Phosphoric Acid - Sulfuric Acid Decomposition Scheelite Flotation

At present, the scheelite flotation method in China is mainly used to treat scheelite with the treatment technology of alkali pressure boilding with wolframite. The process makes the scheelite effectively decomposed under the conditions of high alkali concentration, high alkali dosage and high temperature and high pressure, and the slag containing WO₃ can be reduced to 1-3%. 

However, this process has the disadvantages of large energy consumption, high production cost and large waste water discharge in subsequent process, which does not meet the development requirements of energy conservation, emission reduction and low carbon economy in China.

Because tungsten is and phosphorus, arsenic and silicon impurities such as tungsten formation of mixed ratio of 1:6 to 1:12 soluble in hydrochloric acid decomposition process of heteropoly acid, a small amount of phosphorus can cause a large number of dispersed tungsten and losses, so the main treatment of high grade hydrochloric acid decomposition process of Scheelite Concentrate (for phosphorus and arsenic impurities such as low).

However, some people opposed it and used it to add a small amount of phosphoric acid into the leaching process to make tungsten enter the solution, so as to solve the problem of decomposition of tungstic acid when hydrochloric acid decomposed, but the problem of corrosion and volatilization of hydrochloric acid is still a headache. In order to overcome the above adverse effects, Zhao Zhongwei and others proposed a method of decomposing scheelite with no pollution, low cost, low energy consumption, simple operation and high yield.

With the concentration of P₂O₅ is 5% ~ 35% phosphoric acid solution, adding sulfuric acid and SO₄^2- concentrations in 0.10g/ml ~ 0.40g/ml, heating to 70 to 100 DEG C, the scheelite was added to the solution of the reaction, the ratio of liquid to solid is 3: 1-8:1ml/g and the reaction time is 1 to 6h. After filtration, the filtrated filtrate is extracted by basic ion exchange, alkaline solvent extraction or ammonium salt precipitation.

This method can be used for flotation containing WO₃ is 10% ~ 75% of scheelite, due to complexation of calcium phosphate, leading to the solubility of calcium sulfate with increasing concentration of phosphate in solution increased gradually, reached the maximum of about 80 DEG C to about 20% in the P₂O₅, 5-7 times without the presence of phosphate. Even if the P₂O₅ increases to about 40%, the solubility can still reach 3-5 times that of the non phosphoric acid. Therefore, appropriate high concentration phosphoric acid can reduce the supersaturation of calcium sulfate when the tungsten ore decomposes, and it also may reduce the spontaneous nucleation rate of calcium sulfate, and thus play a role in promoting the formation of coarse crystals. Moreover, high concentration of phosphoric acid is also conducive to the formation of soluble tungstic heteropoly acid, avoiding the encapsulation effect of tungstic acid precipitation. Besides, the corrosion of phosphoric acid is low, and there is no volatilization problem like hydrochloric acid.

Phosphoric acid - sulfuric acid decomposition of scheelite flotation advantage: There is no strict requirement for the phosphorus content of the scheelite impurities to be processed, and the special dephosphorization process need not be set up during the beneficiation process of the scheelite, so that the cost of phosphorus removal reagents and the loss of tungsten are saved; After the reaction is finished, tungsten enters into the filtrate, and only needs simple post-processing methods such as ion exchange, solvent extraction or ammonium salt precipitation, which simplifies operation and reduces the cost.

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