Cyanide 2

1
Module Topics

• Properties and uses of cyanide
• The potential of cyanide to harm people, wildlife
  and the environment
• Actions required for cyanide management at all
  stages of a mines lifecycle
• The interactions between cyanide, metals, water
  and the environment

2
Background

• Cyanide is a widely used industrial chemical
• Cyanide has been used to extract gold for over
  100 years
• Cyanide is highly toxic chemical that should be
  used with great care
• It is important to know the facts about the
  hazards and benefits of using cyanide in mining

3
Some Facts about Cyanide

• The cyanide ion (CN-) is the active agent in
• Gold leaching process
• Poisoning biological systems.
• Cyanide is naturally occurring in the environment
  at low levels.
• Significant man-made sources occur in
• Emissions from iron and steel production
• Coal burning, vehicle exhausts and petroleum
  refineries.

4
Cyanide and Mining

• Cyanide is the preferred leaching reagent for
  extracting gold in mining.
• Mines should aim to use as little cyanide as
  possible to minimise environmental effects,
  maximise worker safety and reduce costs.
• Cyanide, unless it is captured and recycled, can
  be wasted and may ultimately find its way into
  the environment from tailings dams.

5
Basic Principles of Best Practice in Cyanide
Management

• Mines that adopt best practice cyanide management
  gain many benefits
• Improved occupational health and safety
  performance
• Better relationships with the public and
  regulators
• Improved economic and environmental performance
• Reduced risks and liabilities
• Easier access to capital and lower insurance
  costs.

6
The Ten Commandments of Best Practice Cyanide
Management
1. Risk assessment and planning 2. Cyanide
management strategy 3. Management training 4.
Establish well-defined responsibilities 5. Safe
procedures for cyanide handling
7
The Ten Commandments of Best Practice Cyanide
Management
6. Cyanide and water management plans 7.
Options for reuse, recycling and disposal 8.
Regular cyanide audits 9. Environment and
health monitoring programs 10. Emergency
response procedure
8
Cyanide in Gold Extraction

• The role of cyanide in a mining operation must be
  well understood and defined. Factors include
• Types of cyanide
• Key chemical reactions of cyanide and
• Analysing, monitoring and reporting.

9
Types and Names of Cyanide Complexes

• There is such variety of cyanide complexes that
  it is often difficult to compare results of
  toxicological and environmental investigations

• Free cyanide
• Titratable cyanide
• Simple cyanides
• Complex cyanides

• Total cyanide
• Weak acid dissociable cyanide (WAD)
• Cyanide amenable to chlorination (CATC)

10
Key Chemical Reactions

• Understanding the chemistry of cyanide helps to
  predict its behaviour in the environment
• Extracting gold
• Recycling or disposing of cyanide
• Natural degradation by volatilisation
• Natural degradation by oxidation

11
Using Chemistry to Minimise Risks

• Minimising risks
• Metal ion complexes
• Precipitation reactions
• Reactions with sulphur containing compounds
• Photodecomposition reactions with
  hexacyanoferrate (II) and (III)
• Adsorption reactions

12
Analysing and Reporting Cyanide
1. Problem definition 2. Sampling 3. Sample
preservation 4. Sample treatment
5. Standards 6. Measurement 7. Compliance
and reporting 8. Documentation
13
Cyanide Health and Hygiene in the Workplace

• Safety for workers and responsible use of cyanide
  in mining are closely related
• Understanding cyanide poisoning helps to
  implement health and hygiene practices in the
  workplace
• Protecting workers will also help to protect the
  environment

14
Cyanide Poisoning

• Cyanide is toxic to humans and animals
• Cyanide poisoning can cause death
• Cyanide can be breathed in, swallowed or absorbed
  through the skin
• Most safety procedures aim to prevent cyanide
  coming into contact with the human body

15
General Safety Issues PACE-IT for Safety
Policy Accident investigation Communication Emerge
ncy readiness Inspections Training
16
Transport

• Mine operators should develop an emergency
  procedure for cyanide spillage during transport
• Mine operators should work with the manufacturer
  and transport companies on emergency planning

17
Storage

• How cyanide is stored depends on the form used
  (solid or liquid)
• Important aspects of storage facilities are
• Adequate ventilation and protection from water
• Store away from corrosive, acidic and explosive
  materials
• Security
• Bunding to contain accidental spills

