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Sulphate removal from mining effluents. Presentation held at the Enviromine 2009 Seminar

Sulphate removal from mining effluents. Presentation held at the Enviromine 2009 Seminar

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Raymond Philippe Enviromine09 Raymond Philippe Enviromine09 Presentation Transcript

  • Sulphate Removal from Mining Effluents Current Developments in the Southern Hemisphere Raymond Philippe, Hatch Water, Chile Deon Nel, Hatch Water, South Africa Trevor Clarke, Hatch Water, Australia
  • Sulphate Removal from Mining Effluents Current Developments in the Southern Hemisphere
    • Why Sulphate?
      • Actually considered one of the most complicated contaminants in mining effluents
        • Concentration/volume
        • “ Dynamic” Legislation
        • Technology Developments
        • Cost
    • Why Southern Hemisphere?
      • Climate similarities
      • Strong Mining Countries
      • Regulation differences
  • International Sulphate Discharge Regulations
    • Approaches
      • Fixed discharge limits
        • Directly as [SO 4 ] -2
        • Indirectly as TDS (Total Dissolved Solids)
        • Indirectly as Electrical Conductivity
      • Best Practices/Holistic approach
      • International Standards
      • Local Standards
      • Special Situations
    • Most cases: Limits depend on final use of water
  • Effluent Discharge Regulations 2400 - 500 (Class 1-3) - (Class 4) 3000 500 (Cat 4) TDS mg/l 250 (Class 1-3) - (Class 4) Resolution 357 Brazil 1000 NCADE Lib VI, 1 Ecuador 70 - 150 - Water Act 1998 South-Africa 1000 ANZECC 2000/General Water Use Stakeholders / Trigger Values Australia 300 (Cat 3) DS-002-2008-MINAM** Peru 1000-2000 250-500 250 DS90 DS46 NCh1333 Chile Conductivity mS/m [SO 4 ] -2 mg/l Legal Instrument Country
  • [SO 4 ] – TDS – Conductivity
    • EC (dS/m) x 670 = TDS (mg/L) > [SO 4 ]
    • Approx conversion formula (ANZECC 2000)
    • TDS = Σ [salt ions]: Examples Ca, Mg, Na, K, SO 4 , CO 3 , Cl
    • TDS and Conductivity are indirect Sulphate maximum concentration levels
    • Applied on South African and Peruvian Legislation:
      • Peru: 500 mg/l TDS, if present as CaSO 4
        • max SO 4 discharge level = 353 mg/l
      • South Africa: 70-150 mS/m, if present as CaSO 4
        • max SO 4 discharge level = 331 – 709 mg/l
  • Typical mine effluent sulphate concentrations (mg/l)
    • Tailings pond 2.500
    • Acid Mine Drainage 0 – 10.000
    • Copper Raffinate 10.000 – 20.000
    • Smelter gas scrubber 50.000 – 200.000
    • Seawater 5.000
    • Desalinated Seawater (1 pass) < 5
  • Mining effluent types
    • 1. Contaminant driven
    • Contaminant bleed/Complicated Chemistry
      • Saturated
      • Scaling
      • Corrosion
      • Production efficiency
    • 2. Hydraulics driven
    • (Temporary) high flowrate
    • Generally chemically not-saturated
  • Definition of sulphate treatment from effluents
    • Removal of sulphate ions from the aqueous phase, to a concentration level of sulphate compliant with discharge regulations
    • How:
    • Reduction of SO 4 to S° 
    • Precipitation of SO 4 with reagent
    • Precipitation of SO 4 as product of evaporation
    • Retention of a concentrated effluent within process inventory (to avoid effluent generation)
  • Sulphate Treatment Technologies
    • Traditional/Conventional
      • Lime/limestone
        • Industrially proven
        • Discharge compliance issues
    • Advanced Treatment Technologies
      • Great variety of Processes
      • Difficult to evaluate
        • Country/Jurisdiction dependent
        • Commercial processes
        • Various processes still under development
      • Very little comparison studies
        • Available public domain studies are often outdated/ not complete/applicable for specific site conditions
  • Key Factors Advanced Sulphate Treatment Systems
    • Effective, proven high-volume sulphate treatment systems consist of three specific unit operations:
    • Sulphate concentration step
    • Sulphate “solidification”
    • Solid/Liquid phase separation
  • Advanced Sulphate Treatment Concept Separation Step Solidification Step Concentration Step Effluent Solids Treated effluent 2500 mg/l SO 4 <200 mg/l SO 4 5000 mg/l SO 4 2500 mg/l SO 4 CaO CaSO 4 .2H 2 O Advanced Treatment Technologies Black Box
