GB453318A - Improvements in or relating to the manufacture of zinc oxide - Google Patents

Abstract

Zinc oxide is obtained by treating an aqueous solution of an alkali zincate with alkali or ammonium bicarbonate in quantity strictly necessary for the direct formation of substantially pure zinc oxide, filtering and drying the precipitate at a temperature not greater than 100 DEG C. The zincate solution may be obtained by dissolving zinciferous material, for example, calcined calamine, zinc salts or waste material in say boiling 20 per cent caustic soda solution. In a cyclic process, zinciferous material is concentrated if necessary and dissolved in caustic alkali. The filtered solution is neutralized with carbon dioxide until precipitation of zinc oxide begins. The necessary quantity of, say, sodium bicarbonate is then rapidly added under hot conditions, the mass being stirred, and the precipitate filtered, rinsed and dried. Part of the resulting sodium carbonate is treated with carbon dioxide to regenerate the bicarbonate, and part is treated with milk of lime to produce caustic soda for re-use in the process. The calcium carbonate also produced is calcined to calcium oxide which is converted to milk of lime for re-use. The carbon dioxide evolved is used partly for conversion of the sodium carbonate to bicarbonate, and partly for neutralization of the alkaline zincate liquor.