Enhancement on KCl Flotation at Low Temperature by a Novel Amine-Alcohol Compound Collector: Experiment and Molecular Dynamic Simulation

Abstract

To address the challenges of low KCl recovery and high collector consumption during flotation at low temperature, a novel approach with utilizing a compound collector consisting of octadecylamine hydrochloride (ODA) and alcohols (butanol, octanol, and dodecanol) to enhance low-temperature KCl flotation recovery was proposed in this study. The flotation performance and underlying mechanisms of this novel amine–alcohol compound collector were investigated through combination of micro-flotation tests, contact angle measurements, and molecular dynamics simulations. The results revealed that KCl flotation recovery decreased with declining temperature using single ODA as the collector, and the maximum KCl flotation recovery was approximately 40% with an ODA concentration of 1 × 10⁻⁵ mol/L at the temperature of 0 °C. Moreover, amine–alcohol compound collector shows different KCl flotation recovery; among them, dodecanol (DOD) presents the best performance at 25 °C with an ODA concentration of 3 × 10⁻⁶ mol/L. The KCl flotation recovery initially increased and then gradually decreased with increasing the DOD concentration, and 90% KCl recovery was achieved with a DOD concentration of 1.5 × 10⁻⁵ mol/L (DOD:ODA = 5:1 in mole) under 25 °C. Furthermore, this compound collector exhibited high selectivity for KCl/NaCl flotation. Mechanism studies indicated that the trend in contact angle changes on the KCl crystal surface closely mirrored the trend in flotation recovery. Molecular dynamics simulations demonstrated that at 0 °C, the presence of DOD resulted in a higher diffusion coefficient for ODA molecules compared to the system without DOD. Additionally, the water molecules in System 3 exhibited a lower diffusion coefficient and a greater number of hydrogen bonds. This novel compound collector offers a potential solution for improving KCl recovery and reducing ODA consumption during low-temperature flotation. It holds significant theoretical and practical implications for advancing low-temperature KCl flotation technology.

1. Introduction

Potassium chloride (KCl) is a crucial inorganic chemical raw material, particularly widely utilized as a potassium fertilizer in agricultural production [1,2]. Currently, over 80% of the global KCl is produced by froth flotation from the KCl and sodium chloride (NaCl) mixtures [3,4]. Froth flotation is one of the most important and popular selective separation processes, in which hydrophobic mineral particles are selectively captured by air bubbles in their suspensions with hydrophilic particles and transported from the suspension to the surface by bubble [5,6]. Generally, the KCl flotation technologies contain positive flotation and reverse flotation, and more than 90% KCl is produced by positive flotation [7]. The octadecylamine (ODA) is widely used as a positive flotation collector during the KCl flotation due to its high efficiency, low dosage, and low cost [8]. The KCl flotation is carried out in its saturated solution, in which the ODA is adsorbed on the KCl crystal surface, and then it is captured by air bubble, finally completed this process [9]. As we all know, the KCl flotation recovery is a key parameter to decide its production. However, the KCl flotation recovery dropped sharply as the temperature decreased and its recovery is lower than 10% at 5 °C [10]. The low flotation recovery of KCl from salt lakes at low temperatures has limited the development of KCl producer for many years [11]. It was found that the solubility of ODA decreases at the low temperature of 0 °C, making it difficult to dissolve and disperse in water. This indicates that it is challenging to reach the critical micelle concentration in the pulp, ultimately affecting the efficiency of flotation separation at low-temperature conditions [11]. Therefore, improving the KCl flotation recovery from salt lakes at low temperature remains a challenge.

In order to improve the KCl flotation recovery, a lot of efforts have been undertaken by researchers. It was reported that the mixed amine (ODA-60%, dodecylamine hydrochloride (DDA-20%) and icosylamine (20%)) could enhance the KCl flotation recovery at the low temperature [10]. After that, low temperature (0 °C) molecular dynamic simulation of water structure at sylvite (KCl) crystal surface in saturated solution was studied [12]. It was found that the mobility of water molecules, the number of hydrogen bonds made by the water molecules in the membranes, and the molecules exhibited greater order as the temperature decreased. Essilfie et al. [13] found that a modified amine collector (DDA-HCl+PGE) can improve the KCl recovery by 12% at lower temperatures of 10–15 °C. Moreover, the KCl flotation recovery increased effectively with increasing the gas flow rate at 0 °C [14]; the maximum recovery was about 80% with a high ODA concentration of 5 × 10⁻⁵ mol/L ODA under a flow rate of 30 mL/min. To obtain a high KCl flotation recovery, the ODA consumption is big, which increased the cost of the collector. It may be ascribed to the fact that a high gas flow rate can effectively promote the adsorption of ODA on the surface of KCl crystals. To further enhance the KCl recovery, a novel C10 ether diamine (C10-EDA) collector with a concentration of 2.5 × 10⁻⁴ mol/L was used to achieve a KCl recovery of 93.66% at 0 °C [11]. However, the practical application of C10-EDA may face challenges related to environmental risk assessments. Therefore, it still faces a big challenge to enhance the KCl flotation recovery by a simple way at a low temperature. The objective of study is to develop a high efficiency collector to enhance the KCl flotation recovery at the low temperature with a low collector consumption.

