The Raglan concentrator (Xstrata Nickel) does not employ frother. It was considered this might be the result of the high salt content in the process water (ca. 30000 ppm). Two-phase (solution-air) and three-phase (slurry-air) tests were undertaken in a laboratory column to quantify the effect of inorganic ions present in the water (a range of polyvalent ions). The measurements focused on gas dispersion (bubble size and gas holdup) and froth overflow rate. The results were compared to a typical frother (MIBC) system. The two-phase tests revealed reduced bubble size, increased gas holdup and limited froth formation in salt solutions. The gas holdup correlated with ionic streneth. At an ionic strength ca. 0.4 (-0.4 M NaCl) the increase in gas holdup was comparable to ca.10 ppin MIBC. In three-phase tests on a sulphide ore, bubble size and froth overflow rate were again comparable between 0.4 M NaCl and 10 ppm MIBC. The observations help explain why the Raglan plant can operate without frother addition. (c) 2007 Elsevier Ltd. All rights reserved.