Drying of Salt Solutions from Porous Media: Effect of Surfactants

The evaporation of salt (NaCl) solutions from porous media is studied in the presence of surfactants, because surfactants are often used as cleaning agents for salt-contaminated stones. We show that, contrary to what is commonly assumed, the presence of the surfactant and the changed wetting propert...

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Bibliographic Details
Published inTransport in porous media Vol. 128; no. 3; pp. 881 - 894
Main Authors Qazi, Mohsin J., Bonn, Daniel, Shahidzadeh, Noushine
Format Journal Article
LanguageEnglish
Published Dordrecht Springer Netherlands 01.07.2019
Springer Nature B.V
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Summary:The evaporation of salt (NaCl) solutions from porous media is studied in the presence of surfactants, because surfactants are often used as cleaning agents for salt-contaminated stones. We show that, contrary to what is commonly assumed, the presence of the surfactant and the changed wetting properties do not affect the drying kinetics: The impact of the surfactants is rather that of a crystallization modifier for the salt. Upon adding a cationic or nonionic surfactant to salt solution, the drying rate is unchanged initially, but can slow down dramatically at later times due to the formation of a salt crust at the surface. When this happens, the total drying time increases compared to pure NaCl solutions without surfactants, at least for very porous stones for which the pores become completely blocked. Surprisingly, for a low-porosity stone the small pores at the surface remain open. The longer drying time for the large porosity stone increases the risk of, e.g., frost or fungal damage to the stones. Consequently, the use of surfactants in conservation treatments should be done with caution.
ISSN:0169-3913
1573-1634
DOI:10.1007/s11242-018-1164-5