Using a classification system comprising of the three- product cyclone and fine screens to improve circuit performance for challenging ore types A N Mainza 1 and M S Powell 2 1 Centre for Minerals Research, Department of Chemical Engineering University of Cape Town, South Africa 2 JKMRC, University of Queensland, Indooroopilly, 40 Isles Road, Brisbane, QLD, Australia Abstract. The three-product cyclone was developed to address problems encountered in the classification of different density materials. The three-product cyclone investigated in this study has two concentric vortex finders at different lengths, configured to produce two overflow streams with different characteristics, in addition to the underflow. To demonstrate the potential applications of this device, comparative pilot plant tests with a conventional hydrocyclone were performed in a circuit comprising a ball mill, cyclone rig, and fine wet screening and a froth characterisation test rig. The results indicated that the combination of the three-product cyclone and screens has potential to address challenges experienced when classifying multi-component density ore types. In the comminution circuit the circulation loads were lower for the configuration involving the three-product cyclone compared to that with the conventional cyclone and in the flotation section higher metal recoveries were obtained from the circuit containing the three-product cyclone. The tests also showed when assessing potential applications for three-product cyclone the influence of the conical section length should also be considered in addition to the spigot diameter, vortex finder diameters and vortex finder lengths. Keywords: 3-product cyclone, fine wet screening INTRODUCTION Hydrocyclones are the preferred classifiers in the size range where flotation recovery is maximised particularly in the processing of UG2 platinum ore (Mills, 1980). However, for the UG2 Platinum ore losses in recovery were identified in the plus 100 µm and sub 10 µm size ranges. To minimise losses in these size ranges a study to investigate a classification system comprising the three-product cyclone and fine screens was commissioned and carried out at pilot plant scales. Although a total of fourteen tests were performed to assess the concept of the three-product cyclone in a circuit at pilot plant scale only a sub section of the results are reported in this paper. Pilot plant trials were performed to assess the potential improvement that can be achieved by employing the three-product cyclone in conjunction with fine screening to prepare feed for the flotation of the UG2 platinum ore. Prior to extending the study to flotation, several tests were performed to establish the optimal operating conditions for the closed grinding circuit comprising a ball mill and the dual classification system containing the three-product cyclone and the fine screens. After establishing the optimal operating conditions, full circuit tests were performed which included the Floatability Characterisation Test Rig (FCTR). Description and specifications of the hydrocyclones used in pilot plant tests Schematics of the conventional cyclone and the three product cyclone used in the testwork are shown in Figure 1. The three-product cyclone produces fine particles in one overflow stream; intermediate size particles in the other overflow, and a coarse underflow stream. The three-product cyclone shown in figure 1 was developed under the AMIRA P9 and details of the design and influence of some key operating variables have been reported by Mainza and Powell (2003), Mainza et al. (2004) and Obeng and Morrell (2003). Prior to running the full pilot plant circuit extending to the flotation section, trials were performed to establish the optimal conical section length for the pilot scale three-product cyclone. The influence of most of the major design variables in UG2 platinum ore applications were assessed using a full scale three- product cyclone test rig located at Eastern Platinum (Mainza and Powell, 2003). A summary of the cyclone dimensions used in the experimental work is given in Table 1. To operate the same cyclone as a three- product cyclone, an additional smaller diameter vortex finder was inserted concentric to the existing vortex finder and the custom designed overflow arrangement that can accommodate two different overflow streams was used as shown in Figure 1.