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.

Because of the narrow band gap (about 2.80eV), special structure and high stability and other benefits, bismuth tungstate (Bi₂WO₆) is a new type of environmental friendly material, which can be as the visible light photocatalyst. Bismuth tungstate has an excellent photocatalytic activity under the visible light, and can be used for degrading organic matters, such as RhB, phenol, aldehyde, antibiotics, etc; at the same time, it can catalyze the CO₂ and water to generate fuel. The preparation methods of bismuth tungstate are solid reaction process, coprecipitation, sol-gel method, spray and hydrothermal method.

 

Compared to the normal bismuth tungstate, nanometer sheet bismuth tungstate has the larger specific surface area, higher catalytic activity and other advantages. Thus, the study of nanometer sheet bismuth tungstate is popular, and one of important researching direction is how to prepare the tiny nanometer sheet bismuth tungstate with high photocatalytic activity by the simplest operating method and the lowest energy consumption.

 

A study has manufactured nanometer sheet bismuth tungstate by solvent hot method combined with water hot method from the raw materials of ammonium metatungstate (AMT) and bismuth nitrate, the process is showed as the following living example:

1. Fetch 10mol of bismuth nitrate, 15mol of glycerin to dissolve in the 1000mol of isopropyl alcohol with stirring to get the uniform, clear solution;

2. Transfer it into the autoclave, and raise the temperature to 160°C then keep the heat preservation for 12 hours;

3. Stop heating and cool the autoclave to room temperature, then filter to get the filter cake, and then dry the filter cake at 80°C for 12 hours after the it is washed with isopropyl alcohol for 3 times, to get the glycerin bismuth powder;

4. Fetch 1mol of ammonium metatungstate to dissolve into the deionized water, and add in 13mol of glycerin bismuth powder, go on with stirring to get a uniform solution, then transfer the solution to a autoclave for heating to 180°C with thermal insulation for 24 hours after adjusting pH value to 0~1 with the nitric acid;

5. Stop heating to cool down the product to room temperature, filter the solution to get the filter cake, and then dry the filter cake under 120°C for 12 hours after it has been washed with deionized water and ethanol for 3 times, to finally get the product of nanometer sheet bismuth tungstate.

Ammonium trithiotungstate [(NH₄)₂WOS₃] is a kind of important glucosinolates metal ammonium salt, which can generate transition-metaldichalcogenide of WS₂ after the thermal decomposition, and has very well application in the synthesis of biological nitrogenase activity center - tungsten iron sulfur atom cluster compounds, semiconductor, superconducting, photoelectrochemical solar cell, battery, lubricant, electrochemical sensor, nanometer material, super capacitor, new generation of transistor and hydrogen storage and electrode material, and other respects. While it is also the precursor of coal liquefaction and heavy oil hydrogenation catalyst, as well as the raw material for manufacturing supported and non-supported type of tungsten sulfide hydrogenation catalyst.

 

Ammonium trithiotungstate can be prepared by the reaction of tungstic acid of ammonia solution and hydrogen sulfide gas, however, this method is harsh in operating conditions and the process is hard to control; moreover, the used hydrogen sulfide gas has the shortcomings of irritation, poisonous and cacosmia, which will cause serious damage to human body and the environment. So, an invention has pointed out an environmental friendly method to prepare ammonium trithiotungstate from the raw material of ammonium metatungstate (AMT), with the steps like bellow:

1. Weight a certain amount of ammonium metatungstate powder and add them into ammonium sulfide solution with a certain concentration to carry out a reaction, the molar ratio of W/S is controlled at 1:3~3.5, and the condition is optimized of 40~60°C, time for 1~2 hours;

2. Remove the ammonia gas by the way of vacuum or inlet inert gas into the reaction liquid, thus to release the generated ammonia gas out of the reaction system;

3. Add a certain amount of ammonium salt into the reaction liquid, then cool down to room temperature and stay to crystallize for 0.5~24 hours;

4. Filter, wash with a solvent, dry under the room temperature to finally get high purity ammonium trithiotungstate.

 

Vacuum or inlet inert gas into the reaction liquid in the process can play the role of promote the balance to the direction of generating ammonium trithiotungstate; meanwhile, the addition of ammonium salt will be benefit for the exhalation rate of ammonium trithiotungstate, and to get high purity product. The method which based on the raw materials of tungstate (such as ammonium metatungstate) and ammonium sulfide solution to produce ammonium trithiotungstate has the advantages of less waste discharging, no need to use poisonous hydrogen sulfide gas, sample process, environmental friendly and high yield (as high as 98% or even higher), thus to has very high industrial application prospect.