Effect of FeO/MgO Ratio on Dissolution and Leaching of Magnesiowüstite

Abstract

If slag is to be used as construction material, the leaching of some elements, such as chromium must be limited. The leaching of slag depends on the leaching properties of the minerals in the slag. However, the leaching/dissolution properties of individual slag minerals are usually not studied. One common slag mineral that can contribute to the leaching of chromium is magnesiowüstite. The object of this study is to determine whether magnesiowüstite can be modified to avoid chromium leaching. Magnesiowüstite samples with different FeO/MgO ratios with and without chromium content are manufactured. The dissolution is evaluated at pH 7 and 10 using the magnesiowüstite samples without chromium, at size fraction 20–38 μm, by measuring the acid consumption required to maintain constant pH level. The magnesiowüstite samples with chromium content are leached at pH 10; the leachate is analyzed for chromium. The results are unanimous, with increasing FeO content the dissolution of magnesiowüstite and leaching of chromium decrease. At pH 10 the magnesiowüstite, with ≥60 wt% FeO show no sign of dissolution and no chromium leaching could be detected with ≥70 wt% FeO. The results prove that the FeO content can stabilize magnesiowüstite and, thereby, prevent chromium leaching.