Leseprobe
Chair of mining engineering and mineral economics
at University of Leoben
Bachelor Thesis
Characterization of Waterbodies Affected by
Acid Mine Drainage
Classification, sources and effects of acid mine drainage illustrated using
relevant international case studies
Thomas Heise
January 4, 2010
supervised by Dipl.Ing. Dr. G¨
unter Tiess
Abstract
Water is a natural resource of high significance for human beings, fauna and flora. There-
fore, the protection of water resources is one of the highest aims of each industrial site. The
mining sector and its subsectors have a lot of applications for water, also causing a high
potential to interfere with water systems. Mineral extraction, mineral resource storages,
mineral processing and mine waste storage form important potential pollutant emitters.
The weathering of sulphidic minerals cause the most severe mine-water-related problems,
because it involves a decrease in the pH level as well as an increase in dissolved total
solids, especially metal concentrations. This acid mine waters are categorized as acid mine
drainage. The drainage of acidic water represents the biggest conflict between mining and
environment in the world.
This thesis deals with the characterization of waterbodies impacted by acid mine drainage.
A discussion of the fundamental processes forms the basis of this paper. The classification
of mine drainage, the weathering of pyrite and potential pollution sources are discussed in
detail. However, impacts of acid mine drainage, drinking-water-specific values and legal and
political aspects are mentioned as well. Based on this theoretical part, various international,
especially European case studies will be reviewed. Each of these examples includes a brief
introduction to the general mine-water related situation and with a focus on a specific devel-
opment of the site, thus ensuring to illustrate the complexity of this environmental concern.
Finally, a conclusion is drawn from the discussion of the case studies, complementing the
theory part.
i
ii
Zusammenfassung
Wasser ist ein Gut h¨
ochsten Stellenwerts, sowohl f¨
ur Menschen, Fauna und Flora. Aus
diesem Grund ist die Vermeidung und Verminderung von Wasserressourcenverschmutzung
ein prim¨
ares Ziel eines jeden Industriebetriebes. Der Bergbausektor, mit allen seinen Unter-
bereichen, weist eine große Schnittstelle zu Wasser auf. Potentielle Schadstoffemittenten
schließen Gewinnungst¨
atigkeiten, Rohstofflagerung, Aufbereitungsprozesse und Bergbauab-
fallverwahrung ein. Besonders zu Tragen kommt die Problematik Bergbau und Wasser bei
der Verwitterung sulphidischer Mineralien, welche eine Verringerung des pH-Wertes sowie
eine Erh¨
ohung der gel¨
osten Feststoffkonzentration, vor allem Metallkonzentrationen, verur-
sacht. Diese sauren Bergw¨
asser werden als Acid Mine Drainage bezeichnet. Die Abgabe
saurer Bergw¨
asser, vor allem aus stillgelegten Bergwerken, beinhaltet das gr¨
oßte Konflikt-
potential zwischen Bergbau und Umwelt weltweit.
Diese Arbeit setzt sich mit der Charakterisierung von durch saure Bergw¨
asser beeinflussten
Wasserk¨
orpern auseinander. Die Basis dieser Abhandlung stellt eine detailierte Er¨
orterung
der grundlegenden Prozesse dar. Dabei werden vor allem die Klassifizierung von Bergw¨
assern,
die Pyritverwitterung und die potentiellen Emissionsquellen behandelt. Desweiteren wird
auf die Auswirkungen von Acid Mine Drainage, auf Trinkwasserqualit¨
atskennwerte und auf
gesetzliche und politische Aspekte pr¨
agnant eingegangen. Auf diesen theoretischen Teil
aufbauend werden eine Reihe internationaler, prim¨
ar europ¨
aischer Fallstudien erl¨
autert.
Jedes dieser Beispiele diskutiert zumeist die allgemeine f¨
ur Bergw¨
asser relevante Situa-
tion sowie einen Schwerpunkt, um den großen Umfang dieses Umweltproblems darstellen
zu k¨
onnen. Aus diesen Fallbeispielen werden anschließend Schl¨
usse gezogen, welche eine
wichtige Erg¨
anzung f¨
ur den Theorieteil darstellen.
iii
iv
Contents
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
i
Zusammenfassung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iii
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vii
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ix
List of Tables
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xiii
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
List of Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
I
Acid mine drainage theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2
Classification of acid mine drainage . . . . . . . . . . . . . . . . . . . . . . . .
7
3
Acid mine drainage process . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
3.1
Sulphide weathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
3.2
Metal dissolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
3.3
Process acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
3.4
Acidity buffering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
3.5
Metal precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
4
Sources of acid mine drainage . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
4.1
Active surface mining . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
4.2
Abandoned surface mining . . . . . . . . . . . . . . . . . . . . . . . . . .
29
4.3
Active underground mining . . . . . . . . . . . . . . . . . . . . . . . . .
33
4.4
Abandoned underground mining . . . . . . . . . . . . . . . . . . . . . . .
33
4.5
Waste rock and ore stockpiles . . . . . . . . . . . . . . . . . . . . . . . .
36
4.6
Tailings
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
v
4.7
Others . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
5
Effects and impacts of acid mine drainage
. . . . . . . . . . . . . . . . . . . .
39
6
Legal and political aspects of Acid Mine Drainage . . . . . . . . . . . . . . . .
45
6.1
Water in political and socio-economic tension - an introduction . . . . . .
45
6.2
Drinking-water limit values . . . . . . . . . . . . . . . . . . . . . . . . .
45
6.3
The European Union's political and legal instruments
. . . . . . . . . . .
48
6.4
Voluntary international mining-related environmental guidelines . . . . . .
50
II Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
51
7
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53
8
Rio Tinto and Rio Odiel, Spain . . . . . . . . . . . . . . . . . . . . . . . . . .
57
9
Avoca River, Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
67
10 Mine water contamination in Scotland
. . . . . . . . . . . . . . . . . . . . . .
