METHOD OF PREPARING ZIRCONIUM DIOXIDE Russian patent published in 1998 - IPC

FIELD: technology of preparing high purity oxides, preferably zirconium and hafnium dioxides. SUBSTANCE: zirconium containing stock is treated with mixture of hydrofluoric acid and ammonium fluoride used at molar ratio of 1-4: 3 per 1 mole of zirconium dioxide. The resulting cake is leached with water and filtered. Solution is neutralized with ammonia. The resulting zirconium containing residue is separated and treated with solid ammonium bicarbonate in amount of 2.8-3.2 moles per 1 mole of zirconium dioxide to form slightly alkaline solution with pH of 8.3. Prior to being treated with solid ammonium bicarbonate, residue is dried to reduce its weight by not more than 30%. Slightly alkaline zirconium containing solution is filtered, zirconium salt (zirconium oxynitrate or oxychloride) solution is added thereto provided that not more than 5% zirconium hydroxide precipitates. The resulting solution is treated with hydrogen sulfide or ammonium sulfide to saturation. Not more than 1 g of alimethyl glyoxine is added per 1 kg of zirconium dioxide in solution. Pulp is allowed to settle, it is filtered and ammonium sulfate in amount of 90% of stoichiometric amount required to form zirconyl sulfate. Solution is then evaporated and the resulting residue is calcined at 700-750 C. EFFECT: preparation of product of especially high purity, less expensive reactants, lower power requirement and less aggressive reaction medium. 6 cl, 4 ex, 1 tbl