M.Sc. (Eng.), Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2012 / The aim of this research project was to test the response of ultra fine coal sourced at Klipspruit Colliery to froth flotation and the response of the froth flotation products to dewatering using two different types of filter presses, namely the Tecnicas Hidraulicas (TH) and the Ishigakhi presses. During test work, some difficulty was experienced with coarse material feeding the froth flotation pilot plant. This led to pilot plant modifications. Further process complexities necessitated laboratory scale flotation test work on the Klipspruit coal to be carried out. The results for both the laboratory scale and pilot plant test work for froth flotation indicated that froth flotation as applied to the Klipspruit fines was not economically feasible because neither the required quality of the product (calorific value of 27.80 MJ/kg) nor the product yield of 50% could be achieved when subjected to a primary and secondary stage of froth flotation. The coarse material, which fed the pilot plant and the Ishigakhi filter press, gave low moisture values (12.3%) not typical of ultra fine coal moisture values. However when fed with very fine particle size distributions, prior test work with the Ishigakhi showed that moisture values below 20% could be achieved. The moisture values obtained for very fine particles using the TH filter press on product thickener underflow material sourced at Goedehoop colliery reached values below 20%. Thus both of the two dewatering options, i.e. the Ishigakhi filter press equipment or TH filter press equipment for the ultra fine coal dewatering, can be utilized. Since the filter rate is the determining factor specifying filter press size, it was determined that a larger TH filter area is required in 1 comparison with the Ishigakhi press. Based upon the pilot and laboratory scale test work undertaken and the assessment of the results, it appears that both dewatering options could be successfully employed on a technical basis for the dewatering of coal flotation products, tailings and the arising raw ultra fine fraction. Froth flotation for Klipspruit ultra fine coal was deemed unfeasible for both pilot plant and laboratory scale tests conducted. For this reason a capital expenditure for the construction of a froth flotation plant at the Western Coal Complex Phola plant was not considered feasible since Klipspruit coal forms part of the feed that will feed the Phola plant. In conclusion, following dewatering using either the TH filter press or the Ishigakhi filter press, it was established that both froth flotation concentrate and unbeneficiated ultra fines gave acceptable total moisture results (below 20%). These dewatered raw ultra fines may therefore be blended into inland product as thermal coal to be utilised by Eskom for power generation. Based upon this premise, it is estimated that profits of 76.5 million Rand could be generated by blending Klipspruit ultra fine coal into thermal coal production at the new Phola plant.

Due to the increasing demand for processing low-grade ores, larger volumes of material are being processed. Therefore, the size of flotation equipment has significantly increased for the past decades. The studies related to scale-up are and will remain to be crucial in terms of designing larger flotation equipment. One of the most important factors for flotation scaling-up is the “flotation rate constant”. Hence, the main aim of this investigation was to understand the scale-up criteria when the size of different laboratory-scale cells increases, using the Outotec GTK LabCell®. This was done by assessing the influence of impeller speed, as a hydrodynamic variable, on the flotation performance. Recovery was found to increase with an increase in the cell area to rotor diameter ratio. Flotation rate and recovery increased with an increase in the impeller speed until a certain point that it eventually decreased for the 2 l and 7.5 l cells. For the 4 l cell, the flotation rate and recovery decreased with increasing the impeller speed. The impeller speed of 1200 rpm allowed a successful scale-up based on the flotation rate constants and recovery when increasing the size of the cells. Maintaining the impeller speeds constant at 1300 rpm increased the flotation rate constants and recovery when increasing the cell size from both the 2 and 4 l cells to the 7.5 l cell. A further increase in the impeller speed to 1400 rpm also produced the flotation rate constants and recovery to increase as the cell size increased from both the 2 and 4 l cells to the 7.5 l cell. However, when increasing the cell size from 2 l to 4 l, good results were also observed for all impeller speeds. The products concentrate seem to become finer when decreasing the cell size, with only a few exceptions. The recovery of particles larger than 38 μm was found to differ considerably less among the different scales.