Carbon footprint of calcium sulfoaluminate clinker production

Novel cement formulations based on calcium sulfoaluminate clinkers have significantly lower carbon dioxide emissions during production when compared against conventional Portland cement; however, there are no systematic studies of the environmental impact associated in producing these formulations. Previous studies are limited to qualitative evidence that emissions are lower due to a combination of favourable thermodynamics and a reduced usage of limestone. This work evaluates the eco-efficiency of calcium sulfoaluminate clinker production through an analysis of the carbon footprint and costs over the entire clinker production process (cradle-to-gate). Several sulfur sources are considered including calcium sulfate, as both gypsum and anhydrite, and a novel solid-sulfur combustion process in kilns. This latter process has the added advantage of reducing the fuel demand required to reach clinkering temperatures during the manufacturing process. The analysis demonstrates an overall reduction of emissions of 25–35%, which varies largely as a function of the phase composition of the final clinker but is almost independent of the sulfur source. The high aluminium oxide content in the final calcium sulfoaluminate clinker formulation requires the use of alternative raw materials and by-products from the aluminium industry such as high-alumina clays, alumina-rich wastes, or bauxite. Bauxite, which is only abundant in specific regions of the world, is detrimental to the economics of calcium sulfoaluminate clinker production. Despite this, costs of the clinker production remain competitive and the process displays significant potential for improving the environmental impact of cement production.