Bauxite ‘red mud’ in the ceramic industry Part 1thermal behaviour.pdf

Bauxite `red mud in the ceramic industry. Part 1: thermal behaviour Vincenzo M. Sglavo a,*, Renzo Campostrini a, Stefano Maurina a, Giovanni Carturan a, Marzio Monagheddu b, Gerolamo Budroni b, Giorgio Cocco b aDipartimento di Ingegneria dei Materiali, Universita? di Trento, Via Mesiano 77, I-38050 Trento, Italy bDipartimento di Chimica Fisica, Universita? di Sassari, Via Vienna 2, I-07100 Sassari, Italy Received 4 February 1999; accepted 22 March 1999 Abstract Samples of red mud, by-products of alumina production from bauxite, are studied in the 120±1400C interval. An extensive characterization was performed by thermal and X-ray di?raction analyses. The identi?cation of gaseous species released upon heating was carried out by coupling the thermal analizer with a gas-chromatographic/mass spectrometer. Density evolution was also determined as a function of the heat treatment. Results indicate primary H2O release from aluminium hydroxides, followed by carbonate decomposition with CO2 evolution below 900 C. Alkaline oxides, mainly CaO and Na2O, lead to the formation of Ca3Al2O6 and NaAlSiO4 between 900 and 1100 C. At the highest temperatures, reduction of Fe3+ to Fe2+, involving O2 release, promotes the formation of Fe2TiO4, with the disappearance of the rutile-TiO2 phase. The various solid state reactions, ascertained at di?erent stages of the heating process, and possible mass balances are discussed with reference to the state diagrams of principal red mud components. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Bauxite; Red mud; Thermal analysis; Calcination; X-ray methods 1. Introduction The activity of primary industries often yields sub- stantial amounts of by-products. The disposal in the original industrial site is favoured by economic rea- sonsDenergy savings, transport, management and pro- ductivityDthough traditional storage in nearby dumps can be impractical owing to the considerable masses involved and environmental restrictions. The loca