The Utilisation of Victorian Brown Coal Fly Ash in Mineral Carbonation

Approximately 1.3 million tonnes of Victorian brown coal fly ash generated per year and most of this amount is mixed with water to form a slurry, which is then pumped to ash settling ponds. The brown coal fly ash is rich in alkali and alkaline earth metals and transition metals with little aluminium and silicon. Industrial wastes rich in magnesium and calcium are being considered for CO₂ mineralisation as part of the strategy for carbon dioxide capture, storage and utilisation (CCSU). This process also converts the valueless wastes, into value-added products such as magnesium carbonate and calcium carbonate to replace dolomite in industrial applications. The characteristics of fly ash differ substantially according to the coal type and combustion conditions. Fly ash generated from younger lignite or sub-bituminous coal burning has more than 20% CaO and MgO that are essential materials for mineral carbonation. Typical Victorian brown coal fly ash contains ~25% MgO and ~30% CaO which makes it an appropriate feedstock for carbonation of both magnesium and calcium. Since 2011, we have been researching on the utilisation of two types of fly ash, Hazelwood and Yallourn fly ash, collected from the Latrobe Valley via the combination of different leaching and precipitation processes. In this study, the science underpinning the extraction of magnesium and calcium in an aqueous solution and the subsequent precipitations will be investigated. The applications of various products produced from different leaching and precipitation alternatives will also be discussed.