Separation of valuable elements from steel making slag by chlorination

Abstract

Herein, we investigated the volatilization behavior of slag elements during chlorination of converter slag and Kambara reactor slag to develop a method for recycling steelmaking slag. Then, the effects of holding time and carbon addition (carbon reduction) (denoted as a combination of carbon reduction/chlorination) on volatilization were examined in detail. Most of the Fe in the slag was volatilized by chlorination up to 1000 °C, independently from the type of slag. Moreover, it was possible to volatilize most of the Ti and approximately 40% of the Mg by chlorination at 1000 °C for 60 min. That is, Fe and Ti were completely separated from the slag by chlorination. Fe was volatilized below 1000 °C during carbon reduction/chlorination, and remarkable volatilization (40–90%) of Ti and P was also observed until 1000 °C. Therefore, the separation of each element using the volatilization kinetics of Fe, Ti, and P was difficult during the carbon reduction/chlorination. In contrast, when carbon was added to the chlorination residue obtained at 1000 °C for 60 min and then subjected to a carbon reduction/chlorination treatment, most of the Mg, Si, Al, and Ca remained in the solid phase up to 1000 °C, and P was the only element volatilized. The volatilization temperature (>1000 °C) and the proportion of P were lower than those of the conventional carbon reduction method of slag. Therefore, it was found that the combination of chlorination and carbon reduction/chlorination methods is effective for the separation of Fe, Ti, and P from slag.