Mine Water Reuse in South Africa History, Current Status & Ongoing Research Achim Wurster

Presentation Overview Background to Mining in SA, Early Days of Mine Water Re-use, Mine Water Treatment Research, Full Scale Desalination Treatment, Other Mine Water Treatment, Ongoing Mine Water Treatment Research, Conclusion.

Background to Mining in SA Mine development life cycle. Water shortage at start of mining, Excess develops during operations – used onsite, Excess requiring discharge near/at end of life. Mine Water Quality Profile. Saline, or Acidic, high metal concentration & saline.

Early Days of Mine Water Reuse Onsite use of acidic/saline mine water for: Dust suppression, Coal plant – coal washing, Dilution with clean make-up water. Problems identified: Environmental impacts – surface run-off and ground water, Coal Plant corrosion.

Early Days of Mine Water Reuse Initial Treatment using HDS lime process Scaling of Coal Plant piping, Mitigated by large dilution volumes resulting in environmental discharges. Capabilities of existing technologies: Low recovery RO/EDR and high cost thermal/evaporative brine treatment, High cost IX and high cost thermal/evaporative brine treatment.

Brugspruit Example Old defunct shallow underground coal mine complex near eMalahleni, Saline, low pH, high metal concentration mine water, High Density Sludge Lime Treatment – DWAF Removed metals, Near-Neutral pH, But discharge still saline (high sulphate and calcium concentrations) with resulting environmental impact.

Mine Water Treatment Research Coaltech – Mining Industry Funded Various chemical, biological and physical treatment technology trials funded and hosted at Navigation Colliery. CSIR Cost reduction for HDS treatment using Waste Limestone by-product from Paper Manufacturing. Feasibility Studies indicated Biological Sulphate Reduction and High Recovery RO as most cost effective and reliable options.

High Recovery RO Pilot & Biological Sulphate Reduction Demonstration Plant

Full-Scale Desalination Treatment Pacques biological sulphate reduction and partial oxidation. 2 Ml/d demonstration plant implemented at Navigation Colliery. Achieved all performance targets and solving corrosion/scaling problems on coal plant. (Potable quality was never targeted.) Later replaced due to high running cost (price of carbon source and demonstration plant maintenance costs).

Full Scale Desalination Treatment Eskom power stations: Cooling tower make-up water scarcity, Excess cooling tower blow-down, Excess mine water at connected mines, Large need for ash dump dust suppression. EDR and later RO desalination implemented Low TDS boiler feed water, Low TDS cooling tower make-up water, Brine used for ash dump dust suppression.

Full Scale Desalination Treatment Sasol Secunda Tubular RO with sponge ball cleaning, Spiral wound RO, Brine to ash dams and brine ponds Effective at removing divalent ions, Monovalent ions build-up in water circuits. Thermal evaporators / crystallisers implemented to treat brine. Work, but high cost and low availability.

Full Scale Desalination Treatment eMalahleni Water Reclamation Plant Excess mine water with limited internal reuse opportunities, Discharge standard close to or exceeds potable standard, Potable water shortage at local municipality, Open tender, pilot demonstration and life cycle cost analysis indicated multi-stage high recovery RO most reliable and cost effective.

Full Scale Desalination Treatment eMalahleni Water Reclamation Plant First phase of 24 Ml/d implemented, High quality potable water produced, Comprehensive SANS 241 analysis, Risk assessment identified additional parameters to be analysed for, including testing for toxicity, etc. Quality meets SANS 241 and equal to or better than typical SA municipal water for other parameters. Water recovery > 99%, brine to brine pond. Expansion to 60 Ml/d being commissioned.

eMalahleni Water Reclamation Plant

Full Scale Desalination Treatment Optimum Water Reclamation Plant 15 Ml/d implemented, Same high recovery technology as EWRP, High quality potable water produced, 3 Ml/d sent to town of Hendrina, >98% water recovery (slightly higher monovalent ion concentration in feed than EWRP), Brine to evaporative Brine Ponds.

Optimum Water Reclamation Plant

Full Scale Desalination Treatment New Vaal Colliery Treated mine water to Eskom power station, Brine treated using cooling crystallisation / freeze desalination, Sodium Sulphate by-product recovered from brine treatment step.

Other Mine Water Treatment TCTA Witwatersrand Gold Mine Water Western (40 Ml/d), Central (70 Ml/d) and Eastern (110 Ml/d) basin HDS mine water treatment, Currently only neutralisation and metals removal, Future desalination planned, with treatment to potable standard and supply into the Gauteng water systems likely.

TCTA Eastern Basin AMD HDS treatment plant

Other Mine Water Treatment Many smaller active mine water treatment plants in operation Treated water typically re-used on site for mining operations Some passive biological mine water treatment systems in operation Typically applied for small flows and remote locations

Passive mine water treatment Degrading packed bed reactor

Ongoing Research Water Research Commission funded research on: Improved water recovery / zero brine Eutectic Freeze Crystallisation By-product recovery From upstream process steps (metals) or brine (salts) Reagent cost reduction Eskom fly ash to treat mine water Combining biological/passive and active processes Optimised process configurations for specific mine water quality profiles. WRC Research by Universities and Industry.

Ongoing Research Mines and Industry also funding research: Coaltech: Eutectic Freeze Crystallisation trials, Treatment cost optimisation, Solving operational problems associated with high recovery RO processes.

Conclusion Industry and WRC funded research resulting in large treatment cost reductions and technical improvements to treatment processes. Turning a liability, AMD, into an asset - Potable Water. Large volumes of AMD stored in defunct mining voids can aid in climate change resilience.

Acknowledgements Dr Andre van Niekerk, Anglo Coal, BHP Billiton, Glencore, Sasol CoalTech Water Research Commission TCTA Keyplan, Aveng Water, Prentec, Proxa, Pacques, Tecroveer