| 摘要 |
<p>Thorium phosphate is obtained from aqueous sulphuric acid solutions containing thorium, rare earth elements and phosphate by adding ammonia to increase the pH to not more than 0.6, separating the double rare earth-ammonium sulphate which slowly precipitates and then further reducing the acidity of the solution (e.g. by the continued introduction of ammonia to a pH of 1.8). The initial solution may be obtained by heating monozite with concentrated sulphuric acid, diluting the cooled product with water and separating the solution from the insoluble residue. The Provisional Specification refers to the use of agents, e.g. hexamethylene tetramine and acetaldehyde ammonia, which slowly release ammonia by hydrolysis to increase the pH of monazite leach liquors, but their use is not satisfactory in the process of the invention.</p> |
