a b s t r a c tCoal serves as the primary energy source in most parts of the world. It is a fact that coal combustion yields enormous quantities of fly ash some of which are either hydraulically placed or dry dumped. The current study attempts to provide a comprehensive characterisation of a disused alkaline fine coal ash dam (FCAD) towards assessing environmental impact, rehabilitation and utilisation potential. Fine coal ash refers to a combination of approximately 83% power station fly ash and 17% gasification and bottom ash fines (particles <250 lm) at SASOL Synfuels. The hydration products found in Weathered Fine Coal Ash (WFCA) using X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC) are analcime, calcite, C-S-H gel, ettringite, hydrated gehlenite (Strätlingite), magnetite, periclase, pyrrhotite and sillimanite. High resolution Scanning Electron Microscope (SEM) results provide additional proof that hydration products are present in WFCA. No indication of appreciable leaching was given by X-ray Fluorescence (XRF) results except calcium and silicon. Thus evidence exists that pollutants from saline brines are immobilised in WFCA and an insight of reaction kinetics was obtained. High content of amorphous phase and lack of alteration in some geotechnical properties suggest that WFCA can be reutilised with lime addition to increase alkalinity and activate pozzolanic reactions.

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a b s t r a c tTo meet the escalating demand of energy more coal ash and brines are inevitably produced as byproducts. Large volumes of these wastes and increasing environmental awareness necessitate the development of more sustainable methods to mitigate the environmental footprint. Paste backfill is one of the potential solutions to keep the energy industry sustainable. The behaviour of pastes was investigated by strategically varying brine composition mixed with the two types of fly ash. The results showed that fly ash plays a more prominent role in the behaviour of pastes than brines. It is therefore imperative to consider both fly ash and brine characteristics i.e. constituents of paste for the development of an environmentally sound paste backfill practice. Technically there are numerous benefits in pursuing the proposed solution.