Abstract: The recovery of a magnesium carbonate of high purity from an aqueous slurry comprising a mixture of calcium carbonate and hydrated magnesium carbonate is disclosed. Carbon dioxide is introduced into the slurry while the temperature thereof is maintained not higher than about 40.degree. C. to produce an appreciable concentration of magnesium cations in the water of the slurry. Introduction of carbon dioxide is discontinued while most of the calcium is present as the carbonate. Solids are then separated from the aqueous solution of magnesium cations which is produced. Also disclosed is the removal, e.g., by means of a vacuum pump, of carbon dioxide from the aqueous solution of magnesium cations to precipitate magnesium carbonate and the separation of precipitated magnesium carbonate from the aqueous phase.

Abstract: A high compressive strength concrete is disclosed. The concrete is formed by mixing with water a general-use cement, dolomitic limestone as a low-silica manufactured fine aggregate, and from about 5 to 15 percent by weight, based on the manufactured fine aggregate, of a precipitate comprising CaO-MgO from the gaseous effluent from a kiln burning dolomitic limestone, and curing the mixture.