Abandoned Smolník mine ( Slovakia ) a catchment area affected by mining activities

Smolník is a historical Cu-mining area that was exploited from the 14th century to 1990. The Smolník mine was definitively closed and flooded in 19901994. Acid mine drainage discharging from the flooded mine (pH = 3.83, Fe = 542 mg/l, SO4 = 3642 mg/l, Cu = 1880 μg/l, Zn = 9599 μg/l, As = 108 μg/l) acidified and contaminated the Smolník Creek water, which transported pollution into the Hnilec River catchment. The Smolník mine waste area has been used as a model area to document pollution of waters, stream sediments, and soils by metals and other toxic elements. Major goals of this complex study were to document creek water transport of the main pollutants (Fe, sulphates, Cu, Al, As, etc.) in the form of suspended solids, to investigate elements mobility in common mine waste (rock and processing waste heaps and tailing impoundment) and in the soil on the basis of neutralization and leach experiments. Different methodologies and techniques for sampling and chemical and mineralogical characterization of samples were used and checked to evaluate environmental risk of this abandoned mine area.


INTRODUCTION
Mining industry has created wasteland where large quantities of mine-derived wall rock and tailings have been stocked.Especially mining waste with sulphides has caused large-scale and/or long-term pollution of the environment, because it is able to generate acid mine drainage (AMD).Pyrite easily oxidizes in openair conditions in mine areas.Moreover, this process is catalyzed by bacteria, which multiply its efficiency to produce acidity (Jambor & Blowes 1994).The most serious consequences include pollution of superficial water and groundwater, contamination of soils, and damage to local ecosystems.
Copper ore (pyrite enriched in Cu) of the Smolník deposit was exploited from the 14th century to 1990.We started to study the Smolník mine area after 1995, when AMD in the so-called first flush strongly damaged the Smolník Creek catchment (e.g.Lintnerová 1996;Lintnerová et al. 1999Lintnerová et al. , 2003Lintnerová et al. , 2006;;Šoltés 2007).
The paper presents negative effects of the abandoned sulphide mine on the Smolník Creek catchment.Major objectives of the study were to document the transport of main pollutants by creek water (Fe, sulphates, Cu, Al, As, etc.) in dissolved and suspended solid forms and to investigate the mobility of elements in common types of mine waste (rock and processing waste heaps, tailings) and in the soil on the basis of neutralization and leach experiments.Different methodologies and techniques for sampling and chemical and mineralogical characterization of samples were used to evaluate environmental risk in this abandoned mine area.

METHODS
Water, precipitates, suspensions, mine waste, and stream sediments were sampled at the monitoring points shown in Fig. 1. (Lintnerová et al. 2003(Lintnerová et al. , 2006;;Šoltés 2007).Total and partial analyses of stream sediments and alluvial and anthropogenic soils were performed using standardized methods of analyses or the approach published in Sutherland (2002).Especially non-residual parts of soil samples were analysed in 0.5 M HCl leach.The PHREEQC program was used to model equilibrium mineral phases by recalculation of the results of analyses of natural waters and of leaching and precipitation experiments (Parkhurst & Apello 1999).Two sets of samples of AMD and creek water were neutralized by 1 M NaOH and the resulting precipitates and supernatants were analysed (Šoltés 2007).Potential mobility of selected elements in ore and mine waste samples was evaluated from the results of the three sets of batch experiments using the following leach reagents: distilled water, citric acid + natrium citrate, and dilute HNO 3 (Šoltés 2007).

