Waste Tungsten Oxide Recycle and Treatment

At present, the existing processes for recovering and treating waste tungsten oxide to produce ammonium tungstate solution, ammonium paratungstate and ammonium metatungstate are all based on the chemical properties of all tungsten trioxide and blue tungsten oxide which are insoluble or slightly soluble in ammonia water and only soluble in caustic soda or soda ash. The process is to dissolve oxygen in normal pressure or pressure boiling with caustic soda (sodium hydroxide) solution or soda carbonate solution in advance. Tungsten carbide is prepared into sodium tungstate solution, or tungsten oxide is melted with sodium carbonate at high temperature, then tungsten is boiled and leached to form sodium tungstate solution.

Some scholars have found that tungsten oxide, such as tungsten trioxide and blue tungsten oxide, is easily decomposed into ammonium tungstate solution by ammonia under high temperature and pressure, and has high tungsten solubility. This is a new chemical property of tungsten oxide. According to this property of tungsten oxide, a more effective scheme for waste tungsten oxide recycle and treatment is found out. Its specific implementation is as follows:

1. Proportion of Pressing and Cooking Ingredients
(1) Disposal capacity of waste tungsten oxide: In this example, 300 kg of waste tungsten trioxide and 150 kg of blue tungsten oxide are disposed of in each autoclave. After mixing, a total of 450 kg of mixed tungsten oxide is obtained.

(2)Ammonia concentration: dilute concentrated ammonia water to make dilute ammonia water containing 14% ammonia.

(3)The weight of waste tungsten oxide/volume of dilute ammonia water is 321 g/L.

2. Preparation of Ammonium Tungstate Solution by Pressure Cooking with Ammonia
(1) Add 1310 litres of dilute ammonia water, 450 kg of tungsten oxide mixed, 185 litres of industrial grade hydrogen peroxide slowly, press the cover of the reactor under stirring, heat up slowly until the steam pressure in the reactor is 4-6 kg/cm², boil for 110 minutes, stop heating and cool to 35 ℃, then adjust the concentration of free ammonia to 3.8% with ammonia water and water. Tungsten oxide concentration is 276 g/l.

(2)Ammonium tungstate solution cooled to room temperature is filtered by stainless steel vacuum filter, and the filtrate is transferred to ammonium tungstate solution tank for 24 hours.

3. Preparation of Ammonium Paratungstate
(1) The stationary ammonium tungstate solution is discharged from the outlet 20 cm above the bottom of the stationary tank and transferred to an enamel evaporative crystallization kettle with a volume of 2000 litres, heated to boiling, concentrated and precipitated a large number of white ammonium paratungstate crystals by heat preservation and evaporation. When the specific gravity of the solution drops to 1.06, the heating stops, stirring and cooling to 80 ℃. The solution, together with ammonium paratungstate crystals, is put into a stainless steel vacuum filter for filtration and water consumption. Wash 3 to 4 times.

(3)Ammonium paratungstate crystals filtered and washed are put into the drying cabinet with stainless steel loading basin. The loading thickness is 3-5 cm and dried at 100-130 ℃. The finished product is ammonium paratungstate, which passes 80 mesh sieve after cooling, and then passes inspection and packaging.

4. Preparation of ammonium metatungstate
(1) Calcination of ammonium Paratungstate
Ammonium paratungstate was loaded into a stainless steel rotary furnace with a diameter of 300 mm. The calcination temperature was controlled at 245-305 ℃ and the holding time was 70 minutes. The ammonium paratungstate lost part of ammonia and crystalline water and was converted into water-soluble ammonium metatungstate. Sampling at 40 points for boiling test, the solution pH value is 4.5, the dissolution rate is 75.8%. Sampling at 70 points for boiling test, the solution pH value is 3.6, the dissolution rate is 93.6%. Stop heating, cool the calcined material to room temperature and leave the furnace for use.

(2) Dissolution of ammonium metatungstate by boiling
800 liters of water were added to the 1000 liters enamel evaporative crystallization kettle, heated to boiling, and 1500 kg of calcined material was added slowly under stirring. The temperature was controlled at 85-100 ℃, the temperature was kept warm and boiled slightly, and the evaporated water was added to keep the original volume basically. The cooking time is 120 minutes, and the pH value is checked by three sampling times. The first time is checked at 60 minutes, the pH value is 4.7, the second time is checked at 90 minutes, the pH value is 4.1, and the third time is checked at 120 minutes, the pH value is 3.4. At this time, the heating is stopped, the filter residue is washed by hot water for 3-4 times, and the filtrate is ammonium metatungstate solution, which is transferred to the static tank of ammonium metatungstate solution. Stand by for 24 hours. The filter residue is calcined excessive tungsten oxide, collected and returned to ammonia water pressure boiling for recycling.

(3) Preparation of ammonium metatungstate by spray drying
Ammonium metatungstate crystals were prepared by transferring 1800 litres of filtered and stationary ammonium metatungstate solution into an enamel evaporative crystallization kettle with a volume of 2000 litres. The solution was heated to boil and kept boiling. The evaporation concentration was concentrated to 1.4 of solution specific gravity. After stopping heating, the concentrated solution was pumped into a spray dryer to spray drying, and the ammonium metatungstate crystals were prepared. After inspection and packaging, the product was ammonium metatungstate.

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