A tool to draw chemical equilibrium diagrams using SIT: Applications to geochemical systems and radionuclide solubility

Abstract

A set of computer programs has been developed to draw chemical-equilibrium diagrams. This new software is the Java-language equivalent to the Medusa/Hydra software (developed some time ago in Visual basic at the Royal Institute of Technology, Stockholm, Sweden). The main program, now named “Spana” calls Java programs based on the HaltaFall algorithm. The equilibrium constants that are needed for the calculations may be retrieved from a database included in the software package (“Database” program). This new software is intended for undergraduate students as well as researchers and professionals.The “Spana” code can be easily applied to perform radionuclide speciation and solubility calculations of minerals, including solubility calculations relevant for the performance assessment of a nuclear waste repository. In order to handle ionic strength corrections in such calculations several approaches can be applied. The “Spana” code is able to perform calculations based on three models: the Davies equation; an approximation to the model by Helgeson et al. (HKF); and the Specific Ion-Interaction Theory (SIT). Default SIT-coefficients may be used, which widens the applicability of SIT significantly.A comparison is made here among the different ionic strength approaches used by “Spana” (Davies, HKF, SIT) when modelling the chemistry of radionuclides and minerals of interest under the conditions of a geological repository for nuclear waste. For this purpose, amorphous hydrous Thorium(IV) oxide (ThO2(am)), Gypsum (CaSO4·2H2O) and Portlandite (Ca(OH)2) solubility at high ionic strengths have been modelled and compared to experimental data from the literature. Results show a good fitting between the calculated values and the experimental data especially for the SIT approach in a wide range of ionic strengths (0-4 M).

Application of the de Job method in the evaluation of the stoichiometry of uranyl phosphate complexes sorbed on bentonite

“…The formation of (UO2)3(OH)5 + and (UO2)4(OH)7 + is welldocumented [16]. They can locate on silanols Si-OH or aluminols Al-OH.…”

Recovery of MnO2 from a spent alkaline battery leach solution via ozone treatment

“…On one hand, it is important to determine the equilibrium conditions, in order to prevent the generation of undesirable species, such as permanganate. For this purpose, the MEDUSA (Making Equilibrium Diagrams Using Sophisticated Algorithms) [21] software was employed, considering the initial solution composition (6000 ppm Mn(II) in 1 M H 2 SO 4 ; equivalent to 109 mM Mn(II) and 1.11 M SO 4 2À ). In Fig.…”

Design of a Hollow Fiber Supported Liquid Membrane System for Zn Speciation in Natural Waters

“…The fractions of the different chemical species in the experimental aqueous media were calculated using the MEDUSA (Make Equilibrium Diagrams Using Sophisticated Algorithms) software [26] using the constants of the Hydra database that are included in the software. In order to compare the results of these calculations, Visual MINTEQ ver.…”

“…The concentration of each ligand added to the donor solution was set considering both having the same initial Zn(II) in the aqueous media (~2 mg L −1 ), as in experiments performed without the presence of ligands, and having a measurable part of the Zn(II) not complexed by the ligands. Given this, Medusa software [26] was used to calculate the ligand concentrations to be added to the donor solution. Resulting donor solutions consisted of 500 mL of 1.5 mg L −1 citric acid and 2 mg L −1 of Zn(II) in a 0.1 M NaNO 3 aqueous media (pH 5.5) for the citric ligand, and 500 mL of a 5 mg L −1 of EDTA and 2 mg L −1 of Zn(II) solution at pH 5.8 in 0.1 M NaNO 3 aqueous media in the case of EDTA.…”