Though fly ash in South Africa has mainly been utilized in the construction industry, a large portion of it is still discarded. Production of glass-ceramic composites through fly ash devitrification has gradually become one of the applications being examined internationally. This study reports the investigation of producing glass-ceramic composites from fly ash and varying quantities of beverage waste glass and magnesium oxide as main raw materials. Glasses were obtained by melting fly ash and its additives using an arc furnace. Based on their behaviour when subjected to differential thermal analysis, the glasses were then crystallised through a double-staged thermal treatment to form glass-ceramic composites. The composition and behaviour of the glass-ceramic composites were investigated using X-ray diffraction, Scanning Electron Microscopy, mechanical and chemical assessments. The crystal content in the glass-ceramic composites increased as the magnesium oxide content was increased. The desired diopside phase decreased with an increased magnesium oxide content and ultimately resulted in the formation of forsterite and anorthite as the major and second major phases respectively. The glass-ceramic composites with lesser amounts of magnesium oxide were chemically and thermally resistant and they also demonstrated high cold compressive strength.

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Coal mining and washing activities in South Africa often lead to the generation of fine and ultra-fine coal which is in most cases discarded due to high handling and transportation costs. Studies conducted revealed that a large quantity of these fines have market acceptable calorific values and lower ash contents. In order to reduce fines discarded, processes have been developed to re-mine and process the fine coal discards with the aim of improving the calorific value, adding them to coarse washed coal to increase the yield as well as pelletizing the fines so as to meet the market specifications in terms of size. The goal of this study was to evaluate the efficiency of fine coal washing using gravity separation methods and comparing the products thereof to the market specifications with regards to the calorific value and the ash content. Coal fines from the No.4 lower seam of the Witbank coalfield in South Africa resulting from a dry coal sorting plant were subjected to a double-stage spiral test work, heavy liquid separation and reflux classifier test work respectively. The reflux classifier achieved products with low ash content and an increased calorific value, at high mass yields. At higher fluidization water flowrate, the reflux classifier performance was superior to that of the spirals with products of lower ash content and higher calorific value. At low cut point densities, heavy liquid separation yielded the cleanest products with very low ash content but at much lower mass yields. As the density increased, the mass yields increased with the ash content while the calorific value decreased. Most of the products from the different processes met most of the local industries’ specifications but none of them met the export market as well as the gold and uranium industry specifications due to the high ash content.

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