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Abandoned Smolnik mine (Slovakia)--a catchment area affected by mining activities/ Kaevandamisest mojustatud valgala--maha jaetud kaevandus Smolnikis (Slovakkias).

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 Smolnik deposit was exploited from the 14th century to 1990. We started to study the Smolnik mine area after 1995, when AMD in the so-called first flush strongly damaged the Smolnik Creek catchment (e.g. Lintnerovd 1996; Lintnerovd et al. 1999, 2003, 2006; Soltes 2007).

The paper presents negative effects of the abandoned sulphide mine on the Smolnik 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. (Lintnerova et al. 2003, 2006; Soltes 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 (Soltes 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 HN03 (Soltes 2007).

[FIGURE 1 OMITTED]

RESULTS

The abandoned Smolnik mine is an important and permanent source of contamination in the Smolnik 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 Smolnik Creek catchment. The results indicate that each of them contributes a different amount of main contaminants: Fe, sulphates ([S.sub.tot]), Cu, Al, As, Zn, and Mn (Tables 1, 2). Other elements (e.g. Ph, 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 (Lintnerova et al. 2006; Soltes 2007). The major part of the dissolved mine-derived pollutants precipitate as Fe-oxyhydroxide 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 contamination, widening in the Smolnik 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).

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; Soltes 2007). For example, the Al species most hazardous to living organisms, AlS[O.sub.4.sup.+] and [Al.sup.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.

[FIGURE 2 OMITTED]

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 Fe-oxyhydroxide 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.sup.+], which hampered precipitation of the assumed mineral phases with high positive SI, e.g. schwertmannite (Rosse & Elliot 2000; Jonsson et al. 2005). Less typical phases (e.g. hexahydrate or Na-Fe sulphates and gypsum) were identified in dried products (Soltes 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.

[FIGURE 3 OMITTED]

Alluvial soils of the Smolnik 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 near-deposit 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-to medium-acid alluvial soil samples. It is important that 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 Smolnik Creek sediment is bounded to or adsorbed by Fe-oxides and by organic matter (Lintnerova et al. 2003). The contents of exchangeable or bioavailable Fe, Cu, Zn, and Mn have increased due to the generation of AMD and its high-leach 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 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.

ACKNOWLEDGEMENTS

This work was supported by the Slovak VEGA fund (project No. 1/3072/06) and the Slovak Research and Development Agency under the contract APVV-0268-06 "Contamination generated by Sb mining in Slovakia; Evaluation and strategies for remediation".

Received 28 December 2007

REFERENCES

Jambor, J. L. & Blowes, D. W. (eds). 1994. The Short Course of the Environmental Geochemistry of Sulfide Mine Wastes. Mineral Association of Canada, Nepean, Canada, 550 pp.

Jonsson, J., Persson, P., Sjoberg, S. & Lovgren, L. 2005. Schwertmannite precipitated from acid mine drainage: phase transformation, sulphate release and surface properties. Applied Geochemistry, 20, 179-191.

Lintnerova, O. 1996. Mineralogy of Fe-ochre deposits from the acid mine water in the Smolnik mine (Slovakia). Geologica Carpathica., Clays, 5, 55-63.

Lintnerova, O., Sucha, V. & Stresko, V. 1999. Mineralogy and geochemistry of acid mine Fe precipitates from the main Slovak mining regions. Geologica Carpathica, 50, 395-404.

Lintnerova, O., Sottnik, P. & Soltes, S. 2003. Stream sediment and soil pollution in the Smolnik mining area (Slovakia). Slovak Geological Magazine, 9, 201-203.

Lintnerova, O., Sottnik, P. & Soltes, S. 2006. Dissolved matter and suspended solids in the Smolnik Creek polluted by acid mine drainage (Slovakia). Geologica Carpathica, 57, 311-324.

Parkhurst, D. L. & Apello, C. A. J. 1999. User Guide to PHREEQC (Version 2)--a Computer Program for Speciation, Batch Reaction, One-Dimensional Transport and Inverse Geochemical Calculation. USGS, 311 pp.

Rosse, S. & Elliot, W. C. 2000. The effect of pH regulation upon the release of sulfate from precipitates formed in acid mine drainage. Applied Geochemistry, 15, 27-34.

Sutherland, R. A. 2002. Comparison between non-residual Al, Co, Cu, Fe, Mn, Ni, Pb and Zn released by a three-step sequential extraction procedure and dilute hydrochloric acid leach from soil and road deposited sediments. Applied Geochemistry, 17, 353-365.

Soltes, S. 2007. Environmentalne rizikh kyslych banskych vod a banskych odpadov v povodi potoka Smolnik [Environmental Risk of Acid Mine Drainage and Mine Wastes in Creek Smolnik Catchment Area]. PhD thesis, Comenius University Bratislava, Slovakia, 157 pp. [in Slovak].

