Paper no. <3133267> APCChE 2015 Congress incorporating Chemeca 2015 27 Sept – 01 Oct 2015, Melbourne, Victoria 1 Investigating the mineral carbonation of Mg and Ca-rich leachate for utilisation of Victorian brown coal fly ash T. Hosseini 1 *, C. Selomulya 1 , N. Haque 2 and L. Zhang 1 1 Department of Chemical Engineering, Monash University, Clayton, GPO Box 36, Victoria 3800, Australia 2 Mineral Resources Flagship, CSIRO, Clayton, Victoria 3168, Australia * Corresponding author. Email: tahereh.hosseinidashtikhani@monash.edu Abstract: Aqueous mineral carbonation of industrial waste (e.g. fly ash) is a potentially attractive sequestration technology to reduce CO 2 emissions. Therefore, the carbonation capacity of solutions rich in Mg and Ca (similar to those found in suspensions of Victorian brown coal fly ash) was studied in relation to various process variables. This investigation is pivotal to understand the preferred experimental conditions for achieving high CO 2 uptake rate as well as the extent of carbonation of Mg and Ca. About 100% of Ca and Mg were carbonated in less than 40 min in the presence of Mg or Ca only or different mixtures of these two ions in the solution. Furthermore, the presence of Mg in the solution was shown to slow the precipitation rate of calcite. A quantitative comparison of X-ray diffraction spectra for solid precipitates showed that carbonation via Mg or Ca only in the solution resulted in formation of unidentified precipitate, calcite and vaterite, respectively. For the mixtures of Mg and Ca, the predominant phases were calcite, magnesian calcite and aragonite. The results showed that the carbonation reaction rate increased with increasing reaction temperature. However, it exhibited a maximum value at 40°C and a further increase in temperature from 40°C onwards resulted in insignificant change on the carbonation yield. The reason for this is that increasing temperature played a detrimental role on the solubility of CO 2 in the solution which in turn inhibited the extent of carbonation. Keywords: calcite, magnesian calcite, mineral carbonation, Victorian brown coal fly ash. 1 Introduction The amount of solid waste residue generated from large scale industrial processes such as coal- based power plants is increasing substantially [1]. Many processes producing solid waste release large amounts of carbon dioxide. The solid waste residues can directly or indirectly be used as raw materials for CO 2 capture or storage (CCS) [2-5]. One method involves sequestering CO 2 by converting solid wastes containing Ca or Mg into thermodynamically stable form of carbonates [6-8]. The utilisation of alkaline solid wastes like fly ash has several advantages including a low cost of sequestration, close proximity to the place where the CO 2 is emitted, and mostly fine and uniform particle size, which minimises any crushing and milling costs. Moreover, alkaline solid wastes are typically more reactive with CO 2 than natural minerals due to their chemical instability [9]. Fly ash is a valueless waste from the combustion of coal and municipal waste materials, containing magnesium (Mg) and calcium (Ca) at varying proportions. 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 [1]. Typical Victorian brown coal fly ash contains 29.3% MgO and 32.4% CaO. This is an appropriate feedstock for carbonation of both magnesium and calcium [10,11]. Very large amounts of this material are being landfilled, which results in long-term negative impacts on the environment [10]. Due to the fact that fly ash rich in alkali and alkaline earth metals is unsuitable for being added to cement, the use of this kind of fly ash to supplement natural minerals for CO 2 mineralisation has been receiving increased attention [12-14].