GB745075A - Improvements in or relating to process of preparing crystalline magnesia and the resulting product - Google Patents

Abstract

Periclase is prepared by mixing a magnesium compound which will form periclase on firing with vanadium or vanadium compounds in an amount to provide up to 5 per cent by weight of added vanadium, calculated as V2O3 in the fired product, and firing the mixture to form periclase. The magnesium compound used as starting material preferably contains 95 per cent at least of magnesium oxide less than 2 per cent SiO2 and less than 2 per cent CaO, when fired. Suitable compounds are magnesium hydroxide, carbonate, acetate or alcoholate, or magnesite, brusite or amorphanes or cryptocrystalline magnesia. The latter may be obtained by firing a magnesia yielding compound at not over 1100 DEG C. for not over 45 minutes to obtain microcrystalline magnesia with a bulk density of not over 1.5 grams/c.c. The vanadium compound, preferably added to give 1/8 to 1 per cent V2O3, may be the chloride oxychloride ir other halide or vanadyl sulphate, and is preferably added as an aqueous or alcoholic solution or suspension to the periclase-yielding component. Firing may be effected at 1300 DEG C or more, employing an oxidizing atmosphere if vanadium metal is employed. The mixed starting materials, which are preferably all below 200 mesh (U.S.) size, may be fed as a slurry to a rotary kiln and dried and fired in the same operation. When employing cryptocrystalline magnesia, it may be formed in the presence of the vanadium addition or after forming may be mixed with the vanadium. According to a typical example, 6 parts of vanadium oxide are mixed with 494 parts of magnesium hydroxide filter cake prepared by treating calcined dolomite with sea water and the mixture dried, pelletted at about 8000 p.s.i. and fired at 1700 DEG C. for half an hour. The porosity of the product is 6.7 per cent.