Herein, a novel compound collector consisting of octadecylamine hydrochloride (ODA) and alcohols (butanol, octanol, and dodecanol (DOD)) was developed to enhance low-temperature KCl flotation recovery. The flotation recovery and underlying mechanisms of this novel amine–alcohol compound collector were investigated through micro-flotation tests, contact angle measurements, and molecular dynamics simulations. The KCl flotation recovery increased from 40% (only ODA as collector) to 96% (ODA-DOD as collector) with an ODA concentration of 1 × 10⁻⁵ mol/L and DOD concentration of 5 × 10⁻⁵ mol/L at the temperature of 0 °C. This study may help to solve the low KCl flotation recovery at low temperature.

2. Material and Methods

2.1. Material

Octadecylamine hydrochloride (ODA) (purity 99.2%, Tokyo Chemical Industry Co., Ltd., Shanghai, China). The analytically pure KCl, NaCl, butanol, octanol, and dodecanol were purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. Millipore water (Milli Q, Millipore Corp., 18.2 M cm, Beijing, China) was used for all experiments.

2.2. KCl Micro-Flotation Experiment

A KCl saturated solutions at 0 °C, 15 °C, and 25 °C were prepared according to the water–salt phase diagram. KCl-NaCl saturated solutions at 0 °C were prepared according to the water–salt phase diagram. These solutions were stirred for 12 h and allowed to settle for 24 h at their respective target temperatures prior to use.

The KCl micro-flotation experiments procedure is shown in Figure 1. The custom-built laboratory micro-flotation column has an internal volume of 120 mL and is designed for external connection to a circulating water bath (DC-2006 Energy-saving Intelligent Thermostat, Ningbo Xinzhi Biotechnology Co., Ltd., Ningbo, China) to precisely control the flotation temperature. A sintered glass disc (pore size: 5–15 μm) is embedded at the bottom of the column to generate fine gas bubbles. For each micro-flotation test, a specified volume of ODA aqueous solution (0.01 mol/L) was transferred via micropipette into 120 mL of the saturated KCl solution. The mixture was magnetically stirred (60 rpm) for 5 min to ensure homogeneity. Subsequently, 3 g of solid KCl (80–100 mesh) was added, followed by an additional 5 min of stirring. This procedure is termed pulp conditioning. The conditioned pulp was then rapidly transferred into the micro-flotation column. While under magnetic stirring, nitrogen gas was introduced through the bottom disc at a flow rate of 10 mL/min for a flotation duration of 1 min. The temperature throughout both the pulp conditioning and flotation stages was maintained at setting temperature via the external circulating bath, using a water/ethanol mixture as the heat transfer fluid. The condition of KCl flotation was shown in

Table 1. The condition of KCl flotation.

Items	Saturated Salt Solution	Temperature (°C)	Collector
1	KCl	0	ODA
2	KCl	15	ODA
3	KCl	25	ODA
4	KCl	25	ODA-DOD ODA: 3 × 10−6 mol/L DOD:ODA = 1:1, 5:1, 10:1, 20:1
5	KCl	25	ODA-butanol ODA: 3 × 10−6 mol/L Butanol:ODA = 1:1, 5:1, 10:1, 20:1
6	KCl	25	ODA-octanol ODA: 3 × 10−6 mol/L Octanol:ODA = 1:1, 5:1, 10:1, 20:1
7	KCl	0	ODA-DOD ODA: 3 × 10−6 mol/L~6 × 10−5 mol/L (DOD:ODA = 5:1)
8	KCl	0	DOD DOD: 3 × 10−6 mol/L~6 × 10−5 mol/L
9	KCl-NaCl	0	ODA-DOD ODA: 3 × 10−6 mol/L DOD:ODA = 1:1, 5:1, 10:1, 20:1

