Flotation as a separation technique in the coal gold agglomeration process

Existing gold recovery processes available to the small-scale gold mining s ector pose a considerable hazard to the environment, due to the use of leth al chemicals such as mercury and cyanide. A gold recovery method, called th e coal gold agglomeration (CGA) process, whereby hydrophobic gold particles are recovered from ore slurries into coal-oil agglomerates, and the subseq uent 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 th e gold recovery of the CGA process to that of the mercury amalgamation proc ess, to determine the feasibility of implementing the CGA process as an alt ernative to the mercury amalgamation process. Batch tests were performed on a synthetic (7g/t) gold ore containing a fine (+/- 44 mu m) gold powder Agitating an industrial charcoal and oil in an a queous suspension formed agglomerates. After a suitable agglomeration time the ore slurry and a collector such as potassium amyl xanthate (PAX) was ad ded and stirring continued for fifty minutes before the separation was effe cted The gold-loaded agglomerates and residue ore were then dried ashen and treated with aqua regia and analysed. During the experimental program, the process was scaled up from 150 milliliters (using magnetic stirrers and sc raping;) to a one-liter flotation cell, and eventually, to a three-liter fl otation cell. It was found that for both flotation configurations an increase in the stir ring rate results in ail increase in the gold and mass recoveries. Maximum gold recoveries were however obtained at a certain stirring rate above whic h the gold recovery dropped again. Increasing the viscosity, of the oil cau sed the formation of stronger agglomerates and hence gold recovery was also increased The use of larger coal particles gave rise to higher gold recove ries due to increased agglomerate flotation and superior gold particle pene tration into the agglomerates. Recycling of the agglomerate phase showed th at gold loading on the agglomerates could be increased to reduce operating cost. (C) 2000 published by Elsevier Science Ltd. All rights reserved.