LEACHING & SX / EW sessions. He reported that he has looked at chloride extensively, and believes that for a high chloride process, recycle of the chloride and maintaining the water balance is hard work. Whereas it is okay for anode slimes, for ores and concentrates it is more difficult, though not impossible, and needs a good business case. He said that the industry must come up with something, as the currently feasible alternative to cyanide is leaving the gold in the ground, which is a difficult decision if the deposit is high grade. A higher cost process with lower efficiency compared with cyanide may be preferable under those conditions.
He further commented that we need to keep looking at alternative technologies, including revisiting old technologies. We mustn’ t get bogged down into the way a lixiviant has been used in the past, and think outside the box. We need to encourage academics and researchers to keep working on alternatives as one day it may be beyond our control and we may be forced to do something different.
La Brooy agreed and put forward the example of all the work done on copper catalysed ammonium thiosulphate, yet the first plant uses calcium thiosulphate.
Petrus van Staden, Mintek( South Africa), proposed that there are two‘ holy grails’ the industry is searching for – a cyanide free gold process and an in-situ process which avoids mining. He asked whether we could select a subset of the cyanide free processes as contenders for in-situ application. For in-situ application, a reagent needs to be stable underground and controllable from the surface.
Xianwen reported that CSIRO is doing work on in-situ leaching, and has done column leach test work for a gold mine in Australia using a particular product. The results are promising and CSIRO is waiting for the company to decide to go to the next stage. He considers that thiosulphate could be one of the options for in-situ applications.
Van Staden commented that on one hand, we need something stable and controllable, and on the other hand if it escapes into the environment it must biodegrade so that it is not a lasting legacy.
Elsayed Oraby, Gold Technology Group, Curtin University,( Australia) said that glycine covers most of these points and has a wide range of metal stability for gold and copper( pH 7-12). It is non-toxic and environmentally benign, and is a good candidate for in-situ leaching( see Gold without tears, IM, August 2017, pp34-49)
Paul Breuer, CSIRO( Australia), floor, said that, as pointed out by La Brooy in his keynote presentation, for in-situ the issues are very similar to above ground processing for all the alternative lixiviants. The amount of reagent recovery, recycle and re-use that is achievable is probably going to be the biggest driver. It’ s the be treated as an investment and not something complete process, not just having a reagent that the accountants cut off when the going gets can leach gold. tough. Benz emphasised the need for mining
Karel Osten, Amec Foster Wheeler( Australia), companies to keep a strong internal technical reported that many years ago he worked on insitu leaching trials with thiourea. It worked pretty engineering companies, and collaborate around
department, to liaise with universities and well, but the main problem was the loss of the industry. He pointed out that many successful solution and reagent. Apart from anything else, technologies have been developed in this for successful in-situ leaching you have to find manner, but when innovations become isolated in the right orebody with the appropriate technology companies, they tend not to get off permeability. Many gold orebodies don’ t fit this the ground. criterion.
La Brooy added that it’ s only when the mining
Paterson said that in-situ is a niche process for companies become involved in the development gold, applicable to a very small percentage of process that there is someone with the drive to orebodies. Normal mining / leaching applies to a actually do it. It’ s only when there is someone much higher percentage of orebodies and who actually needs the solution that the process therefore deserves more focus. Also, above is commercialised. Barrick put in 15-20 years’ ground mining is much easier to control. work before thiosulphate leaching at Goldstrike
Breuer responded that CSIRO is looking at insitu as a game changer, even for hard orebodies. He also observed that the gold industry used
was commercialised.
Some of the technologies being looked at for to be open, but now companies tend to have IP increasing permeability include hydraulic control departments and safeguards. Conversely, fracturing, cryogenic cracking, chemical means of the aluminium industry has gone the other way; creating microfractures, and electro kinetics. they used to be secretive but now are more open.
Van Staden reported that from the point of Maybe the cyanide challenge will bring the gold view of the South African gold industry, in-situ is industry together to lower the cyanide profile. viewed as a possible long-term solution as mines Summary of key points from the panel become deeper, to reduce underground fatalities. discussion:
Taylor said that a lot of developers of new n The application of a totally closed system processes are technology companies, often very with cyanide recycle designed and operated underfunded, and have a tendency to collapse under chemical industry standards, together with time. Therefore, wouldn’ t it be a good thing to have some sort of
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so that the technologies will still be available if a cyanide ban does come?
Oraby reported that the Curtin work on glycine has received good support and encouragement from the big gold producers.
Turner said that
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NOVEMBER 2017 | International Mining 37