GB650223A - Production of magnesia - Google Patents

Abstract

Periclase crystals are obtained from impure magnesian materials such as dolomite, magnesite, brucite, calcite, serpentine, or olivine by firing the material with the inclusion of lime at a temperature above 2800 DEG F., to combine the impurities as calcium compounds which are separated by physical and/or chemical means such as classification, washing, froth flotation or magnetic separation followed by treatment with sulphuric acid to remove the residual calcium oxide, without affecting the periclase formed. Dolomite may be fired alone at 3000 DEG F. to form periclase crystals of 5 microns size or a small amount of iron oxide may be added forming both dicalcium ferrite which acts as a flux and magnesium ferrite which is absorbed in the periclase, thus facilitating magnetic separation. Alternatively boron compounds, fluorite, topaz or cryolite are added as fluxes and a temperature of 3200 DEG F. employed. If silica is present in the starting material, sufficient lime is added to form calcium compounds of the impurities, and the silica into dicalcium silicate; a temperature above 3450 DEG F. is employed and the dicalcium silicate spontaneously dusts on cooling when it inverts from the a or b to the g form, thus, with or without a light grinding, freeing the crystalline periclase. Further cleansing of the periclase by physical and chemical means may follow.