Ammonium paratungstate is the main raw material of metal tungsten production. Now the factories use extraction or ion exchange process in production, the former one is that the tungsten concentrate with alkali cooking (or alkali fusion) division after removing silicon, phosphorus, arsenic, adding Na2S to make Mo become MoS3 precipitation, and then adjust the pH of supernatant to 2-3, and extracted with a tertiary amine and recovering with NH4OH. Therefore, the defecator will go through stages of pH = 6. APT will then crystallize resulting in difficulties in normal operation. This problem is difficult to resolve from the formula, it is by strengthening stirring to dissolve the crystals again clarified or improved groove geometry of the internal structure of the practice.
It’s not required in removing P, As, Si in the ion exchange method but molybdenum can not be removed, so the tungsten concentrate with low Mo-containing is often the choice. This method can use alkaline feed solution directly, but due to the amount of exchange is small, the material must first be diluted to WO3 contain 25g / L or less, and the amount of the rinse water is also large, therefore the emissions of alkaline wastewater with a pH10-13 is very large, wastewater treatment has become a burden, and tungsten in waste water of these two methods can not be recovered.
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