Ammonium Paratungstate Purification from Complex Scheelite Ore
Tungsten ore is mainly scheelite. The world's scheelite accounts for more than 2/3 of total, and China accounts for 72.1%. Some scholars have improved the method of using ammonium sulphate to decompose scheelite to prepare ammonium partrungstate.
(1) Tungsten containing sulphuric acid and phosphorus mixed acid solution, wherein the concentration of tungsten trioxide is 25-150g/L, the concentration of phosphoric acid is 10 ~ 200g/L, and the concentration of sulphuric acid is 1.5 ~ 2.5mol/L.
(2) The obtained tungsten containing mixed solution of sulphuric acid and phosphoric acid was mixed with oil to extract the two phase volume ratio of oil phase: water phase = 3:1-1:3, and the loading organic phase was obtained.
(3) The obtained load organic phase was extracted by distilling water with volume ratio as oil phase: water phase = 3:1-10:1, and the stripping solution was obtained.
(4) Ammonia was added to the stripping solution to control the free ammonia in the solution at 1-2mol/L and the ammonium tungstate solution was obtained.
(5) Ammonium paratungstate was obtained from ammonium tungstate solution by conventional phosphorus removal and evaporation crystallization.
The improved method can be used as an extractant by increasing the acidity of the material and the alcohols with low concentration. Because the alcohol extractant is a weak neutral extractant, the extractants of iron, calcium, manganese, sulfate and phosphate are not extracted, so the high content of impurities can be processed. A high concentration of phosphotungstic acid solution is obtained by using water as a stripping agent, and then ammonia is added to avoid the problem that the organic phase emulsification can be easily caused by the direct contact between the alkaline reflux and the load organic phase in the traditional process, and the blank organic phase after the extraction of water can be directly extracted without the need of the recycling process of the organic phase. The organic phase after stripping does not have the problem of introducing impurities into the original liquid, the process is short, the manufacturing cost is low, the product yield is high, and the green is pollution-free, and it can be industrialized on a large scale.
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