Cyclic Ammonium Paratungstate Preparing Process

The preparation of ammonium paratungstate from sodium tungstate solution in tungsten metallurgical process mainly involves two steps: the preparation of pure ammonium tungstate solution and the crystallization of ammonium paratungstate. At present, when ammonium paratungstate is prepared by the above method, it is necessary to convert alkali into NaCl or Na₂SO₄ salt in the production system, which is difficult to recycle economically, resulting in serious environmental problems caused by emissions.

In order to recycle alkali and extract concentrated crystals efficiently, a simple method for preparing ammonium paratungstate was proposed. The method includes the following steps:

1)Sodium tungstate-ammonium solution was prepared by adding ammonia or ammonium salts or their aqueous solutions to sodium tungstate solution containing tungsten trioxide of 15-450 g/L. The amount of ammonium was 100-200% of the stoichiometric amount of ammonium tungstate which was converted into ammonium paratungstate in the system.

2)The slurry containing crude ammonium tungstate crystals was obtained by injecting carbon dioxide with a pressure of 0.02-6Mpa into sodium tungstate-ammonium solution and holding it for 1-72 hours at 20-100 ℃.

3)Separating solid solution from the slurry and separating the solution back to the decomposition process of tungsten concentrate.

4)The solid separated from step 3 was first washed with ammonium salt solution, and then washed with water at a temperature of 20-100 ~℃ to obtain ammonium paratungstate.

The specific operation is to prepare sodium tungstate solution with WO₃ as 100g/L by dissolving pure sodium tungstate in pure water. 100 mL sodium tungstate solution and NH₄HCO₃ were placed in a 150 mL reactor. The amount of NH₄HCO₃ added was 100% of the stoichiometry of ammonium paratungstate as tungstate in the solution. Carbon dioxide gas was injected into the reactor to react.

In the new process, ammonium paratungstate is prepared by direct crystallization of carbon dioxide with sodium tungstate-ammonium solution system, and sodium carbonate is produced simultaneously. The obtained sodium carbonate can be used to recycle tungsten ores, thus realizing the circulation of alkali in the system.

• < Prev
• Next >