BIOCYANIDE DEMONSTRATION PROJECT

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BIOCYANIDE DEMONSTRATION PROJECT

• Activity III Project 5

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PROBLEM

• Cyanide is used to extract precious metals from
  ores
• Cyanide is an acute poison and can form strong
  complexes with several metals
• Conventional treatment processes can be expensive
  and chemical intensive

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ADVANTAGES

• Natural Biological Process
• Low Application Costs
• Relatively Quick Method

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OBJECTIVES

• Obtain a significant reduction of weak acid
  dissociation (WAD) cyanide in gold mine process
  water
• Evaluate effectiveness of heavy metal removal
• Develop operating costs for treatment

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TREATMENT RESULTS

• The total cyanide decreased from 275 ppm to 60
  ppm
• The WAD cyanide decreased from 240 ppm to 40 ppm
• Nitrates decreased from 32 ppm to 1 ppm

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COST ANALYSIS

• OPERATING COSTS PER 1,000 GALLONS OF MODERATE
  CYANIDE CONCENTRATION IS 0.81

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CONCLUSIONS

• Significant reduction of total and WAD cyanide in
  gold mine process water
• Effective removal of heavy metals in mine process
  water
• Cost effective treatment technology

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Cyanide Heap Biological Detoxification

• Activity III Project 11

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Background

• Cyanide is used in the mining industry throughout
  the world to improve the efficiency of metals
  separation in extracting precious metals from ore

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Background

• Cyanide has the ability for form strong complexes
  with several metals therefore increasing the
  mobility of those metals. As such, cyanide can
  contribute to environmental concerns

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Project Objectives

• Obtain a significant reduction of weak acid
  dissociable (WAD) cyanide
• Evaluate the effectiveness of heavy metal removal

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Technology

• In general, biological cyanide degradation is
  accomplished by stimulating indigenous bacteria
  through nutrient addition and optimizing growth
  conditions (i.e. pH, temperature and the end
  product produced)
• These bacteria have the natural ability to
  degrade cyanide

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Technology Advantages

• Cyanide compounds are naturally present in the
  biosphere
• Biological treatment is nontoxic to the
  environment as the bacteria return to natural
  levels when the cyanide is depleted
• Detoxification ends possible long-term liability
  and monitoring

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Column Preparation

• Column construction

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Column Preparation

• 9.1 tons of ore per column

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Column Operation

• Initial testing December 3, 1998
• Process solution application rate of 0.004
  gpm/ft2
• Hydrogen peroxide application of 51
  stoichiometric requirement

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Column Operation

• Column operation suspended on December 22, 1998
  due to extreme weather conditions causing the
  columns to freeze
• Columns restarted on December 28, 1998

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Parameters Monitored

• WAD and Total Cyanide
• Ag, As, Au, Cd, Co, Cu, Fe, Mn, Mg, Hg, Ni, Se
  and Zn
• Nitrate
• pH
• Temperature

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WAD CN
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Total CN
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Copper
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Nitrate
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Zinc
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Results

• Hydrogen peroxide column reached the compliance
  level of 0.2 mg/l for WAD CN within 36 days
• Whitlock Associates reached compliance within
  151 days. Applied Microbiology, Compliance
  Technology and Little Bear Laboratories were all
  approaching the regulatory limit when the
  demonstration ended

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Conclusions

• Worst case scenario as the initial CN
  concentration of 700 ppm was higher than the
  expected concentration of 300-400 ppm
• Under optimal conditions, it is speculated that
  three of the biological processes would have
  performed significantly faster and reached the
  regulatory limit

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Photolysis for Cyanide Nitrate Remediation of
Water

• Activity IV Project 3

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OBJECTIVES

• Use Photolysis to Remediate
• CN- NO3-
• Test Compare Photolytic Methods
• Compare results published in literature
• Determine reaction mechanisms using Eh-pH
  diagrams as well as ion chromatography and ion
  selective electrode measurements

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RESULTS CONCLUSIONS

• Photolysis is a viable approach for remediation
• Direct Photolysis is not applicable for cyanide
• Homogeneous Photolysis (with H2O2) was found to
  work the best for cyanide oxidation but product
  analysis showed heterogeneous photocatalysis
  (with TiO2) was more efficient

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RESULTS AND CONCLUSIONS

• Cyanide oxidation occurs as a series of oxidation
  reactions
• Photo-reduction of nitrate can be accomplished