Optimizing Gold Leaching Agitators for Increased Yield
Designing optimal gold leaching agitators means considering many nuanced and often competing factors. Dynamix provides innovative engineered solutions that improve yield by controlling solids suspension, gas dispersion, and carbon attrition. The NMX line of agitators and Dynaflow™ impellers offer practical solutions for both carbon-in-pulp (CIP) and carbon-in-leach (CIL) gold leaching circuits.
Technical Challenges for Gold Leaching Agitators
By far the most common leaching process, gold cyanidation produces a complex ion of gold and cyanide, called aurocyanide. Activated carbon then adsorbs the aurocyanide from the ore slurry, with CIP circuits having adsorption in a separate train, while CIL employs countercurrent adsorption in the main leaching tanks. The production of aurocyanide requires gold, cyanide, oxygen, and water. In order to meet oxygen requirements, air is supplied to the tanks.
Gold leaching agitators are necessary in order to ensure an adequate rate and yield of aurocyanide production. Agitation provides uniform gas dispersion and solids suspension to enable mass transfer. As a reactant in the process, the concentration of dissolved oxygen in the slurry is critical. At typical levels, the leaching rate is directly proportional to oxygen concentration.
Activated carbon provides the means to separate aurocyanide from the slurry through adsorption. The carbon, with the adsorbed gold, is easy to separate from the slurry. Attrition occurs when pieces of carbon break off, taking gold with them. Carbon attrition has a disproportionately negative effect on yield because the gold loading is primarily on the outer shell of the particles, where attrition occurs. Because increasing mixing power increases attrition, a more subtle approach must be taken.
Finding the Right Solution
Optimizing impeller diameter is a critical factor for gold leaching circuits. Inadequate diameter does not provide enough pumping to prevent solids settling. Because solids build up on the bottom and walls of the tank, there is less effective volume. The same flow rate will have a lower retention time, subsequently lowering yield. Low gas dispersion is another primary factor behind low yield. Increasing air throughput by significant amounts would cause impeller flooding. Because the impeller contacts gas instead of liquid, the agitator will not be effective.
With a properly sized impeller that can provide adequate pumping with a large area of effect, the process can avoid these problems. Increasing agitator speed isn’t the correct solution. This will increase carbon attrition and reduce energy efficiency. A real solution must take into account shear and mixing power. Only a carefully designed agitator configuration can ensure optimal gold leaching agitation.
Dynamix’s Engineered Mining Industry Agitators
Dynamix has a wide range of both standard and customized products for the mining and mineral process industry. We offer engineered gold leaching agitators solutions for both CIL and CIP circuits. Our team of mechanical and chemical engineers implements computational fluid dynamics to evaluate every aspect of the process and determine the optimal configuration. The NMX line of agitators can provide optimal designs for tanks up to 300,000 gallons, along with other lines for smaller applications.
Our unique Dynaflow™ impellers provide the low shear, low power pumping best suited to optimizing solids suspension, gas dispersion, and carbon attrition. The design of these impellers reduces turbulence behind the blade to produce laminar flow. Laminar flow keeps activated carbon particles intact by reducing particle collisions and tearing. The Dynaflow™ impeller is the perfect solution for low shear, low power mixing. You can contact us today to find out more about what we can do for your process.
