Compositional Aspects in Valorization of Iron Silicate Slags

Pyrometallurgical copper production is associated with high slag rates, typically ranging from 2.2 to 3.0 tons of slag per ton produced copper. Therefore, slag valorization is necessary to maintain a resource-efficient operation. An attractive application for these iron silicate slags is as supplementary cementitious materials (SCMs), which effectively lowers the CO₂ emissions per ton of cementitious material. Although utilizing iron silicate slags as SCMs has been studied in previous work, the scientific literature has limited data on the isolated effect of composition on the inherent reactivity in cementitious systems. In particular, no reports on compositional aspects related to milling properties and their implication on the performance as SCMs are available. Therefore, the present study aimed to isolate the effects of milling in a synthetic FeO-SiO₂-CaO-Al₂O₃-MgO system. By systematically varying the composition related to FeO/SiO₂ ratio, CaO content, and Al₂O₃ content, a series of slags were subjected to milling studies and subsequent reactivity testing. The data showed a consistent correlation between the depolymerization of the slag and an increased demand for milling to generate the same specific surface area. Consequently, the study highlighted that the proposed slag valorization route encompasses both the isolated contribution of active elements to the cement reaction and the ease of generating surface area during the milling process.