# Presentation: 208683

## 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

**Notes:**
When cyanide forms complexes, this results in increased mobility of those metals

## ADVANTAGES

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

**Notes:**
Non-toxic reactions and by products
Complete treatment
Detoxification of cyanide and nitrates

## 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

**Notes:**
WAD-weak acid dissociable cyanide

## COST ANALYSIS

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

**Notes:**
This is based on the treatment of 1,000 gallons per minute operating 300 DAYS PER YEAR

## 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 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

## Total CN

## Copper

## Nitrate

## Zinc

## 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

## 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

**Notes:**
The point here is that first the columns had frozen and that didn’t help the bugs, and if the companies had been monitoring their columns on a consistent basis, then the technologies would have performed better and would have probably resulted in better performance than the hydrogen peroxide.
columns froze reducing the degradation rate of the biological columns
It is important to note here that the Whitlock process could have operated as well as the hydrogen peroxide granted the conditions had been optimal (the freezing of the columns did not help the bugs)

## Photolysis for Cyanide & Nitrate Remediation of Water

- Activity IV ; Project 3

**Notes:**
Why study cyanide and nitrate?
1.) Remediation of anions is overlooked
2.) Runoff and ground water contamination
3.)Toxicity factors
4.)Prevention of mine and mill closures

## 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

## 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

## RESULTS AND CONCLUSIONS

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