EnviroLeach Technologies successfully developed a unique, cost-effective and environmentally-friendly alternative to cyanide and strong-acid based processes currently used for the extraction of precious metals from mineral ores, concentrates and E-Waste.
It is the world’s only safe, stable, sustainable, eco-friendly and economic alternative to cyanide and strong acids for the extraction of gold and other strategic metals.
The process is similar to the conventional cyanide vat leaching circuits used today but much safer and simpler. The patent-pending EnviroLeach formula consists of simply combining five non-toxic, FDA approved dry ingredients with ambient temperature water. The reagent is uniquely generated and regenerated for re-use with a proprietary electrochemical process using pure diamond based electrodes. The process does not require pressure, elevated temperatures, complex process circuits, intensive gas monitoring or costly detoxification systems.
The reagent is the result of selective inorganic electro-chemistry which results in the dissolution of the precious metals into aqueous solution. This is followed by the extraction of the resulting gold ion complex using conventional methods such as electrowinning, carbon absorption or precipitation.
The EnviroLeach process offers similar or improved leach kinetics to that of cyanide on most ores and concentrates.
The hydrometallurgical extraction of gold from ores, concentrates, and E-Waste in a cost effective and environmentally safe manner offers an interesting challenge. Conventional gold mining operations rely heavily on cyanide leaching as the predominant method for recovering gold from ores and concentrates. Cyanide has been the leach reagent of choice in gold mining because of its high gold recoveries, robustness and relatively low cost. As a result, over 76% of all gold extracted worldwide is produced by hydrometallurgical extraction with the use of cyanide.
The gold mining sector uses approximately 66,000 tons of sodium cyanide annually worldwide. The use and subsequent disposal of cyanide, present significant safety and environmental challenges. As a result, the safety, environmental and associated permitting issues have been a critical driver for the industry to evaluate effective alternatives.
These alternative lixiviants for ores, concentrates and E-Waste have to offer comparable leach kinetics, be environmentally friendly and cost effective. Some of the experimental alternative lixiviants have included; thiosulfate, thiocyanate, ammonia, bromine, chlorine, BioSulfide, thiourea and others. Some of these chemicals offer comparable leach kinetics under certain conditions, but for a variety of reasons, none are reported to be an effective alternative to cyanide.
Although new alternatives such as these and others have been proposed, none have proven to be effective. In-Fact, there has been no significant advances in hydrometallurgy since the introduction of cyanide in the 1800’s.
Cyanide and cyanide gas are both toxic and care has to be taken during ore processing to avoid exposure for workers. Solutions containing cyanide have to be carefully monitored and managed to prevent the formation of deadly cyanide gas. In addition, there are significant costs associated with destruction of cyanide in the tailings streams and final disposal.
Internationally, several countries, like the Czech Republic, Greece, Turkey, Germany, Hungary, Costa Rica, Argentina, Ecuador, and some states of the United States have banned cyanide leach technology in gold and silver mining. Therefore an environmental friendly alternative is crucial for the continued development of the mining sector.
The EnviroLeach reagent is ideally suited for the leaching of gold in an agitated or vat leach type process. This includes the treatment of whole ores, gravity concentrates, flotation concentrates and E-Waste. This segment of the market represents the majority of the worldwide gold produced.
There are numerous potentially economic gold deposits that are unable to secure permitting due to cyanide restrictions. The EnviroLeach process could be an effective alternative for these deposits.
Over 13 months of independent testing and analysis by Met-Solve Labs of Langley, BC, Canada involved the preparation, leaching and assaying of numerous different ores, gravity concentrates, flotation concentrates and tailings. Following the leach cycle, analysis of the aqueous solution was performed by Atomic Absorption spectroscopy, ICP mass spectrometer and the subsequent analysis of the leach residue was done by acid digestion, ICP MS and fire assays.
Extensive test work included the comparison of the leach kinetics of the EnviroLeach process to conventional and high intensive cyanide leaching. Most of the test work was carried out using the bottle roll method, which is employed extensively for cyanide leach test work, however a few tests were done using a stirred reactor and lab scale agitators. The test were done under ambient temperature and atmospheric conditions.
The results of the test work indicated that the EnviroLeach product performed better than cyanide on both kinetics and total amount of precious metal recovered on most materials. The metals are very stable in solution and there are no preliminary indications to a maximum solubility level.
The recovery of gold from the EnviroLeach solution can be accomplished using a number of conventional methods including; carbon absorption and electrowinning. A number of tests were completed to quantify gold recovery from solution with conventional electrowinning (EW) using the Electrometals EMEW® cell. The results indicate that gold in EnviroLeach solutions can be rapidly electrowon to very low tenors.
The results of the extensive testing further supports the objective of replacing cyanide with the EnviroLeach chemistry in that auxiliary processes, e.g. carbon-in-leach and conventional electrowinning, are immediately applicable to the EnviroLeach system, and that the EnviroLeach chemistry may be a viable replacement for cyanide at the commercial and/or industrial level.
Approximately 20,000 individual tests and assays have been completed to quantify the recoveries of the EnviroLeach based process.
EnviroLeach’s formula and process has been tested on the ores and concentrates from some of the most known and accomplished mining companies in the world.
The following chart shows the conclusive and repeatable results of recoveries from one of the top ten annual gold producers of 2017.