DYNAMICS OF SURFACE WATER POLLUTION CAUSED BY OPEN PIT MINING IN COPPER CONCENTRATE PRODUCTION. Grigor Hlebarov, Nikolay Kozarev

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1 Journal Journal of Chemical of Chemical Technology and and Metallurgy, 51, 3, 51, 2016, 3, DYNAMICS OF SURFACE WATER POLLUTION CAUSED BY OPEN PIT MINING IN COPPER CONCENTRATE PRODUCTION Grigor Hlebarov, Nikolay Kozarev Department of Environmental Engineering University of Chemical Technology and Metallurgy 8 Kl. Ohridski, 1756 Sofia, Bulgaria grigor_hlebarov@abv.bg Received 13 January 2016 Accepted 07 April 2016 ABSTRACT The dynamics of surface water pollution around an open pit obtained in the course of pyrite and chalcopyrite mining is studied. The data referring to the water quality in a small river including ph, the river flow rate and the concentrations of Fe 3+, Cu 2+, Mn 2+, SO 4 and NO 3 - is obtained. The influence of the rainfall and snowfall on the surface water pollution is analysed and discussed. Polynomial models of the river flow rate and water pollutants emission are offered. They can be applied to control the water treatment plant operation. Keywords: surface water pollution, open pit mining, pyrite and chalcopyrite, pollutants concentration and emission variation. INTRODUCTION Acid mine drainage is a huge environmental problem connected with current and abandoned mine operations. It occurs when metal sulfides are exposed to oxygen and water in presence of bacteria. Acid water generation depends also on different factors connected with the materials and landfilling technologies used. It is possible to continue for decades, even centuries [1]. The costs required for mining sites stabilization are of the order of billions of dollars [2]. Chalcopyrite (CuFeS 2 ) and pyrite (FeS 2 ) are some of the most common metal sulfides. According to J. Dutrizac and J. Rivadeneira [3, 4] the chalcopyrite ore comprises about 70 % of the copper reserves in the world. It is subjected to pyrometallurgical treatment for copper production after concentration by flotation [5]. The dynamics of the flow rate and the level of water pollution concerning a small river in the region of the open pit mine for pyrite and chalcopyrite are analyzed and discussed in this paper. The study covers five pollutants, namely: Fe 3+, Cu 2+, Mn 2+, SO 4 and NO 3-. EXPERIMENTAL An open pit mine, whose main output is copper concentrate, was the study site. Tailing heaps were formed in the course of the ore extraction progress. These waste rock materials comprised large amount of minerals of a low content of chalcopyrite and pyrite. They were exposed to climate impact (rainfall and snowfall). An acidic solution containing toxic metal ions in presence of pyrite oxidizing bacteria (most common bacterium is Acidithiobacillus ferrooxidans) was released. As a result, a small river appeared in the region of the open pit mine whose water ph value was lower than 4.0. Regular sampling and laboratory analysis were carried out for surface water quality monitoring. ph was measured by ASTM E70-07 Standard Test Method of aqueous solutions ph evaluation using a glass electrode. The metal cation concentrations were determined by ISO 11885:2003 Water Quality - Determination of 33 elements by inductively coupled plasma atomic emission spectroscopy using ICP-AES. The sulphate and nitrate anions were determined by Standard Method: 4110 Deter- 350

2 Grigor Hlebarov, Nikolay Kozarev RESULTS AND DISCUSSION The mine drainage acid formation [6-8] can be expressed by the following reactions: FeS O 2 + H 2 O Fe SO 4 + 2H + (1) 4Fe 2+ + O 2 + 4H + Fe H 2 O (2) Fig. 1. Illustrates the mine drainage acid formation in the region of the open pit mine. mination of Anions by Ion Chromatography. The samples prepared for an analysis were filtered through 0.45 µm polysulfone membrane filter prior to being acidified to ph less than 2.0 using concentrated nitric acid. 4Fe H 2 O 4Fe(OH) H+ (3) FeS Fe H 2 O 15Fe SO H + (4) A noticeable decrease of pollutant concentrations in March, April and May ( ) is clearly outlined as shown in Figs. 2, 3 and 4. Fig. 2. Monthly average pollutant concentrations (mg dm -3 ) for Fig. 3. Monthly average pollutant concentrations (mg dm -3) for

3 Journal of Chemical Technology and Metallurgy, 51, 3, 2016 Fig. 4. Monthly average pollutant concentrations (mg dm -3 ) for Climate impact Both rainfall and snowfall vary in years. They influence the process of acid water generation as well as the river flow rate in its own way. The snow melt is a comparatively long process. Depending on the snow quantity this process can cover a couple of months. The rainfall water and a portion of the snow melting water reach the river very quickly. They both can be characterised as surface water, i.e. they do not penetrate deeply into the bulk of the rock material. The latter surface is known to be covered by a passivating film [9-14]. That is why the waters in question are comparatively clean. They increase the river flow rate and decrease the water pollutants concentration. Vice versa, the remaining snow water penetrates into the pyrite and chalcopyrite containing material. It reaches deeper layers under the ground surface. This water remains in the bulk of the rock material for prolonged periods of time and takes part in the processes of ph reduction and pollutants dissolution. It subsequently reaches the river too bringing about water pollutants. Figs. 5, 6 and 7 illustrate the rainfall and the river Fig. 5. Monthly average rainfall (l m -2 ) and river flow rate (l s -1 ) in Fig. 6. Monthly average rainfall (l m -2 ) and river flow rate (l s -1 ) in

