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

Visa Isteri,Katja Ohenoja,Theodore Hanein,Hajime Kinoshita,Holger Kletti,Christiane Rößler,Pekka Tanskanen,Mirja Illikainen,Timo Fabritius

doi:10.1016/j.cemconres.2022.106715

Visa Isteri, Katja Ohenoja + Show 7 more

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https://doi.org/10.1016/j.cemconres.2022.106715

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Abstract

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.

Highlights

The worldwide manufacturing of 4Gt of cement per year [1] emits more than 3Gt of CO2
Laboratory tests prior to scale-up showed that gehlenite formation can be inhibited in the CSABF clinker by adding excess calcium oxide (CaO) in the raw meal; this reduces the amount of iron (Fe) that can be incorporated into ye'elimite and leads to higher ferrite (C6AF2) content
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

Summary

Introduction

The worldwide manufacturing of 4Gt of cement per year [1] emits more than 3Gt of CO2. More than half of the emissions arise from the breakdown of calcium carbonate (CaCO3 → CaO + CO2) into raw meal, and the remainder is mainly from the combustion of fuels to reach the high temperature required in conventional cement rotary kilns (~1450 ◦C) [2]. Natural limestone (mainly CaCO3) is the only realistic calcareous source for large-scale cement manufacturing. Cements containing ye'elimite, commonly known as calcium sulfoaluminate (CSA) based cements, are one of the important alternative types with a reduced carbon footprint as the production process requires less calcium carbonate to be calcined and has a lower production temperature. The modifications required may include better control of the process temperature and residence time, and more accurate clinker phase determination [3]. Due to the volatile nature of CSA constituents at clinkering temperatures, monitoring/controlling the atmospheric conditions is a crucial aspect of CSA clinker manufacturing [4,5,6,7]

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