A study of the solubility of pure slag minerals

Abstract Large amounts of oxidic by-product are annually produced by the steel industry worldwide. By far the largest in volume is slag, generated from different stages of steel production. In order to avoid landfilling, steelmakers usually try to process the slag into useful resources that can be used externally. However, leaching of different metals can sometimes be a problem. Since steel slags are a mixture of numerous types of minerals, the solubility of each mineral will affect the outcome of the leachability. The aim of this study was to investigate how six common slag minerals behave during dissolution. Mayenite (Ca 12 Al 14 O 33 ), merwinite (Ca 3 MgSi 2 O 8 ), akermanite (Ca 2 MgSi 2 O 7 ), gehlenite (Ca 2 Al 2 SiO 7 ), γ-dicalcium silicate (γ-Ca 2 SiO 4 ) and tricalcium aluminate (Ca 3 Al 2 O 6 ) were synthesized and their dissolution was evaluated through titration using HNO 3 at constant pH. Acidic to alkaline pHs (4, 7 and 10) were selected to investigate the solubility of the minerals under conditions comparable to those prevailing in newly produced slags, and one pH value, representing acid conditions. It can be concluded that all six minerals behave differently when dissolving and that the rate of dissolution is generally slower at higher pH values, which are normal in the case of steelmaking slags. At pH 10, the solubility of merwinite, akermanite and gehlenite is considered low. The dissolution of γ-Ca 2 SiO 4 is not affected in the same way as the other minerals when the pH is changed.