GOLD EXTRACTION
Gold. It is a natural extension to Recyn that can also be applied to mineral sands and alluvial projects.
There are three parts to the evaluation process for Recyn: free cyanide recovery, detoxification, and metal recovery:
Cyanide recovery is simply an economical consideration, although often it will overlap with detox requirements. The two commercial applications in Indonesia are based on free cyanide recovery; but they find this also satisfies detox requirements, resulting in substantial cost savings and recovery benefits. The capital cost is easily justified and usually results in payback in less than one year. Economics are more favourable for larger projects and higher cyanide levels.
Detox is a more complex evaluation because it involves detailed solution chemistry and compliance requirements. The same adsorption plant can be used for detox, but a metal recovery plant must be added. The evaluation generally splits into two areas, compliance for tailings dams and compliance for river discharge. Either level can be accommodated with the Recyn process. The cyanide code level of < 50 ppm CN WAD for discharge to tailings dams is easily achieved, usually just by free cyanide recovery. For river discharge, the levels are more country specific, but can easily be accommodated with the Recyn process, usually by including a metal recovery stage.
Metal recovery is required for the detox of tailings, but can be assessed on a stand-alone economic basis if there is no detox requirement.
Recyn is used directly following the CIL circuit. Slurry flows through several stages of adsorption contactors. The resin stream is pumped countercurrent to the slurry flow to maximise resin loadings and minimise tails values.
Loaded resin is transferred either as a batch or continuously to the elution section of the plant. Metal elution and cyanide elution occur in separate columns at ambient temperature. Stripped resin is returned to the final adsorption stage. The relative flows of loaded resin to the
Commercially, Recyn is proving itself effective on the job: Currently, an integrated full scale operation at the Mirah gold / silver project in Indonesia has demonstrated the commercial viability of the technology. A second larger Recyn plant has been constructed at the Mt Muro project
metal or cyanide recovery sections depends on the CIL tailings solution cyanide and metal levels.
Metal recovery typically involves either EW to remove gold or precipitation to remove copper and other metals.
Cyanide recovery involves volatilisation and scrubbing to form a concentrated cyanide solution that can be returned directly to the leach circuit. The detoxified slurry is discharged to the tailings dam.
MIPs
6th Wave Innovation is a nanotechnology company focused on extraction and detection of target substances at the molecular level that says its products“ provide significant advantages in cost and performance.“ These advantages are derived from application of our patented technologies in the highly specialised field of molecularly imprinted polymers( MIPs).”
6th Wave now offers IXOS ®, a line of extraction polymers for the gold industry. IXOS beads, it says,“ are more selective, more efficient, have higher capacity, are less expensive to use, and more environmentally friendly than competitive solutions. 6th Wave has completed extensive testing in the laboratory and field trials with some of the world’ s largest gold mining
companies. ADR plant design using IXOS technology is similar to conventional ionexchange resins, reducing switching costs.”
In the Alta 2017 paper Molecularly Imprinted Polymers – Initial Field Trials at Kinross Bald Mountain Mine, Glen Southard, Chief Scientific Officer, and co-authors explain“ MIP beads that were imprinted for sequestration of dicyanoaurate were prepared by suspension polymerisation techniques. An imprint molecule, one capable of being chemically incorporated into a polymer, was prepared by chemical condensation of the desired molecule with a hard base ligand featuring a vinyl group. The imprint molecule was polymerised under suspension polymerisation conditions with styrene monomer and divinylbenzene as the cross-linking agent; to yield high quality beads about 600 to 850 μm in diameter. The purpose of the MIP is to provide highly selective and uniform adsorption sites on the polymer because they are keyed to both the charge complex and shape of the target molecule( in this case dicyanoaurate).
“ The MIP beads were found to be mechanically strong and capable of undergoing numerous load, elution, and regeneration cycles without loss of performance or notable breakdown of the resin despite wide swings in pH or ionic strength. Gold loadings of up to 40 g / kg of beads or higher were realised with some formulations, without loss of mechanical strength.”
The bead formulations with the greatest degree of mechanical stability and capacity were chosen for the first IXOS field trial at Bald Mountain mine, located near Elko, Nevada.“ Two formulations of IXOS resin were tested in two campaigns. In each campaign IXOS resign was loaded into a three column carousel pilot system and subjected to roughly the same temperature, humidity, and chemistry variables as found at the site.
“ The IXOS Au resin was to be fed with the same pregnant leach solution( PLS) that was
46 International Mining | AUGUST 2017