Secondary sulfate minerals associated with acid drainage in the eastern US: recycling of metals and acidity in surficial environments

Abstract

Weathering of metal-sulfide minerals produces suites of variably soluble efflorescent sulfate salts at a number of localities in the eastern United States. The salts, which are present on mine wastes, tailings piles, and outcrops, include minerals that incorporate heavy metals in solid solution, primarily the highly soluble members of the melanterite, rozenite, epsomite, halotrichite, and copiapite groups. The minerals were identified by a combination of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron-microprobe. Base-metal salts are rare at these localities, and Cu, Zn, and Co are commonly sequestered as solid solutions within Fe-and Fe-Al sulfate minerals. Salt dissolution affects the surfacewater chemistry at abandoned mines that exploited the massive sulfide deposits in the Vermont copper belt, the Mineral district of central Virginia, the Copper Basin (Ducktown) mining district of Tennessee, and where sulfide-bearing metamorphic rocks undisturbed by mining are exposed in Great Smoky Mountains National Park in North Carolina and Tennessee.Dissolution experiments on composite salt samples from three minesites and two outcrops of metamorphic rock showed that, in all cases, the pH of the leachates rapidly declined from 6.9 to b3.7, and specific conductance increased gradually over 24 h. Leachates analyzed after 24-h dissolution experiments indicated that all of the salts provided ready sources), and base metals (N1000 mg L À1 for minesites, and 2 mg L À1 for other sites). Geochemical modeling of surface waters, mine-waste leachates, and salt leachates using PHREEQC software predicted saturation in the observed ochre minerals, but significant concentration by evaporation would be needed to reach saturation in most of the sulfate salts. Periodic surface-water monitoring at Vermont minesites indicated peak annual metal loads during spring runoff. At the Virginia site, where no winter-long snowpack develops, metal loads were highest during summer months when salts were dissolved periodically by rainstorms following sustained evaporation during dry spells. areas, persist in protected areas when temperature and relative humidity are appropriate, and contribute to metal loadings and acidity in surface waters upon dissolution, thereby causing short-term perturbations in water quality. Published by Elsevier B.V.

Effects of Montmorillonite on the Mineralization and Cementing Properties of Microbiologically Induced Calcium Carbonate

“…Microbial-induced mineralization mainly can be defined as the mineralization process caused by the interaction of microbial life activities with the surrounding environment [2]. Soil mineral-microbial interactions are the most basic biogeochemical effects [3,4]. Microbial metabolic activities play an important role in the elemental cycling, formation, and transformation, as well as the weathering of the earth's environment [5].…”

Characterization and Potential Use of Biochar for the Remediation of Coal Mine Waste Containing Efflorescent Salts

“…The waste heaps in the coal mines studied show features similar to those studied in North-Central Colorado, USA, which appear to be a potential source of trace elements and salinity [1,11]. The XRD pattern of the efflorescent salts is displayed in Figure 2.…”

“…These minerals can be considered as the highest polluting residue in the mining environment. Because of the high solubility of efflorescent minerals, climate plays an important role in their mineral chemistry [11]. The minerals commonly associated with saline soils are gypsum, thenardite, mirabilite, hexahydrate, epsomite, bloedite, konyaite, loweite, eugstgerite, wattevilleite, halite, nitratine, and natrojarosite [1].…”

Use of Multivariate Statistics in Order to Understand the Flow of Acid Rock Drainage from an Abandoned Mining Site

“…Increased aluminum concentrations will also provide latent acidity able to lower the pH further down in the surface water system. Compared to other mining areas in the world concentrations of sulfate and iron are lower [16] [17], maybe reflecting the fact that the mining waste is almost 400 years old and the most reactive period has probably already passed. However, copper and zinc concentrations are comparable to other ARD quality data around the world.…”