Abstract
Coal mine spoil is widespread in US coal mining regions, and the potential long-term leaching of toxic metal(loid)s is a significant and underappreciated issue. This study aimed to determine the flux of contaminants from historic mine coal spoil at a field site located in Appalachian Ohio (USA) and link pore water composition and solid-phase composition to the weathering reaction stages within the soils. The overall mineralogical and microbial community composition indicates that despite very different soil formation pathways, soils developing on historic coal mine spoil and an undisturbed soil are currently dominated by similar mineral weathering reactions. Both soils contained pyrite coated with clays and secondary oxide minerals. However, mine spoil soil contained abundant residual coal, with abundant Fe- and Mn- (oxy)hydroxides. These secondary phases likely control and mitigate trace metal (Cu, Ni, and Zn) transport from the soils. While Mn was highly mobile in Mn-enriched soils, Fe and Al mobility may be more controlled by dissolved organic carbon dynamics than mineral abundance. There is also likely an underappreciated risk of Mn transport from coal mine spoil, and that mine spoil soils could become a major source of metals if local biogeochemical conditions change.
Highlights
Coal mine spoil is an obligate waste product of coal extraction and contains a mixture of residual, non-economically viable mined rock or sediment and overburden material
The mine spoil soil core showed a slight increase in the contribution of sand-sized particles with depth and a slightly higher clay content, the overall particle size distribution was similar to the high wall
We have shown that biogeochemical processes control the potential for long-term contaminant leaching from soils developing on historic coal mine spoil
Summary
Coal mine spoil is an obligate waste product of coal extraction and contains a mixture of residual, non-economically viable mined rock or sediment and overburden material. Mine waste (e.g., spoil) was often left abandoned after cessation of coal production, resulting in an on-going and critical need to continue reclamation and restoration in these regions [2] These mine spoil piles can be a source of AMD which is generated through the microbially-mediated oxidative dissolution of pyrite, remnant coal, and other reduced phases [3,4]. In Ohio alone, it has been estimated that there are approximately 36 billion tons of known coal mine spoil [8] These materials are widespread in US coal mining regions, and the potential long-term leaching of AMD and toxic metal(loid)s to surface and groundwater is a significant and underappreciated issue
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