  • Concentration Technologies
    • Evaporation (Solar, Mechanical)
      • Location (climate/environment)
    • Ion Exchange (Sulf-IX)
      • In general, minimum pretreatment required
      • Process in combination with lime precipitation
    • Membranes (Reverse Osmosis, nanofiltration)
      • Proven: Industrial experience
      • Pretreatment (scaling, solids)
  • Solidification Technologies
    • Lime precipitation
      • Well known process (LDS, HDS)
      • Scaling issues
      • Alternatives with tailings/limestone (NCD)
      • Sludge
      • Effluent discharge compliance
    • Barium precipitation (ABC, BaS)
      • Costs/ reagent availability
      • Sludge
      • Recovery of BaS by thermal conversion treatment
      • Pilot test stage
  • Solidification Technologies
    • Ettringite (SAVMIN, CSER)
      • Precipitation of sulphate as CaO.3CaSO 4 .Al 2 O 3 .31H 2 O
      • Sludge handling
      • Al 2 O 3 availability
      • In piloting stage
    • Biological processes (Biosure, Sulfateq)
      • (Bio) Conversion of SO 4 to S° (or S-2)
      • Industrial scale proven
      • Electron/carbon source availability
    • Crystallization Technologies
  • Phase Separation Technologies
    • Typical proven technologies
      • Clarification/Settling
      • Filtering
      • Centrifuges
      • Flotation
  • Examples:Industrial Advanced Sulphate Treatment Operations Conventional (lime) treatment: 1600-2000 mg/l SO 4 <500 2008 235 NF/RO&evotransp Chile Collahuasi (Anglo/Xstrata) 2009 2005 1994 2006 2007 Year SO 4 discharge mg/l Q (m3/h) Technology Country Operation < 95 (200 μ S/cm) 290 Lime & NF & RO Aus ERA Ranger 1360 120 416 830 <30 NF/RO US Mosaic, Florida < 10 NF&RO&evap Aus Kwinana Nickel (BHP) <200 Biosure SA Ancor Works <200 RO & Lime SA eMalahleni (BHP/Anglo)
  • How to select best combination of Sulphate Treatment Technologies
    • Basic Design Criteria
    • Effluent characterization
    • 1. Concentration Technology
    • Water discharge/reutilization criteria
    • 2. Sulphate Removal Technology
    • Sludge Discharge/reutilization criteria
    • Location/Logistics/Reagents criteria
    • 3. Phase Separation Technology
    • Depends on selected Sulphate Removal Technology
  • Preselection of Concentration Technologies
    • Parameters
    • Required Pretreatment
    • Possible scaling issues
    • Energy requirements
    • Space availability
    • Waste/By product handling
    • Objective:
    • Production of effluent that meets environmental discharge criteria
    • (evt. Reutilization as process water)
  • Preselection of Sulphate Removal Technologies
    • Solidification and Separation Technology are defined in conjunction:
      • Sludge/Solids handling and disposal (legislation)
      • Logistics (reagents supply, energy)
      • Space availability
    • Objective:
    • Removal of Sulphate from water inventory, technically feasible (waste) product management
  • Definition of Integrated Treatment Process
    • Establish integrated flow sheets/mass balances
    • Integration with existing operations
    • Closed circuit design
    • Technical - Economical comparison starting point
      • Integrated Cost estimate (Investment / Operations)
    Concentration Step Sulphate Removal Step Effluent Environmental discharge Solids ?? Recycle
  • Conclusions
    • Advanced Sulphate Treatment Technologies have been proven on industrial scale, making it possible to treat effluents to well below gypsum saturation levels, complying with strict legislation
    • Conceptual Definition: Concentration technologies (such as membranes and IX) do not remove SO 4 from the water inventory, they have to be combined with other technologies to remove sulphate
  • Conclusions
    • Optimized Advanced Sulphate Treatment of high volume effluents is a 3 - step process:
      • Concentration
      • Sulphate solidification
      • Solids removal
    • Every operation is unique: Selection of Optimum Treatment Combination is a multidisciplinary process that should be performed on a case-to-case basis
    • Technical-Economical Technology comparison:
    • Treatment Investment & Operation Cost can only be determined once an integral process design is established