The behaviour of free gold particles in a simulated flash flotation environment

Abstract

The behaviour of free gold in flash flotation is currently poorly understood (Dunne 2005), especially when in competition with a gravity recovery unit in a closed-loop milling circuit, although an overlap has been identified in which both units can recover particles between 212 μm and 38 μm. This research aims to identify parameters that may determine whether free gold particles will be recovered by either unit in this competitive size range. Identifying the impact of variables such as mineralogy, reagents, mechanical factors, and physical characteristics (such as size, shape, surface area, elemental composition, etc.) on floatability will enable optimization of combined gravity and flash flotation circuits. This paper, the second in a series, is focused on the comparison of free gold and pure gold powder recoveries in laboratory flotation tests as a function of collector (potassium amyl xanthate, or PAX) addition. The first paper established the method used to study the behaviour and characterize the ultimate content of free gold recoverable by flash flotation. The knowledge gained from this research contributes to a better understanding of the impact of particle size, milling effects, residence time, and collector additions upon the recovery of free gold in the milling circuit. BackgroundSeveral plants use batch centrifugal concentrators (BCCs) and flash flotation unit operations in a closed-loop milling circuit as an option for processing complex ores containing free gold as well as gold locked in a sulphide matrix. BCC circuits are used to recover the larger particles of free gold, roughly +106 μm, while a flash flotation circuit produces a sulphide concentrate encompassing smaller free gold particles (-106 μm) and gold contained in sulphides. Based on plant surveys undertaken by the Curtin University Gold Technology Group (2008), the two units will tend to compete for particles in the -212 +38 μm range, as shown in Figure 1.Because knowledge of the behaviour of free gold recovery in a closed-loop milling circuit with parallel flash flotation and gravity recovery units is limited, an improved understanding of the behaviour of gold in this situation will provide greater confidence in the application of such processes to the processing of complex gold ores. Gravity concentrationGravity-recoverable gold (GRG) is a specific term that refers to free gold reporting to the concentrate stream with a small mass yield if separations are performed using BCCs. GRG isThe behaviour of free gold particles in a simulated flash flotation environment by T.D.H. McGrath*, J.J. Eksteen*, and J. Heath † SynopsisA reliable laboratory method to characterize the response of free gold particles to flash flotation conditions has been developed. The test has been performed on free milling gold ores as well as synthetic ores, using either a gravity concentrate or gold powder as the gold source, to assess the floatability of gold particles. Trends in free gold flotation kinetics, as well as size and milling effects, were identified for ...