Improving Gold Recovery

Situation

A gold mine located in Quebec, Canada processes ore through a froth flotation processing circuit followed by cyanidation. Previously, the main sulfide collector used in the flotation cell was potassium amyl xanthate (PAX).

During the winter month, when pulp temperature reached below 10℃, overall rate of gold recovery decreased by a range of 90% to 93% of the calculated yield. As a result, between 800 to 900 ounces of gold were lost annually to the tailings. As flotation processing was performed consistently throughout the calendar year, it is reasonable to assume that the 3% drop in recovery likely happened during cyanidation downstream at the lower temperatures. The metallurgical team suspected that the PAX collector had passivated (coated) the gold particles, reducing the overall rate of gold recovery.

Solution

Collector Solution Evaluation and Optimization

The Quadra team of mining specialists reviewed the situational assessment and created a process of structured lab testing to diagnose the existing approach and to create a protocol for trial of potential improvements in hydrophobic particle creation in the processing plant.

COREM conducted lab tests to determine the effectiveness of PAX on gold particles at various temperatures and that would inform the selection of a substitute collector. At temperatures above 10℃, PAX formed stable multilayers (dimers of dixanthogen) through physisorption which lowered the efficiency of dissolution, whereas novel methods in electrochemistry and spectroscopy showed that a Danafloat specialty collector did not.

On-site testing and trials compared the flotation performance of PAX collector solution with that of the Danafloat specialty collector. At equal dosage, gold recoveries were on par, but iron recoveries were slightly in favor of PAX: iron monitoring makes it possible to check the efficiency of the flotation circuit as well as to limit the quantity of sulfides (acid generators) sent to the tailings pond.

Further tests/trials on the flotation concentrate confirmed that Danafloat did not prevent cyanidation and that fluctuations in mineral particle size distribution and mineralogy had no significant impact on the metallurgical performances of the froth flotation process.

Long-Term Plant Trial

Quadra Chemicals’ mining technical services team worked closely with the metallurgical team to trial the Danafloat specialty collector. The dosage was adjusted progressively. The following graph shows its industrial validation:

Results

The plant substituted 70% of potassium amyl xanthate (PAX) with the Danafloat specialty collector; the remaining 30% was employed to mitigate iron recovery loss. The overall gold recovery rate was improved to between 93% and 94% throughout the calendar year, resolving the issue of recovery rate fluctuations in the colder winter months.

Benefits

The efforts of the Quadra Technical Support and Services team of mining experts delivered an improved return in the froth flotation process and additional improvements from the process implemented in the plant. These benefits included:

• Increased gold production by 800-900 oz/year (valued at CA $1.3-1.5M/year)
• Reduced health and safety risks associated with the preparation of PAX such as dust control
• Reduced environmental impact: fewer bags and boxes of PAX to destroy
• Easy handling: Danafloat’s specialty collector is a liquid product which requires no preparation