Mining WWTP covers open-pit/underground drainage, ore beneficiation and cyanide leach circuits. Among the toughest industrial sectors due to acid mine drainage (AMD) and toxic constituents.
Mining effluent: pH 2-4 (sulfuric acid), heavy metals (Fe, Cu, Zn, Pb, Cd, As) 10-1,000 mg/L, cyanide 50-500 mg/L (gold mines), sulfate 1,000-10,000 mg/L. Composition varies per mine type.
Arsistek mining solutions: lime neutralization, multi-metal precipitation, cyanide destruction (INCO/Caro's acid), arsenic adsorption and sulfate reduction. Effluent meets discharge limits and is reusable as process water.
Acid Mine Drainage (AMD)
AMD forms when sulfide ores (pyrite FeS2) contact air and water:
2 FeS2 + 7 O2 + 2 H2O → 2 FeSO4 + 2 H2SO4
Drops pH to 2-3 and dissolves heavy metals. AMD can persist for decades — even after mine closure.
AMD treatment: active (lime + precipitation) for high flows or passive (constructed wetlands, oxic drains) for low flows.
Staged Metal Precipitation
Each metal precipitates at its own optimal pH. Fe at 4, Zn at 9, Cd at 10.5. Staged pH adjustment separates and recovers metals.
For multi-metal effluent: precipitation at pH 9-10 as hydroxide mix. Copper mines use additional sulfide precipitation (CuS) for recovery.
Cyanide Destruction
Gold mines leave free CN and metal-cyanide complexes (Fe(CN)6). INCO (SO2/air) or Caro's acid (H2O2) reduces to <0.5 mg/L.
Thiocyanate (SCN) intermediate destroyed by UV/H2O2. Total 99%+ CN destruction.
Arsenic and Sulfate Removal
Arsenic is naturally present in many mines. As(III) is oxidized to As(V) and co-precipitated with iron or aluminum hydroxide. Effluent As <0.05 mg/L.
Sulfate is high in AMD (1,000-10,000 mg/L). Beyond standard precipitation:
- BaCO3 precipitation: Expensive but effective (<200 mg/L)
- Ettringite process: SAVMIN, COSTECH
- Sulfate-reducing bacteria (SRB): Passive systems
- RO: Membrane for high flow
Mining Sector Advantages
Mining References
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Frequently Asked Questions
AMD can persist for decades, even centuries after mining stops. Pyrite oxidation is natural. Mines plan AMD treatment as long-term liability.
Free CN is easy to destroy, but iron-cyanide complexes (Fe(CN)6) are very stable. Need UV/H2O2 or electrochemical methods. Metallurgical CN requires costly extra steps.
Passive systems (wetlands, oxic drains, ALD) suit flow <50 m³/h and remote sites. Low CAPEX/OPEX, minimal maintenance. High flow/high-metal needs active systems.
Mixed metal hydroxide is hazardous waste. Options: licensed disposal, stabilization (lime), or sale to recovery facilities if rich enough (Cu, Zn).
Water Pollution Control Regulation (mining schedule) and Mining Waste Regulation apply. EIA covers AMD risk. Mine closure plan defines long-term WWTP obligations.
Low flow: sulfate-reducing bacteria (SRB) reactor. High flow + strict limit: RO or ettringite. Hybrid SRB + lime is common.