MAINHOOD d WHELAN-FLOTATION FROTHERS 133 tripolyphosphate anion is sufficient for complex-formation with each of the relevant cations. In contrast, with pyr'ophosphate two anions are required for complex-formation (although complexes with one pyro-anion can be obtained). The ionic size seems to have no noticeable influence on the composition of the complex obtained, so we must conclude that space con- siderations are not decisive. Rather, electronic considerations through the presence of complete d-shells or the absence of d-orbitals must be responsible for this behaviour. Department of Inorganic & Analytical Chemistry The Hebrew University Jerusalem Received 26 July, 1954 IEererence 1 Bobtelsky, M., & Kertes, S., J. appl. Clem., 1954, 4,419 FLOTATION FROTHERS FOR LOW-RANK COALS By J. MAINHOOD and P. F. WHELAN A number of aliphatic alcohols and acids, phenols and other heteropolar compounds were studied a8 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 charaqter 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 (K,) greater than 2 x but no correlation between K, 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. Introduction In an earlier paper1 an account is given of the investigation of a number of monohydric phenols as froth-flotation reagents for the cleaning of fine coals of medium rank. This investi- gation is now continued to include a wide range of amphipathic molecules and the reagents have been applied to the cleaning of fine coals of low rank and high volatile content. Coals of high and intermediate ranks are usually strongly hydrophobic, whereas the accom- panying dirt is hydrophilic. The cleaning of these fine coals is therefore relatively simple since coal and dirt particles are naturally sharply differentiated in surface properties. The raw fine coal suspension in water is agitated in a cell with a small quantity of a frother reagent, a swarm of .air bubbles is made to pass through it and the coal particles collect at the air-water interfaces of the bubbles and are canied to the surface to appear as a coal-bearing froth which is removed. The did remaining in the pulp escapes at a lower level. Hence the only reagent required for the froth flotation of higher-rank coals is a frother. In extreme cases the fine coal stabilizes froth formation and no reagent may be required, or a non-frothing oil only may be necessary for the coal to stabilize its own froth. Normally a frother, a cresylic acid or pine oil, is used with or without a froth stiffener. Hence arise reagents of the creosote/cresylic acid type. In plant practice inexpensive tar oils are often used and their efficiency has been related to their phenol content,a that is, their content of amphipathic material likely to behave as a frother, . Low-rank coals cannot be made amenable to cleaning by froth flotation unless the surface is conditioned with a reagent which gives the coal the required degree of hydrophobicity, Recent work with non-metallic minerals indicates that less than 10% of the total mineral surface, 'as J. appl. Chem., 5, March, 1955
