Alkali Decomposition of High Calcium Tungsten Ore by Thermal Ball Milling Improvement

Tungsten resources are abundant and various in China. At present, wolframite is decomposed by alkali and scheelite is decomposed by hydrochloric acid or boiled by soda. For quite a long time, experts at home and abroad generally believed that it was impossible to decompose scheelite by alkali (NaOH) in industry. Until Professor Li Honggui of Central South University put forward the hot-ball milling alkali decomposition process, which broke the convention.

Some scholars have proposed a method of decomposing high calcium tungsten ore by alkali boiling in a common autoclave. This method can not only treat scheelite concentrate, but also deal with scheelite, wolframite-scheelite mixture, high calcium tungsten slime and high calcium wolframite concentrate containing Ca>3%. It is a high calcium concentrate which can realize large-scale equipment and continuous production. The decomposition process of tungsten ore by alkali pressure digestion is as follows:

The scheel concentrate with a WO₃ content of 67% was ground to a particle size of -0.045 mm to 92%, and 500 g of the concentrate was added to a stirred autoclave with a liquid alkali 600 ml of NaOH concentration of 550 g/l, and NaOH was added. The amount is 2.86 times the theoretical amount (calculated according to the content of WO₃), the solid-liquid ratio is 0.83, and the temperature is 182-190 °C, and the pressure is 0.9-1.0 MPa under the conditions of inhalation for 1.5 hours. Cooling and discharging, filtering and washing at a temperature of 75-85 ℃ and a NaOH concentration of 150 g / l to obtain a washed sodium tungstate solution, the alkalinity (NaOH concentration) of the sodium tungstate solution is 150 g / l, the content of WO₃ in the dry residue is 2.05%, and the decomposition rate of the white tungsten concentrate is 98.78%.

The decomposition rate of Ca-W ore can be stabilized and improved by adding 0-1 times theoretical amount of Na₂CO₃ (calculated by WO₃ content in high Ca-W ore) or 0-0.9 times theoretical amount of alkali metal phosphate or phosphoric acid (calculated by Ca content in high Ca-W ore).

The advantages of this process are that the process and equipment are simple and easy to operate, the continuous and large-scale industrial production can be smoothly realized, and the stable control of the process can be easily realized. Compared with the method of alkali decomposition by hot-ball milling, although ball milling and pressure cooking are divided into two processes, the two complicated auxiliary operations of feeding and unloading of hot-ball milling are omitted. Moreover, the operation of batching and pressure cooking is convenient. Only the valve is switched on and off, the pressure cooking material can be unloaded safely and labor-saving, and the water consumption during hot-ball abrasive unloading is avoided. The uncontrollable defects are beneficial to controlling the temperature and NaOH concentration of the cooking liquid, effectively inhibiting the occurrence of reversible reactions and ensuring a stable high decomposition rate.

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