| 摘要 |
The invention relates to crystalline grains of an acid salt of a polybasic acid selected from phosphoric, vanadic, tungstic, phosphotungstic, molybdic and phosphomolybdic acid and of a metal selected from titanium, zirconium, tin and niobium. The crystalline grains are prepared by heating a compound of the metal with sulphuric acid of density 1.84g./cm.3 to a temperature above 120 DEG C. until a clear solution is obtained, allowing the solution to cool, adding the polybasic acid in anhydrous form to the solution, heating the resulting mixture to a temperature between 100 DEG C. and 200 DEG C. until a gel is obtained, and recovering crystalline grains from the gel. The first heating stage takes place at a temperature preferably between 120 DEG and 180 DEG C., the cooling between the heating stages may be to ambient room temperature, and the second heating stage takes place at a temperature preferably between 150 DEG and 170 DEG C. A solubilizing agent, for example ammonium sulphate, may be added to the sulphuric acid. The crystalline grains are recovered from the gel by conventional methods, for example filtering, washing, and drying. Alternatively, crystalline grains may be prepared directly from the amorphous salt by mixing grains of the amorphous salt with an aqueous solution of sulphuric or nitric acid and of the polybasic acid from which the amorphous salt is derived, the resulting mixture being heated to a temperature between 50 DEG and 80 DEG C. until crystalline grains are obtained. The crystalline product may have a grain size of 1.5 mm. or more. The crystalline grains, which have enhanced ion-exchanging properties compared to those of the corresponding amorphous material, may be used as ion-exchange materials. |
