Kinetics of steel slag dissolution: from experiments to modelling

Carbon dioxide sequestration via carbonation of steel slags is a promising way of combining two waste products to create value. Understanding the dissolution kinetics of steel slags, which are alkaline and rich in calcium, in acidic media is essential to configure such a process. In this study, we seek to analyse the dissolution mechanism from experimental studies and develop a mathematical model considering the heterogeneous characteristics of slag. We found that the reduction in calcium extraction efficiency with an increase in particle size, which is normally associated with surface passivation or non-uniformity of samples, can be explained by considering the morphological features associated with the distribution of MgO-FeO (RO) phase in the calcium silicate matrix. We present a population balance model and show that the reduction in calcium extraction efficiency in coarse particle fractions is due to increased sporulation of the RO phase. The findings in the study suggest that the leaching of metal ions from slag is controlled by proton-promoted surface dissolution reaction, where the dependence of acid concentration follows the Langmuir-Hinshelwood adsorption isotherm. The model shows good agreement with a large set of parametric studies and demonstrates the importance of considering morphological features, as we progress towards development of a priori dissolution models for multi-mineral oxides and silicates.