Production and properties of burnt lime coated with dicalcium ferrite

Ferruginous lime is the term applied to burnt lime (CaO) coated with dicalcium ferrite (2CaO.Fe₂O₃). Its high degradation strength, its resistance to hydration, and its capacity for fast and complete solution of fluxes in the basic oxygen and electric arc furnaces make it extremely attractive as a steelmaking flux. The objectives of the present work were 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 minimisation of problems such as accretions and agglomerations within the reactor. With respect to processing conditions, the trials suggested that ferruginous lime be generated using a peak reaction temperature of 1260°C and allowing 45 min at greater than 1200°C. The optimal oxide addition is 10% by weight of the limestone charge to the rotary lime kiln. When subjected to short duration hydrating conditions, i.e. 30 min in contact with steam at 100°C (according to ASTM specification X6), the ferruginous lime 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 (compared with uncoated lime) in a steelmaking slag.