Co-utilisation of CO2 and steelmaking slags for production of pure CaCO3 legislative issues

The steel industry is characterised by large amounts of CO2 emissions, but there is no easy means to reduce these emissions. One interesting option for the reduction of CO2 emissions could be the utilisation of steelmaking slags for carbon dioxide mineralisation. In this option CO2 is bound with the calcium of the slag material, producing stable carbonate as an end product. The utilisation of steelmaking slags as the raw material for carbon dioxide mineralisation will change the quality of the slags. If, however, this change degrades the slags it could prevent the use of slags in carbon dioxide mineralisation or make it very expensive. The purpose of the research presented here is to evaluate this issue with the help of a case study where the quality of the residual slag from the recently suggested carbonation method was experimentally investigated. The CO2 mineralisation method, based on steelmaking slags and ammonium salt solutions, was found to change the quality of the slags: the calcium content was reduced, the CaO and Ca(OH)2 phases were completely dissolved, and the solubility of the V and Cr increased notably. This residual slag would presumably have to be handled as waste. Currently, the steelmaking slag used in the case study is defined as a by-product, but if it is used for CO2 mineralisation instead of liming its legal status will be re-evaluated. Subsequently, the CO2 mineralisation process could possibly be defined as an end-of-waste procedure.