The reactions between gold and hypochlorite leach solutions containing hydrochloric acid and sodium chloride are demonstrated below: 4Au + 16NaOCl + 10H2O → 4HAuCl4 + 16NaOH + 5O2……………………………………(1) 4HAuCl4 + 4NaCl → 4NaAuCl4 + 4HCl…………………………………………(2) 16NaOH + 16HCl → 16NaCl + 16H2O…………………………………………(3) Overall reaction of equations (1), (2) and (3) can be summarized as follows: 4Au + 16NaOCl … Read more
Black sand may be generally defined as a constituent of “alluvial” gravel consisting mainly of fine particulate grains of heavy, dark colored minerals and rocks. These alluvial gravels, chiefly concentrated by wave, current or surface action, may also contain “eluvial” material that includes black sand. The eluvium, which results from decomposition or disintegration in place … Read more
In view of the tendency of fine gold recover by floating and the dominance of heavy minerals, the prospects for flotation were worthy of re-investigation, particularly with the new tools of the air sparged hydrocyclone (ASH) and the flotation column. Although gold readily and naturally forms a hydrophobic film, dithiophosphates have been advanced as more … Read more
Grinding balls are essential mechanical components in ball and semiautogenous (SAG) mills. Their function is crushing and grinding ore rocks weighing up to 45 kg (100 lb) preparatory to recovery of valuable minerals, from lead through rare earth elements, which are essential to the approaching 21st century technological society. Their design, manufacture, and selection deserve … Read more
Supercritical water alters the structure of common sulfide minerals by partially removing sulfur from the mineral structure. This discovery has been applied to the treatment of pyritic gold ores to improve precious metal recovery without generating or utilizing environmentally sensitive products such as SO2, chlorine, or cyanide. Pretreating pyrite concentrates in supercritical water under mildly … Read more
High-volume, low-pressure water jets have been employed for erosion of loosely consolidated rocks for centuries. This excavation method finds application in specialized circumstances even today. The use of high-pressure, low-volume water jets for rock cutting is more recent and was made possible by the development of high-pressure water pumps. Despite the benefits often claimed for … Read more
World resources of cobalt appear ample for the foreseeable future; however, political and economic events have caused concern over the availability and reliability of an uninterrupted supply. Because of this concern, the U.S. Congress requested that the U.S. Bureau of Mines initiate a study of the flow of cobalt in the economy that would delineate … Read more
Underground in situ leaching is a method of in situ leaching which takes advantage of existing underground mine workings to gain preferential access to a deeply buried ore deposit. With this method of leaching, injection and recovery wells are collared in existing underground mine drifts and drilled into an undisturbed portion of the deposit. The … Read more
Grinding is generally considered to be a size reduction operation. However, in most cases the primary objective of grinding is the liberation of valuable minerals from gangue material, irrespective of the amount of size reduction required. If fracturing of an ore occurs in a random manner, it may be possible to use the grain size … Read more
Bacterial extraction of gold from sulfide bearing ores has been studied by many investigators. If gold occurs finely disseminated within the sulfide ore matrix such as in pyrite, arsenopyrite and pyrrhotite, the leachant can not penetrate into the inside of solid ore in order to leach the enclosed submicron size gold particles. For their liberation, … Read more