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

Natural Biological Process

Low Application Costs

Relatively Quick Method

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

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

COST ANALYSIS

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

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

Cyanide Heap Biological

Detoxification

Activity III; Project 11

Background

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

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

Project Objectives

Obtain a significant reduction of weak acid dissociable (WAD) cyanide

Evaluate the effectiveness of heavy metal removal

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

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

Column construction

Column Preparation

Column Preparation

~9.1 tons of ore per column

Column Operation

Initial testing December 3, 1998

Process solution application rate of 0.004 gpm/ft2

Hydrogen peroxide application of 5:1 stoichiometric requirement

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

Parameters Monitored

WAD and Total Cyanide

Ag, As, Au, Cd, Co, Cu, Fe, Mn, Mg, Hg, Ni, Se and Zn

Nitrate

pH

Temperature

WAD CN

-50

0

50

100

150

200

250

300

350

400

450

500

550

600

650

12/03/98 12/31/98 01/28/99 02/25/99 03/25/99 04/22/99

Date

mg/

l

Process Water Hydrogen Peroxide Whitlock & Associates

Total CN

-100

0

100

200

300

400

500

600

700

800

12/03/98 12/31/98 01/28/99 02/25/99 03/25/99 04/22/99

Date

mg/

l

Process Water Hydrogen Peroxide Whitlock & Associates

Copper

0

100

200

300

400

500

600

12/03/98 12/31/98 01/28/99 02/25/99 03/25/99 04/22/99

Date

mg

/l

Process Water Hydrogen Peroxide Whitlock & Associates

Nitrate

0

10

20

30

40

50

60

70

80

12/03/98 12/31/98 01/28/99 02/25/99 03/25/99 04/22/99

Date

mg/

l

Process Water Hydrogen Peroxide Whitlock & Associates

Zinc

0

10

20

30

40

50

60

70

12/03/1998 12/31/1998 01/28/1999 02/25/1999 03/25/1999 04/22/1999

Date

mg/

l

Process Water Hydrogen Peroxide Whitlock & Associates

ResultsHydrogen 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

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

Photolysis for Cyanide & Nitrate Remediation of Water

Activity IV ; Project 3

OBJECTIVES

Use Photolysis to RemediateCN- & NO3

-

Test & Compare Photolytic MethodsCompare results published in literatureDetermine reaction mechanisms using Eh-pH diagrams as well as ion chromatography and ion selective electrode measurements

RESULTS & CONCLUSIONS

Photolysis is a viable approach for remediationDirect 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

RESULTS AND CONCLUSIONS

Cyanide oxidation occurs as a series of oxidation reactions

Photo-reduction of nitrate can be accomplished