71
11 R¨
otlbach, Austria
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
73
12 Gromolo Creek, Italy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
75
13 Acid Mine Drainage in Macedonia . . . . . . . . . . . . . . . . . . . . . . . . .
83
14 Ala¸sehir Mine, Turkey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
89
15 Ankobra River, Ghana . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
93
16 Banjar River, India . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
97
17 Acid Mine Drainage in Tasmania, Australia . . . . . . . . . . . . . . . . . . . . 101
18 Iron Mountain Mine, U.S.A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
19 Concluding summary of case studies . . . . . . . . . . . . . . . . . . . . . . . . 119
III Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
A Case studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
A.1
Photographs of European case study sites
. . . . . . . . . . . . . . . . . 128
A.2
Photographs of the Iron Mountain mining area . . . . . . . . . . . . . . . 131
vi
A.3
Rio Tinto and Rio Odiel . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
A.4
Avoca River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
A.5
Gremolo river
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
A.6
Acid mine drainage in Macedonia . . . . . . . . . . . . . . . . . . . . . . 149
A.7
Ala¸sehir Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
A.8
Ankobra River basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
A.9
Malanjkhand mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
A.10 Tasmania
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
A.11 Iron Mountain Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
vii
viii
List of Figures
1.1
Impacts of mining activities . . . . . . . . . . . . . . . . . . . . . . . . .
2
2.1
Types of mine drainage by pH . . . . . . . . . . . . . . . . . . . . . . . .
8
2.2
AMD, NMD, and SD as a function of dissolved base metal concentrations
9
2.3
AMD, NMD, and SD as a function of sulphate concentrations . . . . . . .
10
2.4
AMD development trends based on parameter changes . . . . . . . . . . .
10
3.1
Order of discussion of processes involved in AMD generation
. . . . . . .
11
3.2
Pyrite oxidation model . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
3.3
AMD engine model . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
4.1
Major Steps Involved in Extraction Metallurgy of Metals and linkage to
AMD generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26
4.2
Continuous rehabilitation at Garzweiler open pit, Germany . . . . . . . . .
28
4.3
Lavander open pit, U.S.A.; AMD-contaminated water has accumulated at
the open pit floor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
4.4
Acid pit lake at Berkeley Pit, Montana, U.S.A. . . . . . . . . . . . . . . .
30
4.5
Corta de la Atalaya; in background tailings . . . . . . . . . . . . . . . . .
32
4.6
Mine water discharge at Argo Tunnel . . . . . . . . . . . . . . . . . . . .
34
4.7
Hughes Bore Hole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
4.8
Hughes Bore Hole devastated area . . . . . . . . . . . . . . . . . . . . .
35
4.9
Spread of the cyanide spill of Baia Mare . . . . . . . . . . . . . . . . . .
38
5.1
AMD-impacted sediments at the Spring Creek Debris Dam
. . . . . . . .
40
5.2
Possible pH buffering zones under a waste heap
. . . . . . . . . . . . . .
41
5.3
Change in riparian vegetation due to AMD . . . . . . . . . . . . . . . . .
42
5.4
Fish dying of AMD in Tisza River during the Baia Mare tailing dam failure
43
ix
7.1
AMD topic in Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . .
54
7.2
Countries with case study sites . . . . . . . . . . . . . . . . . . . . . . .
55
8.1
Location of the Iberian Pyrite Belt (IBP) . . . . . . . . . . . . . . . . . .
58
8.2
Location of the Rio Tinto and Rio Odiel . . . . . . . . . . . . . . . . . .
59
8.3
Percent sand content (left) and median diameter (right) of the Tinto and
Odiel river bed sand and river bank mud samples . . . . . . . . . . . . . .
61
8.4
Content of copper (left) and zinc (right) in Tinto and Odiel river bed sand
and river bank mud . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
62
8.5
Content of lead (left) and arsenic (right) in Tinto and Odiel river bed sand
and river bank mud . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
63
9.1
Location of the Avoca river and sample sites . . . . . . . . . . . . . . . .
68
12.1 Map of the Libiola mine area and the Gromolo river . . . . . . . . . . . .
75
12.2 Different parameters in colored and colorless mine waters 1 . . . . . . . .
78
12.3 Different parameters in colored and colorless mine waters 2 . . . . . . . .
78
12.4 Relation between metal concentrations and pH in colored and uncolored
Libiola mine water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
79
12.5 pH development in the Gromolo river . . . . . . . . . . . . . . . . . . . .
80
12.6 Development of geochemical parameters in the Gromolo Creek
. . . . . .
81
12.7 Development of river sediments in the Libiola mine area . . . . . . . . . .
82
13.1 Map of the Republic of Macedonia showing the major rivers and mining
locations used in this thesis; . . . . . . . . . . . . . . . . . . . . . . . . .
83
13.2 Bucim mining area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
86
14.1 Location of sample sites at AM . . . . . . . . . . . . . . . . . . . . . . .
90
14.2 Ni, As, Hg and Cr concentrations in stream sediments and mining wastes
at AM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
91
15.1 Map of the Ankobra river system . . . . . . . . . . . . . . . . . . . . . .
93
15.2 Scatter plots of pH versus measured ions for dry season samples . . . . . .
95
15.3 Scatter plots of pH versus measured ions for wet season samples
. . . . .
95
x
16.1 Location map of Malanjkhand mine area. Sampling sites: 1. Karamsara
Lake (S1) 2. Leaching pond effluent (S2) 3. Waste dump (i) (S3) 4.
Waste dump (ii) (S4) 5. Tailing pond (S5) 6. Water holes within Copper
mine (S6); Source: Kant et.al. 2007 . . . . . . . . . . . . . . . . . . . . .
