Recovery of Tungsten From Ferrotungsten-II

In order to achieve high recovery efficiencies for tungsten, it is necessary that the ferrotungsten be completely oxidized. The amount of oxidation can be monitored by measuring the weight gain of the ferrotungsten during calcining. As defined herein, the ferrotungsten is completely oxidized when there is no further weight gain in the calcined material. It is believed that the ferrotungsten is essentially oxidized to WO₃, FeWO₄ and Fe₂ O₃. The rate of oxidation of the ferrotungsten is affected by the calcining temperature, the size of the ferrotungsten scrap, and the oxygen content of the atmosphere in the calciner. In particular, it has been found that above about 900° C. the rate of oxidation of ferrotungsten is greatly enhanced. For example, at 1000° C., complete oxidation of ferrotungsten can be achieved in about 14 hours. Under similar conditions at 925° C., the time to complete oxidation is about 20 hours. At 880° C., about 60 hours are needed. And, at 850° C., the ferrotungsten is only about 80% oxidized after 68 hours. Thus, there is a dramatic increase in the oxidation rate above about 900° C. The rate of oxidation is an important consideration in being able to reclaim tungsten from ferrotungsten on a commercially feasible scale.


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