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Eger, P., Melchert, G., & Wagner, J. (2000). Using passive treatment systems for mine closure – A good approach or a risky alternative? Min. Eng., 52(9), 78–83.
Abstract: In 1991, LTV Steel Mining decided to close an open-pit taconite mine in northeastern Minnesota using a passive-treatment approach consisting of limiting infiltration into the stockpiles and wetland treatment to remove metals. More than 50 Mt (55 million st) of sulfide-containing waste had been stockpiled adjacent to the mine during its 30 years of operation. Drainage from the stockpiles contained elevated levels of copper, nickel, cobalt and zinc. Nickel is the major trace metal in the drainages. Before the closure, the annual median concentrations ranged from 1.5 to 50 mg/L. Copper, cobalt and zinc are also present but they are generally less than 5% of the nickel values. Median pH levels range from 5 to 7.5, but most of the stockpile drainages have pH levels greater than 6.5. Based on the chemical composition of each stockpile, a cover material was selected. The higher the potential that a stockpile had to produce acid drainage, the lower the permeability of the capping material required. Covers ranged from overburden soil removed at the mine to a flexible plastic liner. Predictions of the reduction in infiltration ranged from 40% for the native soil to more than 90% for the plastic liner. Five constructed wetlands have been installed since 1992. They have removed 60% to 90% of the nickel in the drainages. Total capital costs for all the infiltration reduction and wetlands exceeded $6.5 million, but maintenance costs are less than 1% of those for an active treatment plant. Because mine-drainage problems can continue for more than 100 years, the lower annual operating costs should pay for the construction of the wetland-treatment systems within seven years.
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Dunn, J., Russell, C., & Morrissey, A. (1999). Remediating historic mine sites in Colorado. Min. Eng., 51(8), 32–35.
Abstract: This article provides examples of reclamation and remediation in Colorado watersheds. The projects were undertaken by the US Environmental Protection Agency (EPA) Region 8, in cooperation with the Colorado Division of Minerals and Geology (CDMG), Colorado Department of Public Health and Environment (CDPHE), US Forest Service (USFS), the Bureau of Land Management (BLM), Bureau of Reclamation (BOR) and the US Geological Survey (USGS). These agencies collaborated on the environmental problems at abandoned mines. These samples involved the interaction of surface and ground waters with sulfide-bearing rocks, mine workings and surface mine spoils that produce acid solutions charged with heavy metals that are toxic to organisms. In these examples, acid mine drainage from historic mines in Colorado has been approached cooperatively with stakeholders. Each example emphasizes one aspect of the three-stage process. These stages include characterization and prioritization, hydrologic controls and the evaluation of long-term remediation activities.
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Benzaazoua, M., & Bussiere, B. (1999). Desulphurization of tailings with low neutralizing potential; kinetic study and flotation modeling. In D. Goldsack, N. Belzile, P. Yearwood, & G. Hall (Eds.), Sudbury '99; Mining and the environment II; conference proceedings.
Abstract: Environmental desulphurization is an attractive alternative for acid generating tailings management as demonstrated during the last few years. In fact, such process placed at the end of the primary treatment circuit allows to reduce greatly the amount of problematic tailings by concentrating the sulphidic fraction. Moreover, the desulphurized tailings (non-acid generating) have the geotechnical and environmental properties for being used as fine material in a cover with capillary barrier effects. To produce desulphurized tailings, non selective froth flotation is the most adapted method as shown in many previous works. Desulphurization level is fixed by tailings sulphur content (or sulphide content) and neutralization potential NP. The final residue should have enough NP to compensate for his acid generating potential AP. In this paper, the authors present the results of laboratory tests conducted in Denver cells for studying the sulphide flotation kinetics of four mine tailings which are characterized by a weak neutralization potential (under 37 kg CaCO (sub 3) /t). Tailings 1, 2, 3 and 4 contain respectively 5.27, 10, 4.25 and 16.9 sulphur Wt. %. Tailings 1 and 2 are cyanide free and are well floated at pH around 11 by using amyl xanthate as collector. Collector dosage was optimized for these tailings and the results show that Tailing 2 need more collector. However, Tailings 3 and 4, which come from a gold cyanidation process, could not provide good sulphide recovery with xanthate collector because of the pyrite depression. To overcome this problem, amine acetate was used successfully but induces important entrainment. The consumption of this collector was also optimized. The results of kinetic tests and collector dosage were combined and modeled to establish relationships which allow to estimate the desulphurization performances.
