The Effect of Freeze-Thaw Cycling and the Initial Mass of Water on the Unfrozen Water Content of Calcium Bentonites Modified by Copper Ions

Abstract

This research was conducted with the use of the DSC method; it involved the examination of the unfrozen water content in two model (source) calcium bentonites (≥75% smectite), after one to three freeze-thaw cycles in the natural state, as well as after the ion exchange for a potentially toxic element (Cu2+). The freeze-thaw cycles do not affect the unfrozen water content at a given negative temperature in a statistically significant manner. However, a statistically significant influence of temperature, the initial mass of the water, and the clay type on the change of the unfrozen water content was found. Moreover, the empirical models of predicting the unfrozen water in the bentonite after the exchange for Cu2+ ion were created, for which the parameter was the mass of the water and the mass of the dry soil, at the temperature of −2 °C.

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

“…In cases of bentonite's contamination with Cu ions at concentrations of 0.1-0.5 M, 3-6% proportions of atacamite (copper hydroxychloride) minerals were present [13]. Table 1 summarizes the physicochemical properties of the clays based on our prior research [13,18].…”

“…Determining changes in the unfrozen water content in bentonites can be conducted using various methods [14,16,17]. Nuclear Magnetic Resonance techniques (NMR) and Differential Scanning Calorimetry techniques (DSC) are among the most widely used electrical and thermal methods for determining unfrozen water content in soils [18][19][20][21][22]. The DSC process involves simultaneously heating a sample and a reference material and then measuring the difference in the amount of heat absorbed or released by the sample compared to the reference material as a function of temperature.…”

“…Interpreting DSC curves related to unfrozen water can be challenging, requiring experience and knowledge about the specific characteristics of this phenomenon. However, the utility of this method has been confirmed across a wide range of soil materials, including in the study of soils contaminated with copper ions [13,14,18]. The NMR technique is based on the phenomenon of magnetization.…”

Anchor Shear Strength Damage under Varying Sand Content, Freeze-Thaw Cycles, and Axial Pressure Conditions

“…Numerous studies have pointed out that freezing and thawing change the original structure of the soil, as well as the composition of the particles, thus changing the mechanical properties of the soil, leading to changes in the engineering properties of the soil [15][16][17]. Edwin J et al [18][19][20][21] studied the changes in pore size and pore water in the soil in the process of freezing and thawing from a microscopic point of view. Leuther Frederic Eskisar [22] found that the compressive strength of both natural and saturated soils decreased after freeze-thaw cycles.…”

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

“…However, these mechanisms are highly complex, and the situation is challenging because metal ions interact with substances dissolved in the pore solution during migration, which can affect the efficiency of metal migration [ 30 ]. Various factors influence the mobility of toxic metals in clayey soils, including the anthropogenic origin of metals, bentonite quality, metal concentration, temperature, presence of organic matter, proportion of clay minerals, and pH [ 24 , 31 , 32 , 33 ]. Anthropogenic contamination of soils with cadmium (Cd), Zn, and Pb increases their mobility [ 24 ].…”