Abstract: A slag conditioner containing MgO, carbon or a filler and a binder is mixed and formed under pressure to produce aggregates which can have the form of a briquette. The slag conditioner is used to improve the operating performance and refractory life in steel melting furnaces. A slag conditioner comprising by weight a mixture and 2% to 25% binder for bonded agglomerates or larger particles of said mixture, the mixture comprising: 20% to 90% burned aggregates comprised of particles less than 8 mm of which at least 30% is 0.2 mm or greater and containing between 35% and 94% MgO; up to 50% slag-making carbonaceous or other additive; and up to 50% light burned magnesite.