Synthesis of calcium sulfoaluminate cements from Al2O3 rich by-products from aluminium manufacture

The relatively low environmental impact associated with the manufacturing process of calcium sulfoaluminate (CSA) cements can be further reduced through the utilization of industrial wastes as components of the clinker generating raw mix. The use of Al2O3 rich by-products like alumina powders, coming from the secondary aluminium manufacture, as partial or total substitutes for an expensive natural material like bauxite, is particularly worthy of consideration. Various raw mixtures containing 32-35% limestone, 27-34% natural gypsum, 0-38% bauxite and 0-34% alumina powders were heated in a laboratory electric oven for 2 hours in the temperature range 1200°-1350°C. The resulting CSA clinkers were submitted to X-ray diffraction analysis in order to assess the reactants conversion and selectivity towards the desired products. It has been found that, compared to bauxite, alumina powders enhance the formation rate of , the main component of CSA cements, and shift the optimum temperature for its synthesis from 1350° to about 1250°C.