| The red mud is polluting waste produced by alumina industry tailings. At present, the red mud mostly stockpiled by open-air damming, which not only takes up a lot of land and consumes many yard construction and maintenance costs, but also brings a range of environmental issues. The red mud contains a large number of components which the cement is necessary, but too high alkali content and excessive radionuclide is a key factor in restricting the comprehensive utilization. Therefore, studying off the alkali of red mud and alkali recovery can not only improve the comprehensive utilization of red mud and reduce environmental hazards, but also using recovered in alumina production can reduce the cost of alumina production, which has a very active role in development of aluminum industry and cement industry.This paper mainly used the sintered red mud as an object of study produced by Zhengzhou branch company of China Great Wall Aluminium. Reference to relevant standards and using XRD, SEM and other testing system resource studied the characteristics of sintered red mud. It shows that the sintered red mud had a certain activity, which was suitable for the building materials industry, especially as a cement raw material, but too high alkali content (R2O4.2%) greatly limited its utilization efficiency.The first, using the SEM-EDS and XRD analysed the existence status of alkaline in red mud. The results revealed that the alkali in the sintered red mud was mainly divided into two parts, that was attached to the base and the chemical combination of alkali, which the former was about35%. We studied the off alkali trial through a variety of off-alkali agent, and found many different off-alkali agent could all obtain a certain de-alkali effect by ion exchange, but CaO was a high cost-effective de-alkali agent.Secondly, we studied the influencing factors and process parameters of alkaline de-lime method. It shows that reducing particle size of red mud, raising reaction temperature, prolonging reaction time, increasing the lime content and the liquid-solid ratio all could improve the de-alkali effect of red mud, especially the influence of reaction time and the lime content were more pronounced. The optimal parameters of the alkali lime method were that temperature was90℃, time was6h, the lime content was12%and the liquid-solid ratio was4/1. The dealkalization mechanism of red mud from sintering process by adding CaO was that two Na+was replaced by Ca2+in the part of sodalite (Na8Al6Si6O24CO3) to produce a more insoluble calcium nepheline (Na6CaAl6Si6(CO3)O24·2H2O).Finally, the test of alkali concentration and alkali recovery showed it is feasible that the lye after off alkali washing red mud repeat made the lye concentrated. After washing five times, the concentration of Na element in the solution reached26mg/ml. At the same time, using n-butanol extracted from saturated solution and made it crystallization, then found that the recovery of sodium bicarbonate was also feasible. With the increase of volume ratio of n-butanol, and saturated sodium bicarbonate solution, the recovery of sodium bicarbonate significantly increased. When solvent ratio was5:1, the recovery of sodium bicarbonate was84.9%. With increasing temperature, the recovery of sodium bicarbonate first increased and then decreased, which reached the maximum(91.2%) at35℃, but in the whole it had a little change.The red mud after the alkali treatment is more suitable for the production of cement, and if the recovery of the alkali was used in the alumina industry, it would undoubtedly reduce the costs and promote the further development of the alumina industry. |
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