Scheelite (CaWO4) is the principal tungsten mineral, but other important tungsten minerals include wolframite (Fe, Mn) WO4, ferberite (FeWO4), and hubnerite (MnWO4). All of these minerals are floated in alkaline pH (using soda ash) with tall oil fatty acids such as AERO 704 and AERO 726 promoters.
Because of the high specific gravity of the tungsten minerals, they are amenable to gravity concentration methods. However, the fine dissemination of the ore minerals in the gangue usually necessitates fine grinding and requires at least one flotation stage to treat finer sizes.
If the ore contains pyrite or other sulfides, a preliminary sulfide flotation stage is usually employed ahead of both tabling and flotation of the tungsten minerals. Cytec's FM-100 based formulations such as AERO 3738, AERO MX-3753, AERO MX-3754 and AERO MX-6207 promoters can be used to float off the sulfides ahead of tungsten.
The flotation of tungsten minerals is usually conducted at pH of 9.0 to 10.5, adjusted with soda ash, caustic or sodium silicate. The other modifiers may be needed depending on the gangue minerals to be depressed. Quebracho or tannin was used in the past to depress the calcite. Cytec's AERO 704 promoter is an effective collector for tungsten minerals. The dosage will vary between 50 to 750 g/t.Leaching with HCl may be required to clean the final concentrate from carbonate and phosphate diluents.