The role of a flash flotation circuit in an industrial refractory gold concentrator

• Comparison of operating data with and without flash circuit.
• Flash feed higher grade, better liberated than conventional circuit feed.
• Flash circuit observed to reduce plant losses as fines.
• Performance of gold studied, Eh significant in flash cells.
• Significant plant losses when flash circuit taken off-line.

In order to determine the contribution of the flash flotation circuit to the overall plant performance of the Kanowna Belle concentrator, two survey campaigns both with and without the flash circuit in operation have been conducted on two distinctly different ore types: a very high grade ore, and a very low grade ore of higher hardness. Using two different ores with the same target valuable mineral species (gold and pyrite) through the same treatment route allows any trends in performance to be more easily identified. As both survey campaigns involved running the plant with and without the flash flotation circuit in operation, the significant contribution of the flash flotation cell to overall plant recovery and final concentrate grade is highlighted. The flash circuit on this plant may be considered as the primary rougher, contributing in excess of 42% of the valuable material that is recovered to the final concentrate stream, at a grade of approximately 35% sulphur; and in-so-doing reducing the overall plant footprint that would otherwise be required to achieve the same recoveries at the target concentrate grade.Mineralogical analysis of survey samples shows that the feed to the flash flotation cell (cyclone underflow) is of a much higher grade and contains a higher proportion of well liberated valuable material as compared to the conventional flotation circuit feed (cyclone overflow). Maximising the recovery of this material before it re-enters the milling circuit should be of paramount importance to optimising overall plant performance.When the flash flotation circuit is taken off-line the recovery of sulphur (and hence pyrite) is observed to decrease dramatically, and whilst the recovery of gold also decreases, it is to a much lesser extent. The difference in the recoveries of gold and pyrite that is observed without the flash flotation circuit in operation is most likely attributable to a change in the way the gold is being liberated as a function of the change in grinding circuit operation that is required when the flash circuit is taken off-line. The distribution of valuable material in the cyclone overflow stream (conventional flotation feed) undergoes a step change when the flash circuit is taken off-line with an increase in the amount of valuable fines being generated, which is further reflected in the flotation tails with a higher proportion of both pyrite and gold being present in the intermediate and fine size classes. This increase in the amount of pyrite fines in particular may have contributed to the loss in recovery that was observed when the flash flotation circuit was taken off-line.Pulp chemistry data from various points around the flotation circuit highlight the different processing conditions in the flash cell, compared to the conventional circuit, which will impact on the type of minerals able to be recovered by flotation, as well as reagent selection for this type of processing application.

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