Rare earth oxide powder and method for the preparation thereof

A method for the preparation of an oxide powder of a rare earth element or a combination of two or more rare earth elements which comprises the steps of:

• (a) admixing an aqueous solution of a water-soluble inorganic salt of the rare earth element and an aqueous solution of ammonium oxalate or a combination of oxalic acid and ammonia in such an amount that the molar ratio of the carboxyl groups from said oxalic acid in the form of free carboxyl groups and from said ammonium oxalate in the form of an ammonium salt to the rare earth atoms is at least 2 and the molar ratio of ammonia in the form of ammonia molecules and ammonium ions to the rare earth atoms is at least 1, to precipitate a rare earth ammonium oxalate in the aqueous medium at a temperature not exceeding 40.degree. C., the pH value of the aqueous medium being 1 or higher;
• (b) collecting the precipitate of the rare earth ammonium oxalate by solid-liquid separation;
• (c) washing the precipitate of the rare earth ammonium oxalate with deionized water at a temperature not exceeding 30.degree. C. for a period of a lower limit of either 1.5 hours or until no nitrate ions are detected up to 2 hours as an upper limit;
• (d) dispersing the precipitate of the rare earth ammonium oxalate in a bath of deionized water at a temperature of 50.degree. C. or higher for at least 15 minutes;
• (e) collecting the precipitate of the rare earth ammonium oxalate by solid-liquid separation from the bath of deionized water;
• and
• (f) calcining the precipitate of the rare earth ammonium oxalate into an oxide powder of the rare earth element.