Otilia Lintnerova, Peter Sottnik, and Stanislav Soltes Department of Mineral Deposits, Faculty of Natural Sciences, Comenius University Bratislava, Mlynska dolina, 842 15 Bratislava, Slovakia; lintnerova@fns.uniba.sk, sottnik@fns.uniba.sk, soltes@fns.uniba.sk
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 Smolnik Creek,
collected in 2002-2003 (Lintnerova et al. 2006). TDS = total dissolved
solids, n = number of analyses

                                  SM-2                    SM-OD
                                   n=5                     n=5

Al            mg/1           82.7    (70.2-92.5)      0.2     (0.1-0.3)
Fe (total)    mg/1          542       (434-659)       5         (2-8)
[Fe.sup.2+]   mg/1          356       (239-551)       2         (1-3)
Mn            mg/1           35.5    (32.6-38.5)      3.4     (1.2-5.7)
Ca            mg/1          190       (125-249)      44        (19-71)
Mg            mg/1          328       (246-385)      37        (15-60)
S[O.sub.4.    mg/1         3642      (3125-4085)    253       (106-405)
sup.-2]
Zn            [micro]g/1   9599      (6850-12040)    45        (31-55)
Pb            [micro]g/1     81        (68-99)                   <4
As            [micro]g/1    108        (29-380)      46        (14-90)
Co            [micro]g/1    697       (483-914)      15         (7-26)
Ni            [micro]g/1    207       (147-247)      24        (20-29)
Cu            [micro]g/1   1880      (1470-2120)      9         (6-15)
Cd            [micro]g/1      9.2     (7.4-11.1)      3.1     (<03-700)
TDS           mg/1         5127      (4290-5990)    467       (228-752)
pH                            3.83   (3.27-4.12)      6.76     (6.35-
                                                                7.38)
                 SM-3     SM-5      SM-Kar.
                  n=1      n=1       n=1

Al               474.0     58.6      159.5
Fe (total)      3229      321       1091
[Fe.sup.2+]      421      166        222
Mn                25.3     10.1      170.5
Ca               304      160       2539
Mg               442      101       1004
S[O.sub.4.     14800     2220       9058
sup.-2]
Zn             43000     7070      24405
Pb               156       18         42.5
As             16800      140         13
Co              1810      353       1524
Ni               625      179        771
Cu            108000     7130      13665
Cd               101.3     14.5       21.4
TDS            23740     3040      12401
pH                 2.2      2.95       2.92

Table 2. Contents of the analysed elements and sulphates in the mine
drainage precipitates (Lintnerova et al. 2006).

                Precipitates from mine waters

              SM-2      SM-5    SM-Kar.    SM-OD

                            mg/kg

Fe           42700   44900      35210      33150
Al           10000    1203        500       1116
As            2523     842         38.46   10724
Pb             459      41         --         78
Zn              77      45         76       1052
Cu             270     302         68        731
Mg            1696     616         --       3398
Ca              27      77         --      21031
K              272     551         --       1978
Na             226     157         --       5237
Mn             103      35        403        606
S[O.sub.4.    8450     842         --      10724
sup.2-]
Se              --       0.52       0.06      --
Cr              --       3.75      --          8
Co              --       4.8        8.2       49
Sb              --       3.24       0.57      --

             Precipitates from the Smolnik Creek

              SM-4      SM-8       SM-9

                         mg/kg

Fe           35130      40900      20650
Al              --         --         --
As              59         14.25     119.33
Pb              55         50        188
Zn             164        345        854
Cu             217       1057       2164
Mg              --         --         --
Ca              --         --         --
K               --         --         --
Na              --         --         --
Mn             168        124       1973
S[O.sub.4.      --         --         --
sup.2-]
Se               0.22       0.02      --
Cr              14.24      --          7.8
Co               7.2        9.4       39.6
Sb               7.15      29.1        6.52

-- Not detected.

Table 3. Contents of selected elements in suspended solid samples
captured on >0.45 [micro]m membrane from the Smolnik Creek water
(more details in Lintnerova et al. 2006)

             SM-1      SM-4      SM-6     SM-8       H-0       H-1

Fe %          5.26     12.99     16.34     17.61      8.43     14.60
Al %          1.96      7.96      8.68      6.36      3.71      3.76
As mg/kg    112       142       251       135       124       103
Pb mg/kg    196       171       163       166       150       106
Zn mg/kg   1026       512       798      1235      1079      1979
Cu mg/kg    592      1818      2157      2407       665      1856

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

Sample       pH       Eh       Fe       Al      Zn
         65 hours *   mV

K-0         2.52      611     0        0       0
K-1         2.74      460    19.48    91.69    0
K-2         3.43      346    59.85    99.51   40.86
K-3         4.14      220    90.96    99.84   89.90
K-4         6.33       -6    99.91    99.59   98.82
K-5         7.98     -104    99.96    99.59   99.72

