Hydrochemical studies of mine water on abandoned Nagornaya mine showed that they are weakly alkaline with high color, permanganate demand (PD) and content of iron cations compared to Russian state legislation standards for natural water of a different type. Mine water are polluted with Na, Li, Cu, Ni and Sr cations, while gas chromatography identified some saturated hydrocarbons, mainly from С22Н46 to С32Н66. The study demonstrates a developed technology of local mine water treatment with a high color, PD and iron concentration. The scheme offered includes two basic stages: electrochemical oxidation with industrial ruthenium-titanium oxide electrode comprising 30% RuO2 and 70% TiO2, and electric coagulation on Al-anodes. As per the scheme, the content of easily oxidable organic substances, iron cations and color are reduced to environmental quality standards.

INTRODUCTION

The practice of coal mines abandonment worldwide acknowledges the discharge of mine water. Mine water may contain toxic substances in concentrations exceeding maximum allowable concentration (MAC) by tens of times causing the pollution of nearby water bodies related ground waters and soils degradation.

The analysis of literature (Krasnyanskiy 2002; Wolkersdorfer & Bowell 2005; Gusev 2010) and reports by institutes and organizations of coal industry showed that by origin and by physical and chemical composition mine water are the closest to natural underground waters but from ecological point they should be regarded as a special type of industrial waste water. Therefore, the same ecological requirements as for other kinds of waste water are imposed to the quality of such type of spill water, providing for respective treatment.

Mine water treatment method is chosen on the basis of mine waters’ chemical composition and climatic conditions of coal fields. One of the crucial problems of abandoned coal mines is the forming of acid drain waters, containing sulfate and metal. Currently, chemical methods are applied for their treatment. The cost of such treatment is high while sulfates and metals removal efficacy is rather low. Microbiological treatment with sulfate-reducing bacteria (Frank & Lushnikov 2006; Neculita et al. 2007), passive treatment with wetlands (Frank & Lushnikov 2006) and calcite (Jage et al. 2001; Cravotta 2003; Rötting et al. 2008) are alternatives to chemical methods. Authors (Jage et al. 2001) offer to use for the processing of acid mine drainage the systems for gradual alkalinity production, consisting of limestone and organic matter. One of the new mine water treatment methods is the use of liquid products upon desulfatization of fuel gases (Lamminen et al. 2001).

Currently, sorption treatment technology was developed for mine water. As sorbents proposed zeolite containing rocks (Khelmitskiy et al. 1998), rice husk and its ash (Arefieva et al. 2010), Russian Far East modified perlites (Arefieva et al. 2013). However each of those methods does not allow reaching the prescribed quality standards for the discharge of mine water into water bodies.

Electrochemical method is effective for acidic metal containing water. In (Patent 2056361 1991) acidic mine drainage from one of Kizelovskiy coal basin was treated electrochemically in anode and cathode chambers placed in tandem with blade anodes and wire cathodes while treatment level from sulfates and metal cations was 80–100%.

Thus, there is still no universal method for mine water treatment due to diversity of their composition. Therefore this paper is devoted to the study of mine waters chemical composition on abandoned Nagornaya mine in Partizansk city of Primorskiy Krai and the search of methods for their treatment.

METHODS

The object of research was the mine water sampled from settler pond of treatment facilities abandoned Nagornaya mine in Partizansk city in 2010–2013 (Table 1). Nagornaya mine has been flooded since July 1998. The hydrochemical situation of surface, natural underground and mine water within the mining allotment is rather severe.

Table 1

Average chemical composition of mine water of abandoned Nagornaya mine in Partizansk coal basin

                Hardness
 
      
Sampling date pH Color, degree Turbidity, mg·L−1 Dry matter, mg·L−1 Mineralization, mg·L−1 PD, mgO·L−1 Alkalinity, mg-eq.·L−1 Ca2+ + Mg2+, mg-eq.·L−1 Ca2+, mg·L−1 Mg2+, mg·L−1 Fetotal., mg·L−1 Cl-, mg·L−1 SO42-, mg·L−1 
MAC for public drinking water supply (SanPiN 2.1.4.1074-016.0–9.0 20 1.5 –* 1,000 – 7.0–10.0 – – 0.3 350 500 
MAC for fishery water body (Order of RF fishing agency 20106.5–8.5 35 – – – – – – 180 40 0.1 12 100 
2010 7.8 ± 0.4 277 ± 121 9.2 ± 3.8 2,500 ± 196 1,651 ± 262 223 ± 36 38 ± 2 5.0 ± 0.3 68 ± 17 20 ± 9 0.03 ± 0.01 20 ± 2 203 ± 79 
2012–2013 7.9 ± 0.4 197 ± 7 11.8 ± 7.1 2,096 ± 479 1,781 ± 369 22 ± 5 32 ± 2 6.0 ± 2.0 57 ± 3 39 ± 19 0.69 ± 0.23 18 ± 1 105 ± 35 
                Hardness
 
