title: Quantitative X-ray Diffraction (QXRD) analysis for revealing thermal transformations of red mud.
abstract: Red mud is a worldwide environmental problem, and many authorities are trying to find an economic solution for its beneficial application or/and safe disposal. Ceramic production is one of the potential waste-to-resource strategies for using red mud as a raw material. Before implementing such a strategy, an unambiguous understanding of the reaction behavior of red mud under thermal conditions is essential. In this study, the phase compositions and transformation processes were revealed for the Pingguo red mud (PRM) heat-treated at different sintering temperatures. Hematite, perovskite, andradite, cancrinite, kaolinite, diaspore, gibbsite and calcite phases were observed in the samples. However, unlike those red mud samples from the other regions, no TiO2 (rutile or anatase) or quartz were observed. Titanium was found to exist mainly in perovskite and andradite while the iron mainly existed in hematite and andradite. A new silico-ferrite of calcium and aluminum (SFCA) phase was found in samples treated at temperatures above 1100°C, and two possible formation pathways for SFCA were suggested. This is the first SFCA phase to be reported in thermally treated red mud, and this finding may turn PRM waste into a material resource for the iron-making industry. Titanium was found to be enriched in the perovskite phase after 1200°C thermal treatment, and this observation indicated a potential strategy for the recovery of titanium from PRM. In addition to noting these various resource recovery opportunities, this is also the first study to quantitatively summarize the reaction details of PRM phase transformations at various temperatures.
authors.affiliation: Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong.
authors.forename: Chang-Zhong
authors.initials: CZ
authors.lastname: Liao
authors.affiliation: Key Laboratory of New Processing Technology for Nonferrous Metal and Materials, Ministry of Education, Guangxi University, Nanning, Guangxi, China; College of Materials Science and Engineering, Guangxi University, Nanning, Guangxi, China.
authors.forename: Lingmin
authors.initials: L
authors.lastname: Zeng
authors.affiliation: Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong. Electronic address: kshih@hku.hk.
authors.forename: Kaimin
authors.initials: K
authors.lastname: Shih
mesh_terms: D017610:Calcium Compounds; D002516:Ceramics; D005290:Ferric Compounds; D006358:Hot Temperature; D007501:Iron; D007616:Kaolin; D010087:Oxides; D014025:Titanium; D014866:Waste Products / Q000032:analysis*; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D017610:Calcium Compounds; D005290:Ferric Compounds; D010087:Oxides; D014866:Waste Products; C059910:perovskite; C001215:ferrite; C009495:titanium dioxide; C000499:ferric oxide; D007616:Kaolin; D014025:Titanium; D007501:Iron
keywords: Phase transformation; Quantitative XRD; Red mud; SFCA; Thermal behavior