Zeta potentials of perlite samples in various electrolyte and surfactant media

Electrokinetic properties of unexpanded and expanded perlite samples in suspensions of various electrolytes and surfactants were studied as a function of ionic strength, pH and, type and concentration of electrolyte and surfactant. Electrokinetic properties of a series of unexpanded and expanded perlite samples have been investigated using the microelectrophoresis technique. From the experimental results, it was found that (i) zeta potential increased with increasing ionic strength for both perlite samples, (ii) zeta potential values of unexpanded and expanded perlite suspensions in CaCl2 solutions in the studied pH range were higher than that in NaCl solutions and, perlite samples had no isoelectrical point, (iii) Ca2+ ions were potential determining ions for both perlite samples and adsorbed specifically in Stern layer, (iv) Na, Cl-, SO42- and PO43- ions compressed the double layer as indifferent electrolytes, (v) the sign of the surface charge of both perlite samples increased with increasing N-cetyl-N,NN-trimethylammoniumbromide (CTAB) and N-cetylpyridiniumchloride (CPC) concentration, and (vi) when zeta potential values of N-cetyl-NNN-trimethylammoniumbromide (CTAB) and N-cetylpyridiniumchloride (CPC) were positive in all studied pH range, those of other surfactants sodiumdodecylsulfate (SDS) and benzyltriethylammonium chloride (BTEAC) were negative. (c) 2005 Elsevier B.V. All rights reserved.