Use of Bauxite Residue as a Source of Al2O3 and Fe2O3 in the Preparation of Portland Cement Clinker

摘要

The cement industry consumes energy and nonrenewable mineral resources in large amounts and emits volatile compounds and gases into the atmosphere. In an attempt to minimise the adverse effects of Portland cement clinker production, studies have been conducted to develop an environmentally-friendly cement whose manufacturing process is more energetically economical, is less harmful to the environment and emits fewer greenhouse gases. One way to achieve this aim is to use industrial waste and by-products from other industries as alternative materials in the manufacturing process of cement. A continuous push towards sustainable development has encouraged companies to find economical and environmental applications for industrial residues. In the aluminium industry, the major solid waste generated by the Bayer process is called bauxite residue or red mud. This work investigates the possibility of using bauxite residue as a raw material for the production of a commercial CPI-type Portland cement clinker. Such a use of bauxite residue would bring benefits to both industries and to the environment. The clinker samples used herein were produced by heat treating mixtures of limestone, sand, clay and bauxite residue at 1450°C; these mixtures were then cooled rapidly in air. The crystalline phases of the clinker were characterised by X-ray diffraction (XRD). Tests of the compressive strength and porosity were conducted using mortar samples composed of cement, sand and water that had been cured for 7 and 28 days. The fineness effect of the clinker on the mechanical strength of the mortar was also examined. The addition of bauxite residue did not affect the mineralogical composition of the produced clinker because the main mineralogical phases 3CaOSiO2, 2CaOSiO2, 3CaOAl2O3, 4CaOAl2O3Fe2O3 and free CaOwere well formed. Some of the mortars made with the clinker that was obtained from the bauxite residue had higher strengths than mortar made with commercial CPI-Portland cement, which was used as a reference. The fineness of the clinker affects the mechanical strength of the mortar. The material with finer grains showed better mechanical strength than the material with coarser grains. These facts confirm that bauxite residue can be used as a raw material for Portland cement production. Nevertheless, additional studies are still being carried out to assess the viability of this application in terms of factors such as durability.