97
17.1 Map of Tasmania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
17.2 Distribution of sulphate in waters impacted by abandoned mines in Tasmania104
17.3 Distribution of metals in waters impacted by abandoned mines in Tasmania 105
17.4 Comparative distribution of selected acid-producing mine sites . . . . . . . 107
17.5 Hydrogeochemical expression of acid drainage in Ringarooma River
catchment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
18.1 River systems around the Iron Mountain Mine . . . . . . . . . . . . . . . 110
18.2 Cross-chapter of the Richmond and Lawson Adits . . . . . . . . . . . . . 112
18.3 Correlation between decrease of pH and increase of dissolved metals at IMM 114
18.4 AMD effects in the Sacramento river system . . . . . . . . . . . . . . . . 115
18.5 Location of sediment piles in SCR . . . . . . . . . . . . . . . . . . . . . . 116
A.1
Rio Odiel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
A.2
Upper Rio Tinto with sulphidic waste heaps
. . . . . . . . . . . . . . . . 128
A.3
Avoca Mines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
A.4
Avoca River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
A.5
Gromolo river . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
A.6
Gromolo river . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
A.7
Bucim mining pit
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
A.8
Iron Mountain Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
A.9
Richmond portal area . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
A.10 Surface run off at Iron Mountain mine . . . . . . . . . . . . . . . . . . . 132
A.11 Spring Creek just below the debris dam . . . . . . . . . . . . . . . . . . . 133
A.12 View of the Spring Creek arm of the Keswick reservoir and the Spring
Creek debris dam, also note the different water colors . . . . . . . . . . . 133
A.13 View of the Spring Creek arm of the Keswick reservoir and the Spring
Creek debris dam, also note the different water colors . . . . . . . . . . . 134
A.14 Spring Creek entering Keswick Reservoir . . . . . . . . . . . . . . . . . . 134
xi
A.15 Relation between annual rainfall and the contaminant load transported by
the Odiel River into the Huelva Estuary . . . . . . . . . . . . . . . . . . . 135
A.16 Heavy metal concentrations in Rio Tinto mud . . . . . . . . . . . . . . . 136
A.17 Development of heavy metal concentrations in Rio Tinto mud . . . . . . . 136
A.18 Heavy metal concentrations in Rio Tinto sand . . . . . . . . . . . . . . . 137
A.19 Development of heavy metal concentrations in Rio Tinto sand . . . . . . . 137
A.20 Heavy metal concentrations in Rio Odiel mud
. . . . . . . . . . . . . . . 138
A.21 Development of heavy metal concentrations in Rio Odiel mud . . . . . . . 138
A.22 Heavy metal concentrations in Rio Odiel sand
. . . . . . . . . . . . . . . 139
A.23 Development of heavy metal concentrations in Rio Odiel sand . . . . . . . 139
A.24 Cu, Pb and Zn concentrations in Avoca river subsurface sediments . . . . 140
A.25 Cu, Pb and Zn concentrations in Avoca river surface sediments . . . . . . 141
A.26 Fe concentrations in Avoca river subsurface and surface sediments
. . . . 141
A.27 Location of waste rock dumps and tailings in the Libiola mine area . . . . 142
A.28 Litographic sketch of the Gremolo basin and location of sample sites . . . 143
A.29 Gremolo water characteristics during high flow and normal flow season . . 146
A.30 Sediments of the Gremolo, Cattan and Bueno . . . . . . . . . . . . . . . 148
A.31 Distribution of water, mine wastes and stream sediments
. . . . . . . . . 155
A.32 Selected site characterization by sulphate levels in water . . . . . . . . . . 163
A.33 Concentrations of Al, Fe, and Si in sediment pile C . . . . . . . . . . . . . 164
A.34 Concentrations of dissolved metals and SO
4
, specific conductance and pH
in pore waters from pile C sediment . . . . . . . . . . . . . . . . . . . . . 164
A.35 Index map of Keswick Reservoir showing areas B through E . . . . . . . . 165
A.36 Sediment isopach map of Spring Creek arm and adjacent Keswick
Reservoir showing distribution and combined thickness of sedimentary
piles A, B and C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
A.37 Sediment isopach map of Keswick Reservoir below Spring Creek Arm
showing sediment distribution . . . . . . . . . . . . . . . . . . . . . . . . 167
A.38 Sediment isopach map of lower Keswick Reservoir showing sediment
distribution; sediment thickness is below 1 m . . . . . . . . . . . . . . . . 168
A.39 Sediment isopach map of lower Keswick Reservoir near Keswick dam
showing sediment distribution; sediment thickness is below 1 m . . . . . . 169
xii
List of Tables
1.1
Mineral categorization . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
3.1
Mean lifetime of a 1mm crystal at pH5 and 25
°C . . . . . . . . . . . . . . 22
7.1
Case study areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
55
8.1
Summary of Rio Odiel AMD-contaminated water . . . . . . . . . . . . . .
60
8.2
Contaminant load transported by the Odiel River . . . . . . . . . . . . . .
65
10.1 Scottish mine water characteristics (concentrations in mg/l) . . . . . . . .
72
12.1 Composition of Libiola waste heap 1 (concentration in wt%) . . . . . . . .
76
12.2 Composition of Libiola waste heap 2 (concentration in ppm) . . . . . . . .
76
15.1 Summary of geochemical characteristics and mining and processing
technologies of large-scale mines in the Ankobra area
. . . . . . . . . . .
94
15.2 Summary of of measured parameters for dry and wet seasons; all are in
mg/l, except for Hg (ppb) . . . . . . . . . . . . . . . . . . . . . . . . . .
