Waste Tungsten Oxide Recovering Ammonium Metatungstate (AMT)
Waste tungsten oxide, including the scrapped, the not qualified which must be reworked to improve the quality indicators of tungsten trioxide, blue tungsten oxide and others. During the production, using process, or in the case of large inventories, tungsten oxide may not reach a certain specific standards due to various reasons, or directly scrapped. However, these waste tungsten oxide still contains a high content of tungsten, since the tungsten is a rare metal element, thus a more effective approach to reuse waste the tungsten is turning waste into treasure.
Ammonium metatungstate (AMT) is an important raw material in tungsten smelting industry, catalyst for petrochemical industry and other fields. The ways of waste tungsten oxide as raw materials to produce ammonium metatungstate are many; however, since tungsten trioxide and blue tungsten oxide are not soluble or slightly soluble in ammonia water, which only soluble in caustic soda or soda ash. Therefore, the traditional process is cooking and dissolving tungsten oxide under the normal or high pressure by using caustic soda (sodium hydroxide) or soda ash (sodium carbonate) solution, to generate sodium tungstate solution; or melting tungsten oxide with soda ash (sodium carbonate) under high temperature, and then leaching tungsten by water to produce sodium tungstate solution, and then get AMT by the follow-up process, the three processes are as follows:
1. Extract tungsten by an organic solvent and reextract tungsten by ammonia water from the sodium tungstate solution to convert tungsten into ammonium tungstate solution, and finally obtain ammonium metatungstate from the ammonium tungstate solution by evaporation crystallization or neutralization crystallization;
2. The tungstate solution is adsorbed by the ion exchange resin tungsten and ammonia desorption of tungsten, to convert tungsten into ammonium tungstate solution, and finally manufacture AMT from ammonium tungstate solution by evaporation crystallization or neutralization crystallization method;
3. Precipitate the artificial scheelite (calcium tungstate) from sodium tungstate solution with calcium chloride, and then produce tungstic acid by decomposing artificial scheelite with hydrochloric acid, then the tungstic acid is dissolved in ammonia solution to generate ammonium tungstate solution, finally, the AMT is prepared by evaporation crystallization or neutralization crystallization method from the ammonium tungstate solution.
In addition, studies have pointed out the method of using ammonia water to dissolve waste tungsten oxide and to prepare AMT, which is in accordance with the property of tungsten oxide is easily soluble in ammonia water under the high temperature and pressure conditions and generate ammonium tungstate solution, and then produce ammonium metatungstate by neutralization transformation - spray drying method from ammonium tungstate.
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