Pretty much all grades of steel contain some S and P either as impurity or added deliberately. Sulfur content generally improves machinability and
phosphorus and tensile strength. There are more benefits and drawbacks of P and S content, but this is not metallurgy forum
I also have dissolved scrap steel and various acids and the smell was always present. Never bothered to check what exactly was is causing the smell as
dissolution was always outside, just under some sort of canopy to protect from rain.
Always assumed that culprit are compounds of P and/or S.
Even if they were PH3 or H2S the amount was negligible and they had no chance to accumulate when reaction was run outdoors.
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