APPLICATIONS AND DEVELOPMENT OF A MULTI-GEOCHEMICAL REACTION EQUILIBRIUM MODEL (MUGREM)

Keum, D. K.; Hahn, P. S.

Environmental Engineering Research 1999;4(2): 113-126.

D. K. Keum^†, and P. S. Hahn

Korea Atomic Energy Research Institute, 150 Dukjindong, Yusunggu, Daejeon 305-353, Korea

Corresponding Author: D. K. Keum ,

Received: May 13, 1999; Accepted: June 5, 1999.

ABSTRACT

A multi-geochemical reaction model (MUGREM) was developed to analyze complex chemical equilibria among aqueous species, and between dissolved and adsorbed species. The reactions with which MUGREM can deal are aqueous complexation reactions, precipitation-dissolution reactions, ion-exchange reactions, and adsorption reactions by the surface complexation model that comprises the diffuse-layer model, the constant capacitance model, and the triple-layer model. MUGREM uses a Newton-Raphson iteration scheme to solve the set of mass-action and mass-balance expressions, and the Davies equation to calculate activity coefficients for aqueous ions. The predictive capabilities of MUGREM were examined through the calculation of equilibrium concentration for three reaction systems, the aqueous complexation reaction of uranyl with humic acid, the adsorption reaction of U(VI) onto single and composite minerals, and the precipitation-dissolution reaction of Am, Pu, and Np in a groundwater sample. In order to verify MUGREM, comparative calculations were performed between MUGREM and other codes. In addition, the validity of the reaction mechanisms postulated in the application systems was studied through the comparison between models and experimental data. MUGREM and other codes gave virtually identical calculation results when using the same thermodynamic data Agreement between the models and experimental data was also satisfactory.

Keywords: chemical equilibrium | aqueous complexation reaction | precipitation reaction | ion-exchange reaction | adsorption reaction