Low-alumina portland cement from lime-soda sinter residue

Abstract

<p>A byproduct for the Ames Lime-Soda Sinter Process for recovering alumina from power plant fly ash was investigated as a cement raw material. This investigation dealt with a determination of the best method to utilize the process residue from both a clinker quality and an economic perspective. The experimental work was divided into 4 major areas: characterization of the sinter residue, laboratory burnability tests, physical testing of produced residue-cements, and a kinetic study of C[subscript]3S formation. Other important topics were considered such as the effect use of the sinter residue has on the energy requirements of a commercial cement kiln and on the economics of a combined lime-soda sinter, cement plant;It was found that a low-alumina, C[subscript]3S-bearing cement could be readily produced from a raw mix containing significant amounts of sinter residue, which was found to consist of [beta]-C[subscript]2S, C[subscript]3A, CaCO[subscript]3, MgO, and C[subscript]4AF. Based on an energy balance using a typical cement feed containing around 75%[subscript] w limestone as a reference, use of the residue in a cement feed allows for a 50% reduction in required energy for the kiln and a 32%[subscript] w increased throughput;A laboratory produced residue-cement was found to meet all of the specifications for a Type 5 portland cement. The sulfate resistance of the cement, implied by its 3.8%[subscript] w C[subscript]3A content, was demonstrated by use of ASTM test, C-452. The reaction forming C[subscript]3S in the residue-cement clinker is thought to consist of a two-step sequence of early phase boundary control followed by diffusion control defined by the Ginstling-Brounshtein rate equation. Activation energies for the diffusion controlled portion of the reaction for 2 residue-cement formulations (103 and 121 kJ/mole) correspond roughly to those reported for Ca diffusion in a cement clinker (164 kJ/mole) and for the self diffusion of Ca in CaO (142-268 kJ/mole);The rate of return found for a combined lime-soda sinter and cement facility processing 43,800 tons per year (TPY) of alumina and 530,400 TPY of portland cement was 4.7%. This value could be improved by not charging for the fly ash used, by recovering more of the alumina and by increasing the plant size. ftn[superscript]1DOE Report IS-T-1348. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.</p>