Adsorption of Polyoxyethylenic Nonionic and Anionic Surfactants from Aqueous Solution: Effects Induced by the Addition of NaCl and CaCl2

Abstract

The adsorption processes of two different types of surfactant from aqueous solutions have been studied on several solids. The adsorbates used were a nonionic (TX-100) and a series of anionic (NP4S, NP10S, and NP25S) oxyethylenic surfactants. As adsorbent, five nonporous solids, including three quartz (QA, QB, and QC), a kaolin, and a dolomite, were chosen for this study, since these types of materials are frequently found in oil reservoirs. Great differences have been found in the adsorption plateaus, depending on the nature of the surfactant (anionic or nonionic). The influence of the presence of NaCl and CaCl2in the solutions has been also studied. NaCl affects the adsorption of anionic surfactants on quartz and kaolin samples in a similar way. When this salt is added, the amount of anionic surfactants adsorbed on the solid surfaces increases. Some differences in the adsorption of the TX-100 surfactant, depending on the nature of the surface and the type of salt added, have been detected. Basically, three different adsorption behaviors have been found when NaCl is added. The amounts of TX-100 adsorbed decrease when NaCl is added to the solution on the QA sample; the amounts increase on the QB and kaolin samples; no alteration is observed on QC and dolomite samples. Changes in adsorption isotherms, depending on whether NaCl or CaCl2is added, have also been observed. For the same five adsorbents, zeta potential measurements also have been carried out. When the nonionic TX-100 surfactant is adsorbed, a decrease in the negative values of the zeta potential takes place. However, for the adsorption of anionic surfactants, an increase in the negative values of the zeta potential is detected. The surface charge has been also determined by potentiometric titration (in presence and in absence of TX-100), and a decrease in surface charge when TX-100 is adsorbed on the sample surfaces has been detected.