Barton, C. D., & Karathanasis, A. D. (1997). Aerobic and anaerobic metal attenuation processes in a constructed wetland treating acid mine drainage. In AAPG Eastern Section and the Society for Organic Petrology joint meeting; abstracts (1545). 81: AAPG Bulletin.
Abstract: The use of constructed wetlands for acid mine drainage amelioration has become a popular alternative to conventional treatment methods, however, the metal attenuation processes of these systems are poorly understood. Precipitates from biotic and abiotic zones of a staged constructed wetland treating high metal load (approx. equal to 1000 mg L (super -1) ) and low pH (approx. 3.0) acid mine drainage were characterized by chemical dissolution, x-ray diffraction, thermal analysis and scanning electron microscopy. Characterization of abiotic/aerobic zones within the treatment system suggest the presence of crystalline iron oxides and hydroxides such as hematite, lepidocrocite, goethite, and jarosite. At the air/water interface of initial abiotic treatment zones, SO (sub 4) /Fe ratios were low enough (<2.0) for the formation of jarosite and goethite, but as the ratio increased due to treatment and subsequent reductions in iron concentration, jarosite was transformed to other Fe-oxyhydroxysulfates and goethite formation was inhibited. In addition, elevated pH conditions occurring in the later stages of treatment promoted the formation of amorphous iron oxyhydroxides. Biotic wetland cell substrate characterizations suggest the presence of amorphous iron minerals such as ferrihydrite and Fe(OH) (sub 3) . Apparently, high Fe (super 3+) activity, low Eh and low oxygen diffusion rates in the anaerobic subsurface environment inhibit the kinetics of crystalline iron precipitation. Some goethite, lepidocrocite and hematite, however, were observed near the surface in biotic areas and are most likely attributable to increased oxygen levels from surface aeration and/or oxygen transport by plant roots. Alkalinity generation from limestone dissolution within the substrate and bacterially mediated sulfate reduction also has a significant role on the mineral retention process. The formation of gypsum, rhodochrocite and siderite are by-products of alkalinity generating reactions in this system and may have an impact on S, Mn, and Fe solubility controls. Moreover, the buffering of acidity through excess alkalinity appears to facilitate the precipitation and retention of metals within the system.
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Bliss, L. N., Sellstone, C. M., Nicholson, A. D., & Kempton, J. H. (1997). Buffering of acid rock drainage by silicate minerals.
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Cox, M. R., & Peterson, G. L. (1997). The effectiveness of in-situ limestone treatment of acid mine drainage Association of Engineering Geologists program with abstracts, 40th annual meeting; Converging at Cascadia. In Annual Meeting – Association of Engineering Geologists, vol.40 (93).
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Parker, G., Noller, B., & Waite, T. D. (1999). Assessment of the use of fast-weathering silicate minerals to buffer AMD in surface waters in tropical Australia. In D. E. Goldsack, N. Belzile, P. Yearwood, & G. J. Hall (Eds.), Sudbury '99; Mining and the environment II; Conference proceedings.
Abstract: Surface waters in the Pine Creek Geosyncline (located in Australia's “Top End”, defined as the area of Australia north of 15 degrees S) are characterized by their low carbonate buffering capacity. These waters are buffered by silicate weathering and hence are slightly acidic, ranging in pH from 4.0 to 6.0. The Pine Creek Geosyncline contains most of the Top Ends' economic mineral deposits and characteristically shows no correlation between carbonate minerals and sulfidic orebodies hosting gold deposits (unlike uranium deposits). Thus many gold mines do not have ready access to carbonate minerals for buffering acid mine drainage (AMD). It is possible that locally available fast-weathering silicate minerals may be used to buffer AMD seeps. The buffering intensity of silicate minerals exceeds that of carbonate minerals, but their slow dissolution kinetics has ensured that these materials have received little attention in treating AMD. In addition, carbonate mineral dissolution is retarded when contacted with intense AMD solutions due to the formation of surface coatings of iron minerals. The lower pH range of silicate mineral dissolution may prevent the formation of such coatings. The Pine Creek Geosyncline consists of a complex geochemistry, and a number of fast-weathering silicate minerals have been noted in various areas. The difficulty in assessing such minerals for use in buffering AMD is the lack of kinetic data available under conditions prevalent AMD (i.e., low pH solutions saturated with aluminium and silica). This study sets out to evaluate the applicability of using such minerals to treat AMD surface seeps.
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Rees, B., Bowell, R., Dey, M., & Williams, K. (2001). Passive treatment; a walk away solution? Mining Environmental Management, 9(2), 7–8.
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