Production of tungsten via leaching of scheelite with sulfuric acid

A new process for leaching scheelite ore consists of leaching low- and high-grade concentrates with H2S0 4 in the presence of H3P0 4 and NaCl at atmospheric pressure. The resulting tungstic acid solution is then evaporated to produce ammonium paratungstate (APT): (11/H4)10H2W 12 deg 42.4H20. To obtain the yellow oxide (WO 3), the APT is heated at 600 deg to 700 deg C for one hour to evaporate ammonia and water. The reduction of tungsten trioxide with H2 can be controlled by the temperature, time and water vapor partial pressure to produce a-W.