Dense gold particles can be problematic to recover from the grinding circuit of a gold processing operation. A proportion of the feed stream to the classifying cyclones in the grinding circuits is often sent to a separate gravity circuit to recover the gravity recoverable gold (GRG). This type of circuit configuration often results in the regrinding or loss of gold particles which reduces the efficiency of the circuit.
The Cyclone-Gravity Separator (CGS) is a variation on a typical hydrocyclone developed to obtain an additional product stream from the feed material. The proposed outcomes of this project are to characterise the performance of the CGS over a range of particle densities and size fractions to determine if the CGS can achieve a satisfactory recovery of the valuable minerals. The literature has indicated that the CGS can potentially perform an effective separation based on size and density. Thus, the following hypothesis has been formed:
Obtaining a dense product from the classification of a gold grinding circuit stream using a Cyclone - Gravity Separator can reduce the duty required in the proceeding gravity circuit, thereby reducing the amount of gold recycled and increasing the overall recovery of gold.
To thoroughly investigate the validity of the hypothesis, the following objectives were to be achieved:
► Determine the effect of particle density and size on the recovery of the valuable mineral in the port stream from a synthetic quartz gangue in the Cyclone-Gravity Separator.
► Determine the location of the remainder of the valuable mineral and deduce if the total recovery of valuable mineral in the system will be improved.
A testwork regime was developed to attempt to characterize the performance of the CGS over a range of particle sizes and densities. The parameters tested were particle density and particle size to determine the suitability of the CGS for producing a dense product for a gravity gold circuit. Three materials were tested in two separate size fractions as follows:
It was found that particle size had a large impact on the performance of the CGS in effectively separating the dense particles from the silica gangue. The upgrading ratio for coarse (+850 -1180μm) copper ranged between 1.28 and 1.40 while the upgrading ratio for coarse lead was slightly higher (1.38 - 1.64). For fine copper the range was between 2.12 and 2.68 whereas the range for fine lead was 3.68 – 4.49. This increase in upgrading is probably due to the difference in density between the two metals with the more dense lead preferentially reporting to the port stream.
A similar trend was observed for the tests involving gold particles with coarse (+425 -850μm) and fine (+150 -425μm) gold particles being used. It was anticipated that the gold particles in the coarse size fraction would have an upgrading ratio greater than that of the fine lead (3.68 – 4.49) due to the density of gold. This was not observed however with an upgrading ratio between 1.87 and 2.02 and is probably due to the small amount of gold that was added to the system in the coarse gold tests. This may have contributed to unrepresentative sampling or insufficient material may have been collected to allow accurate analysis of the performance of the CGS. Another possible cause may have been the shape of the gold particles which were flakes as opposed to spherical particles in the copper and lead tests. In the fine gold tests, a larger mass of gold was added to the system and the results obtained showed a significant increase in upgrading ratio up to a range of 3.35 to 3.43.
The results indicate that the Cyclone-Gravity Separator can perform an effective separation based on density to produce an enriched feed to a gravity gold circuit but is influenced by the size of dense particles. There are a number of areas in which further work should be completed to fully characterise the performance of the CGS. Further investigation should be undertaken using larger samples of gold or spherical shaped gold particles to better characterise the influence of gold particle size on the performance of the CGS. Also, investigation into the performance of the CGS using a typical gold ore will give a clearer indication of the suitability of the CGS in obtaining a feed stream to a gravity gold circuit.