Tungsten Concentrate Decomposition Method: Fire Method And Wet Method.

① Fire decomposition commonly used sodium carbonate sintering method. This method is to place wolframite concentrate and sodium carbonate together in the rotary kiln sintered at 800-900℃. When dealing with scheelite concentrate, it is also necessary to add quartz sand, in order to obtain the original calcium silicate with small solubility, and the sintering temperature is about 1000℃. After about two hours of sintering, the decomposition rate of concentrate can reach 98～99.5%. Sintered material at 80 ~ 90 ℃ water leaching, filtered to sodium tungstate solution and insoluble residue.
Wet method is divided into alkali decomposition method and acid decomposition method. Decomposition of wolframite concentrate, with sodium hydroxide solution at 110 ~ 130 ℃ or higher temperature leaching. Scheelite concentrate is leached with sodium carbonate solution in an autoclave at 200 ~ 230 ℃, or hydrochloric acid at 90 ℃ decomposition, solid crude tungstic acid. The decomposition rate of tungsten concentrate by wet treatment can reach 98～99%.

Purification of tungsten compounds
Sodium tungstate solution containing silicon, phosphorus and arsenic impurities in solution were sodium silicate, sodium hydrogen phosphate and sodium hydrogen arsenate state. Boil the solution and neutralize it with dilute hydrochloric acid, when the solution pH is 8 ~ 9, sodium silicate hydrolysis into silicate cohesion precipitate, add magnesium chloride and ammonium chloride solution, so that the phosphorus, arsenic generation of solubility is very small magnesium ammonium phosphate and magnesium ammonium arsenate precipitate removed.
Add sodium sulfide to sodium tungstate solution, molybdenum first in tungsten to form sodium thiomolybdate, neutralized with hydrochloric acid, so that the solution pH 2.5 ~ 3.0, molybdenum into insoluble molybdenum trisulfide precipitate removed. In the purified sodium tungstate solution, add calcium chloride solution, calcium tungstate (CaWO) precipitate, hydrochloric acid decomposition of calcium tungstate precipitate industrial tungstic acid, tungstic acid calcined at 700 ~ 800 ℃, to obtain industrially pure tungsten trioxide.
If the production of chemically pure tungsten trioxide can be industrial tungstic acid dissolved in ammonia, ammonium tungstate solution, silicon and other impurities in the slag. The solution is processed by evaporation and crystallization to obtain flaky ammonium sec-tungstate [5(NH) O 12WO 5H O] crystals. As the solubility of ammonium sec-molybdate was larger than that of ammonium sec-tungstate, the molybdenum content of the ammonium sec-tungstate crystals decreased after crystallization. Ammonium paratungstate is dried and calcined at 500-800 ℃ to obtain chemically pure tungsten trioxide.In the 70s, tertiary amine (R N) method or method was adopted to convert sodium tungstate solution into ammonium tungstate solution, which simplified the process and improved the recovery of tungsten.