Flotation frothers for low‐rank coals

Abstract

AbstractA number of aliphatic alcohols and acids, phenols and other heteropolar compounds were studied as flotation frothers for a tetralin‐conditioned low‐rank coal.The effects of these reagents, in the absence of coal, on the static surface tension of water and on froth formation and the character of bubble streams in aqueous solutions were investigated and correlations made with flotation merit. Although some of the most efficient flotation frothers reduced the surface tension of water markedly, the amount of lowering of surface tension appeared to be unimportant. The effects of the reagents on bubble streams and on the formation and stability of froths in a frothmeter tube showed some correlation with flotation merit.The balance between polar and non‐polar groups in the molecule is the most important factor in determining flotation merit for low‐rank coal. For monohydric alcohols and monocarboxylic acids to be good frothers, the molecule must contain between 5 and 10 carbon atoms, the optimum being probably 8. Little variation between isomeric alcohols was observed. No phenol with good frothing properties had a dissociation constant (Ka) greater than 2 × 10−8, but no correlation between Ka and frothing power was found. Molecules of small residual polarity were often good frothers, but the presence of more than one strongly polar group in the molecule reduced the efficiency.