The unfrozen water content in frozen soils strongly influences heat and mass transport processes. Despite massive research work, the actual implications of the freeze–thaw process on unfrozen water still remain unknown. The main objective of this study was to examine the hypothetical effect of a number of previous freeze–thaw cycles on the unfrozen water content during the current cycle. Several bentonites (Stx‐1b from Wyoming, SWy‐2 from Texas, as well as Ca, Na, and K forms of bentonite from Chmielnik) with different water contents were subjected to repeated freezing to −90°C and thawing at 20°C in a differential scanning calorimeter (DSC). The total number of cycles was five. The unfrozen water contents were determined on warming during each cycle by the use of the stochastic deconvolution of the DSC signal. According to the ANOVA results, the freeze–thaw effect on the unfrozen water content w _u in the bentonites was not statistically significant. A clear pattern of alterations of w _u with the number of consecutive cycles could be distinguished, however, depending on the major exchangeable cation. The kind of exchangeable cation played a predominant role in the temperature dependence of the unfrozen water content. The specific surface area strongly affected the unfrozen water content at lower temperatures, i.e., at −5°C and below. Closer to 0?°C, the effect of the specific surface became absolutely insignificant, and the clay fraction content determined by the laser diffraction method proved to be the soil property best correlating with the unfrozen water content at −1°C.

The aim of this article is to assess the potential impact of inorganic salt hydrates used as PCM material in solar installations on the environment and human health and to assess the society’s approach to this technology. The properties of salt are discussed in two ways: first, by analyzing the environmental and health problems caused by chemical hazards on the basis of the available material safety data sheets. Secondly, by analyzing the potential disadvantages of salt hydrates in terms of environmental hazards based on the results of experimental studies available in the literature. Then, using questionnaires, the public approach to solar installations with a built-in converter containing salt hydrates is assessed. Disodium hydrogen phosphate dodecahydrate turned out to be the most prospective salt in terms of environmental, thermophysical, and economic properties for use in solar installations. Understanding the attitudes of the local community toward technologies using inorganic salt hydrates will enable appropriate action to be taken in the future to promote their development. Surveys have shown great public concern about their impact on the environment and human health. In this regard, it is necessary to implement information and promotion activities.

The aim of this study was to determine the influence of potentially toxic metals, such as Cu²⁺ and Zn²⁺ ions, on the microstructural parameters of bentonites and their hydraulic conductivity (K), calculated based on the empirical formulas for clays according to Hazen-Tkaczukowa (formula 1 based on granulometric parameters) and Kozłowski et al., (2011) (formula 2 based on microstructural parameters). Metal ions influence the microstructure changes of bentonites, which can lead to changes in the geotechnical parameters that are used in empirical K formulas. The research was carried out on model clays (SWy-3, Stx-1b and Slovak bentonite), which were modified by introducing Cu²⁺ or Zn²⁺ ions into the structure. A significant dependence was observed between an increase in the Cu²⁺ ion content in clay and an increase in the pore area. Therefore, the value of the hydraulic conductivity was estimated with the use of formula 2, which proved to be a useful tool for determining hydraulic conductivity in the case of bentonites contaminated with Cu²⁺ ions. In contrast, the effect of Zn²⁺ ions on the granulometric parameters was significant, and formula 1 proved to be useful tool for determining hydraulic conductivity in the case of bentonites contaminated with Zn²⁺ ions. The results showed that the behavior of bentonites saturated with Cu²⁺ and Zn²⁺ ions differed. Therefore, the authors believe that the empirical formulas of the hydraulic conductivity of the clays saturated with potentially toxic metals should be based on the selected clay parameters dependent upon the nature of the ion.

The aim of this study was to evaluate the mobility of copper (Cu) and zinc (Zn) and their impact on the properties of bentonites and unfrozen water content. Limited research in this area necessitates further analysis to prevent the negative effects of metal interactions on bentonite effectiveness. Tests involved American (SWy-3, Stx-1b) and Slovak (BSvk) bentonite samples with Zn or Cu ion exchange. Sequential extraction was performed using the Community Bureau of Reference (BCR) method. Elemental content was analyzed via inductively coupled plasma optical emission spectrometry (ICP-OES). Unfrozen water content was measured using nuclear magnetic resonance (¹H-NMR) and differential scanning calorimetry (DSC). Results showed a significant influence of the main cation (Zn or Cu) on ion mobility, with toxic metal concentrations increasing mobility and decreasing residual fractions. Mobile Zn fractions increased with larger particle diameters, lower clay content, and shorter interplanar spacing, while the opposite was observed for Cu. Zn likely accumulated in larger clay pores, while Cu was immobilized in the bentonite complex. The stability of Zn or Cu ions increased with higher clay content or specific surface area. Residual Zn or Cu fractions were highest in uncontaminated bentonites with higher unfrozen water content, suggesting the potential formation of concentrated solutions in sub-zero temperatures, posing a threat to the clay–water environment, especially in cold regions.

The purpose of this study was to determine the effect of copper or zinc ions, absorbed by soil on its physical and physicochemical properties. The change in these properties may reduce the soil usefulness as a mineral protective barrier, for example, on hazardous waste landfills. Parameters such as granulometric composition, effective particle size d10, empirical hydraulic conductivity, Atterberg limits, colloidal activity, specific surface area, sorption moisture content, and montmorillonite content were determined. The tests were carried out on model Na+ or Ca2+ samples of American bentonites (SWy-3, Stx-1b) and Slovak bentonite from Jelšový potok (BSvk), subjected to ion exchange for Cu2+ or Zn2+ ion. The content of elements was determined using inductively coupled plasma optical emission spectrometry (ICP-OES). Regression analysis showed a significant effect of Zn2+ ions on the reduction of sorption moisture content w95 and the increase in the hydraulic conductivity. Nearly complete negative correlation was obtained between the Cu2+ ion content and the specific surface area, sorption moisture content w50, and montmorillonite content (R = -0.99). It was observed that the significance of the influence of Cu2+ and Zn2+ ions on specific clay properties differed, which indicates different behavior of these metals in the clay-water system. The different nature of clays contaminated with Cu2+ and Zn2+ ions justifies the need to continue research on other potentially toxic metals and to further search for prediction equations of the cohesive soil hydraulic conductivity based on soil parameters that are most frequently modified as a result of their impact.

Studies on changes of unfrozen water content in calcium bentonite from Slovakia, with various concentrations of copper ions, were carried out using the method of differential scanning calorimetry (DSC). In this study, the influence of molar concentration of copper(II) chloride solution (1 M, 0.5 M, 0.25 M, 0.1 M), used to saturate clay, was analyzed, as well as the impact of copper ions contained in bentonite and how the copper concentration affects to changes of unfrozen water content versus temperature. The results suggest that new mineral phases originate in bentonite saturated with highly concentrated solutions due to the reaction with copper(II) chloride solutions. These minerals, identified based on XRD and SEM-EDS (X-ray Diffraction and Scanning Electron Microscopy with Energy Dispersive Spectroscopy) studies, are from the atacamite group. ANOVA (Analysis of Variance) has shown a statistically significant relationship between the unfrozen water content and the molar concentration of the solution used to saturate bentonite and between the unfrozen water content and the content of copper ions in the bentonite. The analysis of multiple regression has shown that the change of unfrozen water content in copper bentonites is related to the temperature change, specific surface, and the concentration of copper ions in the clay. An empirical equation was developed to estimate the content of unfrozen water at a given negative temperature in Cu-bentonites, in which the specific surface and copper ions concentration in the bentonite are the main parameters.