Maree SAIMM 2011 09 15 B

Report
Acid Mine Water – Can it be a valuable resource?
Waterfall, Witwatersrand National Botanical Gardens
The farm where gold was first discovered in
1886 by that an Australian gold miner, George Harrison
SA mineral reserves and production (% of World)
(from: DME, South Africa’s mineral industry 2006/2007)
Commodity
Reserves
Productio
n
Platinum
87.7 (1)
59.3 (1)
Vanadium
31.0 (1)
48.0 (1)
Zirconium
19.4 (2)
41.6 (2)
Ferro-chromium
-
40.5 (1)
Vermiculite
38.9 (2)
39.6 (1)
Chrome ore
72.4 (1)
38.7 (1)
Alumino-silicates
-
36.4 (1)
Titanium minerals
18.3 (2)
19.8 (2)
Manganese ore
80.0 (1)
13.3 (2)
Gold
40.1 (1)
11.1 (1)
Ferro-Mn/Fe-Si-Mn
6.0 (4)
Fluorspar
16.7 (2)
5.0 (4)
Coal
6.1 (8)
4.5 (5)
Water quality of gold mines in Gauteng
Parameter
Flow
Flow
pH
Free acidity
Iron(III)
Aluminium
Total acidity
Iron(II)
Total/Free acidity
Alkalinity
Sulphate
Calcium
Magnesium
Manganese
Zinc
Cobalt
Nickel
Copper
Uranium
Silicon
Barium
Chloride
Sodium
Potassium
TDS
(Ml/d)
(m3/h)
(mg/l as CaCO3)
(mg/l as Fe)
(mg/l as Al)
(mg/l as CaCO3)
(mg/l as Fe)
(mg/l as CaCO3)
(mg/l as SO4)
(mg/l as Ca)
(mg/l as Mg)
(mg/l as Mn)
(mg/l as Zn)
(mg/l as Co)
(mg/l as Ni)
(mg/l Cu)
(mg/l U)
(mg/l Si)
(mg/l Ba)
(mg/l as Cl)
(mg/l as Na)
(mg/l as K)
(mg/l)
Western Eastern
basin
basin
Rand
Uranium Grootvlei
IRB
20
108
833
4500
8
700
0
100
0
6.4
0
2 437
183
800
102
0.29
0.00
0
350
4800
1075
528
216
147
128
228
2
11.9
4.55
18
21
0.465
11
0.2
37.03
157
50
202
6 777.1
2 092.0
Central
basin
ERPM
60
2500
3.5
300
3
1 749
800
0.17
4096
582
250
15
4
1.5
5
180
104
14
6 060.6
Decant water from gold mines in Gauteng
Basin
Flow rate
(Ml/day)
Far Western
65
Western
60
Central
100
Eastern
120+
Total for
Gauteng gold
mines
345+
Mpumalanga
coal mines
80+
Limited area
Question
Can we deal with this problem in a cost-effective way?
Neutralized mine water
CONSEQUENCES OF OVERFLOWING
Pyrite (FeS2) or “Fool’s Gold”
remains stable when deep
underground ..
... but if exposed to 0² and H²0
(through decanting) it
decomposes and forms Acid
Mine Drainage (AMD)
Environmental Critical Level is
approximately 23m below
water level – lowest natural
spring
10
National Water Act of 1998
Key Principles
•
•
•
•
Decentralization
Equitable access
Efficiency
Sustainability
Key instruments:
• Polluter pays principle
• Mine closure certificate
Decant started March 2002 –
Apportionment
Harmony emergency measures
Directives and apportionment (2006)
Randfontein Estates Gold
Mine (Harmony 46%)
West Witwatersrand Gold Mine
(DRD 44%)
Mogale Gold Mine (Mintails
0.8%)
Co-operation agreement between
Mintails and DRD
Heads of Agreement between
Harmony, DRD and Mintails
12
What is mine water?
What is mine water not?
Components of AMD
4FeS2 + 14O2 + 4H2O  4FeSO4 + 4H2SO4
1. Free acid: H2SO4 already partially neutralized
2. Fe(II) acid: Cannot react with limestone/dolomite
3. Low concentrations of heavy metals
4. Salt (Ca, SO4)
How does AMD form?
