Sodium Hydroxide Decomposes Scheelite without Pressing and Boiling

In the early tungsten’s extraction, sodium hydroxide was used only to decompose wolframite and did not apply to decomposite scheelite. However, in 1985 Li Honggui's team proposed that alkali hot ball-milling to decompose scheelite and changed the view that sodium hydroxide can’t decompose scheelite thoroughly. However, the method has high equipment-dependence, serious abrasion and salient safety problems.

Recently, some scholars have proposed an improvement scheme, which is sodium hydroxide decomposing scheelite. Compared with the existing alkali-decomposition process, it reduces the equipment of autoclave so that the operation becomes more convenient and safer. The main steps are as following:

(1) The tungsten mineral is ground to less than 0.080mm.

(2) The ground tungsten mineral is mixed with the solid NaOH .

(3) Placing the mixture obtained in step two in a high temperature furnace to roast. Baking temperature is from 500℃ to 900℃, and roasting time is from 30 minutes to 4 hours.

(4) The gotten calcined-product was flooded to obtain sodium tungstate solution. The leaching ratio of liquid to solid is from 2: 1 to 6: 1. The leaching temperature is from room temperature to 95 ° C, and the leaching time is from 30minite to 4 hours.

Take scheelite containing 36.3% of WO3 as a test and grind it to -0.080mm. Ore weight 100g, 2.4 times the theoretical amount of NaOH, roasted at 700 ℃ for 0.5 hours, the roasted product was stirred with water and leaching. The ratio of liquid to solid is 6: 1, the temperature is 80 ℃which is preserved for 2h. After being filtered, washed and dried, the residue contains insoluble WO3 of 0.252%, and decomposition rate is of 99.84%.

The new method for providing tungsten to alkali decomposing of tungsten minerals changes the prior decomposing tungsten minerals with NaOH solution. Instead of using NaOH solid to decompose tungsten minerals to raise the concentration of alkali to the maximum solid alkali, Decomposition of tungsten minerals is carried out at lower temperature and at atmospheric pressure. Compared with the existing alkali decomposition process, the autoclave equipment is reduced, the operation is more convenient and safer, and the energy consumption and the production cost are reduced when the amount of alkali is equivalent. Moreover, the process can not only deal with the wolframite, but also deal with black-and-white tungsten, scheelite, artificial scheelite and tungsten slag, and it is of a wide range of applications.

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