Research On Illite Transformation Under Calcification-Carbonation Process

The rapid development of China's aluminum industry has accelerated the depletion of aluminum resources.Problems such as low recovery ratio of alumina and large discharges of high-alkaline red mud have been encountered in the process of using the Bayer process to treat low-grade bauxite.Therefore,our group proposed a method for low-grade bauxite by the"calcification-carbonization" method,which can change the main equilibrium solid phase structre of alumina production process and realized the efficient and clean utilization of low-grade bauxite.However,the treatment of the same type of bauxite in different regions shows great differences which caused by the composition of the silicon-containing phase in the bauxite.Therefore,the behavior of the silicon-containing phase in the transformation process needs to be studied.In this paper,illite is selected as the main research object,revealing its transformation mechanism,and make a comparative analysis of the behavior of the main silicon-containing phase in the calcification-carbonization process.Investigate the interaction mechanism and equilibrium phase structure of different silicon-containing phases in the reaction.Establish a mathematical model of silicon-containing phase in calcification-carbonization reaction,and the feasibility of the model was verified by using typical bauxite.The specific content and results are as follows:(1)Using the method of estimate the Gibbs free energy of complicate silicates obtained the standard Gibbs free energy of illite and hydrogarnet.The thermodynamic calculation indicated that the reaction of generating hydrogamet with diffenent silicon saturation coefficient can occur.And hydrogamets with higher silicon saturation coefficients are preferentially formed at the same temperature.When the reaction temperature is 120? and the CO2 pressure is 1.2 MPa,the hydrogarnet carbonation decomposition reaction with a lower silicon saturation coefficient is easier to proceed.(2)The calcification process is controlled by chemical reaction,and the activation energy of the reaction is 42.26 kJ/mol.The dissolution reaction of illite mainly occurs in the initial stage of reaction,and the temperatures has a great influence on the dissolution.The characterization of the reaction product showed that as the temperatures increased,the saturation coefficient of hydrogarnet was higher.After completely reaction,the hydrogarnet is uniformly distributed in a spherical shape,and not covered on the unreacted illite surface.(3)Research on calcification-carbonization process of silicon-containing phase shows that kaolinite will form sodalite when calcification is incomplete,so that the content of alkali in tailings will increase.However,when the calcification of illite is incomplete,no sodalite will be formed,and illite remains in the form of ore in the slag.The calcification is more affected by the illite content.In addition,there is no interaction occurred when the two silicon-containing phases coexisted.According to the recovery ratio of alumina,using the reaction temperatures,the mother liquor concentration and the recovery ratio of alumina fitted with the kaolinite content to obtain a mathematical model in calcification-carbonization process.(4)Using the typical bauxite in different regions to verify the feasibility of the model.When the silicon-containing phase in bauxite contains a large amount of clinochlore,the degree of dissolution of clinochlore directly affects the degree of calcification reaction,and then affects the subsequent processes.When the main silicon-containing phases in bauxite are kaolinite and illite,the actual results are consistent with the results of the mathematical model,whether it is studied on silicon-containing phase or bauxite.