Post on 24-Dec-2015
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