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Why is steel pickled in acid before hot-dip galvanizing?
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zinc processing
Sphalerite from Baxter Springs, Kansas.
Steel is pickled in acid before hot-dip galvanizing primarily to clean the metal surface by removing scale. Scale consists of thin layers of iron oxide crystals that form on the surface of hot-rolled steel.12
If this scale is not removed, it prevents the molten zinc from properly adhering to the steel during the galvanizing process. By immersing the steel in acids—typically hydrochloric or sulfuric acid—these oxide layers are dissolved, leaving a clean surface. Following the pickling process, the steel is often treated with flux to further prepare it for the bath of molten zinc, ensuring the formation of a durable, protective coating that guards against rusting.231