This paper presents a numerical study of the gas liquid flow inside a novel Venturi carbonation reactor for red mud processing. The model is based on the Eulerian-Eulerian model, with population balance method being used to describe bubble size distribution. The validity of the model is confirmed through different applications. It is then used to analyze the flow and gas dispersion inside the reactor at different liquid flow rates. The numerical results reveal that the new reactor can produce periodic variations of fluid pressure and gas holdup with time. Correspondingly, the ascending liquid flow presents a vortex column, swinging periodically in the radial direction. This flow oscillation becomes more obvious at an increased liquid flow rate, promoting bubble refining and uniform distribution. The results of this study should be useful not only for better understanding the gas liquid flow but also for designing and controlling this new reactor.