The use of magnetite as a medium in the wet processing of coal has been used since the early days of dense medium separation. The high magnetic susceptibility and density of magnetite make it an ideal medium to use in wet coal beneficiation because it is relatively easily and successfully recoverable. Owing to the need for more sustainable technologies, Coaltech has been investigating alternative dry processing processes: the Bohou process (developed in China) was identified as a possible feasible option. The Bohou process comprises dry dense medium separation using magnetite as the medium. The recovery and re-use of magnetite are, however, problematic. The aim of this investigation was to determine how efficiently magnetite can be recovered and to identify the factors influencing the magnetite losses during this dry processing. The test work for the project was divided into two phases. The aim of Phase 1 was to identify the magnetite losses to the oversize coal fraction for different moisture conditions of the coal and magnetite. In Phase 2, magnetite and high-titanium magnetite (an alternative source of magnetite) were used to conduct test work to determine which medium could be successfully recovered from fine coal. Magnetite or high-titanium magnetite was mixed with the coal sample as a medium. During Phase 2, the effects of using different screens and different moisture conditions were investigated. For both phases, the samples received were divided into three categories containing different moisture contents: dry coal and dry magnetite, dry coal with wet magnetite (4% to 4.4%), and wet coal (3.5% to 6.5%) with dry magnetite. In Phase 1, the coal samples were screened at 13.2 mm, the oversize mixed with magnetite, and then screened again with a 13.2 mm screen: the magnetite losses were then recorded. For Phase 2, the prepared samples were screened at 3 mm, 13.2 mm, and with a 3 mm high-frequency screen. The undersize was passed through a low-intensity magnetic separator. The recovered magnetite was then passed over a magna chute to recover additional magnetite. ii The results for both phases indicated that the highest recovery of magnetite occurred when dry magnetite and dry coal samples were used. The samples with wet magnetite also gave high recovery, but the samples with wet coal were detrimental to recovery and significant losses were observed. It was found that the magnetite stuck to the surface moisture of the coal. The use of a high-frequency screen improved recovery of the magnetite from the wet coal samples from 45.38% to 74.27%. Recovery from the high-frequency screen for both dry and wet magnetite samples was lower than that achieved with a conventional 3 mm screen. The test results indicated that magnetite can be recovered in the dry beneficiation of coal when the surface moistures of both the coal and magnetite are controlled. Use of a high-frequency screen can improve recoveries only for conditions where the surface moisture of the coal is high. / Dissertation (MSc (Metallurgy))--University of Pretoria, 2021. / CoalTech / Materials Science and Metallurgical Engineering / MSc (Metallurgy) / Unrestricted

Beneficiation of fine coal (+500 μm –2000 μm) is a worldwide problem in the mining industry, especially dry beneficiation of fine coal. Coal beneficiation can be divided primarily into two methods, namely wet- and dry beneficiation. Wet beneficiation methods are utilized more in today‘s industry because of the sharp separation efficiency that can be achieved. These processes include wet jigging, dense medium cyclones, spiral beneficiation etc. Due to the lack of a sufficient water supply in some regions around the world including South Africa, dry beneficiation methods are becoming more popular. Recent mechanized mining methods caused the fraction of fines from coal mines to increase over the years. However, due to old inefficient technologies, coal fines contained in slurry ponds could not be beneficiated and had to be discarded. One new dry beneficiation technology that has been used and researched extensively is the fluidized dense medium bed (FDMB) technology. The purpose of this study is to determine whether fine coal can be successfully beneficiated with a FDMB. It also has to be determined whether adding magnetite and introducing a jigging (pulse) motion to the air feed will increase the separation efficiency of the fluidization process. Witbank seam 4 and a Waterberg coal was used in experiments during this study. A coarse (+1180 μm –2000 μm), fine (+500 μm –1180 μm) and a mix of the two samples were prepared and tested. It was found that adding magnetite to the feed of the fluidized bed did not increase the separation efficiency. However, previous studies indicated the opposite results with regards to magnetite addition. The difference in results obtained could be prescribed to the ultrafine nature of the magnetite and the small coal particles size range used. If the presence of fine particles in the bed increases, the stability of fluidization decreases. In turn, the separation efficiency of the process decreases. Subjecting the feed air flow to a pulsating motion did not have a significant effect on separation. Good results were still obtained with jigging experiments, although not better than with normal fluidization. Stratification of coal particles according to quality was evident by the results obtained during experiments. The quality of coal increases from the bottom to the top of the bed. Overall the fluidized bed, in the absence of magnetite, was found to be a sufficient de-ashing process and further research on this technology could be very beneficial to the coal industry. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014

Beneficiation of fine coal (+500 μm –2000 μm) is a worldwide problem in the mining industry, especially dry beneficiation of fine coal. Coal beneficiation can be divided primarily into two methods, namely wet- and dry beneficiation. Wet beneficiation methods are utilized more in today‘s industry because of the sharp separation efficiency that can be achieved. These processes include wet jigging, dense medium cyclones, spiral beneficiation etc. Due to the lack of a sufficient water supply in some regions around the world including South Africa, dry beneficiation methods are becoming more popular. Recent mechanized mining methods caused the fraction of fines from coal mines to increase over the years. However, due to old inefficient technologies, coal fines contained in slurry ponds could not be beneficiated and had to be discarded. One new dry beneficiation technology that has been used and researched extensively is the fluidized dense medium bed (FDMB) technology. The purpose of this study is to determine whether fine coal can be successfully beneficiated with a FDMB. It also has to be determined whether adding magnetite and introducing a jigging (pulse) motion to the air feed will increase the separation efficiency of the fluidization process. Witbank seam 4 and a Waterberg coal was used in experiments during this study. A coarse (+1180 μm –2000 μm), fine (+500 μm –1180 μm) and a mix of the two samples were prepared and tested. It was found that adding magnetite to the feed of the fluidized bed did not increase the separation efficiency. However, previous studies indicated the opposite results with regards to magnetite addition. The difference in results obtained could be prescribed to the ultrafine nature of the magnetite and the small coal particles size range used. If the presence of fine particles in the bed increases, the stability of fluidization decreases. In turn, the separation efficiency of the process decreases. Subjecting the feed air flow to a pulsating motion did not have a significant effect on separation. Good results were still obtained with jigging experiments, although not better than with normal fluidization. Stratification of coal particles according to quality was evident by the results obtained during experiments. The quality of coal increases from the bottom to the top of the bed. Overall the fluidized bed, in the absence of magnetite, was found to be a sufficient de-ashing process and further research on this technology could be very beneficial to the coal industry. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014