The dispersion study was conducted on ultra fines of iron ore collected from two locations, Joda and Noamundi slime ponds in the states of Orissa and Jharkhand (India) respectively using sodium hexametaphosphate as a dispersing agent. The Joda slime has been separated into two parts by using hydro cyclone to identify the effect of particle size on selective dispersion and separation of iron ore slimes. Among the gangue minerals present in the slimes, zeolite is more selective towards separation through dispersion process. Under a particular settling condition, a high grade concentrate containing 67.9 wt.% Fe, 1.2 wt.% Al2O3 and 1.25 wt.% SiO2 with 58% iron recovery is achievable using off grade iron ultra fines containing 57.8 wt.% Fe, 7.55 wt.% Al2O3 and 7.15 wt.% SiO2. The efficiency of selective dispersion process strongly depends on mineral geology and particle size. The iron ore ultra fines collected from the Joda slime pond have better selectivity towards dispersion resulting in better separation of gangue minerals in comparison to iron ore ultra fines collected from Noamundi slime pond. This can be attributed to better liberation of Joda slime and difference in nature of the mineral content in Noamundi slime. (C) 2011 Elsevier B.V. All rights reserved.