PRECIPITATION OF BACO3 IN A SEMIBATCH REACTOR WITH DOUBLE-TUBE GAS INJECTION NOZZLE

BaCO3 crystals were produced in a semi-batch reactor by adding CO2 gas continuously to the agitated BaS aqueous solution through a double-tube gas injection nozzle. Larger crystals were obtained in comparison with the case where the gas directly dispersed in the whole reactor as usually done. The gas bubbles, around which the higher supersaturation regions are thought to be localized, were made to contact only with the solution inside the outer tube of the nozzle. The gas was absorbed there and the adsorbed gas was transferred into the agitated bulk solution through the lower opening of the nozzle and then it reacted with Ba2+ ion in the bulk solution. The larger crystals were thought to be obtained because of lower nucleation rate caused by the limited bubbling region. In addition, the lower pH of the solution in the nozzle was thought to help in lowering the nucleation rate, since CO2 gas was dissolved as HCO-3 ion rather than as CO2-3 ion at such lower pH values. © 1990.