GOLD EXTRACTION
n Total cash costs( C2) 570 n Sustaining capital 74 n All In Sustaining Costs( AISC) 645 n Sulphide preproduction capital 183 n Reclamation 17 n All In Costs( AIC) 844
The project is expected to be commissioned by the end of the second quarter 2018, with the first gold pour in the third quarter 2018. The schedule allows for an 18 month ramp up to achieve initial design capacity of 1.9 Mt / y throughput rate.
Cyanide-based recovery, or not?
Synergen Met has developed what it describes as“ a world-first, transportable, modular process plant that manufactures sodium cyanide( NaCN) at the mine site – revolutionising the supply process for one of the most critical, but dangerous, reagents used in the global mining industry.”
The Synergen NaCN plant is a modular, standalone production plant. Each plant is the size of a standard 40’ shipping container and is readily transportable. Synergen’ s first pilot plant recently successfully completed test work at a mine in Australia, following six years of proof-of-concept, development and optimisation activities. The Synergen team is now talking to a number of mining companies about locating a 400 t / y production plant on a mine site to begin production by June 2017.
The plant eliminates a range of dangerous activities associated with the use of cyanide such as transportation, on-site handling, and maintaining large cyanide inventories. The technology has been through the PCT patent process and full patents have been granted in Australia, Mexico, South Africa and the two African patent regions of OAPI and ARIPO. Patents are under review or are near to review in the USA, Canada and Europe.
NaCN is made on-site to the exact specifications of the minesite, generally a 25 to 30 % dilute solution. It is pumped directly from the production tank to the site’ s NaCN holding tank in a closed system.
The company notes that the process“ can be up to 50 % cheaper than the current market price of NaCN, depending on the cost of various reagents.”
In November 2014, Synergen Met and The University of Queensland were recognised at the Institution of Chemical Engineers’ Global Awards for this process. The modular on-site cyanide production unit took the 2014 Award for Outstanding Achievement in Chemical and Process Engineering, as well as winning the Core Chemical Engineering category.
Synergen Met Managing Director, Chris Dunks, said at the time the company had already fielded interest from gold mining companies in Australia,
Africa and North America, eager to consider the new system.
“ For gold producers, on-site cyanide production is a game changer as it gives the producer control over an essential material in their production process, while cutting costs and risk. Our process will allow mining companies to reduce their transportation and manual handling of cyanide concentrate, and give more certainty over their supply chain while significantly cutting costs.”
The first production unit is a 400 t / y plant and with strong interest being shown from around the world, the company expects rapid uptake as mining companies started to realise the benefits of the new technology.
“ Our work means for the first time, mining companies can produce cyanide on demand and feed directly into existing mills. This removes the risk of supply delays and reduces the need to store large volumes of toxic chemicals in purpose built facilities,” Dunks said.
The process differs from existing cyanide producers by using nitrogen instead of ammonia as a source material. Nitrogen is very abundant and can be extracted from the air for cyanide production using existing, off-the-shelf technology.
Coconut-based activated carbon( AC) is commonly used to recover gold from cyanide leach solutions in CIP, CIL and, to a lesser extent, carbon-in-column circuits. 6th Wave Innovations says that“ while these systems have been perfected over 100 years of use, AC has inherent limitations. Capacity for gold adsorption is highly dependent on the metallurgy of the ore, quality of the AC, pH of the pregnant solution, and other factors.”
“ IXOS™ nanotechnology shows stable and predictable performance across a wide variety of conditions. Gold capacity and selectivity remain significantly higher than AC regardless of the presence / levels of other base metals. Moreover, superior mechanical strength over AC allows for virtually 100 % gold extraction with no loss to
IXOS makes it cheaper and easier, according to 6th Wave Innovations.
fines. The IXOS beads don’ t become poisoned with other base metals; they fully elute; and are re-usable for dozens of loading and unloading cycles.”
The benefits, according to 6th Wave, include the potential for saving over $ 100 per ounce: n Increased gold recovery( no loss to AC fines or solution loss); recent field tests showed as much as 10 % more gold recovered, with essentially zero solution loss n Higher capacity and selectivity translates to smaller plant and lower cost of operations n No significant performance changes through many cycles n Demonstrated to be highly effective with preg-robbing ores n One step elution at low temperature and standard pressure n NO regeneration / reactivation.
Dundee Sustainable Technologies( DST) has recently received independent certification of the performances of its cyanide-free gold extraction process( the DST Gold Process) from Environment Canada, through the Canadian Environmental Technology Verification( ETV) program. This confirms that the process successfully extracted an average of 81 %, with a maximum of 90 %, of the gold content from a refractory gold bearing pyrite concentrate, while the cyanide extraction process achieved an average of 71 % on the same material. This material is from a jurisdiction which has restricted the use of cyanide within its territory. This refractory concentrate was chosen due to the difficulty of extracting its gold using conventional processes, hence demonstrating the effectiveness of the DST Gold Process.
Throughout the ETV program, a total of 170 t of gold bearing refractory pyrite concentrate were processed. The performance test sampling was conducted at DST’ s demonstration plant according to the test protocol developed by STS Canada, and
70 International Mining | AUGUST 2016