SM-2/0      2.73      454     0        0       0
SM-2/1      4.45      190    63.93     3.49    0
SM-2/2      5.33       64    50.24    25.42    0.34
SM-2/3      6.36      -63    50.86    93.42   16.61
SM-2/4      7.54      -67    75.97    99.92   78.56
SM-2/5      8.30       -7    99.97    99.83   99.69

Initial content of element in water, mg/l

K-0         2.52      611   301.6     83.6     9.1
SM-2/0      2.73      454   536      155      19.3

Sample    Cu       Mn     S[O.sub.4.sup.2-]

K-0       0        0           0
K-1      74.85     0           4.31
K-2      94.65     0           4.14
K-3      99.25     1.51        4.28
K-4      99.25    20.64        3.91
K-5      99.44    20.75        5.39

SM-2/0    0        0           0
SM-2/1    2.04     0           1.89
SM-2/2   12.64     0.79        1.71
SM-2/3   50.79     0.46        9.24
SM-2/4   99.34     6.15       15.09
SM-2/5   99.94    67.14       10.41

Initial content of element in water, mg/l

K-0       1.59    27.8      2839
SM-2/0   13.1    126.4      7275

Table 5. Total (analysed after total dissolution) and non-residual
(analysed in 0.5 M HC1 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

Sample            Fe, %       Mn, mg/kg      Cu, mg/kg

              Total   HCl    Total   HCl    Total   HCl

Alluvial soil

SM-1/5-15      5.06   1.21   1190     580    234    170
SM-4/5-15      7.96   1.68    590     248    376    183
SM-6/5-15      8.13   1.36    850     316    436    191
SM-7/5-15      6.57   2.24    440     358    448    213
SM-8/5-15      8.27   3.54    740     293    698    443
SM-7L/5-15     6.16   2.01   1550    1025   1435    875
SM-7L/20-30    5.19   1.06   1390      84    961    650
SM-7N/5-15     5.67   1.40    930     510    310    175
SM-7N/15-25    9.83   4.82    830     401    605    290
SM-7N/30-40    8.57   3.45   1070     590    537    171
SM-7N/40-50    8.69   3.22   1100     550    609    223
SM-7N/50-60    7.27   2.29    630     188    686    358

Court- constructed soil cover

DRP-4/20-30   12.66   2.92    730      54   1558    167
DRP-5/0-15    10.19   2.38    460      68    261     56
DRP-5/15 25    8.98   2.34     40      64    222     63

Sample         Zn, mg/kg     As, mg/kg


              Total   HCl   Total    HCl

Alluvial soil

SM-1/5-15      194    106     64     1.66
SM-4/5-15      187     53    315    10.4
SM-6/5-15      235    113    304     0.82
SM-7/5-15      170    147    180     1.58
SM-8/5-15      202     97    107     2.03
SM-7L/5-15     372    199     92     3.71
SM-7L/20-30    233    104     49     1.17
SM-7N/5-15     213    115     82     2.13
SM-7N/15-25    330    167    136     2.06
SM-7N/30-40    288    155    122     1.76
SM-7N/40-50    280    145    127     2.18
SM-7N/50-60    305    150    125     2.39

Court- constructed soil cover

DRP-4/20-30    315     28   1310     6.19
DRP-5/0-15     105     19    772     1.26
DRP-5/15 25     89     18    406     0.95

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--recul-
tivated area in the vicinity of the monitoring point SM-2, not
presented in the map in Fig. 1

Sample           Fe     Al      Mn    Zn     Cu      As
                 %                   mg/kg

Alluvial soil--bank of the Smolnik Creek

SM-1            3.76   11950    840   157    429     35
SM-Kar          8.33   10800    484   120    580    354
SM-7 1/2        4.67   12450    695   252    810     93
SM-7 2/2        2.40   10250    525    81    262     24
SM-7 5/6        4.88    9200    540   127    378     82

Heaps--anthropogenic soils

Depression      2.08   20600    130   177   6410     63
K-1/3           7.64   14500    337    84   1960    170
CK-1/2          5.59    8200   1165    42    310     33
C-1/2           8.81   17700    333   197    630    735
B-1/2           6.71   11700    232    61    385     27
Rotenberg      12.14   12200    217    92    680    487

Court--constructed soil cover

Pyrite K-2/3    6.23    6200    145    49   2975    640
Pyrite K-2/4    3.16   10000    270    79     55   4027
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Author:Lintnerova, Otilia; Sottnik, Peter; Soltes, Stanislav
Publication:Estonian Journal of Earth Sciences
Article Type:Report
Geographic Code:4EXSV
Date:Jun 1, 2008
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