1. Dissolution of limestone/dolomite
CaCO3 + H2O
 Ca2+ + HCO3- + H+
2. Pyrites oxidation as a result of ingress water running through
broken rock;
4FeS2 + 14O2 + 4H2O  4FeSO4 + 4H2SO4
3. Neutralization (natural attenuation)
H2SO4 + CaCO3
 CaSO4 + CO2 + H2O
4. Reciprocating contact of pyrites-rich ore with water and oxygen
as the water level fluctuates from water being pumped out at
a constant rate while the incoming water flow-rate fluctuates
with seasonal rainfall.
Water quality of gold mines in Gauteng
Parameter
Flow
Flow
pH
Free acidity
Iron(III)
Aluminium
Total acidity
Iron(II)
Total/Free acidity
Alkalinity
Sulphate
Calcium
Magnesium
Manganese
Zinc
Cobalt
Nickel
Copper
Uranium
Silicon
Barium
Chloride
Sodium
Potassium
TDS
(Ml/d)
(m3/h)
(mg/l as CaCO3)
(mg/l as Fe)
(mg/l as Al)
(mg/l as CaCO3)
(mg/l as Fe)
(mg/l as CaCO3)
(mg/l as SO4)
(mg/l as Ca)
(mg/l as Mg)
(mg/l as Mn)
(mg/l as Zn)
(mg/l as Co)
(mg/l as Ni)
(mg/l Cu)
(mg/l U)
(mg/l Si)
(mg/l Ba)
(mg/l as Cl)
(mg/l as Na)
(mg/l as K)
(mg/l)
Western Eastern
basin
basin
Rand
Uranium Grootvlei
IRB
20
108
833
4500
8
700
0
100
0
6.4
0
2 437
183
800
102
0.29
0.00
0
350
4800
1075
528
216
147
128
228
2
11.9
4.55
18
21
0.465
11
0.2
37.03
157
50
202
6 777.1
2 092.0
Central
basin
ERPM
60
2500
3.5
300
3
1 749
800
0.17
4096
582
250
15
4
1.5
5
180
104
14
6 060.6
Volume of mine water under Johannesburg
• Kariba Lake = 185 km3 or 185 000 000 Ml
Parameter
Depth (m)
Rise rate (m/d)
Time before decant (d)
Time before decant (years)
Void volume (Ml)
Mine depte (m)
Total void volume (Ml)
Total void volume (Ml)
Cariba lake (Ml)
AMD/Cariba Lake (%)
Basin
Eastern
700
0.42
1 667
4.57
180 000
3 000
771 429
Central
500
0.61
821
2.25
49 260
3 000
295 560
1 066 989
185 000 000
0.58
Battery acid
Mass fraction Density Concentration
H2SO4
(kg/L)
(mol/L)
10%
1.07
29–32%
1.25–1.28
~1
4.2–5
Common name
dilute sulfuric acid
battery acid
(used in lead–acid batteries)
62–70%
1.52–1.60
9.6–11.5
chamber acid
fertilizer acid
78–80%
1.70–1.73
13.5–14
tower acid
Glover acid
95–98%
1.83
~18
concentrated sulfuric acid
Acid
Eastern Basin
Acidity (mg/l CaCO3)
50
Western Basin
1800
Central Basin
1500
Battery Acid
Gas cool drink
450 000
800
Game Reserve put at risk
Four point plan
1. Encourage mining activities to stimulate job creation (reduced labour cost,
beneficiation of raw materials). The pumping and treatment cost should be offset
by the value of the mined minerals, the treated water, and dissolved by-products
reclaimed from the mine water.
2. Immediate implementation of:
– limestone neutralization for removal of free acid, iron(II) and partial
desalination.
– lime treatment for removal of toxic heavy metals and radioactivity,
– In the case of Grootvlei Mine, water is already neutralized due to natural
attenuation - Passive treatment
3. Implement desalination to meet water demand by 2014. Selected technology
based on capital and running costs, performance, process stability.
4. Pumping or not

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