Tungsten Production

Wolframite and scheelite concentrates with 50-60% WO₃ are the main source from which ferro-tungsten, the alloy of iron and tungsten, which is used in steel production, is fused. Then tungstic anhydride is extracted. There are several methods by which WO₃ may be obtained. Scheelite concentrates are decomposed in autoclave by soda solution at 180-200°C (obtaining the sodium tungstate solution).

Wolframite concentrates are decomposed by sintering with soda 800-900°C followed by Na₂WO₄ water leaching or treating by caustic soda, after which contaminated Na₂WO₄ solution is obtained. After their precipitating H₂WO₄ is extracted. For more crude, easier filtered and higher purified substance CaWO₄ is precipitated from Na₂WO₄ solution with following hydrochloric acid decomposition.

Dried H₂WO₄ contains 0.2-0.3% of contaminations. Hard alloys are produced From WO₃ obtained by H₂WO₄ roasting at 700-800°C. In W metal processing H₂WO₄ is put to an additional purification by ammonia method: solving in ammonia and crystallizing of ammonium paratungstate 5(NH₄)₂O-12WO₃-nH₂O, the roasting of which yields pure WO₃.

W powder is obtained via WO₃ reduction by hydrogen (and, in hard alloys production, also by carbon) in tube-type furnaces at 700-850°C.