In a process for dechroming, and/or depleting the MgO content of, steel slags, oxygen is introduced into the liquid steel slag to an extent sufficient for converting iron quantitatively to iron oxide and at least 5% by weight of the iron oxide contained in the slag to iron-III-oxide. The oxidized slag obtained solidifies and is disintegrated, whereupon the paramagnetic portions formed are magnetically isolated and separated from the dechromed slag.