Invited seminar with Peter Kondos: Alternative Lixiviants to Cyanide – The Thiosulphate Experience

April 12, 2021 @ 10:00 am – 11:00 am
Microsoft Teams

Peter Kondos, YaKum Consulting Inc.

Title: “Alternative Lixiviants to Cyanide – The Thiosulphate Experience”

Hosted by Professor Vladimiros Papangelakis


The use of cyanide in the recovery of precious metals, particularly gold, has been practiced for nearly 150 years, because of its efficiency, selectivity to gold and easiness to use.  The major impetus in seeking alternative lixiviants to cyanide arises from the environmental hazards posed by the toxicity of cyanide, with numerous environmental groups throughout the world actively pursuing a ban on its use.  On a few occasions, cyanide use is uneconomic due to certain characteristics of the gold ore, such as high content of organic carbon, copper, and sulphur.

 Thiosulphate is currently considered the most attractive alternative to cyanide for leaching gold due to its low toxicity and its potential use on carbonaceous ores that cannot be readily treated by conventional cyanidation.  This presentation reviews the development of the ammoniacal thiosulphate leaching process for gold and silver extraction and discusses the underlying leaching mechanism, thermodynamics, thiosulphate stability and gold recovery options.  The chemistry of the ammonia-thiosulphate-copper system is complicated.  However, we found that by maintaining suitable Eh and pH and by controlling the concentrations of thiosulphate, ammonia, copper and oxygen in the leach solution, high gold extraction can be achieved with low reagent consumption:


 The thiosulphate technology was selected by Barrick Gold Corp. to process very refractory gold ores in Nevada, USA.  In November 2014, the Goldstrike mine in Nevada poured its first gold bar produced using their patented thiosulphate leaching technology, with a technology team led by the presenter.  This milestone marked the industrial beginning of a new process developed to extract gold from double refractory ores that could not be treated via the traditional cyanidation/carbon-in-leach (CIL).  The arduous path of technology development and commercialization will also be discussed.


Peter Kondos was born in Athens, Greece, where he completed his Diploma of Engineering at the National Technical University of Athens, followed by a MEng on Computers in Mining and a Ph.D. in Hydrometallurgy, both at McGill University.  He has extensive expertise on leading innovation efforts, technology, IP management & commercialization and consistent track record of implementing new solutions in challenging situations.  He has been involved in building worldwide networks and innovation ecosystems to solve complex challenges.

Peter has worked for:

  • the Canadian Government at CANMET in Ottawa
  • the Noranda Technology Centre in Montreal, leading the Hydrometallurgy group
  • an electronic powders manufacturer for a year as R&D Manager of New Products
  • Inco Technical Services in Mississauga as a Mini-Plant Operations Manager
  • Barrick Gold Corporation, where he held the position of Sr. Director, Strategic Technology Solutions, coordinating step changes and breakthrough technologies
  • YaKum Consulting Inc. as CEO, and Board member in technology organizations

His peer recognitions include:

  1. Sherritt Hydrometallurgy Award
  2. Chair of Canada Mining Innovation Council (CMIC 2014-2016)
  3. Innovation Award for the Thiosulphate Process (2016) and the Hot Cure and Lime Boiling Process to recover silver from the pressure oxidation process (2019)
  4. Has participated in numerous lectures and round tables on Mining Innovation.

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