Abstract: A process for the production of magnesium oxide of moderate activity and high availability from a waste material containing dead-burned magnesium oxide of essentially no activity and lower availability (e.g., spent basic oxygen furnace firebrick) is disclosed. Spent basic oxygen furnace firebrick particles are calcined at a temperature of about 1000.degree. to about 2000.degree. F. for a time of from about 15 to about 60 minutes. The magnesium oxide in the spent, calcined firebrick is thus converted from dead-burned magnesium oxide to a magnesium oxide having a solubility of above about 90% in dilute hydrochloric acid and moderate activity in the nature of light-burned magnesium oxide. The color of the calcined magnesium oxide is also improved and the carbon content of the spent firebrick is essentially removed. The resulting product is generally useful in the same manner as conventional light-burned magnesium oxide.