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Galvanized Steel undergoes several processes before being lowered into a molten zinc bath. One is cleaning the steel with "an acidic solution to remove mill scale."

After some more research I found that hydrochloric acid is the most popular choice, because it is so strong and therefore fast.

What I want to know is, can any acid theoretically serve the exact same purpose? And then, how to calculate how much longer it would take to achieve the desired effect.

Believe it or not, the most interesting acid that I'm interested in right now is acetic acid (vinegar). This is because I have seen many videos demonstrating that rust can be removed by soaking the iron in tub of vinegar (and sometimes salt). So I am guessing that it can also remove mill scale.

How would I calculate the time needed from a chemical equation?

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Mill scale ( FeO , Fe3O4) is not rust, and is more tenaceaous, so remedies for rust will not necessarily remove it. Sulfuric is cheapest acid for mill scale removal. I assume hydrochloric is used because it has some advantage for galvanizing.

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  • $\begingroup$ Sulfuric acid has the added advantage that it's not volatile and so can be used in open baths at elevated concentration without quickly corroding everything in the vincinity. $\endgroup$
    – Karl
    Commented Oct 24, 2022 at 6:59

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