Flotation of coal particles in MgCl2, NaCl, and NaClO3 solutions in the absence and presence of Dowfroth 250

Separation of naturally hydrophobic particles, such as coal, by flotation is known to be enhanced with the addition of salt solutions into the system. However, the exact reasons for this enhancement are not clear yet. In this study, flotation of coal particles in MgCl2, NaCl, and NaClO3 solutions in the absence and in the presence of a strong frother, i.e., Dowfroth 250, was investigated to clarify the flotation enhancement mechanism and to correlate the flotation recovery with froth stability and bubble size distribution at the froth phase. The results of the flotation experiments showed that the presence of electrolytes in the system clearly enhanced the flotation recovery depending on its type and concentration. During the experiments, MgCl2 and NaClO3 solutions showed the highest and the lowest flotation performance improvements, respectively. The froth stability tests indicated that there is a correlation between the flotation recovery and the stability profile of the froth. The most stable froth was obtained with MgCl2 and the lowest froth stability was obtained with NaClO3. Additionally, a direct correlation was found between the flotation recovery and the bubble size distribution of the froth phase. The bubble size measurements revealed that increasing the electrolyte concentration decreased the bubble size, which, in turn, increased the flotation recovery. It is concluded that, the addition of salt solutions to a flotation system produces finer bubble size distribution at the froth phase, which enhances the coal flotation kinetics, depending on the type and the concentration of the electrolyte.

Research Highlights
► Salt transition concentration (STC) for bubble coalescence influences coal flotation.
► Coal flotation changed considerably by adding NaCl and MgCl2 with concentration below STC.
► NaClO3 did not change coal flotation as significantly as frother since there is no STC for NaClO3.
► Influence of frother on coal flotation in the salt solutions was also affected by STC.
► Beyond STC, changes in coal flotation by frother and salts were not significant.