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Bennett, J. W., Timms, G. P., & Ritchie, A. I. M. (1999). The effectiveness of the covers on waste rock dumps at Rum Jungle and the impact in the long term. Mining into the next century : environmental opportunities and challenges Proceedings of the 24th annual environmental workshop Townsville October, , 379–388.
Abstract: Covers are widely used as a means of controlling pollutant generation from sulfidic waste piles. To date, there has been little data available to test the effectiveness of such covers. Monitoring of two waste rock dumps at Rum Jungle over more than fifteen years has provided the opportunity to assess cover effectiveness in the medium term. For the first 9 years the infiltration rate through the cover on Whites dump was less than the design figure of 5 per cent of rainfall. In subsequent years, however, the rate has increased to between 5 and 10 per cent. In the first six years the infiltration rate through the cover on Intermediate dump was also less than 5 per cent. Unfortunately, further measurements had to be abandoned due to equipment malfunction in this dump. Oxygen and temperature profiles measured below the cover have been used to estimate the overall oxidation rate in the two dumps. This is between 30 and 50 per cent of the oxidation rate prior to installation of the cover. The effect these results have on pollutant loads in drainage in the long term depends on the nature of the control mechanisms in the system. If pollutant concentrations in drainage are determined by secondary mineralisation within the dumps then pollutant loads in the long term will be essentially proportional to any further increase in the infiltration rate. If the pollutant loads in drainage are largely determined by the overall oxidation rates then we can expect the pollutant loads from the two dumps to increase in the long term to a level about one third to one half of that prior to rehabilitation. In this context, 'long term' means about 40 years after installation of the cover system. Given the implications this work has for the use of soil covers, the following additional studies should be undertaken: A measurement program to quantify the pollution loads from Intermediate and Whites waste rock dumps. A program of computation, backed by acquisition of mineralogical data on the wastes, to address the question of controls on concentration and load in effluent from the two dumps. A program to determine the reason for the deteriorating performance of the covers at Rum Jungle.
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Beck, P. (2003). CL:AIRE – Providing support for remediation research. Land Contam. Reclam., 11(2), 99–104.
Abstract: CL:AIRE (Contaminated Land: Applications in Real Environments) is a public-private partnership which was established in 1999 to encourage the demonstration of remediation research and technologies on contaminated sites throughout the UK. Project proposals are submitted to CL:AIRE and reviewed and approved by the CL:AIRE Technology & Research Group. CL:AIRE provides independent verification of its projects and plays a crucial role in the dissemination of project information. During the course of the project, progress is reported through the newsletter, CL:AIRE view, which is mailed free of charge to a database of more than 4500 stakeholders with an interest in contaminated land. Progress is also tracked on the CL:AIRE website at www.claire.co.uk. On completion of the project, a project report is published and a one page summary fact sheet is prepared. The fact sheet is distributed to our database subscribers and posted on the website. The project is also presented at the CL:AIRE Annual Project Conference. In addition, aspects of the research which have practical application will be published as CL:AIRE Research Bulletins. Acid mine waters discharging from abandoned mines represent a significant environmental problem in many parts of the UK. Considerable research has been carried out to understand the geochemical process involved, and the knowledge has been used to manage groundwater discharge through physical/chemical treatment and constructed wetlands. CL:AIRE supports the development of a national site for wetland research managed by the University of Newcastle and will encourage collaborative research projects to be submitted through CL:AIRE. CL:AIRE is currently supporting two projects which demonstrate remediation of acid mine drainage and is disseminating the results of this and other research to improve confidence in the use of these techniques.
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