Kinetic study of the reduction reaction of red mud and CO under fluidization condition

Pyrometallurgical method of iron recovery from red mud (RM) has advantages of simple procedures, high recovery efficiency and significant waste minimization. The fluidization reduction process using CO as reductant addresses the issues of high energy consumption and long reaction time of pyrometallurgical method. In order to optimize the operational conditions of the fluidization reduction process, it is necessary to study the reaction characteristics of RM and CO under fluidization condition. In response to the problems of the current kinetic study including the unsatisfied fluidization condition and possible errors introduced by the estimation method, we carried out improvements in both experiment and data processing. In the experiment aspect, thermo-gravimetric analyzer (TGA) test rig with large sample capacity and gas flow was established, and approximate fluidization condition was achieved by intensifying diffusion by increasing the gas flow rate and decreasing the sample mass. In the data processing aspect, we developed a program with data cleaning and kinetic function fitting capabilities, and the goodness of fit was evaluated by Akaike information criterion (AIC). The results indicated that within the temperature range of 500–600°C and CO concentrations of 5%–15%, the reaction between RM and CO can be divided into two steps based on the criterion of complete formation of Fe₃O₄. The first step reaction has a relatively fast reaction rate, conforming to the F1 kinetic function with rate equation given as $k=3.46\exp (-4.48\times 10^3/T)c_{CO}$. The second step reaction displays a more complex pattern and the fitted rate equation is $k=5.57\times 10^{-2}\exp (-4.16\times 10^3/T)c_{CO}^{1.5}$. The obtained results could provide a reliable reference for the operational design of the fluidization reduction of RM.