Guidelines for Fluorite Recovery from Scheelite Flotation

Among skarn tungsten deposits, wolframite and scheelite are the most common phenomena, and scheelite also coexists with calcareous gangue minerals such as fluorite, calcite, apatite and garnet. The flotability of scheelite and fluorite gangue minerals is similar, so the flotation separation of scheelite and fluorite is always a technical problem.

One of the main uses of fluorite is to produce hydrofluoric acid. The main method is fluorite-sulfuric acid method. Fluorite reacts with sulfuric acid to form calcium sulfate solid and HF gas. HF is absorbed and hydrofluoric acid is obtained. The thermodynamic trend of the reaction between sulfuric acid and fluorite is very large, but the CaSO₄ solid film formed during the reaction process will be coated on the surface of the unreacted fluorite, which will affect the further reaction. In view of this situation, a high concentration of phosphoric acid was specially introduced during the decomposition of sulfuric acid, and the concentration of sulfuric acid in the decomposition solution was reduced appropriately, thus the nucleation of calcium sulfate was inhibited. Furthermore, the reaction temperature of the decomposition system is carefully regulated to eliminate the obstacles to decomposition and thoroughly decompose fluorite minerals. The process is decomposed as follows:

1)Complex minerals containing fluorite, SiO₂, scheelite, apatite and calcite are decomposed by a mixed solution of phosphoric acid and sulphuric acid. The total mass percentage of the complex minerals containing CaF₂ and CaWO₄ is not less than 70%, and the mass content of SiO₂ is not more than 5.0%. When decomposed, HF gas or SiF 4 gas or mixed gas containing HF and SiF₄ are formed.

2)After decomposition, the leaching solution is filtered and separated. The leaching solution is directly added to the consumed sulfuric acid, or sulfuric acid and phosphoric acid, and then returned to a new round of leaching recycling, so that tungsten in the leaching solution can be extracted after at least one accumulation.

Introducing a certain amount of phosphoric acid into the sulfuric acid solution to decompose the scheelite in the complex concentrate. The tungsten enters the solution as a heteropoly acid, so that the process can not inhibit other calcium-containing minerals during the scheelite flotation. White tungsten and other calcium-containing minerals enter the concentrate, which is beneficial to the separation of the product calcium sulfate; thus, the simultaneous recovery of fluorine and tungsten in a decomposition process.

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