Thermodynamic properties of layered iron silicates in steel-bentonite interactions

鉄ーベントナイト相互作用における層状鉄ケイ酸塩の熱力学的特性

安楽 総太郎 ; 花町 優次*; Walker, C.*; 三原 守弘  

Anraku, Sohtaro; Hanamachi, Yuji*; Walker, C.*; Mihara, Morihiro

In the present study, fifteen calibration minerals were used to define a polyhedral model that provided estimates for the missing Gibbs free energy of formation () of layered iron silicates. Entropy () and heat capacities () were estimated by additive methods. Enthalpy of formation () could then be calculated. Molar volumes () were calculated from lattice parameters reported in the literature. These methods were carefully used to maintain internal consistency with the JAEA thermodynamic database for geochemical reactions (https://migrationdb.jaea.go.jp). The polyhedral model resulted in a maximum 0.1% error in estimates for the known values of the fifteen calibration minerals. Using the polyhedral model with estimation of and , and calculation of and , a full suite of thermodynamic properties was derived for the layered iron silicates berthierine, cronstedtite, greenalite, minnesotaite, and odinite. These thermodynamic properties were tested in a reactive transport simulation of steel-bentonite interaction. Steel corrosion formed magnetite and siderite, montmorillonite and chalcedony in Kunigel V1textregistered dissolved and sepiolite and greenalite precipitated at the steel-bentonite interface. More detailed studies on the thermodynamic properties of the minerals siderite, sepiolite and greenalite, and their use in reactive transport simulations is ongoing. This work was partly funded by the Ministry of Economy, Trade and Industry (METI) of Japan through the project "The project for validating assessment methodology in geological disposal system" in JFY 2016.