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BIOCYANIDE DEMONSTRATION PROJECT

BIOCYANIDE DEMONSTRATION PROJECT. Activity III ; Project 5. 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. ADVANTAGES.

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BIOCYANIDE DEMONSTRATION PROJECT

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  1. BIOCYANIDE DEMONSTRATION PROJECT Activity III ; Project 5

  2. 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

  3. ADVANTAGES • Natural Biological Process • Low Application Costs • Relatively Quick Method

  4. 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

  5. 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

  6. COST ANALYSIS OPERATING COSTS PER 1,000 GALLONS OF MODERATE CYANIDE CONCENTRATION IS $0.81

  7. 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

  8. Cyanide Heap Biological Detoxification Activity III; Project 11

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

  10. 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

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

  12. 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

  13. 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

  14. Column Preparation • Column construction

  15. Column Preparation • ~9.1 tons of ore per column

  16. Column Operation • Initial testing December 3, 1998 • Process solution application rate of 0.004 gpm/ft2 • Hydrogen peroxide application of 5:1 stoichiometric requirement

  17. 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

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

  19. WAD CN

  20. Total CN

  21. Copper

  22. Nitrate

  23. Zinc

  24. 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

  25. 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

  26. Photolysis for Cyanide & Nitrate Remediation of Water Activity IV ; Project 3

  27. 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

  28. 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

  29. RESULTS AND CONCLUSIONS • Cyanide oxidation occurs as a series of oxidation reactions • Photo-reduction of nitrate can be accomplished

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