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Implications of Cation Exchange on Clay Release and Colloid‐Facilitated Transport in Porous Media
Author(s) -
Bradford Scott A.,
Kim Hyunjung
Publication year - 2010
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2010.0156
Subject(s) - clay minerals , kaolinite , chemistry , ionic strength , adsorption , illite , colloid , zeta potential , ion exchange , quartz , porosity , porous medium , scanning electron microscope , chemical engineering , mineralogy , ion , aqueous solution , materials science , composite material , organic chemistry , nanoparticle , engineering
Column experiments were conducted to study chemical factors that influence the release of clay (kaolinite and quartz minerals) from saturated Ottawa sand of different sizes (710, 360, and 240 μm). A relatively minor enhancement of clay release occurred when the pH was increased (5.8 to 10) or the ionic strength (IS) was decreased to deionized (DI) water. In contrast, clay release was dramatically enhanced when monovalent Na + was exchanged for multivalent cations (e.g., Ca 2+ and Mg 2+ ) on the clay and sand and then the solution IS was reduced to DI water. This solution chemistry sequence decreased the adhesive force acting on the clay as a result of an increase in the magnitude of the clay and sand zeta potential with cation exchange, and expansion of the double layer thickness with a decrease in IS to DI water. The amount of clay release was directly dependent on the Na + concentration of the exchanging solution and on the initial clay content of the sand (0.026–0.054% of the total mass). These results clearly demonstrated the importance of the order and magnitude of the solution chemistry sequence on clay release. Column results and scanning electron microscope (SEM) images also indicated that the clay was reversibly retained on the sand, despite predictions of irreversible interaction in the primary minimum. One plausible explanation is that adsorbed cations increased the separation distance between the clay–solid interfaces as a result of repulsive hydration forces. A cleaning procedure was subsequently developed to remove clay via cation exchange and IS reduction; SEM images demonstrated the effectiveness of this approach. The transport of Cu 2+ was then shown to be dramatically enhanced by an order of magnitude in peak concentration by adsorption on clays that were released following cation exchange and IS reduction.