Fluid dynamic and mass transfer characteristics of a three-phase airlift reactor were studied in a rectangular split-vessel reactor. The gas-liquid-solid system consisted of air, seawater and marine sediment, respectively. Experiments were conducted over a range of downcomer to riser cross-sectional area ratios (A(D)/A(R) = 1.0-0.65) and for five sediment concentrations (5-25% w/v). Simple models were used to simulate the fluid dynamic and mass transfer behavior for all experimental conditions examined. The fluid dynamic model was based on an energy balance which takes into account the energy dissipated at the phases interfaces. The mass transfer model was based on a two-phase fluid dynamic model, the Higbie's penetration theory and Kolmogoroff's theory of isotropic turbulence. Experimental data of gas holdup, liquid velocity and volumetric mass transfer coefficient were simulated with satisfactory accuracy (differences less than 20% for most cases) when assumptions regarding to gas recirculation on the overall gas holdup and the volumetric mass transfer coefficient were made.