A passive acoustic emission (AE) monitoring system has been developed and tested in Australian coal washeries. The system detects naturally occurring stress waves in the pulp and froth zones of a flotation unit, utilising volumetric (hydrophone) and surface (broadband accelerometer) sensing technologies. The analyser has been proof-of-concept trialled on a coal washery Jameson cell. AE signals associated with both hydrophones mounted near and accelerometers mounted on a downcomer are shown to be sensitive to cell process conditions including aeration, feed solids and reagent addition rates. Accelerometers mounted on a Jameson cell downcomer are shown to be particularly sensitive to aeration rate with AE signals containing features that can be interpreted in terms of Minnaert bubble resonance theory. The frequencies of peaks in the Fourier power spectra are in this case used to estimate dominant bubble size and solids loading inside the downcomer. Passive AE monitoring is a promising approach for Rotation cell performance on-line monitoring. (C) 2012 Elsevier Ltd. All rights reserved.