. Following flotation, the concentrate (floated KCl) and tailings (remaining KCl) was collected by filtration. Both fractions were dried at 110 °C for 4 h. The dry weights of the concentrate and tailings were measured separately. To account for potential dissolution or crystallization of KCl due to minor temperature fluctuations during handling, the flotation recovery was calculated using the following formula.

$$Recovery(R)={\displaystyle \frac{m_c}{m_c+m_t}}\times 100\%$$

(1)

where $m_c$ and $m_t$ are the masses (g) of the concentrate and tailings, respectively.

2.3. Contact Angle Measurement

The contact angle on the surface of KCl crystals was measured using the captive bubble method [15]. Prior to measurement, one face of the KCl crystal was polished successively with sandpaper until a smooth surface was achieved. This smooth surface was then rinsed sequentially with saturated KCl solution several times. Finally, the crystal was placed on a horizontal holder within a transparent test cell containing an ODA-saturated KCl solution with varying dodecanol concentrations, ensuring the polished surface was fully immersed. The entire system was equilibrated for 5 min. Subsequently, an air bubble approximately 2–3 mm in diameter was gently introduced beneath the crystal surface using a microsyringe. Once a bubble was stably captured beneath the surface, image acquisition commenced using the camera system of a JC2000C1 contact angle goniometer (Powereach Co., Ltd., Shanghai, China). Images were captured automatically at 5 min intervals over a duration of 40 min. The camera lens operated at a frame rate of 500 frames per second. Contact angle values were determined using the built-in angle measurement method of the instrument, with a measurement precision of 0.1°. Each experiment was replicated at least three times, and the average value was used for subsequent analysis.

2.4. Molecular Dynamic Simulations

2.4.1. Construction of Models

As shown in Figure 2, the KCl (1 0 0) was fixed on the bottom. The thickness of the crystal is about 0.943 nm. A total of 4200 H₂O molecules were inserted into the top of the simulation box, where x = 3.77 nm, y = 3.77 nm, and z = 6.00 nm. The composition and simulation temperature of each system was shown in

Table 2. The composition and simulation temperature of each system.

System	Number of Molecules				Temperature (K)
	KCl	ODA	DOD	H2O
System 1	308	1	0	4200	273.15
System 2	364	1	0	4200	298.15
System 3	308	1	5	4200	273.15
System 4	364	1	5	4200	298.15

.

2.4.2. Simulation Details

All MD simulations were performed in the GROMACS 2021 software package [16,17,18]. The LJ parameters of all molecules were described with the OPLSAA force field [19] and obtained from the AuToFF web server (https://cloud.hzwtech.com/web/product-service?id=36) [5]; the charge used is RESP [20]. Quantum chemistry calculations were first performed to optimize ODA, DOD (lauryl alcohol), and ETO (Ethyl Alcohol) molecular geometries of the other molecules using the Gaussian 16 package [21] at B3LYP/6-311+G(d) level of theory.

In NVT MD simulations, the KCl (1 0 0) was fixed. During the simulation, the steepest descent method was applied to minimize the initial energy for each system with a force tolerance of 1 kJ* (mol⁻¹ nm⁻¹) and a maximum step size of 2.0 fs firstly. The periodic boundary condition (PBC) was used for all cases. Our simulations were performed 40 ns. The Particle-Mesh-Ewald (PME) method [22] with a fourth-order interpolation was used to evaluate the long-distance electrostatic interactions, and the Lorentz–Berthelot method was employed to calculate LJ interactions between different atoms. The cut-off distance was set to 1.4 nm.

3. Results and Discussion

3.1. Effect of Temperature on KCl Flotation Recovery

Temperature is a key parameter during the KCl flotation; therefore, the micro-flotation experiment was conducted to assess the effect of temperature on KCl flotation recovery under varied ODA concentration (Figure 3). The results indicated that the KCl flotation recovery decreased with declining flotation temperature. The KCl flotation recovery exhibits an initial slow increase, followed by a sharp rise, and finally levels off as the ODA concentration increases at 25 °C. When the ODA concentration is 1 × 10⁻⁵ mol/L, the flotation recovery is about 95%. This finding aligns substantially with literature reports [7]. When the flotation temperature is reduced to 15 °C, the KCl flotation recovery presents a slight decrease compared to 25 °C, but with a similar trend. About 89% KCl recovery can still be achieved with the ODA concentration of 1 × 10⁻⁵ mol/L. However, it is noteworthy that the maximum KCl flotation recovery is only approximately 40% at a temperature of 0 °C and an ODA concentration of 1 × 10⁻⁵ mol/L. Furthermore, further increasing ODA concentration yields only slight improvements in KCl recovery at 0 °C. The underlying reasons for this behavior are likely attributable to the solution chemistry of the flotation system being influenced by a low temperature.

