The mass transfer coefficient between solid particle and liquid has been measured in high aspect ratio multiimpeller agitated three phase (gas-liquid-solid) reactors. Experiments were conducted in 0.15 and 0.30 m id acrylic columns of Im length each. Two types of impeller were used : disk turbine (DT) and pitched turbine downflow (PTD). Air used as the gas phase was introduced through a ring sparger of 0.8 D size located 0.1T distance above the bottom. The interimpeller spacing was maintained at the tank diameter. The range of gas velocity used was 0-15 mm/s. A unique correlation between particle-liquid mass transfer coefficient and critical impeller speed for solid suspension has been presented.