Relationship of Structure to Properties of Some Anionic Surfactants as Collectors in the Flotation Process. 1. Effect of Chain Length N. A. Abdel-Khalek* Central Metallurgical Research and Development Institute, P.O. Box 87 Helwan, Cairo, Egypt A. M. A. Omar and Y. Barakat Egyptian Petroleum Research Institute, Cairo, Egypt The surface and thermodynamic properties of some synthetic surfactants, as well as their efficiency as collectors in the flotation of petroleum coke, are studied. These surfactants are monoisomeric alkylben- zenesulfonate of different alkyl chains (C12 to C14). The results show that the length of the hydrocarbon chain of these surfactants plays a major role in determining their surface and thermodynamic properties. The values of surface excess concentration (Γ max ) and Gibbs energy of micellization (ΔG° mic ) are found to increase with increasing number of carbon atoms in the chain while the values of critical micelle concentration (cmc) are decreased. The results indicate, also, that there is a good relationship between effectiveness of adsorption of a surfactant and its efficiency as a collector. A surfactant of higher Γ max produces a concentrate of lower ash content and higher flotation yield. Thus, the surfactant with longer alkyl chain (C14) and highest Γ max value is more selective, as a collector, than others of shorter carbon chain. Introduction The mineral industry requires the use of a wide variety of reagents for its operation. These reagents are commonly used as flotation surfactants, grinding aids, flocculants, and dewatering aids. However, flotation surfactants predomi- nate over any other mineral industry chemicals because the flotation process has become the single most important method for separation of minerals from ores. In flotation practice, mineral selectivity can be achieved through the addition of various reagents that can control the wettability of particular minerals in an ore in the flotation pulp. Flotation reagents are commonly classified into collectors, activators, depressants, frothers, and modi- fiers. Collectors are surface-active organic reagents that adsorb at the surface of the desired mineral so that it becomes hydrophobic and in turn it can attach to an air bubble. Flotation collectors include reagents such as thiol compounds, alkyl carboxylates, alkyl sulfates, alkylsul- fonates, alkyl phosphates, amines, chelating agents, and alkyl phosphonic acids (Fuerstenau and Urbina, 1988). Selection of a collector (surfactant) with the right struc- ture can greatly enhance selective flotation in any number of practical flotation separations (Smith, 1989). The surface- active properties of a collector are therefore determined, among other things, by its numerous structural charac- teristics, which include the following (Smith, 1987): (a) the length and number of hydrocarbon chains in the structure, (b) the configuration of the chain or chains including branching and the number and location of double bonds in the chains, (c) the number, type (anionic or cationic), and cross-sectional area of the polar ionic group in the struc- ture, (d) the position of the ionic group(s) in the structure, (e) the number and nature of nonionic hydrophilic group- (s) in the structure, and (f) the presence, position, and type of cyclic group(s) in the structure (Omar and Abdel-Khalek, 1998; Smith, 1989). As part of a study of the relationships between the chemical structure of well-purified surfactants and their surface and thermodynamic properties, a number of sul- fonate surfactants with different hydrocarbon chains, and a benzene ring attached at carbon atom number four, are synthesized and their properties are investigated. These surfactants are monoisomeric alkylbenzenesulfonates. They have the following alkyl chains: 4-phenyldodecylsulfonate (4φC12), 4-phenyl tridecylsulfonate (4φC13) and 4-phen- yltetradecylsulfonate (4φC14). The properties of these surfactants are correlated with their efficiency as collectors in the flotation of petroleum coke to be suitable for electrode manufacture. Materials and Methods Preparation and Characterization of Surfactants. Three anionic surfactants of sodium salt of monoisomeric alkylbenzenesulfonate were prepared according to recom- mended procedures as follows (El-Mergawy, 1988; Omar, 1994): A tertiary carbinol (φRR′C-OH) of the required chain length was prepared, using alkylphenyl ketone (φRCO) and alkylmagnesium bromide (R′MgBr), where R was C 3 H 7 and R′ varied between C 8 H 17 and C 10 H 21 . The product (tertiary carbinol) was subjected to a hydrogenation process, using Pd/C in glacial acetic acid, to form linear alkylbenzene (φRR′CH). The latter product was subjected to a sulfonation process, using fuming H 2 SO 4 , and a neutralization step, with NaOH, to produce the sodium salt of alkylbenzene- sulfonates. * To whom correspondence should be sent. Current address: Depart- ment of Materials Science and Engineering, Engineering Research Center for Particle Science and Technology, University of Florida, Gainesville, FL 32611. E-mail: nagui@ufl.edu. 133 J. Chem. Eng. Data 1999, 44, 133-137 10.1021/je9801359 CCC: $18.00 © 1999 American Chemical Society Published on Web 12/04/1998