Pyrometallurgical Processes
There are also several pyrometallurgical processes that reduce zinc oxide using carbon, then distil the metallic zinc from the resulting mix in an atmosphere of carbon monoxide. The major downfall of any of the pyrometallurgical process is that it is only 98% pure; a standard composition is 1.3% lead, 0.2% cadmium, 0.03% iron, and 98.5% zinc. This may be pure enough for galvanization, but not enough for die casting alloys, which requires special high-grade zinc (99.995% pure). In order to reach this purity the zinc must be refined.
The four types of commercial pyrometallurgical processes are the St. Joseph Minerals Corporation's (electrothermic) process, the blast furnace process, the New Jersey Zinc continuous vertical-retort process, and the Belgian-type horizontal retort process.
Read more about this topic: Zinc Smelting
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