Phosphorus Decomposes Wolframite and Scheelite Mixing Ore

Although tungsten is mainly derived from scheelite, there is a considerable proportion of wolframite. The largest tungsten ore reserves in China are 747 thousand T, and the ratio of wolframite and scheelite is 3:7. For such minerals, the sulphuric acid phosphoric acid mixed acid process is used directly, and the wolframite does not react completely, and all of them enter the leaching residue. In fact, it is difficult to decompose wolframite without sulphuric acid phosphoric acid mixed system. Even if other acids are used, the leaching reaction of wolframite is very slow.

To sum up, in view of the fact that wolframite can not be effectively decomposed in various acidic systems, new technological ideas may be needed. We think that the transformation of wolframite into scheelite is expected to achieve the efficient decomposition of tungsten in the sulfuric acid phosphoric acid system.

The transformation of wolframite to scheelite can be achieved through the following reactions: (Fe, Mn) WO₄+CanA₂ = CaWO₄+ (Fe, Mn) nA₂

The solubility integral of CaWO₄, MnWO₄ and FeWO₄ is 1.82 x 10-9, 8.71 x 10-10 and 1 x 10-15 at 25°C. In order to make the wolframite (MnWO₄, FeWO₄) with smaller solubility (CaWO₄) into the large solubility scheelite (CaWO₄), it is necessary to simultaneously make the iron and manganese in the wolframite to form a stable compound to promote the reaction to the right. Therefore, by introducing phosphate, Fe²⁺ and Mn²⁺ can form insoluble phosphate. Therefore, apatite (Ca₁₀ (PO₄) 6F₂) is selected as the conversion agent. According to thermodynamics calculation, the thermodynamic trend of FeWO₄ reaction even with the smaller solubility product and Ca₁₀ (PO₄) 6F₂ is very large.

Scheelite resources are often associated with a large amount of apatite in China, and the phosphorus content is close to that of conventional phosphate rock. The transformation of wolframite can be achieved directly by adding high phosphorus scheelite into black and white mixed ores, the mixture of wolframite and high phosphorus scheelite can be treated by ball milling. Through the leaching experiment, it is found that after the treatment, the wolframite and scheelite tungsten ore can be completely decomposed in sulfuric acid phosphoric acid leaching system. 

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