Solid state sintering in the induration of iron ore pellets
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T. Z. FAHIDY
Data is developed to show the relationship between pellet strength and shrinkage which accompanies induration. Systematic measurements of shrinkage kinetics of a pure hematite reagent powder and of a c o m m e r c i a l magnetite concentrate are presented, and rate constants and activation energies evaluated. The discussion links the results of pellet induration r e s e a r c h with sintering theory, developed in support of powder metallurgy and ceramics. Transport mechanisms active during strength development of pellets are dealt with. SUCCESSFUL pilot plant development of the process to pelletize fine iron oxide concentrates and to heat harden the pellets dates back to the mid 1940s, h2 with the f i r s t commercial plants going on s t r e a m in 1955. A recent review, a among others discusses the v e r y extensive growth and development of the industry in the last two decades and its assured potential for further growth. The technological development has been based largely on empirical study. The fundamentals of m i c r o structure development as the cause of heat hardening or induration have received early attention in the papers of Cooke and co-workers. 4-6 Subsequent work s-~8 confirmed these results and provided much additional data on the effect of time, temperature, additives and other p r o c e s s conditions on pellet quality and processing r e quirements in individual cases, but has added only m a r ginally to the understanding of the physico-chemical mechanism and critical p a r a m e t e r s of induration. Heat hardening of powder compacts pressed, or otherwise formed into shape, is also the basis of ceramic, r e f r a c t o r y and powder metallurgy industries. Fundamental work in support of these industries has been conducted under the general subject name of sintering~ defined as ~ the p r o c e s s of solid particles in contact adhering and growing together into a solid body while below their melting point. Systematic and quantitative study of sintering* originated with Frenkel ~8 and Ku*For the sake of good communication between disciplines, the use of the term "sintering" in this context seems appropriate, in spite of the minor confusion which can arise from the use of the term to describe the industrial agglomeration of frees on a travelling grate strand.
czynskt x9 and has continued steadily. Several reviews are available. 2~ This work has great heuristic value in understanding the phenomena connected with iron ore pellet induration and in giving direction to further research, but the pelletizing literature gives little evidence of the awareness of this fact. Accordingly the first objective of the present paper is to draw attention to the results of the most relevant sintering research. Subsequently results of investigations of strength development and shrinkage during induration, and s y s t e matic measurement of shrinkage rates are reported and discussed. J. R. WYNNYCKYJ is Associate Professor and T. Z. FAHIDY is Professor, Department of Chemical Engineering, University
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