Toxic metal(loid) speciation during weathering of iron sulfide mine tailings under semi-arid climate

Abstract

Toxic metalliferous mine-tailings pose a significant health risk to ecosystems and neighboring communities from wind and water dispersion of particulates containing high concentrations of toxic metal(loid)s (e.g., Pb, As, Zn). Tailings are particularly vulnerable to erosion before vegetative cover can be reestablished, i.e., decades or longer in semi-arid environments without intervention. Metal(loid) speciation, linked directly to bioaccessibility and lability, is controlled by mineral weathering and is a key consideration when assessing human and environmental health risks associated with mine sites. At the semi-arid Iron King Mine and Humboldt Smelter Superfund site in central Arizona, the mineral assemblage of the top 2 m of tailings has been previously characterized. A distinct redox gradient was observed in the top 0.5 m of the tailings and the mineral assemblage indicates progressive transformation of ferrous iron sulfides to ferrihydrite and gypsum, which, in turn weather to form schwertmannite and then jarosite accompanied by a progressive decrease in pH (7.3 to 2.3). Within the geochemical context of this reaction front, we examined enriched toxic metal(loid)s As, Pb, and Zn with surficial concentrations 41.1, 10.7, 39.3 mM kg-1 (3080, 2200, and 2570 mg kg-1), respectively. The highest bulk concentrations of As and Zn occur at the redox boundary representing a 1.7 and 4.2 fold enrichment relative to surficial concentrations, respectively, indicating the translocation of toxic elements from the gossan zone to either the underlying redox boundary or the surface crust. Metal speciation was also examined as a function of depth using X-ray absorption spectroscopy (XAS). The deepest sample (180 cm) contains sulfides (e.g., pyrite, arsenopyrite, galena, and sphalerite). Samples from the redox transition zone (25-54 cm) contain a mixture of sulfides, carbonates (siderite, ankerite, cerrusite, and smithsonite) and metal(loid)s sorbed to neoformed secondary Fe phases, principally ferrihydrite. In surface samples (0-35 cm), metal(loid)s are found as sorbed species or incorporated into secondary Fe hydroxysulfate phases, such as schwertmannite and jarosites. Metal-bearing efflorescent salts (e.g., ZnSO4·nH2O) were detected in the surficial sample. Taken together, these data suggest the bioaccessibility and lability of metal(loid)s are altered by mineral weathering, which results in both the downward migration of metal(loid)s to the redox boundary, as well as the precipitation of metal salts at the surface.

Geochemical background of potentially toxic trace elements in reclaimed soils of the abandoned pyrite–uranium mine (south-central Poland)

“…However, cerussite is the most mobile and bioavailable lead phase in soils, and about 40 years after liming, this mineral must have been removed from soil. The Pb sequestration in soils in the form of plumbojarosite PbFe 3þ 6 OH ð Þ 12 SO 4 ð Þ 4 Â Ã À Á has been reported by Root et al (2015). This mineral is more thermodynamically stable than cerussite (PbCO 3 ) and its occurrence is common in abandoned mining sites (Bosso and Enzweiler 2008).…”

Mechanisms of Arsenic Sequestration by Prosopis juliflora during the Phytostabilization of Metalliferous Mine Tailings

“…AZ0000309013) in central AZ. 4 The surficial mineralogy of the IKMHSS tailings is dominated by high iron and sulfur content with the major contaminant of concern being arsenic (ca. 2100 mmol kg −1 Fe, 3100 mmol kg −1 S, and 40 mmol kg −1 As).…”

“…2100 mmol kg −1 Fe, 3100 mmol kg −1 S, and 40 mmol kg −1 As). 4,5 Under the oxidizing conditions of the surficial IKMHSS tailings, ferrous sulfides naturally weather to form ferric (oxyhydr)oxides and (hydroxy)sulfates. 4,5 These arsenic enriched secondary minerals have the potential for off-site transport as geo-dust in wind-driven erosion.…”

“…4,5 Under the oxidizing conditions of the surficial IKMHSS tailings, ferrous sulfides naturally weather to form ferric (oxyhydr)oxides and (hydroxy)sulfates. 4,5 These arsenic enriched secondary minerals have the potential for off-site transport as geo-dust in wind-driven erosion. 6–9 One potential low-cost, long-term remediation method proposed for such abandoned mine tailings involves phytostabilization, i.e., the establishment of a sustainable vegetation “cap” with which to effectively contain legacy tailings particles and the associated metal(loid)s including arsenic, thereby diminishing contaminant exposure to adjacent communities.…”

Caracterización y modelación hidrogeoquímica de lixiviados mineros de San Luis Potosí, S.L.P. México

“…Los procesos que originan o modifican los residuos mineros representan un fenómeno complejo que primero debe comprenderse y después atenderse, analizando diversas alternativas de remediación (Razo et al, 2007;Armienta y Segovia, 2008;Nordstrom, 2011;Lottermoser, 2011;Simate y Ndlovu, 2014;Nordstrom 2015;Gutiérrez et al, 2016). El diseño de un programa de caracterización de un sitio minero-metalúrgico contempla la toma de muestras de sedimentos, lixiviados, residuos, jales, agua superficial y/o subterránea, incluso muestras biológicas, y su análisis en el laboratorio (Castro-Larragoitia et al, 1997;Santos-Jallath et al, 2013;Carrillo-Chávez et al, 2014;Luís et al, 2015;Root et al, 2015). Los estudios de laboratorio y campo sobre residuos minero-metalúrgicos son diversos e incluyen aspectos de caracterización mineralógica: (Moreno et al, 2012;Salas, 2014;Jamieson et al, 2015), geoquímica (Lindsay et al, 2015;Klunk et al, 2015), física e hidrológica (Sán-chez-España y Diez-Ercilla, 2008; Šráček et al, 2013;Schaider et al, 2014;Amos et al, 2015), así como la caracterización de sus efluentes, que en el caso de residuos conteniendo sulfuros pueden llegar a ser los denominados Drenaje Ácido de Roca (DAR) por sus siglas en inglés (Nordstrom, 2011).…”