1. Agar, G.E., 1984. Scheelite flotation process, U.S. Patent 4,488,959.
2. Davey, T.R.A., 1990. Method of extracting tungsten values from tungsten containing ores, U.S. Patent 4,910,000.
3. General Electric, 1959. London Patent 818, 117.
4. The Recovery of Tungsten from South African Low-Grade Scheelite Concentrates, Mintek, Report No: M164D;Fieberg,1986
5. Forward, F.A., Vizsolyi, A.I., 1965. Process for the production of tungstic acid, U.S. Patent 3,193,347.