Patent Issued to Montana Tech Faculty Member, Dr. Courtney Young, for Gold Recovery from Thiosulfate Leach Solutions
On April 26, 2011, Dr. Courtney Young, Department Head of the Metallurgical and Materials Engineering at Montana Tech, filed a patent, “Method for Aqueous Gold Thiosulfate Extraction Using Copper-Cyanide Pretreated Carbon Adsorption,” based on several years of research he and metallurgy graduate students, Nick Gow (BS 2006, MS 2008) and Mariam Melashvili (MS 2010), performed. The research was funded by Newmont Mining Corporation and the Center for Advanced Separation Technologies (CAST), which is sponsored by the U.S. Department of Energy and a consortium of five universities: Virginia Tech, the University of Kentucky, the University of Utah, Montana Tech and West Virginia University. On October 27, 2011, Dr. Young received Application-status for the U.S. Patent (#20110259148). The patent was granted on August 6, 2013 (#8500847) but is pending in Australia (AU #2011201892) and Canada (CA #2738382).
Their patent emanates from a challenge issued by Newmont Mining Corporation to develop a non-resin technology that would recover gold from solution produced by thiosulfate leaching, a leading contender to replace gold cyanidation but is not yet used on an industrial scale due to its cost. The patent is based on favorable thermodynamics calculations that Dr. Young showed as well as preliminary results previously obtained by Montana Tech metallurgy undergraduate researchers, Jennifer Gambill and Amber Linn, through Montana Tech’s Undergraduate Research Program (URP) in 2003. Young subsequently verified and improved upon the results with fellow faculty member, Dr. Larry Twidwell (now Professor Emeritus) and Visiting Professor, Dr. Greg Hope of Griffith University, Brisbane, Queensland, Australia. Hope, Twidwell, and Young then wrote a successful proposal to CAST in 2005 including nearly 1:1 match from Newmont. Funding was received in 2006-2010 setting the stage for Gow to work on his thesis, “Pretreated Activated Carbon for Gold Recovery from Thiosulfate Solution” and for Melashvili to follow-up on hers, “Optimization and Stripping of Au-Loaded Pretreated Activated Carbon.” Both Gow and Melashvili are pursuing their doctoral degrees.
Clearly, Dr. Young met the challenge! The technology allows gold to be recovered from thiosulfate leach solutions using activated carbon which is at least ten times less expensive than resin. Activated carbon strongly adsorbs gold cyanide but, by itself, does not absorb gold thiosulfate. However, if the activated carbon is impregnated with copper cyanide, it allows the copper on the carbon to exchange with the gold in solution similar to copper cementation of gold. The copper becomes part of the thiosulfate solution and makes its way back to thiosulfate leaching, which it helps catalyze. Whereas, the gold is retained on the activated carbon as a cyanide complex and recovered by elution using a strong cyanide solution at high temperature just like the traditional cyanidation practices of today. In this regard, existing technology can be incorporated into the thiosulfate leaching process and thereby keep costs down.
Dr. Young noted in the patent that the amount of copper on the carbon determined how efficient the gold was adsorbed as well as eluted. If the copper was present in low amounts, the copper and gold would exchange in a 1:1 ratio and all the copper would be displaced to the solution. Following elution, the gold could then be electrowon and yield a fairly pure product. If the copper was present in high amounts, not all of the copper would be displaced and, in this case, elution and electrowinning would not yield a pure gold product; however, elution could be done to recover most of the copper selectively for recycle back to the impregnation step. Gold electrowinning would be accomplished in the next step. They also identified optimal operating conditions: for gold extraction, the ratio of copper (on the carbon) to gold (in thiosulfate solution) should not exceed approximately 1.5 and, for gold elution, the ratio of copper (on the carbon) to gold (on the carbon) should be less than approximately 1.5.
Because their results showed that the cost of the new and innovative technology would be similar to traditional cyanidation but would simultaneously avoid the problems and stigma associated with it, Dr. Young and his former students have been contacted by several parties wanting to use the patented invention which the team and Montana Tech own. Although it has only been six months since their patent was awarded, let’s hope it gets used by industry soon. Congratulations, Dr. Young!