Selective fine particle separation is a key unit operation in the mineral and related industries. In flotation, the capture of fine particles by bubbles is inefficient due to their low mass and momentum, which result in low particle-bubble collision efficiency. We demonstrate that it is possible to selectively separate a mixture of very fine hydrophobic graphite and hydrophilic quartz particles by direct contact with an air-water interface without a particle-bubble collision step involved, We demonstrate that it is possible to scale-up the process from a simple batch to a continuous process. Good selective separation of graphite from quartz gangue could be obtained under continuous conditions. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.