Abstract: The present invention relates to a fire brick for a rotary kiln, provided on one or both large surface area portions with at least one concavity extending in the radial direction of the kiln, and opening on at least the face.The present invention further relates to a fire brick for a rotary kiln as described above, further provided with a steel plate having a concavity of dimensions which the sum of the depth of the concavity of said brick plus an expansion absorbing tolerance, and applied to a maximum surface area and lying over the concavity.The present invention still further relates to a fire brick for a rotary kiln as described above, further provided with board or asbestos, etc., on the face end of the steel plate.

Abstract: A refractory lining for a vessel holding pig iron comprises magnesite-chromite bricks containing from 15-30%, by weight, of chromic oxide. The chromite is so highly dissolved in the brick mass that it has no more than a 12%, by volume, residue of chromite.

Abstract: An aqueous solution of magnesium chloride is sprayed into a kiln chamber where it is countercurrently heat treated by a stream of hot gas produced by flames projected into the chamber by burners. Calcined material is removed from the bottom of the kiln chamber and the hot gas stream and any treated material carried thereby is removed from the top of the chamber. Material carried by the hot gas stream is separated therefrom in a cyclone separator and the separated material is returned to the kiln chamber through a zone heated to a temperature in the range of the temperature in the kiln chamber.

Abstract: Magnesia of very high purity is produced industrially from a magnesite waste material wherein impurities are present in such amounts that the weight ratio of the precipitable hydroxide ions, calculated as the sum of Fe.sub.2 O.sub.3 + Al.sub.2 O.sub.3 + Cr.sub.2 O.sub.3 + Mn.sub.3 O.sub.4 to the sum of SiO.sub.2 + TiO.sub.2 + B.sub.2 O.sub.3, is at least 1 : 3. The starting material is dissolved in hydrochloric acid of 15-32% concentration, the impurities are precipitated by adjusting the pH of the acidic solution to 4 - 9, and the purified magnesium chloride solution is thermally decomposed into magnesia and hydrochloric acid gas, the latter being recycled to form the hydrochloric acid of the stated concentration for dissolving the starting material.