Tungsten ore is low-grade, so it must be concentrated into a mineral-rich concentrate to serve as a smelting raw material. There are two types of tungsten ore dressing: wolframite and scheelite mineral beneficiation. At present, mining is dominated by the quartz vein type of wolframite, which accounts for over 90% of the ore extracted. Tungsten ore dressing methods include hand-selection, heavy medium separation, re-election, flotation, magnetic separation, and electrostatic separation.
Wolframite is mainly treated by flotation, while scheelite is mostly treated by re-election. Most of our wolframite is of the easy-to-select type of ore, while scheelite ore has a complex composition, is mostly refractory, and has a low grade, so it is not developed much. In addition, tungsten oxide minerals, such as tungsten in China, are currently not recycled.
Wolframite concentrate or scheelite concentrate can be used, but the smelting process is different, so if there are both wolframite and scheelite deposits, we must calculate the reserves of each ore body separately. When wolframite and scheelite coexist in the same ore, black tungsten concentrate and scheelite concentrate must be selected for smelting, respectively. The smelted mineral raw material is tungsten ore concentrate containing WO3, which should meet or exceed 65%.
The pyrometallurgical method produces tungsten alloy (with W > 70% or > 65%) using Water Act, a positive tungsten smelting sodium, calcium APT, or tungsten, etc. Finally, it is further processed into tungsten trioxide (with WO3 >= 99.9%), then reduced by a reducing agent (usually hydrogen) to tungsten powder (with W >= 99.9%) and so on. Tungsten is recovered from scheelite ore concentrates or other tungsten concentrates that may or may not contain scheelite in the form of sodium tungstate and yields up to 99.5% or more. In this process, ground ore substantially below 200 mesh in particle size is first added to a 50% sodium hydroxide solution while being agitated to such an extent that the resulting mixture becomes a semi-solid as the temperature is raised above 80°C.
The semi-solid is then baked at 135 to 145°C for about 1 to 2 hours, followed by adding sufficient water to the semi-solid to form a slurry having a sodium hydroxide concentration below 6 molar, separating the caustic-insoluble sludge from the slurry and washing the sludge with a dilute sodium hydroxide solution to remove residual sodium tungstate.