Phyllite/bentonite mixture-an alternative effective buffer material for a geological disposal of radioactive waste.

The use of phyllite (Phy) instead of quartz in mixtures with bentonite (B) is recommended as a buffer material for engineering barriers in a geological repository of nuclear waste. The recommendation is based on experimentally determined sorption properties of various Phy/B mixtures. The adsorption capacity of Phy/B mixtures (Phy/B: 75/25, 50/50, and 25/75), the removal efficacy of Eu(III) ions (an analog for fissiongenic lanthanides and actinides), and the rate of their binding reaction were studied using the batch adsorption equilibrium and kinetic experiments at different Eu(III) initial concentrations, solution pH, and solution to adsorbent (L/S) ratio. The adsorption capacity of the Phy/B mixtures increased with the increased bentonite content in the mixture depending on the L/S ratio and solution pH. The highest increase in the adsorption capacity of the Phy/B mixtures compared to phyllite was observed for the Phy/B proportions of 25/75 and 50/50. The rate of the Eu(III) adsorption was the best fitted by the pseudo-second-order kinetic model indicating that the adsorption rate was controlled by chemisorption. The Sips model provided the best correlation of the adsorption experimental data, indicative of more than one adsorption site. The results of this study show the advantage of the Phy/B mixtures in immobilizing Eu and certain fission products by combining adsorption properties of the materials.

Adsorption and bonding strength of chromium species by ferrihydrite from acidic aqueous solutions.

The adsorption behavior of Cr(III) and Cr(VI) ions onto laboratory-synthesized 2-line ferrihydrite was investigated under a batch method as a function of initial chromium concentration (0.1-1000 mg L-1) and pH (3.0 and 5.0). Moreover, the effect of the type of anion (chloride and sulfate) on Cr(III) adsorption was studied. The affinity of Cr(III) ions for the ferrihydrite surface depended on both the type of anion and pH of the solution and the maximum adsorption capacities decreased as follows: q (SO4 2-, pH 5.0) > q (SO4 2-, pH 3.0) > q (Cl-, pH 5.0) > q (Cl-, pH 3.0), and were found to be 86.06 mg g-1, 83.59 mg g-1, 61.51 mg g-1 and 40.67 mg g-1, respectively. Cr(VI) ions were bound to ferrihydrite in higher amounts then Cr(III) ions and the maximum adsorption capacity increased as the pH of the solution decreased and was 53.14 mg g-1 at pH 5.0 and 83.73 mg g-1 at pH 3.0. The adsorption process of Cr species was pH dependent, and the ions were bound to the surface of ferrihydrite by surface complexation. The Sips isotherm was the best-fit model to the results obtained from among the four isotherm models used, i.e., Freundlich, Langmuir, Dubinin-Radushkevich and Sips, indicating different adsorption centers participate in Cr uptake. In order to assess the bonding strength of the adsorbed chromium ions the modified BCR procedure, dedicated to the samples with a high iron content, was used. The results of the sequential extraction showed that Cr(III) ions were bound mainly in the immobile residual fraction and Cr(VI) ions were bound in the reducible fraction. The presence of Fe (oxyhydr)oxides in soil and sediments increases their adsorption capacity for Cr, in particular for hexavalent Cr in an acid environment due to their properties (high pHPZC).

Assessment of elements mobility in anthropogenic layer of historical wastes related to glass production in Izera Mountains (SW Poland).

A geophysical survey conducted in the remote forest glade, located in the Izery Mountains (SW Poland), revealed the existence of an anthropogenic layer of historical glass wastes dumped in this area during the activity of a glass factory in the 18th and 19th centuries and domestic wastes dumped during the second part of the 20th century. The aim of the study was assessment of potential ecological risk related to the release of potentially toxic elements to the soil, groundwater and surface waters. The assessment was done on the base of classical geochemical analysis supported by calculation of environmental indices as well as on mobility of elements (leaching test and BCR sequential extraction). As an innovative aspect in the geostatistical interpretation of the data, some magnetic parameters (magnetic susceptibility-χ, χ/Fe ratio) were also used. It allowed for a better understanding of the relationship of PTEs with various forms of iron. The BCR sequential extraction found that among the PTEs, only Zn (up to 43%) was in a potentially mobile fraction probably occurring in ionic form, associated with iron oxides only by surface adsorption forces. The leaching has shown a slight increase in Zn and Cu content in the surface waters; however, it was not considered to be a real ecological threat because the pH of the waste material and soil cover is >6.0 and the scenario of a radical decrease in pH is rather unrealistic. The other PTEs were associated with more stable E2, E3 and E4 fractions. Zinc, similar to Ni, Co and Cu in waste samples, was highly correlated with magnetic parameters (χ and χ/Fe). It means that a considerable part of these metals was associated with ferrimagnetic iron oxides, although they can also occur in the form of inclusions in aluminosilicates and enclosed in glassy phases.