      
Sampling date pH Color, degree Turbidity, mg·L−1 Dry matter, mg·L−1 Mineralization, mg·L−1 PD, mgO·L−1 Alkalinity, mg-eq.·L−1 Ca2+ + Mg2+, mg-eq.·L−1 Ca2+, mg·L−1 Mg2+, mg·L−1 Fetotal., mg·L−1 Cl-, mg·L−1 SO42-, mg·L−1 
MAC for public drinking water supply (SanPiN 2.1.4.1074-016.0–9.0 20 1.5 –* 1,000 – 7.0–10.0 – – 0.3 350 500 
MAC for fishery water body (Order of RF fishing agency 20106.5–8.5 35 – – – – – – 180 40 0.1 12 100 
2010 7.8 ± 0.4 277 ± 121 9.2 ± 3.8 2,500 ± 196 1,651 ± 262 223 ± 36 38 ± 2 5.0 ± 0.3 68 ± 17 20 ± 9 0.03 ± 0.01 20 ± 2 203 ± 79 
2012–2013 7.9 ± 0.4 197 ± 7 11.8 ± 7.1 2,096 ± 479 1,781 ± 369 22 ± 5 32 ± 2 6.0 ± 2.0 57 ± 3 39 ± 19 0.69 ± 0.23 18 ± 1 105 ± 35 

*Parameter not subject to limitation.

The chemical composition of water is formed under the influence of natural factors and infiltration of dirty waters from city's area and desalination of pollutants from mine rocks in flooded mine's area.

The basic hydrochemical parameters were determined as per approved guidelines: color; turbidity; dry matter; mineralization; hydrogen index; permanganate demand (PD); total hardness; calcium and magnesium ion content; total alkalinity; chlorides; sulfates; total iron.

Metals content was determined by atomic emission spectroscopy by parallel action inductively coupled plasma spectrometer ICPE-9000 (Shimadzu, Japan).

Quantity analysis of hydrocarbons content in mine water was made by gas chromatography method. Hydrocarbons were extracted by methylene chloride. The analysis was done by gas chromatographer GC-2010 (Shimadzu, Japan), equipped with flame ionization detector and capillary column Ultra-ALLOY-5HT (length 30 m, internal diameter 0.25 mm, film thickness 0.1 μm). Temperature program: initial temperature 50 °С (3 min) at the speed of 20 °С·min−1 to 400 °С (20 min). Splitting was 1:40. Injector was heated from 100 to 400 °С. The temperature of flame ionization detector was 420 °С. For quantity analysis ASTM D5442 C12-C60, Supelco standard was used.

Local treatment of mine water was made using the following methods: electric coagulation, electrochemical oxidation and sorption using Kovdor deposit vermiculite modified with chitosan. Mine water treatment process was controlled by the change of pH, color, turbidity, PD and total iron content.

Electric coagulation treatment of mine water was made in electrolytic diaphragmless cell 1 L capacity using six aluminum blade electrodes (three anodes and three cathodes) at density 170 А·m−2 and voltage 150–20 V. Electric coagulation was direct current (DC) and alternating current (AC) for 10, 20 and 25 min respectively.

The process of electrochemical oxidation of mine water was conducted in diaphragmless temperature-controlled electrolytic cell with continuous stirring at anode density of current from 44 to 178 А·m−2. As the anode, industrial oxide ruthenium and titanium electrode (ORTA) was used consisting of 30% RuO2 and 70% TiO2, with the cathode material Ti ВТ1-0 grade. Electrochemical oxidation process took 10–15 min.

Sorption experiments were made in static conditions. Weighed quantity of sorbent was flushed with mine water in 1:100 ratio, then the bottle was shaken by stirring device for 1 hour and filtered off from sorbent.

RESULTS AND DISCUSSION

The industrial area of Nagornaya mine housed reagentless complex of mine water treatment facilities but despite their availability the mine water discharged do not comply with the normative requirements. Average chemical composition of mine water by basic hydrochemical parameters was listed in Table 1.

