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Article

Deep Removal of Fluoride Ions from Spent Ternary Lithium-Ion Batteries Leachate Using Porous La@Zr Adsorbent

by
Zaoming Chen
1,2,
Fupeng Liu
1,2,*,
Bin Liao
1,
Tao Zhang
1,
Feixiong Chen
1,
Jie Wang
1,
Chunfa Liao
1 and
Shengming Xu
3
1
School of Metallurgical Engineering, Jiangxi University of Science and Technology, No.1958 Kejia Avenue, Ganzhou 341000, China
2
Jiangxi Provincial Key Laboratory of High-Performance Steel and Iron Alloy Materials, No.1958 Kejia Avenue, Ganzhou 341000, China
3
Institute of Nuclear and New Energy Technology, Tsinghua University, Shuangqing Road, Beijing 100084, China
*
Author to whom correspondence should be addressed.
Inorganics 2025, 13(11), 369; https://doi.org/10.3390/inorganics13110369
Submission received: 12 October 2025 / Revised: 28 October 2025 / Accepted: 30 October 2025 / Published: 3 November 2025
(This article belongs to the Special Issue Novel Materials in Li–Ion Batteries, 2nd Edition)
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Abstract

Hydrometallurgy is currently the mainstream industrial process for recovering valuable components (nickel, cobalt, manganese, lithium, etc.) from spent ternary lithium-ion battery cathode materials. During the crushing of lithium batteries, cathode materials, anode materials (graphite), and electrolytes become mixed. Consequently, fluoride ions inevitably enter the leaching solution during the hydrometallurgical recycling process, with concentrations as high as 100–300 mg/L. These fluoride ions not only adversely affect the quality of the recovered precursor products but also pose environmental risks. To address this issue, this study employs a synthesized lanthanum–zirconium (La@Zr) composite material, with a specific surface area of 67.41 m2/g and a pore size of 2–50 nm, which can reduce the fluoride ion concentration in the leaching solution to below 5 mg/L, significantly lower than the 20 mg/L or higher that is typically achieved with traditional calcium salt defluorination processes, without introducing new impurities. Under optimal adsorption conditions, the lanthanum–zirconium adsorbent exhibits a fluoride ion adsorption capacity of 193.4 mg/g in the leaching solution, surpassing that of many existing metal-based adsorbents. At the same time as the valuable metals, Li, Ni, and Co, are basically not adsorbed, the selective adsorption of fluoride ions can be achieved. Adsorption isotherm studies indicate that the adsorption process follows the Langmuir model, suggesting monolayer adsorption. The secondary adsorption process is primarily governed by chemical adsorption, and elevated temperatures facilitate the removal of fluoride ions. Kinetic studies demonstrate that the adsorption process is well described by the pseudo-second-order model. After desorption and regeneration with NaOH solution, the adsorbent still has a favorable fluoride removal performance, and the adsorption rate of fluoride ions can still reach 95% after four cycles of use. With its high capacity, rapid kinetics, and excellent selectivity, the adsorbent is highly promising for large-scale implementation.