96
16.1 Composition of the ore, tailings and concentrate obtained from the
Malanjkhand mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
98
16.2 Metal concentration in the land flora of Malanjkhand area . . . . . . . . . 100
17.1 Average surface water quality in catchments impacted by Tasmanian
abandoned mines
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
18.1 Composition of the IMM mine water 1983 - 1991
. . . . . . . . . . . . . 112
18.2 Five very acid mine water samples of Richmond Mine (in mg/l) . . . . . . 113
18.3 AMD contaminated sediments in the IMM area
. . . . . . . . . . . . . . 116
18.3 AMD contaminated sediments in the IMM area
. . . . . . . . . . . . . . 117
xiii
A.1
Composition of Libiola tailing water 1 (concentration in mg/l) . . . . . . . 144
A.2
Composition of Libiola tailing water 2 (concentration in mg/l) . . . . . . . 145
A.3
Composition of Libiola waste dumps 1 . . . . . . . . . . . . . . . . . . . 147
A.4
Zletovo major mine water characteristics 1 (mg/l) . . . . . . . . . . . . . 149
A.5
Zletovo major mine water characteristics 2 (
µg/l . . . . . . . . . . . . . . 150
A.6
Sasa major mine water characteristics 1 (mg/l) . . . . . . . . . . . . . . . 151
A.7
Sasa major mine water characteristics 2 (
µg/l . . . . . . . . . . . . . . . 151
A.8
Toranica major mine water characteristics 1 (mg/l)
. . . . . . . . . . . . 151
A.9
Toranica major mine water characteristics 2 (
µg/l . . . . . . . . . . . . . 152
A.10 Bucim major mine water characteristics 1 (mg/l) . . . . . . . . . . . . . . 152
A.11 Bucim major mine water characteristics 2 (
µg/l . . . . . . . . . . . . . . 152
A.12 Krstov Dol major mine water characteristics 1 (mg/l) . . . . . . . . . . . 153
A.13 Krstov Dol major mine water characteristics 2 (
µg/l . . . . . . . . . . . . 153
A.14 Alshar major mine water characteristics 1 (mg/l) . . . . . . . . . . . . . . 153
A.15 Alshar major mine water characteristics 2 (
µg/l . . . . . . . . . . . . . . . 154
A.16 Chemical analyses of the water samples from the study area
(concentration in
µg/l), part 1 . . . . . . . . . . . . . . . . . . . . . . . 156
A.17 Chemical analyses of the water samples from the study area
(concentration in
µg/l), part 2 . . . . . . . . . . . . . . . . . . . . . . . 157
A.18 Chemical properties of mine wastes and stream sediments . . . . . . . . . 158
A.20 Concentrations of mine drainage-impacted physico-chemical parameters
for dry season; all are in mg/l, except for Hg (ppb) and pH . . . . . . . . 159
A.19 Descriptive statistics of non-impacted waters (background values); all are
in mg/l, except for conductivity (Cond.) (in
µS/cm) and pH . . . . . . . . 160
A.21 Concentrations of mine drainage-impacted physico-chemical parameters
for wet season (also with groundwater); all are in mg/l, except for pH . . . 161
A.22 Composition of the ore, tailings and concentrate obtained from the
Malanjkhand mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
A.23 Surface and ground water quality analysis around Malanjkhand mine
. . . 162
xiv
List of Abbreviations
ABA
acid base accounting
AM
Ala¸sehir Mine
AMD
acid mine drainage
ANC
acid neutralizing capacity
ANFO
Ammonium Nitrate Fuel Oil
aq
aqueous
CIL
cyanidation using carbon in pulp
CMD
coal mine drainage
EAMD
extremely acid mine drainage
EC
electric conductivity
EPA
Environmental Protection Agency (United States of America)
ERMITE
Environmental Regulation of Mine Waters in the European Union
EU
European Union
g
gaseous
IPB
Iberian Pyrite Belt
IMM
Iron Mountain Mine
INAP
International Network for Acid Prevention
l
liquid
ME
any metal, unless otherwise noticed
MD
mine drainage
MPA
maximum potential acidity
NAPP
net-acid producing potential
NMD
neutral mine drainage
OCHA
Office for the Coordination of Humanitarian Affairs (of the United Nations)
s
solid
SCR
Spring Creek Reservoir
xv
SD
saline mine drainage
TDI
tolerable daily intake
TDS
total dissolved solids
UNEP
United Nations Environment Programme
WHO
World Health Organization
xvi
1 Introduction
Modern society depends on mineral resources, and so is the economic and social develop-
ment of developing and emerging countries. The range of mineral products includes ferrous
metals (e.g. iron and manganese), nonferrous metals (e.g. aluminum and copper), precious
metals (e.g. gold and silver), industrial minerals (e.g. phosphates, salt and clays), mineral
fuels (such as coal, oil and gas) and construction minerals (e.g. sand, gravel and crushed
stone). All these categories include different mineral resources (see table 1.1) with different
chemical properties.
Table 1.1: Mineral categorization
Mineral category
Included minerals
Ferrous metals
iron, chromium, cobalt, manganese, molybdenum, nickel,
tantalum and columbium, titanium, tungsten, vanadium
Nonferrous metals
aluminium, antimony, arsenic, bauxite, bismuth, cadmium,
copper, gallium, germanium, lead, lithium, mercury, rare-
earth minerals, tellurium, tin, zinc
Precious metals
gold,
platinum-group
metals
(palladium,
platinum,
rhodium), silver
Industrial minerals
asbestos, baryte, bentonite, boron minerals, diamond (gem
and industrial), diatomite, feldspar, fluorspar, gypsum and
anhydrite, graphite, guano, kaolin (china-clay), magnesite,
perlite, potash, phosphate rock, salt, sulfur, talc (incl.
steatite and pyrophyllite), vermiculite, zircon
Mineral fuels
steam coal (incl. anthracite and sub-bituminous coal), cok-
ing coal, lignite, natural gas, crude oil, oil sands, oil shales,
uranium
Source: Weber and Zsak 2009
1
The mining of mineral resources, depending on the mineral(s) to be mined, causes several
environmental problems (see figure 1.1). Mining affects the air (e.g. dust from blasting,
blasting noise, etc.), climate (e.g. disposal of CO
2
from mineral processing), water (e.g.
mine drainage, pumping of groundwater, etc.), soil (e.g. erosion, waste dumps and heaps,
etc.), flora and fauna (e.g. destruction of habitats, change of living conditions, etc.) and
also the social environment (e.g. employment opportunities at the mining site, etc.).
Mining
Air
Climate
Water
Soil
Flora
Fauna
Social
Environment
Figure 1.1: Impacts of mining activities
In this thesis a specific environmental impact of mining activities will be discussed: the in-
fluence of acid mine drainages on waterbodies. Acid mine drainage mainly occurs at metal
and coal mining sites. The most important elements will be mentioned later on, however, a
lot of them are already displayed in table 1.1. Although this thesis is entitled `Characteriza-
tion of Waterbodies Affected by Acid Mine Drainage' and therefore aims at the discussion
of water problems, the AMD topic extends beyond riverbeds or lakes. The process struc-
ture of acid mine drainage allows contaminants to infiltrate other environmental sectors.
One of the most important secondary receiving systems is the soil. The importance of the
soil and sediments to evaluate the damage of acid mine drainage will be indispensable for
2
this thesis. Flora and fauna are affected by acid mine drainage as well because their food
sources are connected to contaminated soil and water. Since water is one of the most im-
portant natural resources of our modern society, water pollution may also have impacts on
the socio-economic sector. As can be seen from this paragraph, one single mining-related
environmental problem affects all environmental sectors.