As seen from Table 1, industrial water of Nagornaya mine are highly mineralized with moderate hardness, increased PD, color, turbidity, and total iron content. Color, turbidity, mineralization, PD and iron content do not comply with the hygienic requirements to water quality of public drinking water supply. By 2013, color, PD and sulfates content decreased greatly. Meantime, turbidity, mineralization and total iron increased. Thus, a trend for mine water salination and enrichment with iron cations is seen. Discharge of such water without further treatment may cause worsening of the nearby water bodies being the public drinking water supply.

Besides general hydrochemical analysis, metals content was determined by atomic emission spectroscopy. The results obtained are listed in Table 2.

Table 2

Metals content in mine water from abandoned Nagornaya mine of Partizansk coal basin, mg·L−1

Metals MAC for public drinking water supply (SanPiN 2.1.4.1074-01MAC for fishery water body (Order of RF fishing agency 2010MAC for household water use (GN 2.1.5.1315-03Concent-ration 
Aluminum 0.5 0.04 0.2 0.01 
Barium 0.1 0.74 0.7 0.044 
Calcium –* 180 – 19 
Cadmium 0.001 0.005 0.001 <0.005 
Cobalt – 0.01 0.1 <0.005 
Chrome 0.05 0.02 0.05 <0.005 
Lead 0.03 0.006 0.01 <0.005 
Copper 1.0 0.001 1.0 0.008 
Potassium – 50 – 4.4 
Lithium – 0.08 0.03 0.14 
Magnesium – 40 50 9.9 
Sodium – 120 200 400 
Nickel 0.1 0.01 0.02 0.019 
Strontium 7.0 0.4 7.0 1.45 
Manganese 0.1 0.01 0.1 <0.01 
Zinc 5.0 0.01 1.0 <0.01 
Metals MAC for public drinking water supply (SanPiN 2.1.4.1074-01MAC for fishery water body (Order of RF fishing agency 2010MAC for household water use (GN 2.1.5.1315-03Concent-ration 
Aluminum 0.5 0.04 0.2 0.01 
Barium 0.1 0.74 0.7 0.044 
Calcium –* 180 – 19 
Cadmium 0.001 0.005 0.001 <0.005 
Cobalt – 0.01 0.1 <0.005 
Chrome 0.05 0.02 0.05 <0.005 
Lead 0.03 0.006 0.01 <0.005 
Copper 1.0 0.001 1.0 0.008 
Potassium – 50 – 4.4 
Lithium – 0.08 0.03 0.14 
Magnesium – 40 50 9.9 
Sodium – 120 200 400 
Nickel 0.1 0.01 0.02 0.019 
Strontium 7.0 0.4 7.0 1.45 
Manganese 0.1 0.01 0.1 <0.01 
Zinc 5.0 0.01 1.0 <0.01 

*Parameter not subject to limitation.

As seen from Table 2, mine water contains metal cations but most of them do not exceed environmental quality standards. However, the concentration of Na, Li exceed the MAC levels for drinking and fishing water bodies, and the concentration of Cu, Ni and Sr does so only in connection with fishing water bodies. Lithium source in mine waters may be enclosing rocks rich in pyrite sediments (Nazarenko 2003). One more source of lithium accumulation in water maybe the process of sea drying while water is evaporated and lithium salts are accumulated in sea brine. Lithium rich sea brine may be the source of water enrichment with lithium. During the development of Far East as a continent lithium could be accumulated in coal layers from sea brine. Increased copper, nickel and strontium content may be linked with their presence in Partizansk coal basin.

As per the literature's data (The USSR geology 1974), in coal layers of Partizansk coal basin oil hydrocarbons are contained. Therefore the analysis of mine water for hydrocarbons content was carried out. The results are depicted on Figure 1.
Figure 1

Chromatogram of mine water extract from abandoned Nagornaya mine.

Figure 1

Chromatogram of mine water extract from abandoned Nagornaya mine.

As see from Figure 1, alkane hydrocarbons with carbon atoms content from 18 to 38 were identified in mine water. The percent of unidentified compounds is 35% of the total hydrocarbons volume. The concentration of some hydrocarbons is within the range from 13 to 226 μg·L−1. The total content is 2.67 mg·L−1 which exceeds environmental quality standards for various water types in 9 to 53 times (SanPiN 2.1.4.1074-01 2002; Hygienic standards GN 2.1.5.1315-03 2003; Order of Russian Federal fishing agency 2010). Thus, organic matters are the main pollutants of mine water basically represented saturated hydrocarbons and iron compounds.

