Environmental Geochemistry: Acid Rock Drainage and Metal Leaching (ARDML)

The majority of the world’s non-ferrous metal mining is within sulphide ore bodies and when excavated these minerals naturally weather to form ARDML, potentially the biggest environmental impact from mining operations.

Prediction of ARDML:

  1. Undertake representative sampling of waste rock, stockpiled ore and processing waste.
  2. Undertake initial characterisation study:
    • Static testing - rapid screening of ARDML potential
  3. Determine tonnages of:
    • Potentially Acid Forming (PAF) waste
    • Non Acid Forming (NAF) waste
    • Metal Leaching waste
  4. Undertake kinetic testing to determine:
    • Rates at which acid is generated
    • Rates at which metals are leached
    • Rates at which acid buffering minerals are consumed
  5. Predict mine waste facility seepage water quality using quantitative numerical models
  6. Determine impacts to groundwater and surface water
  7. Suggest mitigation options as appropriate to meet environmental targets
Prediction of ARDML
Pre-Mining Stable System Graphic

Importance

  1. Key requirement of International Finance Corporation Environmental Health and Safety Guidelines as agreed by international lenders as part of the Equator Principals for environmental permitting
  2. Prediction of project critical design costs for mitigation of impacts
  3. Key design input at Scoping, Pre-feasibility and Feasibility stages:
    • Tailings management facility design
    • Waste rock dump design
    • Heap leach design
    • Stockpiles design
    • Water treatment design
    • Environmental and Social Impact Study
    • Environmental and Social Permitting
    • Mine closure planning

Further information available at INAP GARD guide

Illustration of a Post Mining Unstable System

Stages of ARDML assessment in mine development

Conceptual / Scoping Study
Look and see
Preliminary sampling and static testing
Preliminary categorisation of waste based on potential to generate ARDML
Requires 2-3 months

Pre-Feasibility Study
Representative sampling
Static testing / full suite
Detailed characterisation of material types and ARDML potential
Preliminary Quantitative Numerical Prediction (QNP) of water quality
Requires 4-8 months

Feasibility Study
Additional representative sampling
Static testing and kinetic testing
Detailed QNP of water quality
Suggest management and mitigation options for life of mine and closure
Requires 12-18 months

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