Effects of the presence of Fe(0) on the sorption of lanthanum and lutetium mixtures in smectites

Abstract

11The sorption of La and Lu mixtures was examined in two bentonites after incubation 12 for three months at 20 and 80 o C with Fe(0), as a laboratory approach to evaluate the effects of 13 waste canister corrosion in a deep repository on the performance of clay engineered barriers. 14 The sorption/desorption parameters were determined from batch tests in two ionic media: 15 deionized water and, to consider the additional effect of cement leachates, 0.02 mol L −1 Ca. 16Results from XRD analyses showed the formation of crystalline FeO(OH), goethite, in 17 a few samples and the degradation of the bentonites due to Fe(0) oxidation during incubation. 18Moreover, the EDX spectra showed that the lanthanides were sorbed primarily at smectite 19 sites, although sorption onto goethite was also observed, whereas Fe(0) particles did not 20 contribute to lanthanide sorption. The formation of goethite could explain the high K d values 21 measured in a few scenarios (e.g., those with single solutions or mixtures with the lowest 22 initial concentration of the competitive lanthanide in which high affinity sites governed 23 sorption), with up to 3-fold increases over the values obtained without Fe incubation. 24However, at higher lanthanide concentration, K d values decreased or remained constant 25 compared to the samples without Fe incubation, which could be explained by bentonite 26 degradation. In the Ca medium, as much as 5 times lower K d values were obtained, because of 27 the competitive effect of the Ca ions, especially for Lu in the MX80 bentonite. This indicated 28 that the small number of high affinity sites had been diminished. 29The sorption data were satisfactorily fitted to a two-solute Langmuir model. In 30 addition, K d values correlated well with desorption data, which showed that the larger the 31 decrease in K d , the larger the increase in sorption reversibility. It is suggested that corrosion 32 products from the metal canister might compromise the long-term radionuclide retention of 33 the clay-engineered barriers. 34

Selection and Configuration of Sorption Isotherm Models in Soils Using Artificial Bees Guided by the Particle Swarm

“…Several researchers obtained excellent fit of phosphate sorption data Advances in Artificial Intelligence 3 with the two-site Langmuir model [36] and metal sorption, that is, Lanthanide on smectite clays [37,38]. Several other isotherm models such as Farley-Dzombak-Morel [39] and Tóth [40] are often used, but the modeling is out of the scope of this work.…”