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 Production

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

ParameterWestern

basinEastern

basinCentral

basinRand

Uranium Grootvlei ERPMIRB

Flow (Ml/d) 20 108 60Flow (m3/h) 833 4500 2500pH 8 3.5Free acidity (mg/l as CaCO3) 700 0 300Iron(III) (mg/l as Fe) 100 0Aluminium (mg/l as Al) 6.4 0 3Total acidity (mg/l as CaCO3) 2 437 183 1 749 Iron(II) (mg/l as Fe) 800 102 800Total/Free acidity 0.29 0.00 0.17Alkalinity (mg/l as CaCO3) 0 350Sulphate (mg/l as SO4) 4800 1075 4096Calcium (mg/l as Ca) 528 216 582 Magnesium (mg/l as Mg) 147 128 250Manganese (mg/l as Mn) 228 2 15Zinc (mg/l as Zn) 11.9 4Cobalt (mg/l as Co) 4.55 1.5Nickel (mg/l as Ni) 18 5Copper (mg/l Cu) 21Uranium (mg/l U) 0.465Silicon (mg/l Si) 11Barium (mg/l Ba) 0.2Chloride (mg/l as Cl) 37.03 157 180Sodium (mg/l as Na) 50 202 104Potassium (mg/l as K) 14TDS (mg/l) 6 777.1 2 092.0 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

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National Water Act of 1998

Key Principles• Decentralization• Equitable access• Efficiency• Sustainability

Key instruments:• Polluter pays principle• Mine closure certificate

Decant started March 2002 – 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

Apportionment

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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/dolomite3. Low concentrations of heavy metals4. Salt (Ca, SO4)

How does AMD form?

1. Dissolution of limestone/dolomiteCaCO3 + 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

ParameterWestern

basinEastern

basinCentral

basinRand

Uranium Grootvlei ERPMIRB

Flow (Ml/d) 20 108 60Flow (m3/h) 833 4500 2500pH 8 3.5Free acidity (mg/l as CaCO3) 700 0 300Iron(III) (mg/l as Fe) 100 0Aluminium (mg/l as Al) 6.4 0 3Total acidity (mg/l as CaCO3) 2 437 183 1 749 Iron(II) (mg/l as Fe) 800 102 800Total/Free acidity 0.29 0.00 0.17Alkalinity (mg/l as CaCO3) 0 350Sulphate (mg/l as SO4) 4800 1075 4096Calcium (mg/l as Ca) 528 216 582 Magnesium (mg/l as Mg) 147 128 250Manganese (mg/l as Mn) 228 2 15Zinc (mg/l as Zn) 11.9 4Cobalt (mg/l as Co) 4.55 1.5Nickel (mg/l as Ni) 18 5Copper (mg/l Cu) 21Uranium (mg/l U) 0.465Silicon (mg/l Si) 11Barium (mg/l Ba) 0.2Chloride (mg/l as Cl) 37.03 157 180Sodium (mg/l as Na) 50 202 104Potassium (mg/l as K) 14TDS (mg/l) 6 777.1 2 092.0 6 060.6

Volume of mine water under Johannesburg

• Kariba Lake = 185 km3 or 185 000 000 Ml

Parameter BasinEastern Central

Depth (m) 700 500Rise rate (m/d) 0.42 0.61 Time before decant (d) 1 667 821 Time before decant (years) 4.57 2.25 Void volume (Ml) 180 000 49 260 Mine depte (m) 3 000 3 000 Total void volume (Ml) 771 429 295 560 Total void volume (Ml) 1 066 989 Cariba lake (Ml) 185 000 000 AMD/Cariba Lake (%) 0.58

Battery acid

Mass fraction H2SO4

Density (kg/L)

Concentration (mol/L)

Common name

10% 1.07 ~1 dilute sulfuric acid

29–32% 1.25–1.28 4.2–5 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 Acidity (mg/l CaCO3)

Eastern Basin 50

Western Basin 1800

Central Basin 1500

Battery Acid 450 000

Gas cool drink 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 treatment3. Implement desalination to meet water demand by 2014. Selected technology

based on capital and running costs, performance, process stability. 4. Pumping or not