Improvements in the manufacture and production of magnesia poor in lime from dolomite

摘要

Magnesium hydroxide is obtained by the reaction of calcined and slaked dolomite with magnesium chloride solution in the presence of ammonia or ammonium salts. From the resulting calcium chloride solution containing ammonia, &c., calcium carbonate may be obtained by treatment with more calcined and slaked dolomite and carbon dioxide with regeneration of the magnesium chloride containing ammonia &c. The reactions are preferably carried out below 20 DEG C., and the carbon dioxide used in obtaining calcium carbonate is preferably that obtained by calcination of the crude dolomite. In burning the latter, material of a grain size of 5--25 mm. may be used, and the burnt material, after slaking to a dry powder, be separated into two fractions of about equal amounts by sifting, it may be through a 100 mesh sieve. The fine fraction is used in the preparation of the magnesium hydroxide, and the coarse fraction, after comminution if desired, in the preparation of the calcium carbonate. If desired, substances such as iron oxides or soapstone may be added during the precipitation of the magnesium hydroxide, to render it suitable for conversion into "sintermagnesite."