Effects of the background electrolyte on Th(IV) sorption to muscovite mica

Abstract

The adsorption of tetravalent thorium on the muscovite mica (0 0 1) basal plane was studied by X-ray crystal truncation rod (CTR) and resonant anomalous X-ray reflectivity (RAXR) measurements and alpha spectrometry in the presence of perchlorate background electrolytes LiClO 4 , NaClO 4 , and KClO 4 ([Th(IV)] = 0.1 mM, I = 0.1 M or 0.01 M, pH = 3.3 ± 0.3). RAXR data directly reveal a strong influence of the background electrolyte on the actinide sorption. No significant Th adsorption was observed in 0.1 M NaClO 4 , i.e., the Th coverage h(Th), the number of Th per unit cell area of the muscovite surface (A UC = 46.72 Å 2 ), was 60.01 Th/A UC , whereas limited uptake (h(Th) $ 0.04 Th/A UC ) was detected at a lower ionic strength (I = 0.01 M). These results are in stark contrast to the behavior of Th in 0.1 M NaCl which showed a coverage of 0.4 Th/A UC (Schmidt et al., 2012a). Th uptake was also influenced by the electrolyte cation. Weak adsorption was observed in 0.1 M KClO 4 (h(Th) $ 0.07 Th/A UC ) similar to the results in NaClO 4 at lower ionic strength. In contrast, strong adsorption was found in 0.1 M LiClO 4 , with h(Th) = 4.9 Th/A UC , a $10-fold increase compared with that previously reported in NaCl. These differences are confirmed independently by ex situ alpha spectrometry, which shows no measurable Th coverage in 0.1 M NaClO 4 background in contrast to a large coverage of 1.6 Th/A UC in 0.1 M LiClO 4 . Alpha spectrometry cannot be obtained in situ, but sample preparation requires several washing steps that may affect Th(IV) sorption, RAXR, however, is considered to reflect the in situ sorption structure. The CTR/RAXR analyses of Th-LiClO 4 show the sorption structure consisting of Th species that are broadly distributed, centered at heights of 4.1 Å and 29 Å distance from the interface. Neither the very large distribution height of the second species nor the high coverage can be explained with (hydrated) ionic adsorption, suggesting that the enhanced uptake is presumably due to the formation and sorption of Th nanoparticles.

Competitive Adsorption of ZrO2 Nanoparticle and Alkali Cations (Li+–Cs+) on Muscovite (001)

“…This work was, in part, motivated by previous work in our group that revealed unusual observations regarding the sorption behavior of Th 4+ on the same mica (001) surface . Here, the highest uptake was observed in the presence of Li + , as in this study, but is followed by K +, with the lowest uptake in the presence of Na + .…”

“…This work was, in part, motivated by previous work in our group that revealed unusual observations regarding the sorption behavior of Th 4+ on the same mica (001) surface. 15 Here, the highest uptake was observed in the presence of Li + , as in this study, but is followed by K +, with the lowest uptake in the presence of Na + . No such behavior was found here, which demonstrates that other effects must be taken into consideration for explaining Th 4+ 's behavior and calls into question the often-used analogy between Zr 4+ and tetravalent actinides (e.g., Th 4+ , U 4+ , or Pu 4+ ).…”

“…11,12 Yet, studies aiming to understand the sorption of nanoparticles on the molecular level remain relatively scarce, 13,14 and there are few studies that systematically focus on understanding the reaction's dependency on basic aqueous chemistry. A recent study 15 revealed a highly unusual dependence of the adsorption of Th 4+ on the muscovite (001) basal plane on the composition of the background electrolyte. Both Li + and K + were found to enhance Th 4+ uptake relative to Na + , while ClO 4…”

“…In addition, technical applications of nanomaterials have led to an increased interest in nanoparticle toxicity and their fate in the environment. , Nanoparticulate transport in the environment also plays an important role in the mobility of highly radiotoxic actinides in the environment, for instance, in the vicinity of highly contaminated “legacy sites”. , Yet, studies aiming to understand the sorption of nanoparticles on the molecular level remain relatively scarce, , and there are few studies that systematically focus on understanding the reaction’s dependency on basic aqueous chemistry. A recent study revealed a highly unusual dependence of the adsorption of Th 4+ on the muscovite (001) basal plane on the composition of the background electrolyte. Both Li + and K + were found to enhance Th 4+ uptake relative to Na + , while ClO 4 – was found to have a detrimental effect compared to Cl – .…”

Selective Immobilization of Highly Valent Radionuclides by Carboxyl Functionalized Mesoporous Silica Microspheres: Batch, XPS, and EXAFS Analyses

“…To date, natural inorganic materials have been widely adopted for radioactive wastewater treatment. − Among these natural existing adsorbents, clay minerals (such as kaolinite, montmorillonite, sepiolite, illite, etc. ,− ) are generally composed of stacked sheets of Al-substituted octahedra, Si-substituted tetrahedra, and water, , frequently along with moderate-to-minor amounts of magnesium, iron, alkalis, and alkaline earths, showing great biocompatibility. Unfortunately, most of these materials inevitably suffer from slow adsorption kinetics, low adsorption capacities, limited selectivity, and poor reusability under harsh conditions of inhomogeneous contaminants, extreme pH, and high salt concentrations, making them unsuitable for practical applications .…”