (∼pH 3.8) after 264 h. The release of U, V, As, and Fe was at least 4-fold lower after reaction with 10 mM bicarbonate (∼pH 8.3). These results suggest that U-V mineral phases similar to carnotite [K2(UO2)2V2O8] and As-Fe-bearing phases control the availability of U and As in these abandoned mine wastes. Elevated concentrations of metals are of concern due to human exposure pathways and exposure of livestock currently ingesting water in the area. This study contributes to understanding the occurrence and mobility of metals in communities located close to abandoned mine waste sites.