Research On The Dealkalization Characteristics Of Bayer Red Mud By Carbonation And Mechanism Thereof

Red mud is the waste residue produced in the production process of alumina smelting industry.Its production volume continues to grow with the development of China's alumina industry.The issue of red mud disposal and resource utilization has attracted people's attention.At present,the final disposal method of industrial waste slag and red mud in the world is mainly storage.Storage not only occupies land resources,but also poses a serious threat to the ecological environment.In order to improve the comprehensive utilization rate of red mud,a lot of research has been carried out at home and abroad.However,the high alkalinity of red mud has always been the main limiting factor for its resource utilization.It is difficult to meet the quality standards by directly applying high alkali red mud to products.Therefore,the research and development of de-alkali technology is the key to the research of red mud solid waste resource research.This research took the alumina industry waste residue–Bayer red mud,one of Guangxi's hundreds of billions of industries,as the research target.It used carbonation,calcification and calcification-carbonation methods to study the dealkalization performance on Bayer red mud.The effects of reaction pressure,reaction time,reaction temperature and liquid-solid ratio on the performance of red mud dealkalization were studied.The X-ray diffraction(XRD),Fourier infrared spectrum(FTIR),automatic specific surface area analyzer(BET),and field emission scanning electron microscopy(FESEM)etc.were used to characterized and analyzed the structure and morphology of Bayer red mud before and after dealkalization.Its morphological changes of alkaline substances and their reaction mechanism were discussed.Furthermore,the thermodynamics of red mud dealkalization were discussed.The results showed that carbonation could reduce the pH value and alkalinity of red mud.The alkali dissolution rate was 6.99%,and the CO₂ sequestration capacity was 13.64 g/kg.The structure of cancrinite in red mud was stable and direct carbonation was difficult to remove.When temperature rose,the gibbs free energy(?G) of sodium aluminosilicate hydrate carbonation decreased,which was favorable for the reaction,but the ?G of katoite carbonation increased,which was unfavorable for the reaction.On the other hand,the reaction pressure has little effect on carbonation.The results showed that the alkalinity of red mud could be reduced by calcification.After calcification,the Na₂O content in red mud was 0.88%.The cancrinite was converted to katoite to remove the bound alkali in red mud.As temperature increased,the ?G in calcification increased,indicating that high temperature was unfavorable to the calcification.The results showed that the alkalinity of red mud could be further reduced by carbonation after calcification.The Na₂O content in red mud after calcification-carbonation was 0.54%.The katoite in calcified red mud reacted with CO₂ to form products such as calcite.During calcification-carbonation,the ?G increased with temperature increased,which was unfavorable to the reaction.The ?G decreased with partial pressure of CO₂ increased,which was favorable to the reaction.In this paper,the above methods were used to systematically study the dealkalization performance on Bayer red mud.The results showed that using CO₂ could effectively promote the conversion of alkaline substances in red mud.The mechanism of Bayer red mud carbonation dealkalization was proposed from the perspective of alkaline substance form change and thermodynamics.It provides reference for carbon emission reduction and comprehensive utilization of highly alkaline red mud.