Low energy synthesis of cement compounds in molten salt

Abstract

Abstract

The world cement industry is responsible for >5% of the total anthropogenic carbon dioxide emissions blamed for causing global warming. The production of cement clinker minerals by precipitation from a molten salt solvent offers a potential route to energy reduction in cement manufacture. Molten salt synthesis of the major cement compounds β-dicalcium silicate (β-Ca₂SiO₄, β-C₂S) and tricalcium silicate (Ca₃SiO₅, C₃S) has been attempted in fused sodium chloride (NaCl). The synthesis of β-Ca₂SiO₄ was carried out by the reaction of CaCO₃ with SiO₂ in molten NaCl (CaCO₃-SiO₂-NaCl mole ratios 2∶1∶19·2 at 908°C, and 2∶1∶20·4, 2∶1∶13·5, 2∶1∶10·3 and 2∶1∶8 at 1140°C). The product was characterised by powder X-ray diffraction, Raman scattering and scanning electron microscopy. For the synthesis of Ca₃SiO₅, reactants with a molar ratio of 3∶1 were used (CaCO₃–SiO₂–NaCl 3∶1∶19·8 at 908 and 1000°C, and 3∶1∶20, 3∶1∶14, 3∶1∶9·9 and 3∶1∶8·1 at 1140°C). In all cases β-Ca₂SiO₄ was the principal product, with the CaO phase still present and (if any) only small quantities of Ca₃SiO₅. These observations, coupled with previous studies on the solid state synthesis of Ca₃SiO₅, indicate that β-Ca₂SiO₄ is an intermediate compound, requiring in excess of 1140°C to react with CaO in order to form tricalcium silicate.

Keywords:

• Cement
• Molten salt
• Low energy
• Synthesis
• Dicalcium silicate
• Belite

This work has been funded by the Engineering and Physical Sciences Research Council (EPSRC) under grant no. EP/F014449/1 (http://gow.epsrc.ac.uk/ViewGrant.aspx?GrantRef = EP/F014449/1). The authors gratefully acknowledge the support of J. K. Cockcroft and M. Vickers in the Materials Chemistry Centre, Department of Chemistry, University College, London, UK and the use of their powder XRD facilities in the study.

Notes

This paper is part of a special issue on Cement and Concrete Science