3.2. Effect of Alcohol Content on KCl Flotation Recovery

Based on the aforementioned KCl flotation tests (Figure 3), the influence of alcohol content on the KCl flotation recovery was investigated at 25 °C under the fixed ODA concentration of 3 × 10⁻⁶ mol/L (Figure 4a). The results indicated that the butanol only slightly enhanced the KCl flotation recovery. As the butanol concentration increased, the KCl flotation recovery showed no significant change. However, the KCl flotation recovery increased first and decreased subsequently with increasing the concentration of octanol. Once the concentration of octanol exceeded 5 × 10⁻⁶ mol/L, the KCl recovery was lower than that of pure ODA system. However, with the alcohol chain increase, the KCl flotation recovery enhanced first and then decreased with the concentration of dodecanol (DOD). The maximum KCl flotation recovery reached approximately 90% with a DOD concentration of 1.5 × 10⁻⁵ mol/L, representing an improvement of about 125% compared to the recovery achieved under pure ODA conditions. However, the KCl flotation recovery began to decline with further increasing the DOD concentration. This suggests that the ODA-DOD collector has a suitable ratio for optimal KCl flotation performance.

Generally, the length of the carbon chain is the primary factor determining a molecule’s hydrophobicity. Butanol (C4) exhibits relatively weak hydrophobicity, octanol (C8) has moderate hydrophobicity, and dodecanol (C12) possesses the strongest hydrophobicity. Moreover, the critical micelle concentration (CMC) of alcohol is affected by the carbon chain. Longer carbon chains correspond to lower CMC values. Therefore, butanol (C4) has the highest CMC, octanol (C8) has a moderate CMC, and dodecanol (C12) has the lowest CMC. This might be the main reason for the above experimental results.

The result of Figure 4a shows that appropriate concentration of DOD could improve the KCl flotation recovery at 25 °C under a low ODA concentration of 3 × 10⁻⁶ mol/L. Therefore, the influence of the ODA-DOD compound collector on KCl flotation recovery was investigated at 0 °C with a fixed DOD and ODA mole ratio of 5:1. As shown in Figure 4b, the KCl flotation recovery increased with the concentration of ODA under a fixed DOD and ODA mole ratio of 5:1 at 0 °C, and the KCl recovery was approximately 96% at an ODA concentration of 1 × 10⁻⁵ mol/L.

3.3. Influence of ODA-DOD Collector on KCl Flotation Selectivity

The ODA-DOD compound collector indeed enhances the KCl flotation recovery at 0 °C (Figure 4b). To further substantiate that ODA and DOD can synergistically improve the KCl flotation recovery, the effect of DOD concentration on KCl flotation recovery in a saturated KCl solution system was investigated (Figure 5a). As shown in Figure 5a, the flotation recovery of KCl was about 0.5% as the DOD concentration increased when DOD was used as collector independently to float KCl, meaning DOD cannot float KCl. This finding confirms that the enhancement in KCl flotation recovery is due to the synergistic effect between ODA and DOD.

To further validate that the ODA-DOD can selectively float KCl, the effect of ODA-DOD compound collector on NaCl flotation recovery was investigated in a KCl-NaCl saturated solution at 0 °C and a fixed ODA concentration of 3 × 10⁻⁶ mol/L (Figure 5b). The results demonstrated that the NaCl flotation recovery was below 0.5% after increasing the DOD concentration. This signifies that the ODA-DOD compound collector is ineffective for floating NaCl, confirming it has a high selectivity towards KCl flotation.

