Evaluation of Surface Sorption Processes Using Spectral Induced Polarization and a 22Na Tracer

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• 作者：Na Hao ; Stephen M. J. Moysey ; Brian A. Powell ; Dimitrios Ntarlagiannis
• 刊名：Environmental Science & Technology
• 出版年：2015
• 出版时间：August 18, 2015
• 年：2015
• 卷：49
• 期：16
• 页码：9866-9873
• 全文大小：434K
• ISSN：1520-5851

文摘

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 卤 0.07 渭S/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 ²²Na tracer support the interpretation of pH-dependent sorption as a dominant process controlling the electrical properties of the silica gel (R² = 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 脳 10¹⁶ sites/m²) was 2.8 times larger than that estimated directly by a ²²Na mass balance (5.13 脳 10¹⁶ sites/m²), suggesting additional contributions to polarization exist.