The production of H 2 by oxidation of FeO, taken here as model compound for steel slags, has been investigated both in pure water and under acidic aqueous conditions in the 373–573 K temperature range. Whereas after 65 h, H 2 yield was negligible in pure water at 423 K, the reaction 3 FeO (s) + H 2 O (l) → Fe 3 O 4(s) + H 2(aq) reached near completion at the same temperature within 10 h in a solution containing 0.05 mol/l acetic acid. Increasing acetic acid concentration by one order of magnitude did not yield significantly more H 2 . At identical initial pH, acetic acid was found to be more efficient than oxalic acid and hydrochloric acid at enhancing H 2 production. Acidic conditions increased FeO dissolution kinetics and, consequently, improved H 2 yield. The specific efficiency of acetic acid resides in its thermal stability as well as in the potential of ligand-promoted Fe(II) dissolution. We show that the positive kinetics effect of mild acetic acid solutions over H 2 yield evidenced on FeO does not apply directly to steel slags which buffer the pH to high values due to the presence of large amounts of CaO. [ABSTRACT FROM AUTHOR]