3.4. Contact Angle Analysis

Contact angle measurements provide insight into the hydrophobicity of KCl crystal surfaces. Figure 6 shows the variation curve of the contact angle on the KCl crystal surface at 0 °C and a fixed ODA concentration of 3 × 10⁻⁶ mol/L as a function of DOD concentration. The results indicated that the contact angle initially increases and then gradually decreases with rising DOD concentration. The change trend of contact angle was similar with the KCl flotation recovery curve. The change in contact angle occurs because the hydrophilic head groups of ODA adsorb onto the surface of KCl crystals, thus altering the hydrophilicity/hydrophobicity of the KCl surface. At the temperature of 0 °C, the ODA diffusion may be limited without DOD; thus, the ODA adsorption weakens, causing a small contact angel. However, once the DOD was added into the ODA, the ODA diffusion was promoted, which increased the contact angle. Nevertheless, the contact angle does not always increase with rising DOD concentration. This phenomenon may be attributed to excessive DOD preferentially adsorbing onto the KCl surface, thereby reducing adsorption sites for ODA and resulting in a subsequent decline in the contact angle.

3.5. Molecular Dynamics Simulation

3.5.1. The Thickness of Hydration Layers at the KCl Crystal Surface

During the KCl flotation process, a hydration layer exists on the surface of potassium chloride (KCl) crystals [23]. The thickness of this hydration layer reflects the extent to which the KCl crystal surface influences the solution at the solid/liquid interface. Accordingly, the hydration layer thickness in different systems was investigated (Figure 7a). The results indicate that the hydration layer thickness is approximately 0.115 nm across all systems studied. Temperature and the presence of dodecanol (DOD) were found to have negligible effects on the hydration layer thickness.

The number of water molecules within the hydration layer for different systems was further calculated (Figure 7b). The data show that in System 1 (0 °C), the number of water molecules within the hydration layer is about 9.5% higher than in System 2 (25 °C). This increase is likely attributable to the lower kinetic energy of water molecules at low temperature (0 °C), making them more readily attracted to the KCl surface. Furthermore, at low temperatures, the tendency of water molecules towards disorder (the entropy-driven force) is reduced, favoring a more ordered arrangement around the ions and the formation of a denser hydration layer. Conversely, elevated temperature increases the thermal motion of water molecules, leading to partial desorption and consequently reducing the number of water molecules within the hydration layer. When DOD is present in the system (System 4), the number of water molecules within the hydration layer increases by approximately 8.3% compared to System 3 (which lacks DOD at 25 °C).

However, the presence of DOD in System 3 (0 °C with DOD) results in a reduction of about 9.5% in the number of water molecules within the hydration layer compared to System 1 (0 °C without DOD). This decrease is likely due to the weak thermal motion of DOD’s alkyl chains at low temperature (0 °C), promoting the formation of a rigid, highly ordered hydrophobic layer. This layer creates significant steric hindrance, preventing water molecules from accessing the KCl surface. Although the hydroxyl group (-OH) of DOD can form hydrogen bonds with water or the amino group (-NH₂) of octadecylamine (ODA), the number of such bonds is limited at low temperatures due to reduced molecular mobility. The net effect is that DOD occupies interfacial sites, reducing available adsorption sites for water molecules and consequently decreasing the number of water molecules within the hydration layer.

At 25 °C, the addition of DOD (System 4) leads to a 7.3% increase in the number of water molecules within the hydration layer compared to System 2 (25 °C without DOD). At this elevated temperature, the thermal motion of DOD molecules may be enhanced. This conformational change may partially expose the KCl crystal surface, allowing it to attract more water molecules and resulting in an increased water count within the hydration layer.

3.5.2. Dynamic Properties of Water Molecules in the Hydration Layer

Typically, during the KCl flotation process, a hydration layer was formed on the surface of KCl crystals. When ODA is introduced into a saturated KCl solution, ODA molecules must penetrate the hydration layer on the KCl crystal surface to achieve adsorption. This adsorption enhances the hydrophobicity of KCl, enabling its subsequent flotation via bubble attachment. Therefore, the dynamic properties of water in the hydration layer on the KCl crystal surface represent a critical parameter for understanding the flotation mechanism. Generally, the dynamic properties of water are characterized by its mean square displacement (MSD) [24,25]. Therefore, the MSD of water molecules within the hydrated layer on the KCl crystal surface were calculated. The MSD was calculated by Equation (2).

$$MSD\left(t\right)={\displaystyle \frac{1}{N}}\sum _{i=1}^N〈{\left|r_i\left(t\right)-r_i\left(0\right)\right|}^2〉$$

