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.

Based on the results of experimental studies concerning the filtration coefficient, the Darcianity of the observed flows for eight cohesive soils at four hydraulic gradients was analyzed. It is observed that linear dependence of flow velocity on hydraulic gradient is an approximation only, and it is the worse the more cohesive a given soil is. Despite this, Darcy’s law can be a correct approximation of the empirical relationship between hydraulic gradient and the flow velocity, also in very cohesive soils. A statistical analysis was carried out to identify correlation between soil properties and permeability coefficient. For each soil, 109 parameters were analyzed, among others applying mercury intrusion porosimetry, scanning electron microscopy, dynamic image analysis, and laser diffraction. Ultimately, three single-variable models best fitted to the experimental data were found, using the plasticity index I_P as the independent variable, the average pore diameter D_P, and the convexity of silt fraction particles. All model parameters are statistically significant at p < 0.05. Comparison with reference multi-variable models showed that the best fit for experimental data is observed by the model with the plasticity index, while the results suggest low usability of single-variable models with structural parameters.

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.

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.