This thesis is split into two main parts. Part I forms the basis for part II. Part I is clearly
structured to ensure a systematic approach to the acid mine drainage basics. First of all,
acid mine drainage is distinguished from other mine drainages. For the further development
of this thesis, it is essential to define all possible mine drainages. The main chapter of part
I deals with the acid mine drainage process, which includes the weathering of sulphide ores,
metal dissolution, involvement of microorganisms, acidity buffering and mineral precipita-
tion. Mineral weathering is represented by the oxidation of pyrite. Still, other minerals will
also be mentioned. Following the chemical basis and the chemical sources, the focus will be
turned on the sources in operational mining and processing sites, followed by a discussion
of impacts and effects of acid mine drainage contamination. Political and legal aspects,
especially the definition of maximum values of metals, will be dealt with in the final chapter
of part I. Part II characterizes several case study sites. The majority of these study sites is
located in Europe. Each of these examples is meant to draw a specific conclusion, e.g. to
show the impact on fauna or the development of the pH levels.
3
4
Part I
Acid mine drainage theory
5
2 Classification of acid mine drainage
The impacts of mining on water is a broad field of research. Therefore it is very important
to emphasize the term mine drainage. In the Longman Dictionary of Contemporary English,
drainage is described as `the process or system by which water or waste liquid flows away'
[14]. From this it follows that mine drainage is a process where water escapes active or
abandoned mining sites. As will be shown in part II, environmental problems resulting
from mine drainage are primarily caused by abandoned mining sites. Furthermore, it will be
clarified later on that mine drainage may have different pH developments. The determination
of different categories of mine drainage is a very important initial step in this thesis and is
discussed in the following paragraph:
In general, there are four kinds of mine drainage [40, pp. 90ff.]:
extremely acid mine drainage (EAMD)
acid mine drainage (AMD)
neutral mine drainage (NMD)
saline mine drainage (SD)
Extremely acid mine drainage is categorized by a pH of less than 1 [40, p. 91]. This kind of
mine drainage, however, can only be observed in a few cases and shall not be discussed in
detail in the theory section. In part II, the Iron Mountain Mine area and its extremely acid
mine drainage will be mentioned. Acid mine drainage has a pH between 1 and 5.5 up to 6.
The difference between EAMD and AMD is that acid buffering reactions ensure that the
AMD water pH is over 1, whereas EAMD water lacks of acid buffering potential, mainly
caused by the absence of acid buffering minerals. Acid mine drainage is very common at
base metal, coal and gold mining sites [40, p. 90]. In neutral mine drainage waters, different
geochemical reactions keep a pH balance between 6 and 10 [40, p. 90]. It is very important
to define the term neutral mine drainage, because the word `neutral' seduces to think
7
about unaffected water. In fact, mine water contains dissolved minerals (e.g. zinc) [34].
NMD affected water has a circumneutral pH due to balancing of acid production and acid
buffering. Due to the depletion of acid buffering minerals, NMD may turn acid over the
time [40, pp. 90ff.]. Saline drainage has a wide-ranged pH parameter and a high influence
on ion concentrations in the water. SD can be observed at coal and industrial minerals
mining sites [40, p. 90]. Since mine water influenced by coal mining can be of acid, neutral
or alkaline pH, the term coal mine drainage (CMD) can be used for this special kind of
mine drainage. The chemical parameters of CMD may vary between single deposits or even
within one deposit. Those differences have their source in the genesis of the coal deposit
(especially in the paleoenvironment)[38]. Figure 2.1 summarizes the types of MD.
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
NMD
SD
EAMD
AMD
Figure 2.1: Types of mine drainage by pH
(after Lottermoser 2003 and INAP 2009)
There are several chemical parameters, which help describing mine waters. Two of them have
been mentioned already: pH and dissolved minerals (TDS - total dissolved solids). Other
important parameters are: reduction-oxidation potential, electrical conductivity, hardness,
alkalinity, acidity dissolved oxygen, turbidity, temperature and salinity [40, p. 88]. Out of
these parameters, the pH has been used to classify mine drainage. Still, there are several
other classification types, e.g. by major cations and anions as well as pH in combination
with Fe
2+
and Fe
3+
concentrations or other combined metals [40, p. 89]. In this thesis,
mine water will generally be classified by the overall chemical composition, the pH and the
pH versus combined metal concentrations (so called Ficklin diagrams).
Acid mine drainage has several characteristics. One of them, the different pH level, has
already been mentioned. Other very important parameters of AMD water are dissolved
metals and sulphate. In aquatic environment dissolved minerals may result in the dissolution
of other minerals, such as heavy metals (Fe, Cu, Pb, Zn, Cd, Co, Cr, Ni and Hg), metalloids
(As, Sb) and various other mineral resources (e.g. Al and Mn). Specifically, AMD water
contains sulphates on a high level (more than 1,000 mg l
-1
) as well as high concentrations
of Fe and Al (more than 100 mg l
-1
) and also elevated concentrations of heavy metals (more
8
than 10 mg l
-1
) [40, p. 90].
The concentrations of both metals and sulphate can be used to differentiate between AMD,
NMD and SD, using Ficklin diagrams. In these diagrams different base metals as well
as sulphate are plotted against pH. In figure 2.2, following metals are considered: zinc
(Zn), copper (Cu), lead (Pb), cadmium (Cd), cobalt (Co) and nickel (Ni). Various mining
sites located in different climatic zones using different mining and processing techniques
in different mining phases are represented in the diagram and summarized to an outline.
Figure 2.3 shows the pH in consideration of the sum of sulphates. Figure 2.4 shows several
parameter changes and their effects: increasing water evaporation, increasing base metal
sulphide content and increasing pyrite content lead to a more acidic composition of the
mine drainage, whereas increasing carbonate content and dilution decrease the acidity [35].
Figure 2.2: AMD, NMD, and SD as a function of dissolved base metal
concentrations
(Source: INAP 2009; http://gardguide.com/index.php/Chapter 2)
9
Figure 2.3: AMD, NMD, and SD as a function of sulphate concentrations
(Source: INAP 2009; http://gardguide.com/index.php/Chapter 2)
Figure 2.4: AMD development trends based on parameter changes
(Source: INAP 2009; http://gardguide.com/index.php/Chapter 2)
10
3 Acid mine drainage process
This chapter deals with the chemical process of AMD generation. This process can be
structured into five steps, which can be seen in figure 3.1. In the first process step, mineral
weathering, is essential for the formation of acid waters. In this step the mine drainage
becomes acid, laying the basis for the next step: metal dissolution. An important part
of AMD is the process acceleration due to the activity of microorganisms. Acid buffering
reactions take place during the whole acidity and metal leaching process, causing a constant
or decreasing pH level, which may also lead to the precipitation of the solved minerals [62,
p. 10ff.]. Still, the processes mentioned above and below do not have to form a real cycle.
