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Studies on changes in unfrozen water content in copper bentonite from Slovakia were conducted using both differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) methods. The aims of this study were to 1. optimize the method for determining changes in unfrozen water content using the 1H NMR technique in model bentonites based on the DSC results; 2. analyze the relationship between unfrozen water content, as determined via DSC and the optimized NMR technique, and the physicochemical parameters of bentonites; and 3. identify the limitations in determining changes in unfrozen water content using the 1H NMR technique in relation to copper-contaminated bentonites. The results obtained using the optimized NMR method applied to the model bentonites correlated well with the DSC results. The unfrozen water content in the Cu-contaminated bentonites was 2–18% lower after NMR compared to the DSC results, likely due to the mobility of copper ions and their paramagnetic properties. Statistically significant differences in unfrozen water content between the DSC and NMR methods were observed, depending on molar concentration, copper ion concentration, and temperature, confirmed via Analysis of Variance (ANOVA). Calorimetric studies are recommended for investigating unfrozen water content changes in contaminated clays. Further NMR research could identify metals influencing free induction decay signals under varying physicochemical conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]