18
Handling and Emergency Procedures

• Hazardous operations include
• Opening storage containers
• Dissolving sodium cyanide pellets and
• Cleaning up cyanide spills
• Operators handling cyanide should wear protective
  clothing and work in pairs
• Emergency response procedures should be practiced
  regularly

19
Protective Gear and Hygiene

• Working with cyanide demands a culture of
  cleanliness
• Wash after working with cyanide
• Use protective gear when working with cyanide
• Respirators, gloves, overalls, waterproof boots

20
Monitoring the Working Environment

• An air monitoring and sampling program can help
  protect workers
• Samples should
• Be representative of worker exposure
• Be collected and analysed by an approved method
  and
• Not be tampered with
• Continuous sampling gives fast results and more
  time for action in an emergency

21
Risk Assessment

• Best practice means identifying, planning and
  training for contingencies
• Workers and emergency services must be able to
  react efficiently and effectively in an emergency

22
Minimising Environmental Impacts

• Use the minimum amounts of cyanide required
• Dispose of cyanide in ways to minimise or
  eliminate environmental impacts
• Monitor all operations, discharges and the
  environment
• Conduct regular cyanide audits

23
Cyanide Balance

• Similar to a water balance
• The balance between uptake and loss of cyanide
  from the environment
• The collection of baseline data during mine
  planning will help identify problems and find
  solutions. Key factors include
• The ore composition
• Local meteorology

24
Cyanide Treatment and Reuse

• The ways in which cyanide concentrations in
  tailings ponds can be reduced include
• Natural degradation
• Enhanced natural degradation processes
• Chemical, physical or biological methods
• Recovery or recycling

25
Natural Processes

• Main processes
• Dissociation of metal cyanide complexes
• Volatilisation of cyanide as hydrogen cyanide gas
• Other processes
• Hydrolysis
• Photodegradation
• Chemical and bacteriological oxidation
• Precipitation as metal complexes

26
Enhancing Natural Losses

• Some simple procedures can increase the speed of
  natural degradation
• Aeration
• Mixing
• Use of shallow pond with large surface area
  increases the contact with CO2 in air and lowers
  pH and so increases volatilisation

27
Chemical, Physical and Biological Interactions

• Methods to detoxify residual cyanide
• - Degussa peroxide process
• - Caros acid
• Inco sulphur dioxide/air process
• Oxidative chlorination
• Biodegradation

28
Recovery or Recycling

• Free and WAD cyanide can be recovered using
  various non-oxidative processes
• Two of these processes rely on reducing pH to
  release HCN
• AVR (acidification-volatilisation-absorption)
• CYANISORB

29
Protecting Wildlife and Livestock

• Ensure cyanide levels in the tailings dams are as
  low as practicable
• Prevent access or scare away wildlife using
  methods including
• Fencing
• Floating balls
• Netting
• Hazing (fireworks, lights, music)

30
Spillage and Unintended Process Losses

• Response to a spill depends on
• The physical form (solid or liquid) and the
  amount of cyanide lost
• The size and area of the incident
• The response time - how quickly the incident is
  noticed
• How accessible the spill is - underground or on
  the surface
• The environment involved - land or water

31
Mine Closure and Rehabilitation

• After closure a mine needs to be rehabilitated
  for future use
• Include cyanide management in planning for mine
  closure
• Heap leach pads and mine tailings become more
  acidic as they age
• WAD cyanide in heap leach pads and tailings will
  dissociate and release cyanide into the
  environment

32
Monitoring Cyanide in the Environment

• Monitoring cyanide is an essential part of best
  practice environmental management
• Monitoring should include
• Baseline information before operations begin
• Water levels and water quality in drinking water,
  process ponds and tailings dams
• Fauna
• Dust generation
• Rehabilitation progress

33
Conclusion

• Sound and systematic systems are needed for
• Cyanide analysis
• Understanding and predicting the environmental
  chemistry and fate of cyanide
• Cyanide removal processes
• Education and communication programs for better
  understanding between mine operators, regulators
  and the community

34
Benefits of Implementing Best Practice

• Economic and environmental performance in mining
  are inextricably linked.
• The mining industry is judged by the community on
  environmental performance
• Implementing best practice is to the advantage of
  the mining industry