Contribution à I'étude du gonflement des boulettes de minerais de fer lors de leur réduction

Abstract Le gonflement des boulettes d'hematite a ete etudie a I'aide d'une methode de mesure standard ISO ainsi qu 'a I'aide d'une methode de mesure dilatometrique.
La premiere methode a servi a I'etude des boulettes haute silice (5% SiO2 dont I'indice de basicite (IB = CaO + MgO ÷ SiO2 + Al2O3) a ete ajustee soil a I'aide d'une addition de dolomie, soil a I'aide d'une addition de pier re a chaux, soil a I'aide d'une addition de ces deux composes. L'indice de basicite variait de 0.05 a 0.12. Les resultats de gonflement obtenus a 1000°C dans une atmosphere de 40 CO - 60 N2 ont permis de montrer qu'independamment de I'indice de basicite c'est la dolomie qui contribue leplus a diminuer le gonflement par rapport a la pierre a chaux. L'utilisation de I'indice de basicite comme critere de selection des boulettes est discutee.
La methode dilatometrique a servi a I'etude du gonflement de deux types de boulettes preparees a partir de deux concentres defer et dont la teneur en silice a etefixee a 2.5% et a 5%. Ces deux types de boulettes ont revues les memes additions de liant en quantite et en nature. La determination en continue du gonflement, a 950°C dans 40 CO - 60 N2, a permis d'une part de mieux cerner le niveau de reduction auquel correspond le maximum de gonflement et d'autre part de montrer que /'allure des courbes de gonflement est etroitement liee a la nature du liant. Une augmentation de la teneur en silice des concentres contribue a diminuer le gonflement des boulettes.
Des essais de reduction de gonflement non isothermes ont ete realises a des montees de temperature a 10 et 20°C/min. Les resultats indiquent que le gonflement determine dans les conditions non isothermes est inferieur a celui obtenu lors des essais isothermes. On discute alors de la validite des essais standards de gonflement qui sont utilises pour predire le com-portement des boulettes lors de leur reduction dans un haut-fourneau.
Keywords: Pellets, Swelling, Reduction, Dilatometer, Basicity index
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