Glycine Leaching Technology

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.