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Mechanochemical reaction involves simultaneous chemical reaction and particle crushing; the latter increases the effective reaction area and improves the reactivity, thus enhancing its kinetics. The classical shrinking core model was used to model the kinetics of bastnaesite mechanochemical decomposition in NaOH solution, which shows a questionable result. Mechanochemical reaction is a dynamic process, where the particle shape and concentration in reaction interface undergo constant change. Thus, a physically consistent model was applied to describe the kinetics. The variations in OH(-) concentration and particle shape were considered in the revision of model. Considering the variation in OH(-) con-centration in solution with time, the model with varying OH(-) concentration agrees better with the experimental data, improving the regression coefficients to between 0.936 and 0.992. By introducing fractal geometry to deal with the irregular system, the model was further optimized, and the regression coefficients increase to between 0.940 and 0.997. All these models considere shrinking particle ap-proaches and controlling mechanisms for the diffusion and chemical reaction. Finally, the fractal model with varying OH(-) concentration was selected to describe the mechanochemical decomposition of bastnaesite, which indicates that the process is controlled by chemical reaction.