Losses of gold in CIP cyanide leaching operations is typically due to one or more of three main causes:
♦Free gold which was not leached
♦Gold locked in silicates
♦Gold locked in sulphides
Due to the high value of gold, the need for recovering these particles from finer grinding operations is becoming increasingly important. Recent investigations into the concentrating ability of the enhanced gravity Falcon B type concentrator resulted in the hypothesis: Through parameter optimisation of bowl speed, feed rate and bowl angle, the recovery of fine gold bearing particles and sulphides from Pajingo tailings can be maximised using Falcon B technology.
Pajingo tailings material was chosen as it has a very fine grind size of 80% passing 38 microns and contains a high proportion of gold locked in silicates as well as liberated sulphides. The recovery of sulphur, hence sulphides, was intended to mimic the behaviour of free gold give to give an indication as to how effectively a dense material can be recovered from a lighter gangue. The main focus of the project was the recovery of both gold and sulphur in the -20 micron fraction.
From the operational parameters tested, bowl angle had the greatest impact on both gold and sulphur recovery. The steepest bowl angle tested, 10 degrees, gave the highest sulphur recovery at the highest bowl speed, 350G, and the lower feed rate, 50kg/hour. Optimum gold recovery, close to 50%, was slightly different with the 14 degree bowl at the lower bowl speed, 250G and the lower feed rate, 50kg/hr giving the highest recovery in the -20 micron fraction. Mass recovery to the concentrate was found to be a function of both bowl angle and feed rate with the concentrate size distribution remaining constant for all testing conditions.
At the parameter combination which gave the highest gold recovery, another three tests with increased feed masses were conducted. The three tests used Pajingo leach tailings, Pajingo leach feed and Jundee leach feed as feedstock materials. The test with Pajingo leach tailings showed that a significant increase in gold grade can be achieved in the fine fraction with only a slight drop in recovery. Substantial recovery in both the fine and coarser size fractions was possible from Pajingo leach feed and the much coarser Jundee leach feed due to the higher presence of free gold particles. Sulphur recovery for all increased feed mass tests was very poor due to overloading of the concentrate particle bed.
A detailed risk analysis plan was implemented to identify and mitigate/remove the risks associated with the completion of the testwork procedure and analysis. As part of the risk analysis, it was identified that a project management be created and used to ensure timely completion of the project.