Gold recovery from waste activated carbon-a comparison between mechano-chemical pretreatment and charcoal augmented oxidation

摘要

The use of activated carbon in recovering dissolved gold from solution has been embraced at virtually all gold process-ing plants worldwide. Technically, activated carbon may be added in the course of leaching, a process known as carbon-in-leach (CIL), or after leaching in the carbon-in-pulp (CIP) ocess. CIL has advantages when carbonaceous materials e present in the ore since it brings about competitive Isorption between the added carbon and the preg-robbers. Activated carbon may also be loaded into columns or up-flow ntactors before the solution is passed through; it is referred as carbon-in-column (CIC). The loaded carbon is then ipped and the gold recovered mainly by electrowinning. The carbon is reactivated, sized, and recycled. Activated carbon breaks into fragments during usage as a result of impact stresses against tank walls, screening, transportation, elution, and regeneration. Part of these fines (usually -20 mesh) may be retrieved as waste-activated carbon (WAC). A worldwide survey shows that the WAC may contain from about 0.11 to 0.14 kg of gold per tonne of carbon. With its relatively high gold content, WAC represents a potential source of extra revenue. The methods that have been proposed for pretreating and/or recovering gold from waste carbon may be generally classified as follows: (1) incineration, (2) electrochemical, and (3) competitive adsorption. In this research, two methods that augment combustion of waste-activated carbon are evaluated. These are mechano-chemical activation before oxidation and direct combustion using charcoal as fuel. Mechano-chemical activation caused structural modifications of the waste carbon, which were measured by X-ray diffraction analysis. The quantitative changes in the crystallinity of the samples were determined by measuring the relative intensities at a specific lattice plane for the milled material (I) and an undisturbed reference standard (I_o). The intensity ratio (l/I_o), also known as the J-factor, decreased from a value of one for the undisturbed lattice to 0.56 after six hours vibration milling, which resulted in a reduction in the temperature for complete oxidation from above 700 deg C to 450 deg C.