Ferritic calcium sulfoaluminate belite cement from metallurgical industry residues and phosphogypsum: Clinker production, scale-up, and microstructural characterisation

The production of ferrite-rich calcium sulfoaluminate belite (CSABF) cement clinker, also containing MgO, from ladle slag, Fe-slag, and phosphogypsum was translated from a lab-scale to a pilot demonstration in a 7-metre kiln at 1260 C. An account of the pilot trials/manufacturing is presented, and the process was robust. Laboratory tests prior to scale-up showed that gehlenite formation can be inhibited in the CSABF clinker by adding excess CaO in the raw meal; however, this reduces the amount of iron (Fe) that can be incorporated into ye'elimite and leads to higher ferrite (C6AF2) content. Detailed microstructural analyses were performed on the clinker to reveal the clinker composition as well as the partition of the minor elements. Different ferrite phases with varying amounts of titanium and iron are distinguished. Eighty-five percent of the clinker raw meal was comprised of side-stream materials and the clinker produced in the kiln had chemical raw-material CO2 emissions 90% lower than that of Portland cement made from virgin raw materials. These results can have a significant impact in regions with a prospering metallurgical industry, enabling industrial decarbonisation and resource efficiency.

Automated summary

The production of ferrite-rich calcium sulfoaluminate belite (CSABF) cement clinker, containing MgO, from ladle slag, Fe-slag, and phosphogypsum was successfully scaled up from lab-scale to a pilot demonstration. Excess CaO was found to inhibit gehlenite formation in the clinker, but it also resulted in higher ferrite content. Microstructural analysis of the clinker revealed different ferrite phases with varying amounts of titanium and iron. This study demonstrates the potential of reducing CO2 emissions and improving resource efficiency in regions with a thriving metallurgical industry.