Free gold recovery by coal-oil agglomeration

Environmental protection has become the focus of world-wide research in the gold mining industry and favours the development of environmentaly sound processes, such as the Coal Gold Agglomeration (CGA) process, which is an alternative to existing gold processing methods, such as cyanidation and mercury amalgamation. The CGA process was developed and patented by the British Petroleum (BP) research team in the early eighties and is based on the recovery of hydrophobic/oleophilic gold particles from ore slurries into agglomerates formed from coal and oil. The oil acts as the bridging liquid between the coal and gold particles where the coal is the carrier of the mineral and enables effective separation of the oil phase. The coaloil agglomerates are recycled to increase their gold loading, after which they are separated and further treated to produce gold bullion1-6. Figure 1 shows a schematic representation of the basic concepts involved in the CGA process. Gold bearing ores containing liberated/free gold particles, such as alluvial/free milling ores, gravity concentrates or gravity plant tailings was found to be suitable for the CGA process, as associations with other minerals/metals, such as pyrites, arsenopyrite etc. reduce the oleophilicity of gold, and hence limits gold recoveries2,3,6. High gold recoveries, irrespective of the gold grain size (ranging in size from 1–500 μm) were found, therefore providing an alternative to amalgamation or intensive cyanidation3,4,6. Although the CGA process is not a novel process, sensu stricto, and many further studies besides those done by BP have been conducted7–11, it was attempted in this study to investigate and optimize the process route of the CGA process so as to provide a valid alternative to small-scale mining operations, such as mercury amalgamation.