It is possible that in some AMD waters the role of microorganisms is insignificant, acidity
is not buffered at all, etc. A lot of possibilities of AMD cycles and processes exist. Thus, in
this thesis the AMD process is described in an theoretical approach, shown in figure 3.1.
Sulphide
weathering
Metal dissolution
Process
acceleration due
to microorgansims
Acidity buffering
Mineral
precipitation
Figure 3.1: Order of discussion of processes involved in AMD generation
(after Lottermoser 2003 / Wolkersdorfer 2006)
On the following pages, the AMD cycle will be discussed in detail. It is very important to
mention chemical reactions for the understanding of this global mining-related problem.
Pyrite (FeS
2
) plays an important role. It is the most common sulphide that can be found
11
in the earth crust. Still, pyrite is not the only mineral to cause AMD. Other important
minerals connected to AMD will be mentioned later on. For the general explanation of
AMD, attention will be turned to pyrite, because it occurs in almost every metal and coal
deposit [40, p. 32].
3.1 Sulphide weathering
At the beginning of AMD there are three requirements (also see process reactions below):
water
oxygen
sulphidic minerals or mining waste
Both surface and underground mining may allow oxygen to reach parts of the sulphidic
deposit. This encounter is the basis for the weathering of those minerals. A mineral within
a structure may have three options of reactions:
to produce acid
to buffer acid
to stay neutral
The sum of all weathering reactions determines whether the dissolved weathering products
turns the containing medium (water, waste, etc.) acid or not [40, p. 32].
The AMD formation process begins when pyrite is confronted with oxygen. There are four
major possibilities of pyrite oxidation [40, p. 32]:
1. Abiotic direct oxidation
2. Biotic direct oxidation
3. Abiotic indirect oxidation
4. Biotic indirect oxidation
12
Resulting from the above listing, pyrite oxidation can take place with or without the presence
of microorganisms, even directly or indirectly. The difference between direct and indirect
may be explained easily. For a direct oxidation (abiotic or biotic) oxygen is used as oxidant,
whereas for indirect oxidation oxygen and ferric iron are needed [40, p. 32].
First, the direct oxidation (which is not the primary source of AMD) shall be reviewed.
Equation 3.1 shows the chemical process of direct pyrite oxidation [40, p. 32]:
F eS
2
(s) +
7
2
O
2
(g) + H
2
O(l) F e
2+
(aq) + 2SO
2-
4
(aq) + 2H
+
aq
+ energy
(3.1)
As seen on the educt side of the process, sulphidic minerals, water and oxygen are the
requirements for the start of the process. The above reaction is exothermic. The hydrogen
ion in aquatic phase is the indicator for the lowering of the pH level, which is defined as
pH = -log([H
3
O
+
]). The abiotic (and biotic) indirect oxidation of sulphide minerals is the
primary source of AMD and EAMD. As discussed before, this reaction requires the presence
of oxygen and iron, in particular ferric iron (Fe
3+
). The indirect oxidation of pyrite forms
a complex chemical concurrence. The process, which consists of three process steps, will
be mentioned in two ways: reaction equations where products and educts are combined to
their real chemical structures (see equations 3.2 to 3.4) and, for further explanation, such
where educts and products reagents are separated (see equations 3.5 to 3.7) [40, p. 33].
F eS
2
(s) + 14O
2
(g) + 4H
2
O(l) 4F eSO
4
(aq) + 4H
2
SO
4
(aq) + energy
(3.2)
4F eSO
4
(aq) + O
2
(g) + 2H
2
SO
4
(aq) 2F e
2
(SO
4
)
3
(aq) + 2H
2
O(l) + energy
(3.3)
F eS
2
(s) + F e
2
(SO
4
)
3
(aq) + 2H
2
O(l) + 3O
2
3F eSO
4
(aq) + 2H
2
SO
4
(aq) + energy
(3.4)
or
F eS
2
(s) +
7
2
O
2
(g) + H
2
O(l) F e
2+
(aq) + 2SO
2-
4
(aq) + 2H
+
(aq) + energy
(3.5)
F e
2+
(aq) +
1
4
O
2
(g) + H
+
(aq) F e
3+
(aq) +
1
2
H
2
O(l) + energy
(3.6)
13
F eS
2
(s) + 14F e
3+
(aq) + 8H
2
O(l) 15F e
2+
(aq) + 2SO
2-
4
(aq) + 16H
+
(aq) + energy
(3.7)
All reactions mentioned are exothermic. The indirect weathering of pyrite is characterized
by the involvement of ferrous and ferric iron. The first step shows the oxidation of pyrite into
dissolved iron, sulphate and hydrogen. This initial reaction causes an increase of dissolved
solids and a simultaneous decrease of the pH. The difference to the direct oxidation of
pyrite is that the pyrite oxidation into ferrous iron is just the initial reaction. If the oxygen
concentration is high enough, ferrous iron oxidizes into ferric iron (shown in reaction 3.6).
In the following reaction (reaction 3.7), the ferric iron oxidizes more pyrite [40, p. 33]. In
summary, the reactions mentioned above can be shown in an overall reaction [3]:
F eS
2
(s) +
15
8
O
2
(g) +
13
2
F e
3+
(aq) +
17
4
H
2
O(l)
15
2
F e
2+
(aq) + 2SO
2-
4
(aq) +
17
2
H
+
(aq)
(3.8)
The pyrite oxidation process can also be illustrated in a simplified diagram (see figure 3.2).
