Extracting tungsten from scheelite concentrate with caustic soda by autoclaving process

A technology has been developed for extracting tungsten from scheelite concentrate with caustic soda by an autoclaving process. In this process, the effects of different variables on the digestion of scheelite, and on the evaporation of the crude sodium tungstate leach solution, has been investigated. The results showed that 98.8% W was leached in 2 h at 160 °C under the conditions of 2.2 stoichiometric ratio of NaOH and liquid /solid ratio 0.8:1 stirred at 400 rpm. After evaporation, about 90% sodium tungstate was crystallized, leaving impurities of PO42-, AsO42− and SiO32− in the mother solution. The filtered mother solution contained about 93% of the unconsumed caustic soda which can be recycled for a new round of leaching. This technology has been successfully put into industrial practice and can treat almost any tungsten ore, including scheelite middling and wolframite–scheelite mixed concentrates.

Research Highlights
► Scheelite concentrate can be digested well with caustic soda in general equipments.
► The unconsumed NaOH can be recovered by evaporation.
► The impurities P, As, Si were precipitated in the leach residue.
► The technology has been put into industrial practice successfully in China.