Flotation as a separation technique in the coal gold agglomeration process

Abstract

Existing gold recovery processes available to the small-scale gold mining sector pose a considerable hazard to the environment, due to the use of lethal chemicals such as mercury and cyanide. A gold recovery method, called the coal gold agglomeration (CGA) process, whereby hydrophobic gold particles are recovered from ore slurries into coal-oil agglomerates, and the subsequent burning of these agglomerates to recover the gold, was developed some years ago. The objective of this study was to optimise the separation phase of the CGA process through a flotation technique. It was also necessary to compare the gold recovery of the CGA process to that of the mercury amalgamation process, to determine the feasibility of implementing the CGA process as an alternative to the mercury amalgamation process. Batch tests were performed on a synthetic (7g/t) gold ore containing a fine (± 44 ,μm) gold powder. Agitating an industrial charcoal and oil in an aqueous suspension formed agglomerates. After a suitable agglomeration time the ore slurry and a collector such as potassium amyl xanthate (PAX) was added and stirring continued for fifty minutes before the separation was effected. The gold-loaded agglomerates and residue ore were then dried, ashed and treated with aqua regia and analysed. During the experimental program, the process was scaled up from 150 milliliters (using magnetic stirrers and scraping) to a one-liter flotation cell, and eventually to a three-liter flotation cell. It was found that for both flotation configurations an increase in the stirring rate results in an increase in the gold and mass recoveries. Maximum gold recoveries were however obtained at a certain stirring rate above which the gold recovery dropped again. Increasing the viscosity of the oil caused the formation of stronger agglomerates and hence gold recovery was also increased. The use of larger coal particles gave rise to higher gold recoveries due to increased agglomerate flotation and superior gold particle penetration into the agglomerates. Recycling of the agglomerate phase showed that gold loading on the agglomerates could be increased to reduce operating cost.