In the figure, the steps are marked with numbers [35]:
Figure 3.2: Pyrite oxidation model
(Source: International Network for Acid Prevention 2009)
14
Number 1 represents the pyrite weathering reaction 3.5
Number 1a represents pyrite dissolution and reaction, which shall not be part of this
thesis
Number 2 represents reaction 3.7
Number 3 represents reaction 3.6
The reaction marked 4 in the figure has not yet been mentioned, but is dealt with in
the next paragraph (and also reactions 3.9 and 3.10)
From figure 3.2 it is visible that reactions 3.6 and 3.7 form a cycle. The basis of this fact is
the conversion of ferrous to ferric iron. This cycle goes on until either the supply of pyrite
or ferric iron is depleted [40, p. 33f.]. Also is oxygen an important reagent in the formation
of ferric iron. The pH is the very important value here. Since ferric iron has a low solubility
in neutral- or high-pH waters, its concentration can increase in acidic water [40, p. 34]. The
AMD process underlies acid buffering reactions (see chapter 3.4) and therefore the pH of
the AMD water can increase. Even a small increase to a pH of about 3 causes the following
reactions [40, p. 34]:
F e
3+
(aq) + 3H
2
O(l) F e(OH)
3
(s) + 3H
+
(aq)
(3.9)
F e
3+
(aq) + 2H
2
O(l) F eOOH(s) + 3H
+
(aq)
(3.10)
These reactions cause a decrease of dissoluted ferric iron. This precipitation reactions,
however, also release hydrogen to the solution, which again leads to a reduction of the pH
value, still favoring the acidity generation process [40, p. 34]. Before turning attention to
further steps in the AMD process, the so-called AMD engine shall be discussed (see figure
3.3). The AMD engine summarizes all mentioned AMD generation reactions, which also
can be put together to one overall chemical reaction [40, p. 34f.]:
F eS
2
(s) +
15
4
O
2
(ag) +
7
2
H
2
O(l) F e(OH)
3
(s) + 2H
2
SO
4
(aq) + energy
(3.11)
Oxygen is the `starter switch' of the whole process. Oxygen, together with pyrite and
ferric iron, can be considered the `fuel'. Sulfuric acid, heat and iron hydroxide are `emitted
15
through the exhaust pipe'. The AMD engine again highlights that the whole AMD process
is dependent on the presence of pyrite, ferric iron and oxygen [40, p. 34f.].
+O
2
2
2
4
2-
+
2+
3+
2
4
+ + ()
3
Starter switch
Fuel
Engine room
Exhaust pipe
Figure 3.3: AMD engine model
(after Lottermoser 2003)
The speed of the acid generation process is dependent on several factors, which are men-
tioned in the two lists below, but not discussed any further [3]:
pH
temperature
oxygen content of the gas phase, if saturation is less than 100%
oxygen concentration in the water phase
degree of saturation with water
chemical activity of ferric iron
surface area of exposed metal sulphide
chemical activation energy required to initiate acid generation
bacterial activity
and furthermore [40, p. 35ff.]:
16
pyrite particle size, porosity and surface area
pyrite crystallography
trace element substitution (mineral inclusion in sulphide minerals)
presence of other sulphides
carbon dioxide concentration in the water and air phase
All reactions mentioned concern the oxidation of pyrite, which is also the most important
sulphide mineral. Still, pyrite is not the only source of AMD. Many other sulphide minerals
may weather analogous to pyrite, perhaps with a different acid production rate. An impor-
tant value affects the acid production: the metal to sulphur ratio [40, p.41f.]. Pyrite, for
example, has a ratio of 1:2, whereas for e.g. sphalerite it is 1:1. Besides pyrite, the following
minerals are important sources of AMD
1
[40, p.41f.] [35]:
marcasite (FeS) with oxygen as oxi-
dant
pyrrhotite (F e
1-x
S; x=0.0 to 0.2 )
mackinawite ((F e, Ni)
9
S
8
)
chalcopyrite (CuFeS
2
)
bornite (Cu
3
F eS
4
)
arsenopyrite (FeAsS)
sphalerite (ZnS)
covellite (CuS)
cinnabar (HgS)
molybdenite (MoS
2
)
millerite (NiS)
Furthermore, several non-sulphide minerals may produce acid. One example is the precip-
itation of iron hydroxide. Also the precipitation of aluminium hydroxides. Other minerals
generating acid are sulphate salts of Mn
2+
, Fe
2+
, Fe
3+
and Al
3+
, such as halotrichite
(F eAl
2
(SO
4
)
4
· 22H
2
O), jarosite (KF e
3
(SO
4
)
2
(OH)
2
) and alunite (KAl
3
(SO
4
)
2
(OH)
6
)
[40, p.42]. Since reactions for the acid production by precipitation and sulphide oxidation
were mentioned, the dissolution of sulphate and hydroxysulphate salts shall be discussed
1
With different oxidizing agents: oxygen, ferric iron or both. The minerals listed above represent ex-
amples only. The list could be continued.
17
using the example of halotrichite (see reaction 3.12) [40, p. 43]:
F eAl
2
(SO
4
)
4
(s) · 22H
2
O(l) + 0.25O
2
(g)
F e(OH)
3
(s) + 2Al(OH)
3
(s) + 13.5H
2
O(l) + 4SO
2-
4
(aq) + 8H
+
(aq)
(3.12)
3.2 Metal dissolution
This chapter represents a short overview of the metal dissolution process in connection
with AMD. Some parts of this chapter were already discussed in the previous subchapter.
Nonetheless, those parts shall be mentioned again in the context of this subchapter.
The AMD generation involves pyrite or/and other especially sulphidic minerals. Like the acid
generation process, the concentration of dissoluted metals is dependent on the pH. Since the
dissolution of metals and the production of acid are caused by the same chemical reactions,
the previous subchapter's reaction shall be supplemented with several simplified reactions
underlining the metal dissolution process. In detail, the oxidation of galena, sphalerite,
chalcopyrite and millerite shall be listed in reactions 3.13 to 3.16 [62, p. 14f.]:
P bS
2
(s) + 2O
2
(aq) P b
2+
(aq) + SO
2-
4
(aq)
(3.13)
ZnS
2
(s) + 2O
2
(aq) Zn
2+
(aq) + SO
2-
4
(aq)
(3.14)
CuF eS
2
(s) + 2O
2
(aq) Cu
2+
(aq) + F e
2+
(aq) + 2SO
2-
4
(aq)
(3.15)
N iS
2
(s) + 2O
2
(aq) N i
2+
(aq) + SO
2-
4
(aq)
(3.16)
The solution of metals can also be summarized in one overall reaction, where Me represents
any metal [62, p. 14f.]:
M e
n+
S
s
(s) + nO
2
(aq) M e
2+
(aq) +
2
n
SO
2-
4
(aq)
(3.17)
18
Another possibility of metal dissolution is the presence of ferric iron representing the oxi-
dizing agent. This reaction pathway shall be illustrated by reaction 3.18 and 3.19, showing
the dilution of chalcopyrite and pitchblende [62, p. 15]:
CuF eS
2
(s)+16F e
3+
(aq)+8H
2
O(l) Cu
2+
(aq)+17F e
2+
(aq)+2SO
2-
4
(aq)+16H
+
(aq)
(3.18)
U O
2
(s) + 2F e
3+
(aq) U O
2+
2
(aq) + 2F e
2+
(aq)
(3.19)
Together with acid production, dissoluted metals represent a serious problem connected
with AMD. Some examples of metal concentrations in AMD water are mentioned in part
II.
