Low Activity of Regenerated Carbon and Fine Particle Issues at a Gold Mine in Victoria, Australia
Introduction
The following example illustrates how our team supported the technical troubleshooting and mine audit process at a gold mine in Victoria, Australia, which was facing two primary issues: low activity of regenerated carbon and a finer-than-expected particle size distribution.
Following a preliminary assessment by our engineers, it was determined that the root cause of the operational inefficiencies and carbon attrition was the malfunctioning screw feeder in the regeneration kiln.
Problem Identification
Activated Carbon Activity
The sample of regenerated carbon showed an activity level of just 59.7%, which is significantly lower than with new activated carbon. This indicates ineffective regeneration, adversely affecting the overall efficiency of gold recovery. Ideally, the activity of regenerated carbon should fall within the optimum range of 85% to 95%.
Root Causes
The low activity observed in regenerated carbon is often not due to the regeneration process itself, but rather the quality of water used for quenching. If the quench tank water is of poor quality (e.g. using process water with a higher percentage of contaminants), the regenerated carbon may adsorb contaminants at this stage, including both organic and inorganic substances.
As evidenced by ICP analysis, the quench water sample showed higher concentrations of inorganic contaminants. This significantly reduces the carbon’s activity, affecting its kinetic properties, gold adsorption capacity, and overall recovery rates. However, this issue does not occur in all gold processing operations.
In this process, froth flotation utilizes organic reagents to recover gold concentrate. However, these reagents often carry over into the CIL process, contaminating the activated carbon and diminishing its gold adsorption efficiency. This indicates that the activated carbon regeneration process was flawed.
In this case, regeneration must be performed under more stringent conditions and at higher temperatures than usual because some reagents, particularly Potassium Amyl Xanthate (an organosulfur compound), bind very strongly to the carbon pores.
Particle Size Distribution
The sample had a high concentration of fine carbon which led to increased carbon loss and consequently, gold loss. The regenerated sample contained 36.5% fine carbon (% mass finer than 1.7 mm), which exceeds acceptable norms for efficient carbon circuits. To minimize gold loss, it’s recommended to keep fine carbon content below 10%, as fine carbon can pass through interstage screens and be discharged into tailings. This is the root cause.
Root Cause
Screw Feeder Issues
In this process, froth flotation utilizes organic reagents to recover gold concentrate. However, these reagents often carry over into the CIL process, contaminating the activated carbon and diminishing its gold adsorption efficiency. This indicates that the activated carbon regeneration process was not fully successful.
In this case, regeneration must be performed under more stringent conditions and at higher temperatures than usual because some reagents, particularly Potassium Amyl Xanthate (an organosulfur compound), bind very strongly to the carbon pores.
Solutions
Maintenance of expected regenerated carbon activity​
The sample had a high concentration of fine carbon which led to increased carbon loss and consequently, gold loss. The regenerated sample contained 36.5% fine carbon (% mass finer than 1.7 mm), which exceeds acceptable norms for efficient carbon circuits. To minimize gold loss, it’s recommended to keep fine carbon content below 10%, as fine carbon can pass through interstage screens and be discharged into tailings. This is the root cause.
Improvement:
As the mine acquired the appropriate kiln tube and increased the kiln temperatures, they managed to achieve activities greater than 90%
Improvements to Screw Feeder operations
Immediate replacement of the worn screw feeder was recommended. The materials used should be mild steel or stainless steel, with a preference for stainless steel (SUS 316L) due to its superior resistance to corrosion and wear. To enhance control capabilities, it was suggested to implement variable frequency drives like the Techno Variable Driver – 1HP. Additionally, it is crucial to maintain the clearance below 2.00 mm, with a maximum allowance of 5.00 mm.
Improvement:
Following changes to the screw feeder, there was a significant reduction (40-50%) in fine carbon content. This improvement underscores the importance of continuous monitoring and adjustments to the feeder systems to maintain optimal performance.
General Recommendations by Our Experts to Improve Performance & Efficiency
Improve Kiln Parameters
Optimize Particle Size
Enhance Screw Feeder Design
Regular Maintenance
Partner with Haycarb Today
Please fill in the required information and our team will be happy to help you find the right solutions.