The historic catastrophe and subsequent ban of cyanide in parts of the U.S., Europe, and South America, prompted the mining industry to begin researching alternative solutions to the use of cyanide when mining gold and other metals. Chlorine has emerged as a safe, effective, and environmentally sound solution to the problem.
Dr. Jean-Marc Lalancette is co-founder and Chairman Emeritus of Dundee Sustainable Technologies (DST), which focuses on the development and commercialization of environmental-friendly technologies for the treatment of materials in the mining industry. Dr. Lalancette leveraged his significant industry experience to transform standard extraction methods, developing and testing a groundbreaking hydrometallurgical process for the extraction of base and precious metals from ores, concentrates, and residues. Key to this revolutionary approach is the use of chlorine and bromine as hypohalides, and the introduction of hypochlorite, an ion composed of chlorine and oxygen, most commonly used as the active ingredient in household bleach. Chlorine and a catalytic amount of bromine combined as oxidizing agents deliver a particularly fast reaction with gold, with only a small concentration of bromine required in the brine. Chlorination also emerged as an ideal option based on the relatively low temperature of the reaction with a wide variety of minerals.
A closed-loop circuit is an important feature of DST’s design, preventing the generation of liquid effluents and eliminating the need for expensive tailings ponds. The tailings from the process are inert from toxic substances, free of sulphide, and do not produce acid leach, making it an extremely environmentally-safe process. It only requires a brief contact time of about one hour to give high gold recovery.
DST set up a demonstration plant at Thetford Mines in Quebec, Canada in 2013. Using gold concentrate provided by its partner in Chile, DST was able to evaluate the effectiveness of its technology in a live setting. The company requested proposals from a number of suppliers for on-site sodium hypochlorite generation (OSHG) systems to produce the hypochlorite that is so critical to the process. De Nora, a leading designer of safe, innovative, and sustainable water disinfection, oxidation and filtration technologies, was among those considered.