RESULTS
The abandoned Smolník mine is an important and permanent source of contamination in the Smolník Creek with negative impact on the Hnilec River (Table 1).The AMD-outflows (SM-2, SM-Kar.) and seepages (SM-3, SM-5) fall into the hazardous waste category (according to the Council Directive from 12 December 1991, 91/689/EEC).Tailing impoundment in the vicinity of the abandoned mine is the second important source of the creek water contamination, because it permanently produces drainage water with increased contents of Fe, As, and sulphates (SM-OD, Table 1).Various types of mine water/drainage and waste were studied in the Smolník Creek catchment.The results indicate that each of them contributes a different amount of main contaminants: Fe, sulphates (S tot ), Cu, Al, As, Zn, and Mn (Tables 1, 2).Other elements (e.g.Pb, Sn, Se, Cr, Co, Ni, Cd) are potentially or quantitatively less important contaminants.The monitoring of the creek water indicates that the amounts of released pollutants vary seasonally (Lintnerová et al. 2006;Šoltés 2007).The major part of the dissolved mine-derived pollutants precipitate as Feoxyhydroxide and sulphate minerals when AMD mixes with creek water (Table 2).The precipitates accumulate under sites of the AMD discharge, in the tailing drainage conduits, and finally in the creek sediments.However, fresh precipitates are extremely fine-grained and are easily removed by the stream in the form of suspended matter (Table 3).Both forms of pollutants, water-dissolved and suspended, play an important role in the mine-derived Table 1.Average, minimum, and maximum values of selected elements and sulphates in waters from the abandoned mine (SM-2), tailings (SM-OD), and other AMD (SM-3, SM-5, SM-Kar.)pollutants of the Smolník Creek, collected in 2002-2003 (Lintnerová et al. 2006).TDS = total dissolved solids, n = number of analyses  Assumed changes in element species in the creek water, caused by the inflow of AMD to the creek, and saturation indices (SI) of mineral phases were calculated using the PHREEQC program (Parkhurst & Apello 1999;Šoltés 2007).For example, the Al species most hazardous to living organisms, AlSO 4 + and Al 3+ , predominated in water under the site of AMD inflow (Fig. 2).The distribution of SI values corresponds to the Fe-oxyhydroxide mineral phases observed in the natural precipitates when AMD is mixed with the creek water.The results of the modelling of water composition indicate that small changes in pH and water temperature could explain the observed seasonal changes in mineral composition (indicated also by changes in colour) and/or mineral distribution in the area during different seasons.
Generation of solid matter/precipitates was studied experimentally in the laboratory, using the analysed samples of AMD and creek water.The results documented progressive precipitation of amorphous Feoxyhydroxide and co-precipitation or capture of Al, Cu, Zn, and Mn into the solids with increasing pH (Table 4).Contents of sulphates are low in all solids probably due to the high content of Na + , which hampered precipitation of the assumed mineral phases with high positive SI, e.g.schwertmannite (Rosse & Elliot 2000;Jönsson et al. 2005).Less typical phases (e.g.hexahydrate or Na-Fe sulphates and gypsum) were identified in dried products (Šoltés 2007).Products were transformed progressively to goethite (Fig. 3).Relatively crystalline goethite was identified by X-ray analyses of products after elimination of dissolved salts by dialysis in distilled water.Feryhydrite and goethite occurred in precipitates when AMD samples were neutralized/diluted by water from the creek (SM-1) with diminutive NaOH adds and after 65 days "ripening" in stabilized pH and normal temperature conditions.
The aim of the experimental leach was to document the mobility of elements in rocks with pyrite, ores and in metallurgic slag samples and to estimate pollution potentials of these common materials in the mine waste area.The experimental study confirmed high Fe, Cu, and Zn leaching ability under strong acid conditions.The leaching kinetics of elements depend on the initial content of elements, their presence in more soluble forms/minerals, and many other properties (e.g. grain size, surface activity, secondary mineral coats).Weathered waste (e.g.recent to "ancient" heaps) continually supplied sulphates, iron, Cu, and other elements to pore water and therefore they could accumulate in soils.
Alluvial soils of the Smolník Creek catchment and anthropogenic soils covering mine waste were also studied.The simple 0.5 M HCl leach approach was used to estimate the non-residual content of elements (Sutherland 2002), because pH monitoring documented extreme soil acidity (pH < 3 to 4) in the mine-waste area.The total content of Fe, Mn, Cu, Zn, and As demonstrates the geochemically anomalous character of these neardeposit soils when compared to the national limit of risky elements in soils (Table 5).The increased contents of non-residual Cu, Zn, and Mn were observed in strong-Table 5. Total (analysed after total dissolution) and non-residual (analysed in 0.5 M HCl leach) contents of elements in soil samples collected in 2002.SM-1 = sample point, 5-15 = depth in cm, DRP -samples from the abandoned mine area near the monitoring point SM-2, not presented in the map in Fig. 1 Fe As is not intensively liberated from residual (lithogenic) components of alluvial soil (Table 5).However, high non-residual contents of As, Al, and Cu were detected in samples of anthropogenic soils from old dumps and also from the recently "constructed" soil cover in the previous mine-work area (Tables 5 and 6, court).High As content is obviously combined with fresh amorphous Fe-oxyhydroxides precipitated near the sites where acid drainages discharge to the air, i.e. mainly near the abandoned mine and tailing impoundment (Tables 2, 3).
A previous multistep sequential study documented that the largest part of metals in the Smolník Creek sediment is bounded to or adsorbed by Fe-oxides and by organic matter (Lintnerová et al. 2003).The contents of exchangeable or bioavailable Fe, Cu, Zn, and Mn have increased due to the generation of AMD and its highleach potential.In the polluted parts of the creek the amount of Fe-oxyhydroxide phases accompanied by other mine-derived elements is comparable to the amount of elements bounded in the residual part of the sediments.Bioavailability of elements could potentially increase due to transformation of "fresh" Fe-oxyhydroxides into stream sediments.
The results of soil analyses indicate that simple leaching by dilute (0.5 M) HCl could be a valuable tool in environmental assessment.These results are less selective than multistep sequential analyses but highly informative, while the analytical approach is rapid and cost-effective.

