Tungsten smelting process
Decomposition method of tungsten concentrate: fire method and wet method.
① sodium carbonate sintering is commonly used for pyrolysis. In this method, wolframite concentrate and sodium carbonate are placed together in a rotary kiln and sintered at 800-900 ℃. Quartz sand is also needed to be added in the treatment of Scheelite Concentrate in order to obtain calcium orthosilicate with low solubility and sintering temperature of about 1000 ℃. After sintering for about two hours, the decomposition rate of concentrate can reach 98-99.5%. The sinter was leached with water at 80-90 ℃ and filtered to obtain sodium tungstate solution and insoluble residue.
② the wet method is divided into alkali decomposition method and acid decomposition method. When the wolframite concentrate is decomposed, it is leached with sodium hydroxide solution at 110-130 ℃ or higher. The scheelite is leached by sodium carbonate solution in autoclave at 200-230 ℃, or decomposed by hydrochloric acid at 90 ℃, to obtain solid crude tungstic acid. The decomposition rate of tungsten concentrate can reach 98-99%.
Purification of tungsten compounds
The impurities such as silicon, phosphorus and arsenic in sodium tungstate solution are in the state of sodium silicate, sodium hydrogen phosphate and sodium hydrogen arsenate respectively. Boil the solution and neutralize it with dilute hydrochloric acid. When the pH value of the solution is 8-9, sodium silicate is hydrolyzed to silicic acid coagulate and precipitate. Add magnesium chloride and ammonium chloride solution to remove the precipitate of magnesium ammonium phosphate and magnesium ammonium arsenate with small solubility.
Adding sodium sulfide to sodium tungstate solution, molybdenum forms sodium thiomolybdate prior to tungsten, neutralizing with hydrochloric acid, when the pH of solution is 2.5-3.0, molybdenum forms insoluble molybdenum trisulfide precipitation to remove. Calcium chloride solution was added to the purified sodium tungstate solution to obtain calcium tungstate (CaWO) precipitation. Calcium tungstate was decomposed by hydrochloric acid to obtain industrial tungstic acid. Tungstic acid was calcined at 700-800 ℃ to obtain industrial pure tungsten trioxide.
If the chemical pure tungsten trioxide is prepared, the industrial tungstic acid can be dissolved in ammonia water to obtain ammonium tungstate solution, silicon and other impurities left in the slag. After the solution was evaporated and crystallized, the lamellar ammonium paratungstate [5 (NH) o12wo 5ho] crystal was obtained. As the solubility of ammonium paratungstate is higher than that of ammonium paratungstate, the molybdenum content of ammonium Paratungstate Crystal decreases after crystallization. After drying, ammonium paratungstate is calcined at 500-800 ℃, and then the chemically pure tungsten trioxide is obtained. In the 1970s, the sodium tungstate solution was converted into ammonium tungstate solution by the tertiary amine (RN) method, which simplified the technological process and improved the recovery rate of tungsten.