Behavior of Ag species in presence of aquatic sediment minerals - In context of aquatic environmental safety.

In recent years, there has been a growth in the number of products containing Ag nanoparticles (AgNPs) in many areas and their use suggests that the water-soil environment may be exposed to the contaminant with different Ag species. Therefore, the sorption of two Ag forms (i.e. Ag(I) ions and nanoparticles - AgNPs) on clay minerals (montmorillonite and kaolinite) and iron (oxyhydr)oxides (ferrihydrite) as a function of solution:mineral ratio (100:1, 250:1, 500:1), solution pH (3.0, 5.5 and 7.0) and initial Ag concentration (0.1-100 mg/dm3) was studied using batch method. In addition the binding strength/mobility of the bonded Ag species was researched. The results show a great sorption potential of clay minerals for both Ag forms and lower sorption capacity of ferrihydrite, in particular for Ag(I) ions. The maximum sorption capacities of montmorillonite, kaolinite and ferrihydrite estimated from three-parameter isotherm model of Sips were 94.39 mg/g, 117.8 mg/g and 26.48 mg/g for AgNPs and 17.92 mg/g, 21.14 mg/g and 3.072 mg/g for Ag(I) ions, respectively. Aggregation process plays an important role in sorption and mobility of AgNPs. The sequential extraction study indicated different binding mechanisms of the Ag forms onto the clay minerals and ferrihydrite, which depended on the active sites of minerals as well as the Ag species nature in the solution. Ag(I) was weakly bound by clay minerals but presence of iron (oxyhydr)oxides decreased the Ag(I) mobility and bioavailability. On the other hand, AgNPs bound with the active centers of minerals in a very strong way and were not able to release into water. The study of the binding of Ag forms by clay minerals and (oxyhydr)oxides allows to determine the influence of their physicochemical and structural properties, including e.g. pore size on Ag sorption. These results allow these properties to be taken into account in the study of environmental samples, including waters and soils. Moreover, the results showed that in the study of behavior of Ag forms in contact with the minerals, in addition to the sorption capacity, the susceptibility to their release is very important. Studies on sorption/desorption of AgNPs and Ag(I) ions as a form of oxidation of AgNPs is important for understanding the transport and fate of the Ag species in soil, sediments and surface water because of different their behavior in contact with the minerals.

Sorption of Acid Black 1 dye onto bentonite - equilibrium and kinetic studies.

The present study shows sorption capacity of bentonite from the Slovak Jelsový Potok deposit for the anionic dye (Acid Black 1) from aqueous solutions and uses it as an effective and economical adsorbent for the removal of anionic dye. The laboratory experiments were carried out in batch method at 3 different sorbent doses (20, 10 and 5 g L-1) and an initial concentration of dye ranging from 1 to 1,000 mg L-1. The adsorption equilibria data were fitted by Freundlich, Langmuir, Dubinin-Radushkevich and Temkin isotherms. The Langmuir equation provided the best description for the sorption, indicating that adsorption occurred on a mono-layered surface. The maximum sorption capacity of bentonite has been estimated as 31.29 mg g-1. Moreover, the results showed that non-linear method could be a better way to obtain the isotherm parameters. The pseudo-first- and pseudo-second-order equations have been applied for the determination of time effect on sorption/removal of dye from solution. The highest determination coefficient values were observed for the pseudo-second-order model, suggesting chemical character of the adsorption process. Acid Black 1 was probably bound through chemisorption by forming hydrogen bonds between the Si-OH and Al-OH groups in the bentonite and the -NH, -NH2 and -OH groups in the dye.