1. Introduction

Fluorine is widely distributed across the Earth. Fluorine in the earth’s crust is mainly in the form of minerals, such as fluorspar, cryolite and sellaite, and fluoride ions also naturally exist in water [1,2,3]. In the human body, fluorine, one of the trace elements indispensable to the maintenance of normal physiological activities, can be harmful in quantities of either too much or too little. A moderate intake of fluorine can promote the metabolism of calcium and phosphorus in the body, which is conducive to the normal development of teeth and bones [4]. However, when the fluorine level in the body is too high, it can cause fluorosis, dental fluorosis, osteoporosis, and other diseases, which can even be life-threatening in serious cases [5]. According to statistics, many regions in the world have excessive fluoride ion content in drinking water, which seriously threatens human life and health, and fluorine pollution has become a global environmental problem [6,7]. Therefore, the treatment of fluorinated wastewater is of great significance to safeguard the health of residents. Fluorinated wastewater from metallurgical, battery, and fertilizer industries is a major source of fluorine pollution [8,9]. According to the relevant regulations, China’s industrial wastewater discharge standards require that the fluoride ion concentration should be less than 10 mg/L, and the standard for domestic drinking water stipulates that the concentration of fluoride ions should not exceed 1.0 mg/L in drinking water [10].
Lithium-ion batteries are mainly composed of four parts: cathode material, anode material, the electrolyte, and the diaphragm. Among them, the main chemical composition of the electrolyte comprises LiPF6, LiBF4, etc., which inevitably enter into the cathode material or anode material during the dismantling process, and which are the main sources of fluorine contamination in the recycling process [11,12]. At present, at home and abroad, the main process of recycling spent lithium-ion batteries is to first crush, pyrolysis, and sieve the used batteries, then to use the H2SO4-H2O2 system to obtain a sulfate solution of each metal ion by acid leaching, and finally to carry out a series of operations, such as impurity removal, purification, and separation, and to extract the valuable metals in the used batteries [13,14]. In the process of acid leaching, fluoride inevitably dissolves into the leaching solution along with various metal ions, which can cause corrosion damage to the instrument and fluorine pollution to the environment if the fluorine ions are not dealt with in time [15,16,17].
When treating fluorinated wastewater, it is important not only to take into account the wastewater acidity and alkalinity, and the fluoride ion content and other components in the solution, but also to make a reasonable assessment in terms of fluoride removal effectiveness and economy. At present, the methods reported at home and abroad for treating fluorinated wastewater mainly include chemical precipitation, coagulant sedimentation, membrane separation, ion exchange, adsorption, etc. [18]. The method of chemical precipitation is mainly applied to remove fluoride ions from the solution via fluoride precipitation, by adding calcium salts such as lime and calcium sulfate to the fluoridated wastewater [19]. In addition, aluminum salts, magnesium salts, and phosphates are also added in appropriate amounts to further improve the fluoride removal performance. The chemical precipitation method is a simple and low-cost process, but the amount of calcium salt is large, generally 2–5 times the theoretical amount. Moreover, CaF2 itself has a certain solubility, and the wastewater treated with the chemical precipitation method still contains 20~30 mg/L of fluorine [20]. Therefore, it is difficult to decrease the fluorine ions concentration to below the standard in the wastewater, and this method is only suitable for treating industrial high-fluorine wastewater. The coagulation sedimentation method uses iron and aluminum salts to form positively charged colloids on the surface of the water, which are electrostatically and physically adsorbed to remove fluoride ions in the wastewater [21]. Compared with the calcium salt precipitation method, the coagulation sedimentation method has less reagent input and can reach the discharge standard after one treatment. However, the treatment process is susceptible to the influence of anions, such as SO42−, NO3−, and Cl-, in the solution, and the fluoride removal effect is unstable. The ion exchange method involves the fluoride ions complexation using ion exchange resins to remove the fluoride ions in the solution [22]. Commonly amino-phosphate resins were mainly used as fluoride removal resins. The ion exchange method is effective in removing fluoride and has a high adsorption capacity, but the disadvantage is that while the fluoride ions are removed from the solution, the minerals that are beneficial to humans are also removed and amines are introduced [23]. Meanwhile, the high price of the ion exchange resin itself limits its widespread application. In contrast to other methods, the adsorption is extensive in the fluoride removal process, with the advantages of a simple preparation process, high fluoride removal efficiency, economic and practical, less secondary pollution, etc. [24]. Adsorbents are extensively used in fluorine removal due to their large specific surface area and their ability to form chemical groups with the adsorbed substances [25]. Commonly used adsorbents include activated alumina [26], zeolite [27], hydroxyapatite [28], zirconium oxide, and rare earth adsorbents [29]. In recent years, rare earth adsorbents have become popular because of their high adsorption capacity and the absence of secondary pollution [30]. While rare-earth-based adsorbent has the disadvantage of low specific surface area and high cost, compared to the expensive rare earth adsorbents, zirconium-based composites with high fluoride affinities have drawn great attention, being of moderate price, in recent investigations [31].
Currently, the hydrometallurgical recycling process of lithium-ion batteries involves fluoride ion concentrations ranging approximately from 100 to 500 mg/L, which adversely affects the quality of subsequent products such as nickel, cobalt, manganese, and lithium. Even after the separation of valuable metals, the fluoride ion concentration in the residual solution still exceeds China’s national discharge standards. To achieve the deep removal of fluoride ions, a characteristic pollutant in the leaching solution of lithium-ion battery hydrometallurgical recycling, this study synthesized a lanthanum–zirconium composite adsorbent. The effects of various conditions—including pH, adsorption time, temperature, and initial fluoride ion concentration—on fluoride ions’ adsorption were investigated. Under optimized conditions, the fluoride ion concentration in the leaching solution was reduced to below 5 mg/L; moreover, the adsorption thermodynamics and kinetics were analyzed. The developed adsorbent and new process are conducive to achieving the clean production of spent lithium batteries.

