Precipitate-redissolution phenomenon

It has been reported by Celik and Somasundaran T381 that the interaction of divalent (and trivalent) cations with sulfonate surfactants causes surfactant precipitation followed by dissolution of the precipitate at higher concentrations. The precipitate redissolution phenomenon is not observed with monovalent ions. Indeed, some surfactant precipitation in the spinning drop tube was observed above concentrations corresponding to the first minimum of Figure 8 it is not known whether redissolution took place at higher concentrations resulting in the second tension minimum. 

The interaction of inorganic species, such as those of calcium and aluminum that are normally present in reservoir fluids, with surfactants is found to produce precipitation of the surfactants followed by their redissolution above the critical micelle concentration. A maximum is often observed in the adsorption isotherm of surfactants on reservoir rocks. The contribution of the surfactant precipitation/dissolution phenomenon to the occurrence of adsorption maximum has been investigated in this study using the kaolinite/sulfonate system. The magnitude of the adsorption maximum is found to be minimized when the precipitation/redissolu-tion of the surfactant is taken into account, suggesting the important role of the latter phenomenon in determining the apparent adsorption. 

Since precipitation has often been observed during adsorption studies when surfactants are contacted with certain mineral suspensions, the role of it in determining the nature of isotherms for the important reservoir system made up of kaolinite and dodecylbenzenesulfonate was investigated in this study. Results showed a complex and interesting behavior of the system involving precipitation followed by redissolution at higher sulfonate concentrations that was markedly dependent upon the salt concentration and the type of inorganic ions involved (5). Also, the phenomenon of precipitation and redissolution whenever it occurred proved to have a definite influence on the shape of the isotherm. 

It is clear from these results that surfactants of the sulfonate type can undergo precipitation and redissolution upon interacting with solutions containing dissolved inorganic ions and that such phenomenon can play a major role in producing a maximum in abstraction isotherms. 

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