title: Spectral induced polarization signatures of hydroxide adsorption and mineral precipitation in porous media.
abstract: The spectral induced polarization (SIP) technique is a promising approach for delineating subsurface physical and chemical property changes in a minimally invasive manner. To facilitate the understanding of position and chemical properties of reaction fronts that involve mineral precipitation in porous media, we investigated spatiotemporal variations in complex conductivity during evolution of urea hydrolysis and calcite precipitation reaction fronts within a silica gel column. The real and imaginary parts of complex conductivity were shown to be sensitive to changes in both solution chemistry and calcium carbonate precipitation. Distinct changes in imaginary conductivity coincided with increased hydroxide ion concentration during urea hydrolysis. In a separate experiment focused on the effect of hydroxide concentration on interfacial polarization of silica gel and well-sorted sand, we found a significant dependence of the polarization response on pH changes of the solution. We propose a conceptual model describing hydroxide ion adsorption behavior in silica gel and its control on interfacial polarizability. Our results demonstrate the utility of SIP for noninvasive monitoring of reaction fronts, and indicate its potential for quantifying geochemical processes that control the polarization responses of porous media at larger spatial scales in the natural environment.
authors.affiliation: Rutgers University-Newark, Newark, New Jersey 07102, United States. chizhang@pegasus.rutgers.edu
authors.forename: Chi
authors.initials: C
authors.lastname: Zhang
authors.forename: Lee
authors.initials: L
authors.lastname: Slater
authors.forename: George
authors.initials: G
authors.lastname: Redden
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Fujita
authors.forename: Timothy
authors.initials: T
authors.lastname: Johnson
authors.forename: Don
authors.initials: D
authors.lastname: Fox
mesh_terms: D000327:Adsorption; D002119:Calcium Carbonate / Q000737:chemistry*; D011232:Chemical Precipitation; D052918:Environmental Restoration and Remediation; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000737:chemistry*; D016062:Porosity; D058428:Silica Gel / Q000737:chemistry; D014508:Urea / Q000737:chemistry; D014510:Urease / Q000737:chemistry
chemical_list: D006878:Hydroxides; D058428:Silica Gel; D014508:Urea; C031356:hydroxide ion; D014510:Urease; D002119:Calcium Carbonate