Recent hydrodynamic studies suggest that small air bubbles can be used to improve the performance of column flotation. Tests carried out at Virginia Tech during the past several years have shown that various types of inline motionless (or static) mixers can successfully produce microbubbles for column flotation. Unfortunately, few guidelines exist for selecting the proper size and type of motionless mixer for generating microbubbles. In the present work, the mean bubble size produced by various types of in-line motionless mixers has been experimentally determined over a wide range of operating conditions and generator geometries. Test results indicate that generator performance is described by a series of expressions derived from a dimensional analysis. These expressions demonstrate that bubble diameter is primarily determined by the generator geometry and a dimensionless term known as the Weber number. Tests have also been conducted to determine the reduction in the performance of centrifugal pumps under air admitting conditions. A semi-empirical pump model has been utilized which allows the proper size of pump to be selected for microbubble generation. This information should prove useful for the design and operation of microbubble generation circuits on an industrial scale. / Master of Science