2. Experiment

2.1. Reagents and Materials

All reagents, including lanthanum chloride heptahydrate (LaCl3·7H2O), zirconyl chloride octahydrate (ZrOCl2·8H2O), sodium fluoride (NaF), nitric acid (HNO3), and sodium hydroxide (NaOH) were analytically pure, and were provided by Maclean Chemical reagent (Shanghai, China). Deionized water was used throughout the experiment. The main chemical composition of leachate is supplied by a company engaged in spent lithium-ion battery recycling (Jiangxi, China), as shown in Table 1. The concentrations of Li, Ni, Co, Mn, and F in the leaching solution were 6065, 24,780, 9565, 14,195, and 200 mg/L, respectively, which is comparable to that reported in the literature [32].

2.2. Preparation of La@Zr Adsorbent

First, a mixture of 1 mol/L LaCl3 (99.9%, AR) and 0.125 mol/L ZrOCl2 (99.9%, AR) was prepared in a volumetric flask and then transferred to a conical flask. Next, the conical flask was heated to 80 °C in water, and sodium hydroxide solution (3 mol/L) was gradually added while stirring to control the end-point pH at around seven, and it was kept at 80 °C for 1 h. Then, the obtained sediment was washed 3~4 times by distilled water, after being extracted and filtered. The filter cake was put into a drying oven, and dried and ground into powder to obtain La@Zr adsorbent [33,34]. The flow chart of the preparation process of La@Zr composite adsorbent is shown in Figure 1.

2.3. Adsorption Experiments

2.3.1. Adsorption of Fluoride Ions

Simulated solutions, containing various fluoride ion concentrations, were prepared by dissolving sodium fluoride in deionized water. Each time, 100 mL of the simulated solution and a certain amount adsorbent was used for experiments in the conical flask, and the pH of solution was adjusted by the HNO3 or NaOH solution (3 mol/L). Then, the conical flask was put into thermostat shaker at the speed of 150 rpm. After the reaction, the concentration of fluoride ions was characterized using a fluorine ion concentration meter in the solution (PXSJ-216F, Lei-ci Instrumentation, Shanghai, China). The effects of the removal of fluoride ions and adsorption capacity were analyzed in different experimental conditions: initial fluoride concentration (16–310 mg/L), temperature (25–75 °C), and pH (3–9). The adsorption rate (Ads, %) and equilibrium adsorption capacity (qe, mg/g) are used to measure the removal performance of fluoride of the adsorbent, and the calculation formulae are Supplementary Equations (S1) and (S2).

2.3.2. Adsorption Isothermal and Adsorption Kinetics Processes

The adsorption isothermal of fluoride was carried out three times for the La@Zr adsorbent in the ranges of temperatures (25–45 °C). Specifically, in a 250 mL conical flask, 0.1 g of the adsorbent was added to 100 mL of a solution with different fluoride concentration gradients and mixed thoroughly. The initial pH of the mixed solution was set to three, and which was shaken at 25 °C for 1 h in the shaker to ensure sufficient adsorption. As described above, the fluoride ion-selective electrode was used to character fluoride ion concentrations in the filtrate after filtration.
The adsorption kinetics of fluoride were investigated in triplicate for the La@Zr adsorbent in the range of initial fluoride concentration (100–280 mg/L). Briefly, the process is as follows: take 100 mL of fluoride ion solution with concentrations of 100, 200, and 280 mg/L, respectively, in conical flask, adjust the solution pH = 3 with 1 mol/L HNO3, add 0.1 g adsorbent, stir adsorption in water bath at 45 °C, and take 1 mL of supernatant at a certain intervals to measure the fluoride ion concentration.

