This study investigates the fate of Cu in organic-rich soils contaminated by mining related activities at the Timmins Kidd Creek metallurgical site, Ontario, Canada.
Mineralogical studies of contaminated soils affected by smelter emission and dust from mining activities indicate that minerals of the spinel group are one of the common hosts of metal-bearing contaminants. Spinel group minerals typically originate from high temperature processes, but an increasing number of studies indicate that metal-bearing spinel group minerals can also form under ambient Earth surface conditions in surficial soils. In this contribution to honor Donald Sparks, we show that the spinels Zn-bearing magnetite (Zn0.5Fe2.5O4) and minium (Pb3O4) form during low temperature alteration of Pb-bearing silica glass in surficial organic rich soils in proximity to a former Cu-smelter in Timmins, Ontario, Canada. The glass most likely formed during high-temperature processes and has been either emitted by the smelter or wind-blown from waste rock piles to near-by soils. The alteration of the glass by percolating pore solutions has resulted in the formation of large micrometer-size dendritic etch features and in nanometer-size dendritic alteration halos composed of nano-size prismatic crystals of Zn-rich magnetite and spherical nanoparticles of minium. Both spinel-type phases are embedded in an amorphous silica matrix which formed during the alteration of the glass at low temperature. A review on the occurrence of spinel-group minerals in smelter-affected soils or mine tailings indicates that the formation of these minerals under ambient Earth surface conditions is quite common and often results in the sequestration of contaminants such as Cu, Ni, Zn and Sb. The pedogenic spinels often occur as euhedral crystals in nano-size mineral assemblages within alteration features such as dendritic etch patterns, mineral surface coatings and mineralized organic matter. Their well-developed crystal forms indicate that (a) they have not formed during a rapid cooling process in a smelter or refinery which typically creates spherical particulate matter, and (b) they have not been part of particulate matter added via fluvial or Aeolian processes which most commonly yield anhedral morphologies. The formation of nano-size spinel-group minerals in low temperature environmental settings may lead to the long-term storage of metal(loid)s in mineral phases and their transport over vast distances via fluvial, alluvial and Aeolian processes.Electronic supplementary materialThe online version of this article (10.1186/s12932-019-0061-3) contains supplementary material, which is available to authorized users.
Gunshot residue is emitted as fine particulate matter upon the ignition of percussion-sensitive explosives among other additives in a firearm barrel. The particulates condense from a vapor phase and contain material from the Pb-Sb-Ba-bearing primer, S-bearing gunpowder, and the Pb-bearing bullet fragments. Shooters can inhale or ingest the fine particulates which also attach to their hands, clothing, and other surfaces. Estimation of the bioavailability of the emitted toxic Pb- and Sb-bearing particulates requires detailed knowledge of their mineralogical composition and those of their weathering products. For this purpose, gunshot residue particulates have been collected from soils in front of a firing line of a shooting range in Ontario, Canada. Bulk mineralogical and chemical features of the soils have been characterized using X-ray powder diffraction, inductively coupled plasma-mass spectrometry, and scanning electron microscopy. The focused ion-beam technique has been used to extract a section containing numerous altered gunshot residue particulates from a soil grain. Subsequent transmission electron microscopy shows for the first time that gunshot residue particulates are composed of metallic δ-Pb, α-Sb, galena (PbS), and an unidentified Ba-bearing phase. Weathering of the gunshot residue particulates results in the formation of incidental nanoparticles (i.e., not purposely engineered to occur at the nanometer scale) in the form of δ-Pb, massicot, PbO, and galena. The formation and mobilization of some of these nanoparticles within the soil grain suggest that their release during the weathering of bullets and gunshot residue contributes to the release of Pb into the environment. Hydrocerussite, Pb3(CO3)2(OH)2, cerussite, PbCO3, and massicot and anglesite, PbSO4, are the major secondary Pb-phases in and around altered GSR particulates. These phases form during the weathering of metallic Pb, massicot, and galena nanoparticles in a Ca-carbonate rich environment. Secondary Sb-bearing phases are valentinite, Sb2O3, and amorphous Sb-Pb phases (Sb:Pb ratio = 2:1–4:1). The latter phases have partially replaced large proportions of the Ca-carbonates surrounding the gunshot residue particulates. The larger abundance of the amorphous Sb-Pb phases relative to valentinite suggests that their solubility most likely controls the release of Sb into the bulk soil. The SEM and TEM characterizations and chemical analyses of mineral surface coatings and the colloidal fraction of a leachate from the collected surficial soils indicate that Pb occurs predominantly in the colloidal fraction, is often associated with sulfate-bearing colloids, and is sequestered in sulfate and carbonate/hydroxide coatings.
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