Preparation Of Building Materials From Wastes In Alumina Production Of Bayer Process And Their Mechanism Of Strength

Red mud bricks and fly ash bricks have been prepared from Bayer red mud, fly ash, coal-burning slag, lime or calcium carbide residue, gypsum and cement. The preparation process comprises wheel-rolling blending, molding with high pressure, and steam curing process. Bayer red mud, fly ash and coal-burning slag are from Coalmine Alumina Sanmenxia Company Limit. Effects of the factors on the compressive and bending strength and frost resistance are analyzed. The mechanism of strength is studied by XRD and FSEM techniques. The construction and the engineering economy studies of the actualized fly ash bricks production line are introduced.The experimental results of red mud bricks show that when the bricks prepared from 25% red mud, 15% fly ash, 38% coal-burning slag, 10% hydrated lime, 12% cement, pressure molding at 20MPa, then autoclaving for 8h at 180℃, 0.8MPa, the strength can reach the standard of 15C(GB11945-1999); radium activity concentrations are lower the limit in main building materials (GB6566-2001); the coefficient of carbonization is 1.00 ; and the drying shrinkage is 0.48mm/m. While substituting quicklime for hydrated lime, reducing the content of cement and adding a small amount of gypsum, steam curing for 16h at 80℃, the compressive and bending strength and frost resistance of bricks can also reach the standard of 15C(GB11945-1999).The experimental results of fly ash bricks show that when the bricks prepared from 30%～34% fly ash, 45%～51% coal-burning slag , 12%～15% hydrated lime or calcium carbide residue, 3%～5% cement and 0%~3% gypsum, pressure molding at 20MPa, then steam curing for 11h at 80℃or autoclaving for 8h at 180℃, 0.8MPa, the compressive and bending strength and frost resistance can reach the standard of MU15 (JC239-2001).The XRD and FSEM analysis of the specimens indicate that ettringite and other kinds of Calium Hydroaluminosulfate are generated when the red mud bricks and fly ash bricks steam curing at 80℃and their raw materials added into gypsum. Ettringite contributes mostly to the strength of the bricks when steam curing at 80℃. When the bricks are autoclaving at 180℃, ettringite decomposed. The decomposition of ettringite induces the decline of the strength of the bricks.On the base of numerous experiments, integrating with local situation of the Shan county, Sanmenxia city, Henan province, a fly ash brick production line with an output of 50 million blocks per year was built. The total content of calcium carbide residue which is as main activator, fly ash and coal-burning slag is more than 95%. At present, the technology of this production line is advanced at home. The engineering economy studies of the production line show that the total investment is about 9.5 million yuan, the cost per block is 0.14 yuan. The gross profit is 2 million yuan per year if the selling price is 0.18 yuan per block. The total investment could be taken back in five years.