(2)

where $N$ is the number of molecules of water membrane and $r_i\left(t\right)$ is the position of molecule i at time t. The $MSD$ indicates the motion of molecules with respect to their original position. Based on the $MSD$ values, the diffusion coefficient ($D$) was calculated by Equation (3).

$$D={\displaystyle \frac{1}{6}}\underset{t\to \infty }{\mathit{lim}}{\displaystyle \frac{d}{dt}}{\displaystyle \frac{1}{N}}\sum _{i=0}^N〈{\left|r_i\left(t\right)-r_i\left(0\right)\right|}^2〉$$

(3)

Figure 8a–d depict the initial configurations of the simulated systems. Figure 8e shows the MSD curves of water molecules within the hydrated layer of the KCl crystal surface. The corresponding diffusion coefficients are presented in Figure 8f. The results show that the mobility of water molecules in the hydrated layer of System 1 is lower than that in System 2. This indicates that the mobility of water molecules at 0 °C was lower compared to 25 °C in the same simulated system. This difference is attributed to the lower energy and diminished thermal motion of water molecules at lower temperatures. At 0 °C, the presence of DOD in System 3 further reduces the diffusion coefficient of water molecules in the hydrated layer compared to System 1. This decrease in diffusion coefficient likely results from the formation of hydrogen bonds between DOD and water molecules, which restricts the diffusion of water.

3.5.3. The Hydrogen Bonds of Water Molecule in the Hydrated Layer

To further prove the aforementioned results, the average number of hydrogen bonds per water molecule within the hydration layer of different systems was calculated (Figure 9). The data reveal that the average number of hydrogen bonds per water molecule in the hydration layer of System 1 is lower than in System 2. This reduction is likely attributable to the periodic arrangement of ions (K⁺, Cl⁻) on the KCl crystal surface, which disrupts the tetrahedral hydrogen-bonding network characteristic of bulk water. At low temperature (0 °C), adsorbed water molecules, forced to conform to the ionic surface sites, sacrifice some H₂O-H₂O hydrogen bonds. At 25 °C, enhanced thermal motion of water molecules allows for dynamic adjustments that partially restore a more ideal hydrogen-bonding configuration, resulting in a higher average hydrogen bond count. At 0 °C, the number of hydrogen bonds per water molecule in the hydration layer of System 3 increased by 8.3% compared to System 1. This finding further corroborates the result (Figure 8f) that the presence of DOD reduces the diffusion coefficient of water molecules within the hydration layer on the KCl crystal surface in System 3.

3.5.4. Dynamic Behavior of ODA Molecules in the Systems

The interaction between ODA and KCl is a crucial step in the KCl flotation process. Therefore, understanding the dynamic behavior of ODA molecules provides deeper insights into the KCl flotation mechanism. Figure 10a displays the mean square displacement (MSD) curves of ODA molecules across all simulated systems, with the corresponding diffusion coefficients (D) shown in Figure 10b. As seen in Figure 10, at 0 °C, the presence of DOD results in a higher diffusion coefficient for ODA molecules in System 3 compared to the system without DOD (System 1). This higher diffusion coefficient consequently increases the contact probability between ODA molecules and the KCl crystal, thereby facilitating their adsorption onto the KCl surface. Simultaneously, ODA molecules exhibit greater mobility at 25 °C than at 0 °C, owing to their higher molecular energy and enhanced thermal motion at the elevated temperature.

4. Conclusions

In summary, the low temperature (0 °C) can reduce significantly the KCl flotation recovery during the flotation, and it is only about 40% KCl flotation recovery under the condition of 0 °C. The amine–alcohol compound collector shows different KCl flotation recovery; among the studied alcohols, DOD showed the best performance. ODA-DOD complex collector increased the KCl flotation recovery from 40% to 96% at the temperature of 0 °C under an ODA concentration of 1 × 10⁻⁵ mol/L and showed a high selectivity of KCl to NaCl. There was a hydration layer with a thickness of 0.115 nm at the KCl crystal surface, and temperature and the presence of dodecanol (DOD) were found to have negligible effects on the hydration layer thickness. However, DOD reduced the water mobility within the hydrated layer at 0 °C, and DOD promoted the formation of hydrogen bonds of water molecules in the hydration layer. For ODA dynamic properties, the presence of DOD increased the diffusion coefficient of ODA molecules at 0 °C compared to the system without DOD, which may be the key factor in enhancing the KCl flotation recovery at low temperature. This study may provide insight into enhancing the KCl flotation recovery under low temperature.