Zhiyuan Cong, China University of Mining and Technology (Beijing), Key Laboratory of Coal Resources, Ministry of Education, P.R.C, XueYuan Road, Ding 11#, Haidian District, Beijing 100083, China, Fax: 86-10-62325016, Email: zhiyuancong@hotmail.com
Fenghua Zhao, China University of Mining and Technology (Beijing), Key Laboratory of Coal Resources, Ministry of Education, P.R.C, XueYuan Road, Ding 11#, Haidian District, Beijing 100083, China, Fax: 86-10-62325016, Email: zfh@cumtb.edu.cn

Acid mine drainage (AMD) represents a serious environmental problem for coal mining industry worldwide. Acid mine drainage is generated when metal sulphides in coal and the associated strata, particularly pyrite (FeS₂), react with water and oxygen in the presence of thiobacillus bacteria to produce sulfuric acid and iron hydroxide or iron sulphate. The low pH may result in further dissolution of country rock and the subsequent leaching of metals into water, and thereby adversely impact on aquatic life and surrounding vegetation. In China, coal is the most important energy sources and has been mined about several hundreds of years. In the meanwhile, most of the water systems in the vicinity of the coal mining areas suffered from the water pollution, especially discharges of untreated AMD.

In this research, several water samples and sediments from the Sitai coalmine were investigated to confirm the mechanism of contamination and to identify the major processes affecting the attenuations of heavy metals. The analysis results show that the concentrations of major constituents in AMD are tens to hundreds times high than those in background stream. With the application of the PHREEQCI program, predominant species of some toxic metals were also determined. The saturation index of goethite was pronounced positive. Furthermore, XRD analysis confirmed the occurrence of goethite in ochrous precipitates.

Acid Drainage from Rich-in-Pyrite Mining Wastes in a Uranium Deposit

I.I. Spasova, Department of Engineering Geoecology, University of Mining and Geology, Studentski grad – Durvenitza, Sofia 1700, Bulgaria, Tel: +359 2 687396, Fax: + 359 2 687396, Email: spasova@mgu.bg
F. Veglio, Department of Chemistry, Engineering Chemistry and Materials, University of L’Aquila, L’Aquila, Italy, Tel: + 34 862434223/4236, Fax: + 34 862434203, Email: veglio@ing.univaq.it
M.V. Nicolova, Department of Engineering Geoecology, University of Mining and Geology, Studentski grad – Durvenitza, Sofia 1700, Bulgaria, Tel: +359 2 687396, Fax: + 359 2 687396. Email: mnikolova@mgu.bg
S.N. Groudev, Department of Engineering Geoecology, University of Mining and Geology, Studentski grad – Durvenitza, Sofia 1700, Bulgaria, Tel: +359 2 687396, Fax: + 359 2 687396 , Email: groudev@mgu.bg

The uranium deposit Curilo, Western Bulgaria, for a long period of time was a site of intensive mining activities including both the open-pit and underground mining techniques as well as in situ leaching of uranium. The ore was rich in pyrite and, apart from uranium, contained several non-ferrous metals. The mining operations in the deposit were ended in 1990 but since that time the dumps consisting of mining wastes are, after rainfall, a large source of acid drainage waters. These waters have pH in the range of about 2 – 4 and contain radioactive and heavy metals (uranium, radium, iron, manganese, copper, zinc, cadmium, nickel, cobalt), arsenic and sulphates in concentrations usually 2 – 10 times higher than the relevant permissible levels for waters intended for use in the agriculture and/or industry.

The investigations carried out in the deposit revealed that the generation of the polluted waters was connected with the activity of the indigenous acidophilic chemolithotrophic bacteria, which oxidized the pyrite, other sulphides and uranium bearing minerals present in the dumps. Acidithiobacillus ferrooxidans and Leptospirilum ferrooxidans were the prevalent microorganisms of this group and their number usually exceeded 10⁸ cells/g mining wastes. The growth and activity of these bacteria markedly depended on some essential environmental factors such as pH, temperature, and water, oxygen and nutrient contents in the dumps. These data will be used for development of technology to inhibit the microbial growth and activity and in this way to prevent the generation of polluted waters from the dumps.

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