A: Glycine is an amino acid that appears commonly in nature and is present in our bodies. However it is also produced synthetically and so is traded as a commodity. It is a very benign substance.
Answer: Glycine is sold in different grades. This varies from high purity manufactured for the pharmaceutical industry as well as a standard bulk product which we would use for our process. The standard product is adequate for any glycine leaching application. Currently Australia does not manufacture it but is a user. China and the US are the major producers of it and there’s several other countries also manufacture it. We did a market study a few years ago that suggested that any uptick in projected use in the mining industry could be easily accommodated within the current supply/demand balance without material impact on pricing.
Answer: With the testwork we’ve done so far with hypersaline and seawater we’ve seen no adverse effect. We’ve just recently had a partner complete a pilot plant using seawater and they successfully demonstrated the technology.
Answer: There’s no real difference between Cyanide and Glycat – they both require carbon to recover, and so, we’ve proven in pilot campaigns (both CIP and CIL) that we can effectively recover the gold from solution.
Answer: Glycine is in the water, so simply put if you’re able to recover your water you can recover your glycine. These days with the use of thickeners and a need for filtration of the tails for dry-stacking you pretty much recover 100% of the glycine in the process.
The detection method of Glycine we’ve developed uses titration, to quickly determine the glycine concentration solution, but the more accurate method is HPLC. This can be introduced into operations to monitor the true glycine concentration in the leach solution and this will be balanced out by the amount of addition added into the circuit.
Next week’s question: Does Glycine leach Arsenic?
Answer to be released 21st April, follow us on LinkedIn to be the first to see it!
Yes, glycine can complex arsenic under certain acidic conditions but under the alkaline, targeted leaching conditions of pH 9.5 to 12 we have found arsenic is not stable in solution and precipitates out the residual, most likely as an oxidised by-product.
Yes, Glycine can leach silver but we find the extraction is slightly lower than cyanide but we have got a lot less cyanide in a glycine leach solution. Additional oxygen or using CIL can improve the recovery of silver to be comparable to cyanidation.
Answer: Glycine Leaching technology has the best impact where high levels of cyanide are consumed where there’s a high level of base metals or iron competing or consuming that cyanide. With GLT we find we can directly reduce that need where fir that cyanide where the glycine goes in pacifying or completing with hose base metals and that allows the cyanide to effectively leach the gold.
Answer: Lead can be leached with glycine under certain conditions but under the alkaline conditions used for glycine leaching at pH 8 to 12 we find the soluble compounds are unstable as complexes and precipitate out of solution.
Answer: It is very easily implemented so it requires very little Capex requirements, except for the cost of the means of switching the reagent from cyanide to glycine and cyanide so it has very low impact as well as very low capex requirements.
Answer: It is necessary to start with low cyanide as a control, however only 30-50% of gold can be recovered at the same amount of cyanide used with the Glycine. In the absence of Glycine, you will only get 30-50% of gold recovery, but in the presence of Glycine, gold recovery is increased to 88-95% (from sample to sample).
Answer: One of the benefits of glycine is it is very stable under acidic and alkaline conditions. The Glycine can oxidise in aggressive conditions (such as high pH, high temperature, high oxygen or high sulfite), and will oxidise to oxalate and ammonia. Oxalate can be fixed by lime as calcium oxalate, and ammonia will stay in the solution to improve the leaching or can be dealt with if required. Typically there is only a low level of ammonia in the solution.
Answer: The risks are very low. It’s simply changing cyanide for glycine and cyanide. In an implementation, if it fails, then you can always revert back to cyanide.
Answer: The kinetics is slow for a glycine only system at room temperature and at low pH. Heating, increasing pH or oxygenating the glycine can lead to accelerate the kinetics. Additionally other additives such as thiourea and other oxidants can increase the kinetics significantly. In many cases the addition of starved levels of cyanide with glycine results in faster leach kinetics than straight cyanide.
Answer: We’ve tested for a year, out in sun and we saw no difference. It is very stable.
Answer: The most accurate way of measuring glycine in solution is with HPLC, but we have developed a simple titration method to monitor the glycine in solution.
Answer: Traditionally you would use acid to recover the copper, and you neutralise then add cyanide to recover the gold onto activated carbon. Instead, using the GlyCat™ process, both leach out in an alkaline environment, using glycine and cyanide. Therefore, the copper you recover with ion exchange resin or Sodium Hydrogen Sulphide (NaHs) precipitation, which we piloted and successfully demonstrated. The gold you recover onto activated carbon.