Assessment of desulphurizing capacity of the slag as a function of the lime reactivity

Optimizing the removal of impurities like phosphorus and sulphur is crucial for producing high-quality steel and enhancing process efficiency. This study systematically assesses how the firing conditions of lime – a primary slag-forming agent – directly influences the desulphurization capacity of refining steelmaking slag. A series of controlled laboratory-scale equilibrium experiments have been performed to determine the partition coefficient of sulphur between iron and slag. The experimental design utilized slag samples with an identical target chemical composition varying only the calcination history of the lime component. Limes produced under different firing temperatures and residence times have been characterized for key properties such as reactivity, specific surface area and crystalline structure. The results demonstrate a clear dependency of the slag refining performance on the lime features. Variations in lime reactivity significantly altered the kinetics to approach the thermodynamic equilibrium of the impurity-removal reactions. Specifically, lime with higher reactivity, achieved through optimized firing, promoted more efficient sulphur assimilation into the slag. Consequently, the final partition coefficient for sulphur has been sharply enhanced, confirming that lime quality is a critical (yet often overlooked) process variable. This investigation provides actionable insights for steel producers, emphasizing that precise control over lime manufacturing parameters is not merely a quality concern for the refractory industry, but a powerful lever for metallurgical control. By specifying lime characteristics, plants can achieve deeper impurity removal, reduce flux consumption and improve slag management, contributing to both economic and environmental sustainability in steelmaking operations.