Why is sulfur released as sulfur dioxide during roasting?

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Molten copper pours from a large industrial furnace into rectangular molds at a copper smelting facility, with glowing metal and industrial equipment visible. — copper processing Molten copper being made into plates.

During the process of roasting in copper processing, sulfur is released as sulfur dioxide because the ore is heated in the presence of air (oxygen).12

This procedure, specifically known as an oxidizing roast, is designed to transform sulfide ores into oxides. When the sulfide compounds—such as copper(I) sulfide—react with oxygen during this combustion-like process, the sulfur is oxidized and driven off as a gas. This step is essential because it reduces the sulfur content in the material to a level suitable for subsequent smelting operations.1342