Characterization of bonding and crystalline phases in fluxed pellets using peat moss and bentonite as binders
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I.
INTRODUCTION
IN recent years, increasing attention has been given to the use of fluxed pellets as blast furnace iron-bearing burden material. The reason is that suitably produced fluxed pellets can meet progressively stringent quality requirements in terms of physical strength, reduction behavior at low and high temperatures, swelling characteristics, softening temperature, and narrow range of temperature within which softening takes place. In general, the quality of pellets is affected by the type and nature of ore or concentrate, gangue and other additives, and their subsequent treatment to produce pellets. These factors result in variation in the physicochemical properties of coexisting phases, structure, distribution, number of pores, etc., in the pellets. The properties of the pellets are, therefore, largely governed by the form and degree of bonding achieved between ore particles and also by the stability of these bonding phases during the reduction of iron oxides. Hence, characterization of the bonding a,ad crystalline phases is of prime importance in understanding the basis for the production of pellets of desired quality. A limited number of investigations have been done on the bonding in fluxed hematite pellets in the basicity range of 0.5 to 1.0. tl-71 It is important to note that the conditions and parameters to be controlled are typical of a given concentrate/ore. It is in this context that this research was undertaken for a typical Canadian specular hematite.
In general, the bonding in fluxed pellets is achieved primarily through melt formation during induration. The bonding phase consists mainly of silicates formed from the melt. The various components contributing to melt formation are the gangue of the concentrate, lime and magnesia of the fluxes, bentonite, and iron oxides. Lime and magnesia react with the gangue and/or with the iron oxides. When they react with the gangue, they form part of the intergranular melting phase. The lime also simultaneously reacts with Fe203 to form different calcium ferrites. These melting phases interact with each other and dissolve a variable amount of iron oxides. While very fine particles of the ore components are easily dissolved, the larger ore particles are attacked at the acute angles and faces, causing a certain amount of surface smoothing. On cooling, the iron oxides and their compounds precipitate from the melt, and calcium ferrites and silicates of various compositions are formed depending on the local chemistry. In this paper, the effects of basicity, the type of flux (limestone and dolomite), and the type of binder (bentonite and peat moss) on the bonding mechanism of pellets produced from specular hematite concentrates are examined. The changes in both physical and reduction properties of pellets are also discussed. Special emphasis has been placed on using peat moss as a binder as it is noncontaminating and is abundantly available near the iron ore mines in Quebec. II.
S.C. PANIGRAHY, Research Scientist, and M. RIGAUD, Professor, are with the De
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