Treatment of Acid Drainage in a Uranium Deposit by Means of a Reactive Zone

Stoyan N. Groudev, University of Mining and Geology, Studentski grad, Sofia 1700, Bulgaria, Tel/Fax: +359-2-687396, e-mail: groudev@mgu.bg
Irena I. Spasova, University of Mining and Geology, Studentski grad, Sofia 1700, Bulgaria, Tel/Fax: +359-2-687396, e-mail: spasova@mgu.bg
Plamen S. Georgiev, University of Mining and Geology, Studentski grad, Sofia 1700, Bulgaria, Tel/Fax: +359-2-687396, e-mail: ps_georgiev@mgu.bg
Marina V. Nicolova, University of Mining and Geology, Studentski grad, Sofia 1700, Bulgaria, Tel/Fax: +359-2-687396, e-mail: mnikolova@mgu.bg  

Acid drainage waters heavily polluted with radionuclides, heavy metals (mainly iron, manganese, copper, zinc, cadmium) and arsenic are generated in a uranium deposit located in Bulgaria. A part of these waters is treated by means of chemical neutralization and different passive systems (natural and constructed wetlands, permeable reactive barriers). However, the other part is collected in a small ravine and outside the deposit is discharged in the river system. There is an intensive seepage of these polluted waters into the neighbouring soils and rocks. A system to prevent their distribution was created in the deposit. The system consisted of several drillholes reaching an area within and around the polluted plume in the aquifer. Alkaline water solutions containing active mixed cultures of sulphate-reducing bacteria, dissolved organic substrates (lactate and acetate) and ammonium and phosphate ions were injected periodically through these drillholes. As a result of such treatment an abundant and diverse population of sulphate-reducing bacteria and other metabolically interdependent microorganisms was established within a period of about 4 – 5 months. This population created an efficient reactive zone in which the pH of the drainage waters was stabilized near the neutral point and the pollutants were precipitated as solid compounds refractory to solubilization. Uranium was precipitated mainly as uraninite (UO2) and heavy metals and arsenic – mainly as the relevant insoluble sulphides. This system was maintained for over 5 years and its long-term efficiency depended on the periodic injecting of the above-mentioned alkaline solutions.

Short-term and Long-term Passive Treatment of Acid Mine Drainage in Bioreactors

Student Presenter

Carmen M. Neculita, M.A.Sc., PhD. Candidate, Department of Civil, Geological and Mining Engineering, École Polytechnique de Montréal, P.O. Box 6079, Station Centre-ville, Montreal, Quebec, Canada H3C 3A7, Tel: 514-340-4711, 4965, Fax: 514-340-4477, Email: carmen-mihaela.caras@polymtl.ca
Gérald J. Zagury, Eng., Ph.D., Department of Civil, Geological and Mining Engineering, École Polytechnique de Montréal, P.O. Box 6079, Station Centre-ville, Montreal, Quebec, Canada H3C 3A7, Tel: 514-340-4711, 4980, Fax: 514-340-4477, Email: gerald.zagury@polymtl.ca
Viktors Kulnieks, M.A.Sc., Department of Civil, Geological and Mining Engineering, École Polytechnique de Montréal, P.O. Box 6079, Station Centre-ville, Montreal, Quebec, Canada H3C 3A7, Tel: 514-340-4711, 4965, Fax: 514-340-4477, Email: victors.kulnieks@polymtl.ca

Passive biological treatment of acid mine drainage (AMD) relies on sulfate-reducing bacteria (SRB) supported by a biodegradable organic carbon source. Treatment long-term performances can be limited by degradation rates of organic carbon available to SRB, and low metal stability in spent reactive mixtures.

The first part of this study focused on characterization of six natural organic materials and their short-term effectiveness in sulfate-reduction and metal removal from synthetic AMD. In the second part, long-term performance and metal forms in the reactive mixtures were assessed.

Maple wood chips, sphagnum peat moss, leaf compost, conifer compost, poultry manure and conifer sawdust were analyzed in terms of their carbon and nitrogen content, as well as their easily available substances content (EAS). Single substrates and a mixture of them were tested in a 70-day batch experiment (2-L reactors) and in an extended study for up to 350 days. Geochemical modeling and scanning electron microscopy (SEM) was used to assess the minerals present in the solid phase.

The highest EAS content and the lowest C/N ratio suggested poultry manure as the best substrate. Nevertheless, the lowest efficiency was found in the poultry manure reactor, whereas the mixture of three organic materials was the most effective. After 350 days, the mixture of organic carbon sources was still efficient for AMD treatment. SEM analysis of the solid phase indicated the presence of iron sulfides.

Substrates’ characterization provided insight on organic carbon availability but did not inform of their ability to promote sulphate-reduction and metal removal. Further research is needed to accurately predict long-term carbon availability and to assess the metal forms in spent reactive mixtures.

An Overview of Occurrence and Evolution of Acid Mine Drainage in the Slovak Republic  

Student Presenter

Andrea Slesarova, Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 04001 Kosice, Slovak Republic, Tel: 00421-55-7922618, Fax: 00421-55-7922604, Email: aslesar@saske.sk
Maria Kusnierova, Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 04001 Kosice, Slovak Republic, Tel: 00421-55-7922618, Fax: 00421-55-7922604, Email: kusnier@saske.sk
Alena Luptakova, Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 04001 Kosice, Slovak Republic, Tel: 00421-55-7922622, Fax: 00421-55-7922604, Email: luptakal@saske.sk
Josef Zeman, Institute of Geological Sciences, Faculty of Science, Masaryk University in Brno, Kotlarska 2, 61137 Brno, Czech Republic, Tel: 00420-549-49-8295, Fax: 00420-541-111-214, Email: jzeman@sci.minu.cz  

At the present time acid mine drainage (AMD) belongs among the worst environmental problems associated with mining activity.  At the beginning and in the middle of Twentieth Century the attenuation of mining activity in the Slovak Republic gave rise to extensive closing of deposits using wet conservation i.e. their flooding. The negative results of AMD activity can be observed mainly at localities after the mining of sulphide ores and raw materials containing sulphides. At the deposits Roznava, Pezinok and Rudnany the surrounding carbonate system is partly buffering the evolution of AMD. During the last decade at the locality of Sobov there was applied various remediation and restoration methods aimed at reducing the environmental impact of AMD but without marked success. The deposit of Smolník represents from the point of occurrence and generation of AMD the classical example. All the area of deposit is markedly affected by AMD activity. The mine waters have pH 3.8; contain high concentrations of sulphates, Fe, Mn, Cu, Zn, Al and are discharging straight in the stream Smolnik. In order to propose the effective and economically available method to prevent the negative influence of AMD at this locality it is necessary to understand the reasons of changes in evolution of mine water composition and real estimation of their long-term evolution. The article presents the results of monitoring of AMD quality at the locality of Smolník in years 1986 – 2005. It appears from trends that although it is in evolution of monitored components observed certain stability the situation at the locality is henceforward critical. In order to better understand processes running at the locality there was also realized the modeling of AMD evolution after the mine waters reach the surface. According to results during this ascension of water the intense decrease of pH and the precipitation of Fe compounds are assumed.      

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