Local and overall mixing characteristics were studied for the gas-liquid-solid reactor operating with an internal draft tube and low-density particles. The experimental reactor had a working volume of 7.6 L, column diameter of 80 mm, draft tube diameter of 50 mm, ratio of the draft to annulus cross-sectional areas of 0.7, and total height of 1.6 m. Experiments were carried out using air, water, and calcium alginate particles (d(p) = 2 mm, pp = 1030 kg/m3). Mixing in the liquid phase was assessed using the tracer-response technique and fast conductivity measurements. The reactor was considered as a system consisting of five interrelated zones : draft and annular regions and three top sections. Our objective was to compare liquid mixing in individual reactor compartments and to estimate their contribution to the overall liquid mixing in the reactor. It was shown that mixing efficiency is due to the circulation of liquid and solid particles around the draft tube and to the backmixing in top sections of the reactor.