Simulating uranium sorption onto inorganic particles: The effect of redox potential

Abstract

An analytical expression is proposed to simulate the effects of pH and redox potential (E) on the sorption of uranium onto model inorganic particles in aquatic environments instead of following an experimental approach providing a list of empirical sorption data. The expression provides a distribution coefficient (Kd) as function of pH, E and ligand concentration (complex formation) applying a surface complexation model on one type of surface sites (>SuOH). The formulation makes use of the complexation and hydrolysis constants for all species in solution and those sorbed at the surface, using correlations between hydrolysis constants and surface complexation constants, for the specific sorption sites. The model was applied for the sorption of uranium onto aluminol, iron hydroxide and silanol sites, mimicking respectively 'clean' clay or 'dirty' clay and 'clean' sand or 'dirty' sand ('dirty' referring to iron hydroxide contaminated), in absence or presence of carbonates in solution. The calculated distribution coefficients are very sensitive with the presence or absence of carbonates. The Kd values obtained by applying the model are compared with values reported in the literature for the sorption of uranium onto specific adsorbents. It is known that in surface water, U(VI) and its hydroxides are the primary stable species usually observed. However, reduction to U(IV) is possible and may be simulated during sorption or when the redox potential (E) decreases.Similar simulations are also applicable to study the sorption of other redox sensitive elements.

Modelling the reaction of uranium with carboxylic groups on surfaces through mono- and multi- dentate surface complexes on the basis of pH and redox potential

“…The uranium Kd vs E diagrams for fixed pH were replotted as proposed in Degueldre & McGowan [38] in the case of carbonate free solution followed by carbonated solutions. In all cases and to mimic the tests performed in McGowan et al [16], the particle concentration is 30 g L −1 and the site density is 2.18 × 10 −8 mol g −1 after correction in Eq.…”

“…In previous implementations of this model, such as Degueldre & McGowan [38], the surface site density was taken directly from empirical (experimental) results. Calculations based on fixed physical characteristics allowed this value to be intrinsically justified.…”

Application of mineral and organic modifications of peat near the sludge storage facility for uranium immobilization

“…Uranium (VI) is a common source of pollution around the world due to both natural (weathering of uranium-containing rock) and technogenic (accumulation at uranium mining, recovery or enrichment sites) factors [1,2]. The mobility of uranium (VI) in the environment is largely controlled by the reduction and precipitation as a U-containing solid phase, sorption on inorganic particles and on biomass, including humic acids (HA) and/or transfer by colloids or natural organic substances -mostly often fulvic acids (FA) [3][4][5][6][7][8][9]. It is important to understand these mechanisms for predicting the deposition or release of U (VI) in contaminated water and sediments and to develop the appropriate technologies for its bonding or removal.…”