METHOD OF PRODUCING MAGNESIA OF DESIRED COMPOSITION FROM NATIVE MAGNESITE

摘要

Technical magnesia is manufactured by caustic calcination of a magnesite of suitable SiO 2 and Al 2 O 3 content and subjecting it to the action of hydrogen chloride gas, in the absence of combustible or reducible gases, at a temperature between 800 and 1100 C., iron and manganese being converted to volatile chlorides, whilst calcium is converted to its chloride which remains in the material to give an intermediate product which by a post-treatment of the residual chlorides is converted to technical magnesia of the desired final composition and at least a part of the hydrogen chloride used is recovered from the volatile chlorides. Products of the process which are practically free from iron and manganese may be (a) more than 97% by weight MgO with SiO 2 and CaO, (b) more than 94% by weight MgO with CaO and SiO 2 less than 5% by weight in a weight ratio either greater than 2 to 1 or less than 1 to 1 respectively. The CaO and SiO 2 content is preferably less than 4% by weight. The post-treatment comprises an oxidation of the residual chlorides by means of steam. The amount of calcium in the product may be regulated by leaching out a part or all of the calcium chloride present prior to the steam oxidation. The recovery of hydrogen chloride is carried out using known methods.