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Recovery of Precious Metals Precious metal aqueous solutions are all fundamentally similar, and recovery of the precious metal ions themselves from those solutions is all fundamentally similar. In aqueous solutions, metals occur in the form of an ionic complex, as for example in the form of Au(CN)- ions (gold cyanate). Just as with copper, precious metals occur in aqueous solutions either as metal ions or ion complexes, both of which are ionic, charged forms. In fact, it is the objective of hydrometallurgical, mineral recovery processes to place such ions into aqueous solution in ionic form, implicitly using the water as the motile fluid to wash the valuable ions away from the zero value tailings and ores in which they are originally entrained and bring them to a point of processing. As examples, gold, silver and platinum ores are treated with cyanide solutions to dissolve the precious metals into aqueous solution in the form of cyanate or similar complexes, thereby separating the valuable ions from the zero value tailings which are left behind, and thereafter moving the ionic solution to a point of recovery. The term "hydrometallurgy" is revealing and insightful—hydro (water) is used to get the metal out of the ore and into the point of final recovery. Once valuable precious metal ions are placed into aqueous solution (the pregnant solution), the first (and easier) half of the battle is won. Thereafter, the pregnant, ion bearing solutions must be processed to remove the sought after precious metal ions. Often those pregnant solutions are first concentrated (preconcentrated) and thereafter reduced to metallic form (e.g., metallic gold or other metal). To date, the methods for doing so have been crude, bulky, and not particularly cost effective. For example, with cyanide complexes, typically granulated (uncharged) activated carbon columns are used to collect and concentrate the cyanide complexes from the highly dilute form in which they exist in the original pregnant leach solution, i.e., to a concentration that can be more effectively recovered. Typically, adsorbing activated carbon columns are used to adsorb and retain the gold from the highly dilute pregnant leach solution. In practice, approximately 270 oz of metallic gold can be concentrated/collected on one ton of activated carbon before such columns become saturated with gold cyanide ions and must be regenerated by eluting the gold off using hot, concentrated cyanide solutions. With cyanides, the metal-cyanide complexes are negatively charged ion complexes dissolved in water, so a Reticle Carbon electrode pair concentrates the complexes on the anode. Regeneration of the anode desorbs the valuable ion complexes previously adhered to the anode and produces a concentrated solution in much the same way that salt is removed using CDI cell. This highly concentrated solution can then be subjected to an intensive and expensive electrochemical process to break down the metal-cyanide complex and recover the metal in elemental form. The quantity of metallo-cyano complex that can be recovered on Reticle carbon anodes is dramatically higher than the quantity that can be recovered using today’s best in class technology (activated carbon column adsorption). The reason is simple—Reticle Carbon electrodes are inherently and proactively charged, but the activated carbon column is not charged. It cannot be charged. To wit, Reticle succeeds by virtue of applying a charge, which is impossible to accomplish with carbon column adsorption. Application of the charge ensures more efficacy, efficiency, and effectiveness of the Reticle-based operation. Reticle allows far more efficient use of the carbon employed in the process. With regard to sustainability, Reticle has no pernicious chemicals and no byproducts other than pure and clean water. Power consumption is low, there are no chemicals, and all exiting water is pure and can either be recycled or delivered to the local water company or industries for local use. |
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