Assessment of Unfrozen Water Content in Copper Bentonites Using the 1H NMR Technique: Optimization, the Method’s Limitation, and Comparative Analysis with DSC

Abstract

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.

Mobility of Zn and Cu in Bentonites: Implications for Environmental Remediation

“…Unfrozen water was calculated according to Equation (2). The highest FID signal value for a given sample above 0 °C was determined according to Nartowska et al [ 58 ]: where w u is the unfrozen water content (% of clay dry weight), SI FID is the signal intensity of the free inductive decay at a given temperature (in this study, the highest signal value for a given sample above 0 °C was determined [ 58 ]), and w n is the natural water content of the clay (% clay dry matter).…”

“…Based on preliminary studies of changes in unfrozen water content in Cu bentonites using the 1 H NMR technique [ 26 , 58 ], it was suspected that the determination results might be affected by ion hydration, which requires further research [ 58 ]. Therefore, DSC was used to evaluate the changes in unfrozen water content in the Cu bentonites.…”

“…Unfrozen water was calculated according to Equation (2). The highest FID signal value for a given sample above 0 • C was determined according to Nartowska et al [58]:…”

“…where w u is the unfrozen water content (% of clay dry weight), SI FID is the signal intensity of the free inductive decay at a given temperature (in this study, the highest signal value for a given sample above 0 • C was determined [58]), and w n is the natural water content of the clay (% clay dry matter).…”

Pore Water Microscale Response of Different Water-Saturated Coal Samples under a Freeze–Thaw Degradation Effect

“…Pore water is commonly tested by calorimetry, time-domain reflectometer method, ultrasonic method, etc., but they are not universal due to the shortcomings of test maneuverability and accuracy. The nuclear magnetic resonance (NMR) technique is a measurement method that records the different relaxation behaviors of hydrogen-containing fluids under the influence of radio frequency field interference.…”