The Existing Form Of Alkali In Red Mud And The Research Of Immobilization Methods

Red mud is the waste from the refining of bauxite for the production of alumina and havehigh level of output.It is difficult to effective use of red mud with the high alkali and lowactive. In the present technological conditions，the principal treatment way of red mud need tobe deposited in the open-air place. But it would cause serious problems, like occupation of theland, air pollution. These problems become pressing problems of the day.In accordance with the high alkali of red mud which causes alkali-aggregate reaction andefflorescence. Reference to relevant standards and using XRD, flame photometer and othertest resource studied the existence form of alkali(soluble alkali and insoluble alkali) and theproportion. Meanwhile, the dissolving rate of alkali and the compressive strength of cementslurry as the controlling aims to study the variety laws of soluble alkali and insoluble alkali,the activity of red mud with different activation methods(thermal activation and calcining redmud with calcite). According to the principle of phase coupling, this paper study the newtechnology of fly ash absorb soluble alkali and reduce the content of soluble alkali from redmud with high temperature. Content and fineness of fly ash, curing time were systematicallyresearched in order to research the mechanism of alkali of fly ash. The major conclusions ofpresent paper as follow:(1) The alkali of Bayer red mud can be divide into two parts: one of them is solublealkali which is the attachment of lye from productive process; another is insoluble alkaliwhich from insoluble sodium aluminosilicate hydrate, it is produced from SiO2and sodiumaluminate, in this paper is cancrinite. The content of soluble alkali is54%of all the alkali ofred mud and the insoluble is46%.(2) In the process of thermal activation, the dissolving rate of alkali increases with thetemperature grows and then decreased.700℃is the maximum value, it indicate theintegration degree of sodium aluminosilicate hydrate was low, the rate of dissolution of ion was high and red mud has the highly reactive. With the increase of temperature, aqueousmineral diminished before500℃-600℃due to lose the bound-water, the decomposition ofcancrinite at the same temperature and the content of soluble alkali was increased. At800℃,gehlenite phase and NaCaAlSi2O7are detected, Na2O was compacted in the NaCaAlSi2O7andthe content of soluble alkali was low. At900℃, the active of red mud was decreased becausethe degree of crystallization of gehlenite phase and NaCaAlSi2O7were increased, and thecontent of soluble alkali was reduced. The variety laws into line with3d and7d compressivestrength value of net cement slurry. Compressive strength were increase with temperaturebelow900℃among the age growth and a little decrease at900℃. In the process ofcalcination, the content of alkali decreased with the increase of temperature, the volatile rateis high before800℃, because Na2O absorbed by NaCaAlSi2O7after800℃.(3) Red mud mixture with different percent of lime will react C2S and sodium aluminateat1200℃, thus improve the activity of red mud, the dissolving rate of alkali as much as82.55%. The3d and7d compressive strength value of net cement slurry were agreement withthe dissolving rate of alkali. Hydration degree of C2S increase with the age growth, and so asthe compressive strength of net cement slurry.(4) Fly ash react with red mud will reduce the content of soluble alkali under high curingtemperature. The result shows that, the dissolving rate of alkali was low with the proportionbetween red mud and fly ash1:2.5. With the increasing of curing periods and fineness of flyash, the dissolving rate of alkali was reduced. Through detecting of XRD, Na2O will reactwithAl2O3、SiO2from fly ash forming chabazite-Na which is insoluble.