Mining allotment of Nagornaya mine based upon mine's drainage chemical composition utilizes comprehensive system of treatment facilities consisting of a water discharge complex, ponds, regulating containment ponds, filtering massive with carbon-bearing argillite filling. Filtering fillings used at the existing treatment facilities are not always effective therefore a search for alternative treatment methods is continuous. The results of mine water treatment study are listed in Table 3.

Table 3

Chemical composition of treated mine water of abandoned Nagornaya mine

Local treatment methods pH Color, degree Turbidity, mg·L−1 PD, mgO·L−1 Fetotal, mg·L−1 
MAC for public drinking water supply (SanPiN 2.1.4.1074-016.0–9.0 20 1.5 0.3 
MAC for fishery water body (Order of RF fishing agency 20106.5–8.5 35 –* – 0.10 
Initial sample 8.3 173 8.2 18 0.47 
Electric coagulation (Al-anode, 10 minutes, DC) 8.8 189 17.6 28 0.05 
Electric coagulation (Al-anode, 20 minutes, DC) 9.0 324 32.7 23 0.05 
Electric coagulation (Al- anode, 10 minutes, AC) 8.5 202 28.7 20 0.09 
Electric coagulation (Al- anode, 25 minutes, AC) 9.8 147 52.0 19 0.04 
Sorption (chitosan-modified vermiculite) 8.6 46 6.5 155 0.14 
Electrochemical oxidation by ORTA and electric coagulation (Al-anode, 20 minutes, DC) 4.3 1.78 
Electrochemical oxidation by ORTA and electric coagulation (Al-anode, 20 minutes, AC) 8.3 11 0.4 
Local treatment methods pH Color, degree Turbidity, mg·L−1 PD, mgO·L−1 Fetotal, mg·L−1 
MAC for public drinking water supply (SanPiN 2.1.4.1074-016.0–9.0 20 1.5 0.3 
MAC for fishery water body (Order of RF fishing agency 20106.5–8.5 35 –* – 0.10 
Initial sample 8.3 173 8.2 18 0.47 
Electric coagulation (Al-anode, 10 minutes, DC) 8.8 189 17.6 28 0.05 
Electric coagulation (Al-anode, 20 minutes, DC) 9.0 324 32.7 23 0.05 
Electric coagulation (Al- anode, 10 minutes, AC) 8.5 202 28.7 20 0.09 
Electric coagulation (Al- anode, 25 minutes, AC) 9.8 147 52.0 19 0.04 
Sorption (chitosan-modified vermiculite) 8.6 46 6.5 155 0.14 
Electrochemical oxidation by ORTA and electric coagulation (Al-anode, 20 minutes, DC) 4.3 1.78 
Electrochemical oxidation by ORTA and electric coagulation (Al-anode, 20 minutes, AC) 8.3 11 0.4 

*Parameter is not subject to limitation.

Electric coagulation treatment method showed that iron compounds are removed while other parameters increased compared to the initial sample. Kovdor deposit chitosan-modified vermiculite sorption method did not drop the PD either. For the tasks set forth, electrochemical oxidation method by ORTA together with electric coagulation is the most compliant.

pH is an important factor for electric coagulation. When pH is moved to the acidic side iron compounds remain in ionic form while in alkaline medium at pH = 8, coagulation process of iron compounds begins. Thus, for the treatment of mine water the following local treatment scheme may be offered (Figure 2).
Figure 2

Scheme of local treatment of mine water.

Figure 2

Scheme of local treatment of mine water.

CONCLUSIONS

The study showed that by the chemical composition the mine water of abandoned Nagornaya mine of Partizansk coal basin are weakly alkaline with increased PD, color, turbidity and total iron content. Observations over the chemical composition of mine water in 2010–2012 showed that on one hand there is a drop of color but on the other hand there is a rise of salts and iron cations content.

It was found that the concentration of Na, Li, Cu, Ni and Sr exceed the prescribed MAC. Saturated hydrocarbons were identified in mine water, mainly from С22Н46 to С32Н66, the total content of which exceeds environmental quality standards for various water types.

A method was offered for the development of mine water local treatment technology with increased color, PD and high iron concentration. The scheme suggested includes the two basic stages: electrochemical oxidation by ORTA and electric coagulation.

ACKNOWLEDGEMENTS

The study was supported by The Ministry of education and science of Russian Federation, project № 4.1517.2014 К.

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