The crude lead bullion, containing significant quantities of copper will then undergo'copper drossing '.
2.
In this step elemental sulphur, usually in solid form is added to the molten crude lead bullion to react with the contained copper.
3.
A " matte " layer forms in this step, containing most of the copper originating from the crude lead bullion and some other impurities as metal sulfides.
4.
Bismuth travels in crude lead bullion ( which can contain up to 10 % bismuth ) through several stages of refining, until it is removed by the Kroll-Betterton process which separates the impurities as slag, or the electrolytic Betts process.
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