Scheelite with High Calcium by Alkali Boiling Process Decomposition

Tungsten metallurgical raw materials are classified into wolframite, scheelite and wolframite mixed ores according to their types, and tungsten concentrate, tungsten intermediate ore and tungsten slime according to their tungsten grade. There are many methods for decomposition of tungsten minerals. At present, atmospheric pressure alkaline boiling process is widely used in our country. It is characterized by the decomposition of tungsten minerals with a certain concentration prepared by fine grinding and NaOH under pressure control of 0.15-0.25 Mpa in the reactor. Because of its long service life, low cost and easy operation, this decomposition method has been used all the time.

Wolframite, scheelite and wolframite-scheelite mixtures of WO₃:20-76% and Ca:0.2-20% are used as high calcium tungsten minerals.

According to the content of calcium and silicon dioxide in tungsten mineral raw materials, additives such as silica or quartz sand are added to the raw materials.

B.The mixture is added to the ball mill for fine grinding until the particle size of the mixture is less than 43 micron, which accounts for 96% of the total, and then transferred into the alkali boiling reactor.

C.NaOH aqueous solution of 1.7-3.5 times theoretical quantity was added to the reactor to react with the above mixture. The control pressure in the reactor was 0.15-0.25 Mpa, and the optimal control pressure was 0.2-0.23 Mpa. The reaction temperature was 110-130 ℃, and the optimal temperature was 120-125 ℃. The optimal holding time was 2-4 hours and the optimal holding time was 2-2.5 hours.

D.After heat preservation, the material is discharged and diluted in a pre-prepared phosphate solution with a volume ratio of 1-2 to the material. Then the solid-liquid separation is carried out. The sodium tungstate solution, which is the product of reaction formula (1) (2) filtered and washed, enters the system and completes the decomposition process. The decomposition rate of tungsten minerals is over 98%.

The key to the process is to add additives such as silica and phosphate to effectively inhibit the chemical reaction, so that the decomposition rate of tungsten ore can reach more than 98%, thus greatly expanding the use of raw materials and improving the utilization rate of tungsten resources.

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