FLOTATION OF INHERENTLY HYDROPHOBIC PARTICLES IN AQUEOUS-SOLUTIONS OFINORGANIC ELECTROLYTES

The flotation of graphite particles in aqueous solutions of inorganic electrolytes was shown to depend on both the nature of the cation/anio n pair and the range of the bubble/particle electrostatic interaction. For several electrolytes, as the reduction in the Debye length of the solution approached the decay length of the hydrophobic attraction, t hen flotation began to occur. Also using earlier reported data, it was possible to relate the flotation to surface tension/electrolyte conce ntration gradients and bubble coalescence behavior of the different el ectrolyte solutions. Higher flotation recoveries were attributed to an increased collision probability between the graphite particles, a hig her concentration of small noncoalescing bubbles, and an increased sta bility of the froth. Furthermore, it has also been shown from previous studies that increasing electrolyte concentration causes a decrease i n gas solubility. In fact, gas solubility has been shown to be depende nt on the hydration entropy of the cation. This phenomenon was explain ed in terms of competitive utilization of water molecules in the hydra tion of cations and a consequent loss or gain in gas solubility. Overa ll, it was shown that a reduction in the electrostatic interactions be tween particle and bubble assisted flotation. However, in addition, an increase in flotation performance resulted from the inhibition of coa lescence of bubbles, which is also linked with dissolved gas concentra tion gradients (structural differences at the air/solution interfacial region relative to the the bulk electrolyte solution).