Waste Rock Management

Mine site closure and rehabilitation to the point of relinquishment is becoming increasingly more difficult, primarily due to water quality issues that require active ongoing management. The principal source of these water quality issues is contaminant generation and release from waste rock piles (WRP). Increasing numbers of mine sites are progressing to “care and maintenance” at the end of operations partly because of the management requirements associated with WRP related issues.

Contaminant (e.g. acid, metals, salinity) generation is most often associated with the oxidation of sulfide minerals, with lesser contributions from secondary acid generating sulfate salts (eg. jarosite). The oxidation of sulfide minerals leads to the generation of acid / neutral metalliferous drainage (AMD) or neutral metalliferous drainage (NMD), known in some parts of the world as acid rock drainage (ARD) and metalliferous drainage (MD). This drainage often requires active ongoing management and treatment to minimise it’s impacts and allow discharge or reuse of the affected drainage. Oxidation within WRP’s is now understood to be controlled by air movement within the pile, which is unfortunately optimised by current WRP construction practises.

Earth Systems advanced understanding of sulfide oxidation, AMD generation and the role of secondary acid generating sulfate salts has enabled us to develop leading practice strategies for managing waste rock from the design of waste rock piles, through planning / management of waste rock during operations to closure / rehabilitation / relocation strategies. We assist Clients in identifying the key controls on contaminant generation and release and developing appropriate management strategies. All our strategies seek to minimising risk and ongoing costs involved with development, operation and transition to closure.

Earth Systems’ has been providing expertise in Waste Rock Management to the mining sector for over 25 years, with our expertise recognised by our involvement in the following;

• Contributed to the Australian Government’s Leading Practice Sustainable Development Program for the Mining Industry Handbook – Preventing Acid and Metalliferous Drainage (2016).

Life of Mine Waste Rock Management

We can assist with complete life of mine waste rock management aiding with:

• Planning and Approval
  • Waste rock pile design – incorporating oxygen minimisation and air entry controls, designs that minimise the reliance on cover systems
  • Waste rock characterisation
  • Static and kinetic testwork
  • Waste rock scheduling
  • Forward planning and development of waste rock closure strategies
  • Drainage water quality
  • Metal release rates.
  • Acid & metalliferous drainage / neutral metalliferous drainage management plans

• Operations / Mine Expansions
  • Laboratory and large-scale pad testing of optimum WRP design
  • Design and implementation of remediation plans
  • Water quality monitoring plans – surface drainage, seepage, groundwater
  • Assessment and review of water quality data
  • Passive and active water treatment
  • Pollution generation rates
  • Pollution minimisation (dissolved metals / salinity)
  • Instrumentation and monitoring of gas compositions, temperatures, pressures within dumps
  • Regulatory reporting associated with ongoing operations and expansion programs
  • Problem solving – identifying and solving unexpected problems associated with the storage and disposal of waste rock
  • TreatSIM – modelling water quality treatment requirements

• Closure / Post-Closure
  • Closure strategies
  • Transition from operations to closure
  • Remediation strategies and works
  • Laboratory and large scale trials for closure strategies
  • Waste rock cover systems (oxygen consuming covers, moisture retention/exclusion covers)
  • Changes to water management and treatment

• Derelict / Historical Waste Rock Piles
  • Geochemical assessment
  • Pollution minimisation strategies incorporation air entry controls and oxygen consumption technologies
  • Water quality management and treatment options (active and passive treatment)
  • Engineered WRP modifications to minimise pollution

We offer expertise in;

• Waste Rock Pile Design
  • Geochemically engineered waste rock facilities
  • Controlled air entry and movement layers – thin highly compacted layers
  • Atmospheric compositional controls – thin layers of oxygen consuming materials to act as oxygen exclusion barriers
  • Base-Up, Layered and Compacted (BULC) waste rock pile design and construction. more info…..
  • Encapsulation of potentially acid forming (PAF) materials
  • Alkalinity generating layers
  • Cover designs – oxygen consuming covers, air retardation covers
  • Closure and rehabilitation

• Geochemical characterisation of waste rock
  • Routine static and kinetic geochemical testwork
  • Specialist kinetic testwork programs – Oxygen Consumption Test (OxCon) / Oxygen Penetration Tests (OPT)
  • Potential to generate acid and/or metalliferous and saline drainage
  • Wall rock acidity generation rate tests
  • Sulfide oxidation/reaction rates
  • Sulfide reactivity as a function of moisture
  • Pollution generation rates
  • Duration of pollution
  • Lag time before onset of pollution
  • Key controls on pollution generation
  • Spontaneous combustion
  • Use of whole rock geochemistry to estimate mineralogy and net acid producing potential (NAPP)
  • Predictive modelling of acidity generation and acidity loads from waste rock under various closure scenarios

• Water quality and water quality management
  • Surface and groundwater
  • Pore water
  • Dissolved metals and salinity management
  • Water treatment solutions (active and passive)
  • Water quality monitoring and reporting
  • Water and acidity balances
  • Indicative leachate chemistry
  • Predictive water quality and treatment modelling

Contact Earth Systems for further information on how we can assist with minimising the risk associated with the primary source of pollution at most mine sites – waste rock.