Glycine can leach most of the nonferrous transition base metals, specifically copper, but also nickel, cobalt and zinc. It is also capable of leaching the Precious metals under certain conditions, gold as well as silver, some of the platinum group metals, and finally lead under special circumstances. Various minerals leach at varying speeds and different chemical conditions. As an example all copper minerals except silicates and copper that is chemically bound within iron oxides are leached by glycine. Leaching takes place at pH values between approximately 8 and 12.5, with the higher pH values being used to leach the sulphides and in particular chalcopyrite. This supplies the base needed to fix the Fe that is leached from this mineral. In contrast to acid leaching, Fe, Mn, Ca, Mg and many other elements are simply not put into solution. There is no soluble unfixed Fe to deal with, or difficult solids like jarosite to dispose of.
Glycine leaching is low cost because the main reagent, Glycine, is chemically regenerated.
Glycine (a dry harmless powder) is reacted with a solution of sodium hydroxide to provide sodium glycinate as the major reagent. This has a natural pH value of around 11 to 12. For example, when the copper mineral malachite is put into solution, the released copper is chelated onto the glycine, with each copper molecule sequestering 2 molecules of glycine. This releases Sodium (Na) from the glycine that is then paired with the carbonate ion and hydroxide ions from the malachite. Glycine is wholly regenerated when the stripped solution is reacted with lime or calcium hydroxide. This precipitates all of the carbonate and sulphate (from the oxidation of sulphides), and regenerates the caustic which then pairs with the glycine again. Thus it is in a locked cycle, not being consumed. The loss is limited to the glycine that is not physically recovered from the tailings and this will be low.
Cupric glycinate solution can be treated in a number of ways. First, it can be contacted with a conventional copper SX reagent such as LIX64 or other series to replace the copper with hydrogen ions that have been charged into the solvent. The loaded solvent is then stripped of the copper with a high acid spent electrolyte. This is then sent to the Electrowinning, where the copper is plated as commercial LME Copper cathode, and the anode acid added back into the solution preparing it to strip solvent again. There is no need to purchase an outside source of acid unless impurities demand a bleed from the electrolyte circuit.
Where SX is not available, one could use precipitation or ion exchange. Chelating ion exchange resins will extract cupric copper from solution releasing the glycine for further leaching. The loaded resin is stripped the same as SX where it can be electrowon or alternatively, the cupric glycinate in solution can be precipitated using NaHS or even Na2S as a high purity CuS product that can then be sold to a smelter in the normal manner.
Glycine is a readily available chemical that is manufactured in large quantities in the USA, Germany, Japan, China, and India. It is manufactured by combining chloroacetic acid and ammonia and finds it principal use in the formulation of herbicides, a food supplement, and nutrient. Prices vary between manufacturers, but it is generally cheaper than cyanide and readily available from at least 20 different manufacturers.
Glycine is a totally non-toxic chemical that is fully bio-degradable. It is used as a feed supplement in animals and is even used therapeutically to reduce inflammation in humans. It is a slightly sweet tasting crystalline solid that looks like sugar.
We believe these technologies will allow currently ‘orphaned’ deposits to become economically attractive. We offer a unique solution to several significant types of copper and gold ore deposits such as:
Stranded copper oxide deposits, particularly those that are carbonate hosted, are heavy consumers of acid and hence are not a viable proposition. Glycine leaching (known as GlyLeach™) with its ability to be selective and therefore not consumed by gangue mineralogy, coupled with its ability to be regenerated in the process; means much lower operating costs can be considered. Because it is an alkaline process it also means lower capital costs for any equipment with little/no special or expensive materials required in construction.
Gold oxide and transition ores with elevated copper often don’t make attractive gold heap leach opportunities as the copper can be a heavy consumer of cyanide. Curtin University and MPS have discovered that a Glycine-cyanide mix (we call this GlyCat™) can be a catalytic process at normal ambient temperatures where the glycine prevents the cyanide being consumed in leaching the copper and can in fact accelerate the cyanide leaching of gold. The copper can be recovered also, adding additional value. This is a game changer for those gold deposits that have in the past been passed up from consideration as a low cost heap leaching option. Cyanide consumption using GlyCatTM is generally reduced by over 80% to that required by conventional cyanidation and the resulting solution has much lower WAD cyanide and the cost of detox can be greatly reduced or eliminated.
For ores with a high fines content, agglomeration is essential to create stable heaps and provide even solution distribution. The copper industry has always had to rely on the natural properties of the ore to produce agglomerates. Cement cannot be added with acid leaching as it simply dissolved. Polymer binding agents have been tried but generally show high cost and poor effectiveness. As a result, there have been numerous projects where copper recovery is dramatically lower than that projected from column leach experiments. High clay content is often considered a potential show-stopper for copper heap leach projects.
The gold industry, by contrast, has been very successful in heap leaching a wide range of materials using cement agglomeration in an alkaline cyanide system. The ability to agglomerate with cement makes the process far more robust with respect to the physical properties of the ore, and recovery projections from test results are much more reliable. Finer crushing can be considered without the risk of excessive fines generation. Cement also acts to raise the solution pH and thereby lowers the lime consumption. GlyLeach™ thus enables a fresh look at high-clay copper ores previously considered unsuitable for heap leaching.
Further, many copper oxides have precious metals (Gold, Silver) credits that are not realised in acid leaching. In fact, a survey of copper oxide heap leaches has shown that gold is rarely reported formally for many copper oxides. GlyCatTM can recover both copper and gold so it is an attractive option for copper oxides with gold and silver credits.
Glycine leaching will also be a viable solution in more sensitive environmental locations around the world where acid leaching (and its associated acid mine drainage issues) and cyanide leaching are no longer acceptable.
MPS are excited by the potential our technologies offer. We are keen to get samples tested and the technology demonstrated as rapidly as possible and are prepared to work with complementary organisations to ours to make it happen. Hence, we are looking to follow a dual strategy by performing as both technology provider and project enabler.
The technology provider strategy is a more traditional approach where MPS will undertake testing, evaluation and piloting on a fee for service basis with royalties paid if the client proceeds with a full-scale plant. The project enabler strategy, is centred on partnering with clients to identify,test and evaluate “orphan deposits” that are amenable to transformation through its technologies. We are prepared to consider earn-in arrangements for the right projects in these cases.
Our target clients are quite broad as a result, including mining companies (big and small), engineering companies that we can work with on particular projects, other complementary technology developers and suppliers, entrepreneurs, and owners of stranded or underperforming projects.
We want to make this technology as accessible as possible. So, we have a strategy of global reach where we are forming partnerships to establish a network of agents and certified laboratory partners. For example – If you are in North America you can engage Hazen Laboratories in Denver to independently have your ore samples tested and piloted and if you are in South America, we have a partner in Santiago, Chile who can undertake amenability testwork. In Australia we have a well-established laboratory facility at the Australian Mineral Research Centre in Perth. More testing centres will be established going forward and we can also work with clients in their own laboratories if necessary.