An Efficient Extraction Method of APT from Scheelite

For a long time, China's tungsten concentrate mining is dominated by wolframite ore resources, and the output once accounted for more than 90% of tungsten concentrate production. At present, the reserves of wolframite ore have been depleted, and the replacement of black tungsten ore with scheelite concentrate is of great significance and imminent. 

 Traditionally, the decomposition of scheelite has mostly been carried out by acid or alkali techniques. The traditional acid decomposition process has the following issues: severely corrosive to equipment, volatile HCl, high acid consumption, high production cost, and severe environmental effect. Tungsten and phosphorus are easy to form polyacid mixture in acidic solution, which is difficult to separate. This method has been basically used as the main process.  In the other hand, the alkali decomposition and boiling method generally adopts high temperature, high pressure and high alkali addition amount to achieve decomposition purpose, high process energy consumption; easy to form calcium carbonate passivation film on the surface of scheelite concentrate, which will cause a large amount of alkali during decomposition.  It must be equipped with an alkali recovery process, and the subsequent ion exchange process requires a large amount of water to be diluted to 16-25 g/L into the exchange column, resulting in high process cost, large waste water volume, and small unit capacity.

 Thus, some scholars have proposed a method and system for decomposing scheelite concentrate, which can overcome the problem that tungsten and phosphorus are difficult to separate in the traditional acid decomposition process, and phosphorus easily affects the quality of the product; phosphorus-free oxalic acid is used instead of sulphur  Mixed acid, oxalate in oxalic acid can form a complex with tungsten, and oxalic acid combines with calcium to form calcium oxalate which is hardly soluble in water. Calcium oxalate can be treated with sulfuric acid to obtain oxalic acid and calcium sulfate; it can completely decompose scheelite concentrate.  The tungsten, oxalic acid can be recycled and recycled; it can significantly reduce the decomposition cost of scheelite concentrate and simplify the decomposition equipment. The experimental process of the method is:

 Decompose 10.0kg scheelite concentrate in a 50L reactor. The WO3 content of scheelite concentrate is 25%, the amount of oxalic acid added is 5.0kg, the decomposition temperature is 25 °C, the reaction time is 14h, and the tungsten in the scheelite concentrate  The decomposition rate reached 99.21%.  The decomposed liquid (tungsten oxalate solution) obtained by filtration has a tungsten concentration of 24.18 g/L, a Ca concentration of 3.12 g/L, a Zn concentration of 3.93 g/L, a Mg concentration of 4.34 g/L, and a Fe concentration of 4.50 g/L.  By extraction method, the extraction rate of tungsten reaches 99.51%. After the organic phase is back-extracted by ammonium chloride, the obtained ammonium tungstate solution is evaporated and crystallized to obtain APT zero-grade product.  After the decomposition slag is treated with sulfuric acid, the concentration of sulfuric acid is 2mol/L, the treatment time is 30 minutes, and the obtained oxalic acid solution is further supplemented with 1.9kg of oxalic acid solids to return to the decomposed scheelite concentrate. The WO3 content of the scheelite concentrate is 25%, and the decomposition  The conditions were the same as above, and the decomposition rate of tungsten after completion of the decomposition reaction was 99.31%.

The research shows that the decomposition rate of tungsten trioxide in scheel concentrate can reach more than 99% by using oxalic acid under direct atmospheric pressure. After extraction, the extraction rate of tungsten can reach over 99%. The whole process can get zero-grade APT products with low pollution and low cost.

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