4 Grigor Hlebarov, Nikolay Kozarev Fig. 7. Monthly average rainfall (l m -2 ) and river flow rate (l s -1 ) in flow rate variation for the period It is comparatively high during the spring period because of intensive snow melting. The peaks observed during the other seasons are referred to rainfall events. The monthly average flow rate of the river F (l s -1 ) is approximated by the polynomial equation with a coefficient of determination R² = Here M is the number of the months. Emission of water pollutants Not only the pollutant concentrations but also the pollutant emissions are very important from a point of view of environmental protection. The pollutant emissions are calculated on the ground of the metal concentrations and river flow rate evaluations. Although the pollutant concentrations are lower during the spring Fig. 8. Average monthly emission of pollutants (mg s -1 ) for

5 Journal of Chemical Technology and Metallurgy, 51, 3, 2016 Fig. 9. Average monthly emission of pollutants (mg s -1 ) for Fig. 10. Average monthly emission of pollutants (mg s -1 ) for period, the pollutant emissions are comparatively high because of the higher flow rate of the river. It is noteworthy to mention that ph as a parameter does not change in accord with the pollutant concentrations. The latter decrease even twice during the wet periods, whereas ph varies in a small interval from 3.6 to 4.0. The monthly pollutant emissions during the period of are shown in Figs. 8, 9 and 10. A noticeable increase of pollutant emissions in March, April and May is clearly outlined. The average monthly emissions of water pollutants for the period of , shown in the figures above, can be calculated using the polynomial equations listed in Table 1. Here M stays for the number of months, while E denotes the emission of the corresponding water pollutant. 354

6 Grigor Hlebarov, Nikolay Kozarev Table 1. Polynomial equations used for modeling of pollutants emission. Pollutant Emission E, mg s -1 R 2 Cu Mn Fe SO 4 NO CONCLUSIONS The emissions of certain water pollutants depend both on the river flow rate and the pollutant concentration. The maximum values of the river flow rate are observed from April to June each year during the period of Eventual rainfall events during the dry periods cause short time demotions of the pollutant concentrations because of pollutants dilution. Although the concentration of all five pollutants is quite low around April, the emissions are definitely high because of the high flow rate of the river. The latter is a significant factor, because it defines the wastewater residence time in the water treatment plant. This has to be taken into account with regard to its operation. REFERENCES 1. N.M. Dubrovsky, J.A. Cherry, E.J. Reardon, A.J. Vivyurka, Geochemical evolution of inactive pyritic tailings in Elliott Lake uranium district, J. Can. Geotech., 22, 1985, D.G. Feasby, M. Blanchette, G. Tremblay, L.L. Sirois, The mine environment neutral drainage program, in: Proceedings of the 2nd International Conference on the Abatement of Acidic Drainage, Montreal, PQ, 1, 1991, J.E.Dutrizac, The dissolution of chalcopyrite in ferric sulfate and ferric chloride media, Met. Trans. B, 12 B, 1981, J. Rivadeneira, Introduction Mining Innovation in Latin America Report, Santiago, Chile, 2006, E.M. Córdoba, J.A. Muñoz, M.L. Blázquez, F. González, A. Ballester, Leaching of chalcopyrite with ferric ion. Part IV: The role of redoxpotential in the presence of mesophilic and thermophilic bacteria, Hydrometallurgy, 93, 3-4, 1988, B.J. Baker, J.F. Banfield, Microbial communities in acid mine drainage, FEMS Microbial Ecology, 44, 2003, P.C. Singer, W. Stumm, Acidic mine drainage: the rate determining step, Science, 167, 1970, L.M. Prescott, J.P. Harley, D.A. Klei, Microbiology, 4th ed., McGraw-Hill, New York, Q. Yin, G.H. Kelsall, D.J. Vaughan, Atmospheric and electrochemical oxidation of the surface of chalcopyrite (CuFeS2), Geochimica et Cosmochimica Acta, 59, 1995, R.P. Hackl, D.B. Dreisinger, E. Peters, J.A. King, Passivation of chalcopyrite during oxidative leaching in sulfate media, Hydrometallurgy, 39, 1-3, 1995, A. Schippers, W. Sand, Bacterial leaching of metal sulfides proceeds by two indirect mechanisms via thiosulfate or via polysulfides and sulfur, Applied Environmental Microbiology, 65, 1, 1999, Y.L. Mikhlin, Y.V. Tomashevich, I.P. Asanov, A.V. Okotrub, V.A. Varnek, D.V. Vyalikh, Spectroscopic and electrochemical characterization of the surface layers of chalcopyrite reacted in acidic solutions, Applied Surface Science, 225, 2004, D. Bevilaqua, A.L.L.C. Leite, O. Garcia Jr., 355

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