3.3 Process acceleration
As mentioned before, the AMD generation process can take place in an abiotic or biotic
environment. Bacteria, fungi, yeasts, algae and archae appear in AMD water [29]. Microor-
ganisms living in extreme alkaline or acidic environments are called extremophiles [62, p.
17]. In mine water, several hundreds of such organisms accumulate. An example is the Rio
Tinto in Spain, which will be discussed in part II: in this river more than 1,300 different
microorganisms can be identified [40, p. 93]. As far as the AMD process is concerned, some
microorganisms which require acidic living conditions may accelerate the sulphide oxidation
and therefore the metal dissolution. Furthermore, microorganisms play an important role in
AMD water remediation [62, p. 17]. Two forms of microorganisms have a significant ability
of accelerating the AMD process [62, p. 17] [40, p. 93]
2
:
Acidithiobacillus ferrooxidans
Acidithiobacillus thiooxidans
Both acidithiobacillus can be classified as autotrophic chemolithotrophs [62, p. 18]. The
characteristics of these bacteria are:
2
The two mentioned bacteria are not the only important examples. Furthermore, ferrobacillus sul-
fooxidans, leptospirillium ferrooxidans, thiobacillus concretivorus, thiobacillus thioparus, sulfobacillus
thermosulfidooxidans and metallogenium shall given as examples [40, p. 93].
19
function best at low pH: below 5 [40, p. 93]
autotrophic: `capable of manufacturing complex organic nutritive compounds from
simple inorganic sources'[57]; acidithiobacillus use carbondioxide as source
chemolithotroph: micoorganism using anorganic electron-donating sources as energy
supply [62, p. 18]
The acidithiobacilli are capable of catalyzing the AMD process. Acidithiobacillus ferrooxi-
dans oxidizes ferrous iron to ferric iron. Acidithiobacillus ferrooxidans and acidithiobacillus
thiooxidans produce sulphate [62, p. 22].
Since a discussion of the detailed involvement of microorganisms in AMD would exceed
the scope of this thesis, the detailed biotic AMD process shall not be mentioned here. In
conclusion, minerals which are oxidized by the bacteriae mentioned before, are listed below
[62, p. 21]:
antimonite (Sb
2
S3)
arsenopyrite (F eAsS)
orpiment (ASs
2
S
3
)
bismuthinite (Bi
2
S
3
)
bornite (Cu
5
F eS
4
)
chalcopyrite (CuF eS
2
)
chalcocite (Cu
2
S)
cinnabar (HgS)
covellite (CuS)
enargite (Cu
3
AsS
4
)
galena (P bS)
greenockite (CdS)
marcasite (F eS
2
)
millerite (NiS)
molybdenite (MoS)
pentlandite ((Ni, F e)
9
S
8
)
pyrite (F eS
2
)
pyrrhotite (e.g. F eS)
sphalerite (ZnS)
tetrahedrite (Cu
3
SbS
3.25
)
20
3.4 Acidity buffering
AMD-producing minerals generally occur with acidity-buffering minerals (proton acceptors).
Depending on the amount and ratio of proton acceptors and proton donators (e.g. pyrite),
the buffering minerals prevent the mine water from becoming acid or acid at all. Silicates
and carbonates are the most notable acid buffering minerals, but hydroxides can play an
important role as well [62, p. 23].
Since silicates are the major components of the Earth's crust, silicates are the most common
acidity-buffering minerals concerning AMD. Two possibilities of silicate weathering exist:
congruent and incongruent weathering. In congruent reactions, the total silicate mineral is
dissolved. Reaction 3.20 shows the general reaction of congruent weathering. The following
reaction 3.21 mentions the overall reaction process for incongruent silicate weathering,
which is characterized by a change in the physical phase of the silicate. The weathering
of silicate minerals consume hydrogen ions and release dissolved cations and silicic acid.
Incongruent weathering is more common than congruent. [40, p. 43 ff.].
2M eAlSiO
4
(s) + 2H
+
(aq) + H
2
O(l) M e
x+
(aq) + Al
2
Si
2
O
5
(OH)
4
(s)
Me = Ca, Na, K, Mg, Mn or Fe
(3.20)
M eAlSiO
4
(s) + H
+
(aq) + 3H
2
O(l) M e
x+
(aq) + Al
3+
(aq) + H
4
SiO
4
(aq) + 3OH
-
(aq)
Me = Ca, Na, K, Mg, Mn or Fe
(3.21)
Before turning the attention to the carbonate acid buffering system, the dissolution of iron
hydroxides shall briefly be discussed. In the AMD process (see AMD engine) ferric hydroxide
precipitates. Thus, iron hydroxide is available in AMD waters, representing another way of
acid buffering: hydrogen ions can be consumed, forming dissolved ferric iron (see reaction
3.22) [40, p. 45].
F e(OH)
3
(s) + 3H
+
(aq) F e
3+
(aq) + 3H
2
O(l)
(3.22)
Carbonates, e.g. calcite or dolomite, have an enormous acidity buffering potential. Calcite
is the most important mineral buffering the impacts of AMD. Calcite weathering influ-
ences the acidity of the water in two ways, dependent on the water's pH. Reaction 3.23
21
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- Thomas Heise (Autor:in), 2010, Characterization of Waterbodies Affected by Acid Mine Drainage, München, GRIN Verlag, https://www.grin.com/document/148142
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