Proceedings of ICORAFSS 2009 2-4 June 2009, The ZON Regency Hotel, Johor Bahru, Malaysia The Mineralogy Changes in Red Mud after Reaction with SO 2 Nabilah Aminah Lutpi 1 *, Leon Munro 2 and John Zhu 2 1 School of Environmental Engineering, Universiti Malaysia Perlis, 02600 Perlis, Malaysia 2 School of Chemical Engineering, University of Queensland, Brisbane QLD 4027, Australia *email: nabilah@unimap.edu.my Abstract An incentive to investigate the mineralogy of red mud after the reaction with SO 2 was carried out in this study to iden- tify whether that the chemical properties of red mud are suitable for use as a sorbent in the flue gas desulphurisa- tion process. The main purpose of this study is to evaluate how SO 2 gas affects the minerals in solid and liquid phase of the red mud at different contact time. Red mud samples from Worsley Alumina Pty. Ltd.(WAPL), Western Australia were used in this study and were examined using XRD, XRF and ICP analysis to identify the changes in the red mud composition. From the XRD analysis, WAPL red mud prior to reaction with SO 2 implied that it was mainly com- posed of goethite, hematite, aluminium silicate, potassium magnesium hydrogen aluminium silicate hydrate, and so- dium titanium silicate. However, after the reaction between red mud and SO 2 , it is observed that goethite is the domi- nant mineral while other minerals were fluctuates over time. This scenario is different for the XRF analysis where- by main constituent of the treated red mud is hematite. This is followed by alumina, quartz, and anatase while the rest of elements present comprise < 1.0%. However, the ICP analysis of treated red mud at different contact time implies that there are six main elements (Na, Al, S, K, Ca, P) which are most highly concentrated in the liquid phase of red mud, while other elements (Co, Cu, Fe, Ga, Mg, Mn, Ti, Zn) disappeared into the solid phase, explaining why only trace amounts of them were detected in the liquor. Keywords Red Mud, SO 2 , minerals 1. INTRODUCTION Red mud is alkaline bauxite residue generated from the Bayer process [1]. This residue has a high pH value, in the range of 10-13, as a result of the presence of hydroxide [2]. In addition, red mud is produced after the filtration of a caustic solution that contains 1-6% w/w sodium hydroxide and sodium carbonate [3]. The chemical, physical and mi- neralogical composition of red mud depends on three as- pects – the bauxite source, the temperature and the manner of operation of the Bayer process [1, 4]. This means that the properties of red mud from the same bauxite source will differ with both temperature and the amount of flocculation agents added (eg. polyacrylamides and polyacrylates) [4, 5]. Red mud contains approximately 15-40 % solids and has several basic components such as Fe 2 O 3 , Na 2 O, Al 2 O 3 , SiO 2 and TiO 2 [4, 6]. In 1977, a desulphurisation plant was built by a Japanese company, Sumitomo Chemical Co. Ltd, which discovered the chemical properties of red mud and its use as an agent to remove SO 2 from flue gas [7]. This process is able to convert SO 2 to sodium sulphite and sulphate, while simul- taneously neutralising the red mud. Red mud, which func- tions as a sorbent in the process, contains a reactive com- pound called desilication products (DSP). The compound, which is also known as sodalite, facilitates the exchange of Na + ions between the solutions they react with [3]. The process, referred to as the Sumitomo Bauxite Residue De- sulphurisation System (BRDS), has the capacity to effec- tively remove up to 96% of the SO 2 in flue gas [7]. Howev- er, a detailed description of the BRDS process from authen- tic sources is still unfounded; hence most information about the plant is uncertain. Therefore, the aim of this study is to evaluate on how SO 2 gas affects the minerals in solid and liquid phase of the red mud at different contact time. This is to prove whether the chemical properties of red mud are suitable to be used as sorbent in the flue gas desulphurization process as claimed by Sumitomo Chemical Co. Ltd.