日本地球惑星科学連合2018年大会

講演情報

[EE] Eveningポスター発表

セッション記号 B (地球生命科学) » B-CG 地球生命科学複合領域・一般

[B-CG07] 地球惑星科学 生命圏フロンティアセッション

2018年5月21日(月) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:高野 淑識(海洋研究開発機構)、鈴木 庸平(東京大学大学院理学系研究科)、福士 圭介(金沢大学環日本海域環境研究センター、共同)、加藤 真悟(国立研究開発法人理化学研究所)

[BCG07-P03] A comprehensive predictive model for sulfate adsorption on oxide minerals

*北台 紀夫1 (1.東京工業大学 地球生命研究所)

キーワード:固体-水界面、水環境地球化学、表面錯体モデリング

This presentation provides a set of equations that enables the prediction of sulfate adsorption behavior on all oxide minerals over a wide range of pH, ionic strength, sulfate concentration, and solid/water ratio based on the extended triple-layer model (ETLM). Although surface complexation models including the ETLM have been frequently applied to describe sulfate-surface interactions on oxides, the proposed adsorption stoichiometries and equilibrium constants have been mutually inconsistent even in a specific sulfate–oxide system. Here, I show that the outer-layer capacitance (C2), a TLM parameter that has been traditionally set to 20 uF cm-2, has a significant impact on the model prediction of sulfate adsorption. With the capacitance value being the same as the inner-layer one (i.e., C2 = C1), which is a theoretically and spectroscopically reasonable assumption, our ETML calculation adequately represents all adsorption, surface titration, and proton co-adsorption data for various sulfate-oxide systems reported in the literature (oxides; goethite, ferrihydrite, r-alumina, gibbsite, and hematite) and those obtained in the present study (oxide; anatase). The combination of a monodentate-mononuclear inner-sphere and a bidentate-binuclear outer-sphere surface complex was found to explain all experimental data. Analysis of the retrieved equilibrium constants for the two surface species with the Born solvation theory led to the development of predictive equations for sulfate adsorption constants on all oxides. Considering the abundant and ubiquitous distribution of sulfate in natural environments, the proposed model should significantly contribute to a better understanding of the geochemical processes occurring at the mineral-water interface.