CONCLUSIONS
A flooded mine is a permanent source of acid mine water with stabilized (or balanced) composition.The environmental risk of the area will have the tendency to lowering its "hazardous content".Human activity in the mine-waste area is a very important risk factor, which includes especially the mining waste management, the utilization of the area, and the remediation and construction of an AMD treatment plant eventually.Negative impacts (exploitation of dumps, mine and dump stability changes, covering by landslide, and changes in ground water circulation) on this relatively stabilized environment will probably accelerate mobilization of potentially toxic elements and decrease pH of mine water.Otherwise, stabilization of mine dumps, maintenance of superficial water drainage in the waste area, and final Table 6.Non-residual contents of elements in soil samples collected in 2006.All samples from the 5-15 cm depth, K-1, CK-1/2, C-1/2, B-1/2, Rotenberg -samples from mine dumps, pyrite K-2/3, pyrite K-2/4 -recultivated area in the vicinity of the monitoring point SM-2, not presented in the map in Fig. 1 remediation would prevent increase in contamination and speed up the return to the initial or natural geochemical level of contamination, which is limited by the geological environment.

Table 3 .
Lintnerová et al. 2006)ements in suspended solid samples captured on > 0.45 µm membrane from the Smolník Creek water (more details inLintnerová et al. 2006) contamination, widening in the Smolník Creek catchment, and transport nearly equal volumes of mobilized (minederived) elements.On the basis of the measurements conducted in 2002-2003 we estimated that approximately 280 kg of Fe, 3.54 kg of Cu, and 1.44 kg Zn per day in suspended solids could have been transported by creek water into the river (measured near the creek-river confluence in the average runoff and climatic conditions).

Table 4 .
Content of elements after progressive neutralization of samples from K-0 to K-5 (Karitas) and SM-2/0 (New drainage) by 1 M NaOH in supernatants expressed in wt % of the initial content of the element.* measured 65 hours after neutralization