title: Evaluation of Surface Sorption Processes Using Spectral Induced Polarization and a (22)Na Tracer.
abstract: We investigate mechanisms controlling the complex electrical conductivity of a porous media using noninvasive spectral induced polarization (SIP) measurements of a silica gel during a pH dependent surface adsorption experiment. Sorption of sodium on silica gel surfaces was monitored as the pH of a column was equilibrated at 5.0 and then successively raised to 6.5 and 8.0, but the composition of the 0.01 M NaCl solution was otherwise unchanged. SIP measurements show an increase in the imaginary conductivity of the sample (17.82 ± 0.07 μS/cm) in response to the pH change, interpreted as deprotonation of silanol groups on the silica gel surface followed by sorption of sodium cations. Independent measurements of Na(+) accumulation on grain surfaces performed using a radioactive (22)Na tracer support the interpretation of pH-dependent sorption as a dominant process controlling the electrical properties of the silica gel (R(2) = 0.99) and confirms the importance of grain polarization (versus membrane polarization) in influencing SIP measurements of silicate minerals. The number of surface sorption sites estimated by fitting a mechanistic, triple-layer model for the complex conductivity to the SIP data (13.22 × 10(16) sites/m(2)) was 2.8 times larger than that estimated directly by a (22)Na mass balance (5.13 × 10(16) sites/m(2)), suggesting additional contributions to polarization exist.
authors.affiliation: †Environmental Engineering and Earth Sciences, Clemson University, Clemson, South Carolina 29634, United States.
authors.forename: Na
authors.initials: N
authors.lastname: Hao
authors.affiliation: †Environmental Engineering and Earth Sciences, Clemson University, Clemson, South Carolina 29634, United States.
authors.forename: Stephen M J
authors.initials: SM
authors.lastname: Moysey
authors.affiliation: †Environmental Engineering and Earth Sciences, Clemson University, Clemson, South Carolina 29634, United States.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Powell
authors.affiliation: ‡Earth and Environmental Sciences, Rutgers University, Newark, New Jersey 07102, United States.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Ntarlagiannis
mesh_terms: D000327:Adsorption; D003198:Computer Simulation; D004553:Electric Conductivity; D055664:Electrochemical Techniques; D004566:Electrodes; D006863:Hydrogen-Ion Concentration; D058428:Silica Gel / Q000737:chemistry; D012964:Sodium / Q000737:chemistry*; D013057:Spectrum Analysis; D014865:Waste Disposal, Fluid
chemical_list: D058428:Silica Gel; D012964:Sodium