2.4. Desorption and Regeneration Processes

After adsorption, the mixed solution was centrifuged and filtered, the precipitate was rinsed twice with pure water, and was dried at 60 °C for 12 h in an oven and ground into fine powder. Subsequently, the powders were immersed in sodium hydroxide solution with different concentrations for 2 h under ultrasonic conditions at a controlled temperature of 80 °C. The regenerated adsorbent was filtered, washed, dried, and then subjected to fluoride ion removal experiments. Finally, the experiments of adsorption and desorption were conducted four times.

2.5. Analytical Methods

The morphological characteristics of the adsorbent were examined using a scanning electron microscope (SEM, Hitachi Regulus 8100, Tokyo, Japan). The specific surface area and pore size distribution of the zirconium-based adsorbent were determined via N2 adsorption–desorption isotherms at 78 K using an automated surface area analyzer (Micromeritics ASAP 2460, Norcross, GA, USA). Particle size distribution was analyzed via laser diffraction (Bettersize BT-9300HT/2000E, Dandong, Liaoning, China) with triplicate measurements under dry dispersion mode. The adsorbent before and after adsorption was determined via a Fourier transform infrared spectrometer (FTIR, ALPHA, Bruker Corporation, Ettlingen, Germany). The solution pH and fluorine ion concentration were monitored using a PXSJ-261F meter (Leici, Shanghai, China). The ion concentrations in aqueous solutions were tested via inductively coupled plasma optical emission spectrometry (ICP–OES, Perkin Elmer Optima 7100 DV, Hopkinton, MA, USA).

3. Results and Discussion

3.1. Characterization of La@Zr Adsorbent

Numerous studies have shown that the adsorption performance of an adsorbent depends on its own morphological size, pore volume, and specific surface area, and that the adsorption capacity of an adsorbent increases with increasing pore volume and specific surface area under certain conditions. Figure 2 shows that the morphologies of La@Zr adsorbent consists of many irregular, fine, rod-shaped particles with a particle size of around 100–300 nm and a loose and porous surface. During the adsorption process, the rough structure can provide more adsorbing sites.
The adsorbent has the multi-point BET specific surface area (67.41 m2/g), the total pore volume (0.39 cm3/g), and the average pore size (22.84 nm), with has a good pore structure, as measured by the static capacity method. Figure 3 shows the nitrogen adsorption and desorption isotherms of the adsorbent; the adsorption curve exhibits a sharp increase in gas uptake at relative pressures (p/p0) above 0.9, which is attributed to capillary condensation within mesopores. This phenomenon results in the formation of a hysteresis loop, confirming the isotherm as Type IV, according to the IUPAC classification [35]. Figure 4 demonstrates the curve of the pore size distribution of the adsorbent, from which it can be further seen that the pore size of the adsorbent is mainly concentrated between 2 and 50 nm.

