Recovery of Fluorite from Scheelite Flotation

Fluorite is the most important mineral in fluoride. It has unique physical and chemical properties and wide uses. It plays an important role in industrial development. Like tungsten, fluorite reserves, mining and exports in China rank first in the world.

Because scheelite is similar to fluorite and other calcium-bearing gangue minerals in flotation, inhibitors have to be added in the process of scheelite flotation to strongly inhibit calcium-bearing minerals such as fluorite. On the one hand, such inhibition also has a negative impact on the recovery of scheelite, on the other hand, fluorite floatability deterioration seriously affects subsequent recovery, every year hundreds of thousands of tons of fluorite flow to the tailings pond, resulting in a large amount of waste of resources. Therefore, it is necessary to break the routine and develop the processing technology of mixed concentrate.

Researchers have tried to decompose fluorite minerals by sulfuric acid sintering with phosphoric acid, so that the scheelite in the mineral is converted to heteropoly acid (or heteropoly anhydride) in the fluorine gypsum residue during roasting, and then soaked the fluorine gypsum with a small amount of phosphoric acid solution, while effectively utilizing the excess sulfuric acid in the fluorine gypsum. The tungsten is added into the solution in the form of heteropoly acid to achieve separation from calcium sulfate. The specific experimental procedures are as follows:

1kg tungsten containing fluorite concentrate (containing CaF₂ 95.6%, WO₃ 2.7%) was decomposed by sulfuric acid and phosphoric acid. The molar ratio of 98% sulfuric acid to calcium in minerals is 1.2, the molar ratio of phosphoric acid to WO₃ in minerals is 1.0, the calcination temperature is 250 ℃ and the calcination time is 6 h. The HF gas generated during the calcination process is absorbed and used to prepare hydrofluoric acid. The decomposition rate of CaF₂ is 96.2%. After the sintering process, the fluorogypsum was leached for 4 hours with the concentration of H₃PO₄ 100g/L, the liquid-solid ratio was 5:1, the leaching temperature was 80 ℃, the leaching rate of tungsten was 96.5%, and the WO₃ content of slag was 0.056%. The filtrate obtained after the leaching process can return to a new round of leaching of tungsten containing fluorogypsum. The tungsten in the leaching solution was adsorbed on the primary amine anion exchange resin, and the adsorption rate was 98.5%.

This method changes the concentrating idea of single flotation scheelite and fluorite concentrate, and obtains mixed concentrate, which can ensure the high comprehensive utilization of tungsten and fluorite resources; the decomposition rate of fluorite is above 95%, the recovery rate of tungsten is above 90%, and the WO₃ content in fluorogypsum is below 0.1%.

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