Recovering and concentrating gold and silver differs from recovering other common heavy metals in that precious metals are generally present in solution as anionic complexes, except when thiourea is used as leaching agent. Since these complexes are large and often have a valence greater than one, anion exchange resins are very selective for them compared with other anions commonly found in water. Gold extraction metallurgy has experimented big changes the last years and countries with important gold deposits have done significative investments on gold projects to be developed in the short time. As must be expected, this development promotes the researching of new and appropriate technologies on the treatment of specific auriferous ores in order to recover the gold with low cost and high efficiency.
Carbon-in-pulp (CIP) and Carbon-in-Leach (CIL) are processes very popular for the treatment of aurocyanide solutions but have some limitations such as regenerate the carbon employing high temperatures, its loading efficiency is affected by organic material and clayey minerals, and also have long cycles of extraction. Considering the aspects mentioned above, ion exchange resins have the great possibility to be used in the gold recovery from a cyanidation process. The ion exchange resins present some advantages over activated carbon such as higher loading capacity, regeneration of cyanide ions, periodic reactivation, and organic material does not affect the loading capacity.
The pregnant solution is commonly contacted with beds of activated-carbon or anionic ion exchange resin that adsorb the gold. The precious metal loaded on the activated carbon or the resin is recovered by elution or simply by incineration of the carrier at high temperature. Ion exchange resins are more versatile substrates than activated carbons because specific functional groups can be fixed on the resin matrix during the synthesis. Therefore the resins can be tailor-made to improve the carrier features such as selectivity, resistance to poisoning by calcium or organic materials and loading capacity. In addition, activated carbons require much higher temperatures for elution and require thermal reactivation which is unnecessary for resins.
The use of ion exchange resins has been proposed as an alternative to more conventional processes such as Merrill-Crowe and Carbon-in-Pulp, and specific testwork programs have been done in order to show the viability of the processes with resins. The motivation of this research work was make note the special characteristics of resins that make them adequate for its industrial application. Considering the ideas exposed above, it is important to indicate the benefits of employing ion exchange resins to recover gold from cyanide solutions.
Screening device used to classify ion exchange resins
Ion Exchange Resins | Resin Structure | Ion Exchange Resin Manufacturers | First Studies on Gold Recovery by Ion Exchange Resins | Ion Exchange Resin Properties | Strong-Base Resins | Weak-Base Resins | Ion Exchange Process for Gold Recovery | Loading | Elution | Effect of Flotation Reagents on Resin Adsorption Capacity | Application of Ion Exchange Resins | Considerations for Industrial Application | Efficiency of Gold Adsorption by Resins | Industrial and Pilot Plant with Ion Exchage Resins