Silver recovery

International Mining
The section on processing silver ores also had to go. This noted that Hochschild’s Ares mine is expanding the size of its plant and has ordered five additional Gekko Systems’ InLine Leach Reactors (ILR5000 Batch Manual) to add to its two existing ILR5000s. Once installed, Ares will boast the largest intensive leach application worldwide. It is the first application on silver flotation concentrates.

Hochschild intends to increase metal production at the site, situated 4,900 m above sea level in the Peruvian Andes, to capitalise on the current high price of silver and the recent expansion of its Explorador mining operation. Gekko Product Manager, Nick Katsikaros: “It is our experience that the South American region is a leader in the adoption and successful application of new technology. The mining community is well educated, sites generally have strong operating skills and there is a positive attitude to change. Hochschild’s Ares mine is an excellent example. The technical and operating team have achieved excellent recoveries – over 99% – in a new application of a proven technology” he said.

Hochschild will benefit by having the capacity to produce metal doré on site, eliminating the need to sell concentrate to a refinery. Overall cost savings will be achieved through eliminating costs associated with selling concentrates including transport, insurance, security, payment timing and charges at the refinery.

Gekko says its ILR “has proven itself to be the best metallurgical processing solution for producing silver from flotation concentrates and, as a result, increasing production outcomes. It is the only intensive leach system that can effectively leach fine flotation concentrate. The unique combination of Gekko’s process chemistry and design capability combined with Hochschilds’ expertise in silver has made the application possible. Furthermore, the robust and unique design of the ILR has resulted in outstanding operability and recovery results.”

The leaching of silver from high purity silver, high purity silver minerals (acanthite, stephanite and pyrargyrite) and a mixture of silver minerals has been determined under various conditions and compared to the new ‘CANMET Enhanced Leaching Process (CELP)’. In the absence of sulphide minerals, increased dissolved oxygen of the slurry produced the fastest silver leaching kinetics. For a slurry containing acanthite, a 23% improvement in silver extraction (from 76% to 99%) was obtained with the CELP whereas silver extraction increased from 75% to 90% for the slurry with pyrargyrite. No improvement was obtained for the slurry with stephanite (99% extraction in 72 hours).

However, the silver leaching rate was much faster with the CELP. The slurries containing the mixtures of minerals showed improvements of 21% Ag (from 75% to 96%) and 37% Ag (from 56% to 93%) with the CELP. Leaching of a high grade gold/silver ore with the CELP resulted in higher silver and gold extractions while using a lower cyanide concentration.

According to a paper3 at this year’s SME meeting, a joint effort by research teams at the University of British Columbia, the University of Cape Town, CSIRO Minerals and CSIRO Land and Water, AMIRA P768 – Improving Heap Bioleaching – ”is the most significant collaborative research effort on heap leaching to date. The purpose of the project is to develop a complete understanding of heap bioleaching in all of its aspects – hydrological, mineralogical, chemical and biological – culminating in a comprehensive mathematical model.”

2. Deschenes, G. Improvement of silver leaching from high silver grade ores using the Celp. SME Annual Meeting, Salt Lake City, February 2008.
3. Dixon et al, AMIRA P768: Progress towards a comprehensive understanding of heap bioleaching. SME Annual Meeting, Salt Lake City, February 2008.

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