Study On The Basis Of Stabilization Of Alkali In Red Mud Building Materials

Bayer red mud is by-product of alumina industry. As Bayer red mud is alkaline waste solid in slurry state, so many limited factors lowered the recycling utilization rate of Bayer red mud. As demand quantity of baking-free brick, which is a new type building material, is increasing, baking-free brick prepared by Bayer red mud is a good way of utilization of Bayer red mud. But excessive amounts of Na+in Bayer red mud could reduce the strength of brick and durability of brick. So one main question of baking-free brick, in which prepared by Bayer red mud as one main raw material, was how to stabilize Na+in baking-free brick.In this paper, on the one hand, through leaching experiment in different lixiviants to explor the Na-containing mineral phase in Bayer red mud and the optimum leaching condition of soluble Na+in Bayer red mud; on the other hand, through the leaching rate of soluble Na+in baking-free brick, which prepared by Bayer red mud as one main raw material, explor the stabilized way of soluble Na+in Bayer red mud. Studies showed that:(1) When baking-free brick, which prepared by Bayer red mud as one main raw material, taken efflorescence, the white things on the surface of baking-free brick was sodium carbonate. From the XRD patten of raw material of baking-free brick, there was no Na-containing mineral phase in the raw material of baking-free brick except Bayer red mud. The Na-containing mineral phase is sodium hydroxide, sodium carbonate and sodalite in Bayer red mud.(2) According the result of leaching experiment:When the deionized water is lixiviant, the soluble Na+in Bayer red mud couldn’t be completely leached in one time. The leaching rate of Na+for many times in deionized water was equalled to the leaching rate of Na+for one time in ammonium chloride. So the optimum way of monitoring soluble Na+was that Bayer red mud leached by ammonium chloride in the condition of leaching time is4h; leaching temperature is60℃; liquid-solid ratio is100; the concentration of ammonium chloride is1mol/L. After Na+in Bayer red mud had been leached out, the content of Na+in leaching solution could be determined by flame atomic spectrophotography. (3) The soluble Na+in baking-free brick came from Bayer red mud in completely. There are soluble Na+(NaOH&Na2CO3) and citric soluble Na+(Sodalite) in raw material of baking-free brick. So the content of soluble Na+in baking-free brick could be determined by the optimum way of monitoring soluble Na+(4) When the same technological formula of baking-free brick in different curing condition, the strength and the leaching rate of soluble Na+were greater than difference in baking-free brick. When the technological formula is40%of Bayer red mud,20%of silica sand,40%of slag, the strength of baking-free brick is3.52MPa after steam cured, but strength could be up to10.18MPa after cured in high-pressure steam. The leaching rate of Na+in baking-free brick after cured in steam fall from34.49%to29.86%. But the leaching rate of Na+in baking-free brick after cured in steam could fall to21.87%.(5) Through baking-free brick was prepared in different amount of Bayer red mud and binding material, the optimum technological formula had been explored. In this paper, the binding materials were lime, tails of bauxite, fly ash and slag. Lime couldn’t add the strength of baking-free brick up in alone, also couldn’t fall the brick’s leaching rate in alone. In the other binding material, the order of baking-free brick’s strength, from strong to weak, is slag, tails of bauxite, fly ash; the order of baking-free brick’s leaching rate of soluble Na+, from high to low, is fly ash, tails of bauxite, slag.(6) After a comprehensive analysis of multiple factors, the optimum technological formula of baking-free brick is40%of Bayer red mud,20%of silica sand,10%of lime,30%of slag. After high-pressure steam cured, the strength of baking-free brick in the optimum technological formula of baking-free brick could be19.65MPa, the leaching rate of Na+also fall to5.07%. Although the soluble Na+in Bayer red mud still could be leached out, the baking-free brick, which prepared by Bayer red mud in the optimum technological formula, couldn’t take efflorescence. From the brick powder’s XRD and SEM-EDS pattern, the stabilizing product of soluble Na+might be Cancrinite in brick powder.(7) Through the analysis of chemical composition in the liquid film on surface of powder of raw material in the optimum technological formula of baking-free brick, the ratio of silicium-aluminum is1. Use sodium silicate and sodium aluminate to simulation the ratio of silicium-aluminum in the liquid film on surface of powder, through the hydrothermal method to simulate the curing condition of baking-free brick in different alkaline condition. From the pattern of XRD, SEM-EDS and IR, the synthetic product was sure to be Cancrite.(8) In the liquid environment containing H+、Ca2+, K+, NH4+and Li+, Na+in Cancrinite couldn’t be replaced. In the liquid environment of pH<3, Cancrinite would dissolve in the liquid. In the liquid environment of pH>4, Cancrite could be stable in the liquid. The soluble Na+in Bayer red mud could be stabilized in baking-free brick, which prepared by Bayer red mud, slag, lime and silica sand in proper technical formula, by the form of Cancrinite.