Ferruginous lime as a flux in primary steelmaking

Abstract

Ferruginous lime—i.e. burnt lime coated with dicalcium ferrite (2CaO.Fe2O3)—has attractive properties as a steelmaking flux. Work was undertaken to assess the feasibility of producing ferruginous lime in a rotary kiln-type reactor and to determine the operating conditions favourable for both the formation of a hydration-resistant product and the minimization of such problems as accretion and agglomeration within the reactor. The trials indicated that a period of 45 min at temperatures in excess of 1200°C with a peak reaction temperature of 1260°C provides appropriate conditions for the production of ferruginous lime. The optimal oxide addition is 10% by weight of the limestone charge to the rotary lime kiln. When subjected to hydrating conditions of short duration, i.e. 30 min in contact with steam at 100°C (in accordance with ASTM specification X6), the product exhibited good resistance to hydration relative to pure CaO and moderate physical degradation. Laboratory tests demonstrated the significantly enhanced rate and degree of dissolution of ferruginous lime in a steelmaking slag relative to that of uncoated lime.