In this study the fundamental science underpinning the interaction of saline water and clay minerals was studied under flotation contexts to address important problems confronting the coal industry. For the first time, the beneficial effect of clay minerals in some flotation scenarios was revealed after testing a typical coal sample having a low content of clay minerals and its mixture with another coal sample having a high content of clay minerals in de-ionised water and saline water with medium conductivity. Equipped with a range of techniques including froth stability measurements, modelling true flotation, settling tests and Cryo-SEM analyses, it was found that froth stability was higher in the flotation with a higher concentration of clay minerals in both de-ionised water and saline water, corresponding to increased combustible matter recovery and ash recovery. A synergistic interaction was evident between saline water and clay minerals in stabilising the froth and recovering combustible matter by true flotation. This is because saline water promoted the formation of association of clay platelets that sustained in the dynamic flotation condition, entered the flotation concentrate and altered the froth property and coarse coal flotation behaviour. (C) 2014 Elsevier Ltd. All rights reserved.