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    ALTERNATIVE BINDERS TO BENTONITE FOR IRON ORE PELLETIZING - PART I: EFFECTS ON PHYSICAL AND MECHANICAL PROPERTIES
    (Centro Federal Educacao Tecnologica Rio Grande Norte, 2014) Sivrikaya, O.; Arol, A. I.
    The use of conventional bentonite binder is favorable in terms of mechanical and metallurgical pellet properties, however, because of its acid constituents bentonite is considered as impurity especially for iron ores with high acidic content. Therefore, alternative binders to bentonite have been tested. Organic binders are the most studied binders and they yield pellets with good wet strength; they fail in terms of preheated and fired pellet strengths. This study was conducted to investigate how insufficient pellet strengths can be improved when organic binders are used as binder. The addition of a low-melting temperature and slag bonding/strength increasing constituent (free in acidic contents) into pellet feed was proposed. Addition of boron compounds such as colemanite, tincal, borax pentahydrate, boric acid together with organic binders such as CMC, starch, dextrin and some organic based binders, into iron oxide pellet was tested. Wet and thermally treated pellet physical-mechanical qualities (balling - moisture content - size - shape - drop number - compressive strengths porosity - dustiness) were determined. The results showed that good quality wet, dry, preheated and fired pellets can be produced with combined binders (an organic binder plus a boron compound) when compared with bentonite-bonded pellets. While organic binders provided sufficient wet and dry pellet strengths, the boron compounds provided the required preheated and fired pellet strengths at even lower firing temperature. Especially, the contribution of boron compound addition is most pronounced for hematite pellets which do not have strengthening mechanism through oxidation like magnetite pellets during firing. Therefore, addition of boron compound is beneficial to recover the low physical-mechanical qualities of pellets produced with organic binders through slag bonding mechanism. Furthermore, lowering the firing temperature thanks to low-melting boron compounds will be cost-effective for firing part of the pelletizing plants.
  • [ X ]
    Öğe
    ALTERNATIVE BINDERS TO BENTONITE FOR IRON ORE PELLETIZING - PART II: EFFECTS ON METALLURGICAL AND CHEMICAL PROPERTIES
    (Centro Federal Educacao Tecnologica Rio Grande Norte, 2014) Sivrikaya, O.; Arol, A. I.
    This study was started to find alternative binders to bentonite and to recover the low preheated and fired pellet mechanical strengths of organic binders-bonded pellets. Bentonite is considered as a chemical impurity for pellet chemistry due to acid constituents (SiO2 and Al2O3). Especially addition of silica-alumina bearing binders is detrimental for iron ore concentrate with high acidic content. Organic binders are the most studied binders since they are free in silica. Although they yield pellets with good wet strength; they have found limited application in industry since they fail to give sufficient physical and mechanical strength to preheated and fired pellets. It is investigated that how insufficient preheated and fired pellet strengths can be improved when organic binders are used as binder. The addition of a slag bonding/strength increasing constituent (free in acidic contents) into pellet feed to provide pellet strength with the use of organic binders was proposed. Addition of boron compounds such as colemanite, tincal, borax pentahydrate, boric acid together with organic binders such as CMC, starch, dextrin and some organic based binders, into magnetite and hematite pellet mixture was tested. After determining the addition of boron compounds is beneficial to recover the low pellet physical and mechanical qualities in the first part of this study, in this second part, metallurgical and chemical properties (reducibility - swelling index - microstructure mineralogy - chemical content) of pellets produced with combined binders (an organic binder plus a boron compound) were presented. The metallurgical and chemical tests results showed that good quality product pellets can be produced with combined binders when compared with the bentonite-bonded pellets. Hence, the suggested combined binders can be used as binder in place of bentonite in iron ore pelletizing without compromising the pellet chemistry.