The flotation of clayey ores is also complicated by the use of saline water. In Australian, all coal sites have introduced water reuse
as a conventional practice due to scarcity of fresh water and stringent policy on the quality of water that can be discharged into local
river systems. One of the consequences of increased water reuse is a
concomitant increase in salinity on sites and subsequently in flotation. A number of studies have been conducted to investigate the
effect of saline water on coal flotation. In general, saline water
increases combustible recovery compared to fresh water and three
mechanisms have been proposed to explain this phenomenon.
Klassen and Mokrousov [11] and Blake and Kitchener [12] proposed
that the lowering of electrokinetic potential of coal surfaces by the
adsorbed ions reduced the stability of the hydration layers facilitating their disruption. The destabilisation of hydration layers
increased the surface hydrophobicity and therefore coal flotation.
Secondly, it was proposed that the electrolytes increased the electrical repulsive forces at bubble surfaces, inhibiting bubble coalescence [13–18]. The reduced bubbles increase bubble–particle
collision efficiency and the overall flotation efficiency. Thirdly, the
compression of the electrical double layer in saline water was
attributed to the opening of hydrophobic surface sites enhancing
the thinning and rupture of the wetting film between the particles
and bubbles which is a critical step in the formation of a stable particle–bubble aggregate leading to an increase in flotation [19]. In
the previous study addressing fine coal flotation using saline water,
we found that saline water reduced the bubble size increasing the
entrainment of clay minerals, and also enhanced the aggregation
of fine coal particles exacerbating the entrapment of clay minerals