Impacts of detrital nano- and micro-scale particles (dNP) on contaminant dynamics in a coal mine AMD treatment system

Abstract

Pollutants in acid mine drainage (AMD) are usually sequestered in neoformed nano- and micro-scale particles (nNP) through precipitation, co-precipitation, and sorption. Subsequent biogeochemical processes may control nNP stability and thus long-term contaminant immobilization. Mineralogical, chemical, and microbiological data collected from sediments accumulated over a six-year period in a coal-mine AMD treatment system were used to identify the pathways of contaminant dynamics. We present evidence that detrital nano- and micron-scale particles (dNP), composed mostly of clay minerals originating from the partial weathering of coal-mine waste, mediated biogeochemical processes that catalyzed AMD contaminant (1) immobilization by facilitating heterogeneous nucleation and growth of nNP in oxic zones, and (2) remobilization by promoting phase transformation and reductive dissolution of nNP in anoxic zones. We found that dNP were relatively stable under acidic conditions and estimated a dNP content of ~0.1g/L in the influent AMD. In the AMD sediments, the initial nNP precipitates were schwertmannite and poorly crystalline goethite, which transformed to well-crystallized goethite, the primary nNP repository. Subsequent reductive dissolution of nNP resulted in the remobilization of up to 98% of S and 95% of Fe accompanied by the formation of a compact dNP layer. Effective treatment of pollutants could be enhanced by better understanding the complex, dynamic role dNP play in mediating biogeochemical processes and contaminant dynamics at coal-mine impacted sites.

Sulfur Isotope Fractionation as an Indicator of Biogeochemical Processes in an AMD Passive Bioremediation System

“…Two monitoring wells were also completed: B-1 into the underground mine pool and B-2 within mine waste saturated with AMD from the mine pool. Details regarding the site, bioremediation system, and geochemical monitoring are presented in our previous reports [5,6,17,18]. Figure 2 presents a simplified conceptual model of S cycling in a typical PBS, such as the Tab-Simco PBS.…”

“…Figure 2 presents a simplified conceptual model of S cycling in a typical PBS, such as the Tab-Simco PBS. In the open limestone channel, S sequestration occurs through precipitation of amorphous and crystalline SO 4 2 6 ] and by adsorption and incorporation into the Fe(III)-rich nNP such as goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) [6] (Figure 2a). The presence in AMD of the detrital nano-and micro-scale particles (dNP), originated in the coal mine waste, promotes heterogeneous nucleation and growth of SO 4 2− -bearing nNP [6] and thus contributes to increased SO 4 2− sequestration.…”

“…However, such precipitates would also form coatings on limestone, thus inhibiting alkalinity production [18]. Although the high capacity of nNP to sequester SO 4 2− has been well documented, recent studies have shown that subsequent abiotic and biologically-mediated processes promote recrystallization and/or dissolution of nNP, which results in SO 4 2− remobilization [6,29].…”

“…Although the high capacity of nNP to sequester SO4 2− has been well documented, recent studies have shown that subsequent abiotic and biologically-mediated processes promote recrystallization and/or dissolution of nNP, which results in SO4 2− remobilization [6,29]. In the bioreactor and the wetland, SO4 2− is sequestered as SO4 2− -bearing nNP and by microbially-mediated reduction of SO4 2− to H2S and precipitation of low-solubility metal-sulfide minerals.…”

“…Sulfate (SO 4 2− ) is a major contaminant in many watersheds impacted by coal and metal mining activities and is difficult to remediate [1][2][3][4][5][6]. The increased SO 4 2− presence in ecosystems affected by mining has negative environmental and human health effects [7] since SO 4 2− can (1) promote secondary water quality impacts related to sulfur (S) redox processes and biological hydrogen sulfide (H 2 S) production; (2) stimulate methylation of mercury to methylmercury, the most toxic and bioaccumulative form of mercury; (3) enhance biodegradation of organic matter in soils; and (4) promote release of nutrients and potentially toxic compounds from sediments during biologically-mediated sulfate reduction processes [8][9][10][11].…”