Abstract
Secondary minerals could be effective scavengers of toxic arsenic (As) and thallium (Tl). In environments polluted by mining, these elements are abundant both in acid rock/mine drainage scenarios, as well as in carbonate-buffered environments. In this study we have investigated the behavior of As and Tl during weathering in mine waste dumps and an associated technosol sample from the Crven Dol locality (Allchar Tl–As–Sb–Au deposit, North Macedonia) contaminated with up to 142 g kg−1 of As and 18 g kg−1 of Tl, making it an As- and Tl-extreme environment. We identified As and Tl reservoirs and discuss their difference from those observed in other naturally As- and Tl-rich environments. The pore waters show high concentrations of As (up to 196 mg L−1) and Tl (up to 660 μg L−1). Mild extractions mobilized up to 46% of the total Tl and 11% of the total As, indicating that a large amount of these toxic elements is weakly bound and can be easily mobilized into the environment. Apart from the recognition of Tl storage in several secondary phases (mainly as Tl(I) in members of the pharmacosiderite and jarosite groups, as well as Mn oxides, but also as very minor Tl(III) in other secondary phases), this study also provides the first evidence of Tl uptake by previously unknown thallium arsenate phases (with Tl:As ratios ∼ 2 and 4), detected in carbonate-buffered (near-neutral pH) As- and Tl-rich technosols and waste dumps. These results indicate the need for further studies on Tl speciation in extremely As- and Tl-rich environments.
Highlights
Both historical and modern metal mining areas and accompanying waste material related to the extraction and processing of ore very often contain considerable amounts of heavy metals and metalloids
Apart from the recognition of Tl storage in several secondary phases (mainly as Tl(I) in members of the phar macosiderite and jarosite groups, as well as Mn oxides, and as very minor Tl(III) in other secondary phases), this study provides the first evidence of Tl uptake by previously unknown thallium arsenate phases, detected in carbonate-buffered As- and Tl-rich technosols and waste dumps
We remind that the sample CD-4 was taken from a spot where the run-off waters bring the waste material from the localities where the other three samples were taken
Summary
Both historical and modern metal mining areas and accompanying waste material related to the extraction and processing of ore very often contain considerable amounts of heavy metals and metalloids. These sites represent one of the most important latent hazards for water, soils, biodiversity, and the food chain They are due to continuous metal release from mechanically unstable, chemically labile, and non-remediated mine tailings and from abandoned former mine sites where waste materials are subjected to atmospheric conditions, runoffs (underground or meteoric waters), or biotic effects (organisms living on the site or nearby) (Hud son-Edwards, 2016). Some of these elements, such as arsenic (As) and thallium (Tl) may often occur together and may mobilize and disperse extensively into surrounding areas. High concentrations of As and Tl can be naturally attenuated by a series of pH-buffering, precipi tation, and sorption reactions, significant when fresh sec ondary solid phases are formed (Carbone et al, 2013)
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