A method for preparing high-density particles of rare earth carbonate comprises precipitating rare earth ions with aqueous carbonate or bicarbonate ions, in the presence of rare earth carbonate crystals, and separating the resulting precipitate. The method can be conducted to prepare individual batches or, alternatively, a continuous precipitation method can be used, wherein rare earth and carbonate or bicarbonate ions are mixed at a controlled rate to maintain an optimum pH condition. High-density rare earth oxide is obtained by calcining the precipitate.
An improved method is proposed for the preparation of a composite carbonate powder of lanthanum, cerium and terbium as a base material of a green-emitting phosphor for which the carbonate powder is desired to have a uniform particle size distribution and a particle configuration as close to spherical as possible. The improved method is characterized by two-step heat treatment of the carbonate slurry formed by the addition of, for example, ammonium hydrogen carbonate to a mixed aqueous solution of lanthanum, cerium and terbium nitrates each under specified conditions while the pH of the aqueous slurry is adjusted to 5.0 to 7.5 after the first step heat treatment but before the second step heat treatment.
An improved method is proposed for the preparation of a powder of a rare earth oxide having good dispersibility containing no agglomerates of particles even without undertaking disintegration indispensable heretofore. The improved method comprises precipitation of a rare earth carbonate by the admixture of an aqueous solution of an inorganic rare earth salt with an aqueous solution of ammonium hydrogen carbonate in an excess amount over the stoichiometrically equivalent amount to give a slurry of the rare earth carbonate which is subjected to heating treatment in two steps each under specified conditions to effect aging of the carbonate precipitates. Characteristically, the aqueous slurry after the first aging treatment is subjected to an adjustment in three differently specified ways prior to the second aging treatment including, first, admixture of an additional amount of ammonium hydrogen carbonate, second, addition of water to decrease the solid content in the slurry and, third, addition of an inorganic acid to decrease the pH of the slurry.
A process for the production of ferrous carbonate is provided wherein a mixture of an alkali metal bicarbonate and a ferrous compound such as a ferrous salt in solution is heated to a temperature in the range of about 100.degree. C. to about 300.degree. C. for a sufficient time to allow a precipitate to form. A molar ratio of alkali metal bicarbonate to ferrous compound is at least 2:1, such a ratio giving an extremely pure precipitate of ferrous carbonate.
A sinterable yttrium oxide powder is produced useful for pressureless sintering a compact thereof into an optically translucent or transparent body. The yttrium oxide powder has a specified particle size range and specific surface area. It is formed by preparing yttrium oxalate hydrate powder by means of the wet chemical oxalate method, comminuting the yttrium oxalate hydrate powder to a required degree and calcining the yttrium oxalate hydrate.
Proposed is an improvement in a multi-stage solvent extraction process of a metal value such as rare earth elements from an acidic feed solution containing the metal value in the form of a water-soluble salt by bringing the aqueous solution into contact with a water-immiscible organic extractant solution containing an extractant compound which releases an acid when combined with the metal ions. While the concentration of the acid in the aqueous feed solution is increased when contacted with the organic extractant solution containing an extractant agent of the above mentioned type so as to cause a shift of the extraction equilibrium unfavorably against further extraction of the metal ions, the acid in the aqueous feed solution prior to contacting with the organic extractant solution in a succeeding stage of extraction is at least partly decreased, instead of the conventional expensive way of neutralization by the addition of an alkaline neutralizing agent to the aqueous solution, by ion exchange dialysis with dialyzing water through an anion exchange membrane.