3.2. Selective Removal of Fluoride Ions

In addition to fluorine ions, a large number of metal elements are present in actual solutions. Therefore, the selective adsorption of fluoride ions in mixed solutions has also become an important index to evaluate the performance of adsorbents. Figure 5 shows the selective adsorption performance of the La@Zr adsorbent on ions, such as Li, Ni, Co, Mn, and F, at 45 °C for 1 h with an adsorbent dosage of 1 g/L. As can be seen from Figure 5, before and after the adsorption reaction, the Li, Ni, Co, Mn, and other metal elements in the solution were basically unchanged, while the fluoride ions in the solution decreased from 200.00 mg/L to 3.49 mg/L before and after the adsorption.
According to the FTIR, before and after adsorption (Figure 6), pronounced changes occurred in the spectra after fluoride ion adsorption, and the broad and intense hydroxyl stretching vibration peak at 3417.2 and 3501.7cm−1 weakened considerably, suggesting that fluoride ions replaced surface hydroxyl groups (M-OH) to form La–F or Zr–F bonds [36]. The remaining hydroxyl groups, due to the strong electronegativity of fluoride ions, lost their original hydrogen-bonding network, reducing the intermolecular interactions among hydroxyl groups. This resulted in a sharper peak at 3417.2 and 3501.7cm−1, and the appearance of new absorption peaks, confirming the participation of surface hydroxyl groups in fluoride adsorption. Additionally, the intensity of the original peaks at 1698.1 cm−1 and 1104.2cm−1 decreased, indicating competitive adsorption between fluoride and sulfate ions for surface sites, caused by strong La–F or Zr–F interactions.
Therefore, the adsorbent has good selectivity for the removal of fluoride ions in mixed solutions containing Li, Ni, Co, Mn, and F ions. A fluorine-containing simulated solution was prepared using NaF to determine the optimum conditions of fluoride removal by the adsorbent. The effects of the fluoride removal performance were carefully investigated at different pHs, temperatures and initial fluoride ion concentrations. Additionally, the isothermal model and kinetic model were explored in this process.

3.2.1. Effect of Initial pH

The effects of the fluoride adsorption ion on the La@Zr adsorbent were investigated at initial solution pH = 2–6, with a fluoride ion concentration of 200 mg/L, a reaction temperature of 45 °C, an adsorbent dosage of 1 g/L, and an adsorption time of 1 h, as shown in Figure 7, which illustrated that the adsorption capacity of the La@Zr adsorbent first increased and then decreased with an increase in the initial pH value of solution, and that the adsorption capacity reached its maximum with 193.4 mg/g at pH = 3. The adsorption capacity dropped to 88.5 mg/g as the pH of the solution increased from three to four, which indicated that acidic conditions were favorable for the adsorbent to adsorb fluoride ions in the solution. In addition, the adsorption capacity also decreased slightly as the initial solution pH decreased to two, which indicated that the internal structure of the adsorbent may be broken when the acidity of the solution is too high, resulting in a decrease in the adsorption capacity.
The possible adsorption mechanism of La@Zr adsorbent on fluorine is presented in Equations (1)–(3) [32]:
≡Me-OH + H+ → ≡Me-OH2+
≡Me-OH2+ + F− → ≡Me-OH2+F−
≡Me-OH + F− → ≡Me-F + OH−
where ≡Me means the La@Zr adsorbent. The hydroxyl groups on the surface of the adsorbent in the acidic environmental condition are protonated. The fluoride ions in the solution form complexes on the adsorbent surface under the action of electrostatic attraction. In addition, hydroxyl groups on the adsorbent surface may undergo ion exchange with fluoride ions in solution. The adsorption of fluoride is accompanied by the release of hydroxyl ions. It could be inferred that the surface hydroxyl groups had a crucial role in the fluoride removal process. Under the condition of suitable acidity, it is conducive to the adsorption of fluoride ions in the presence of hydrogen ions in the solution.

3.2.2. Effect of Reaction Temperature

The effects of the fluoride adsorption ion on the La@Zr adsorbent were investigated from 25 to 75 °C with a fluoride ion concentration of 200 mg/L, an initial solution pH value of three, a adsorbent dosage of 1 g/L and an adsorption time of 1 h. As shown in Figure 8, the adsorption capacity gradually increases with an increase in the reaction temperature. The adsorption capacity increases from 170.6 to 197.6mg/g as the temperature increases from 25 to 75 °C. The adsorption capacity basically remains unchanged at changing reaction temperatures, and when the temperature is higher than 55 °C, after the adsorption equilibrium, the residual fluorine ions in the solution are less than 10 mg/L, while when the reaction temperature is 25 °C, the residual fluorine ions in the solution are 29.3 mg/L.

3.2.3. Effect of Initial Fluoride Concentration

The effect of the adsorption performance at different initial concentrations of fluoride with a solution pH of three, an adsorbent dosage of 1 g/L, a reaction temperature of 45 °C, and an adsorption time of 1 h was explored. The results showed that the adsorption rate of fluoride ions by the adsorbent firstly increased and then decreased with the continuous increase in the initial fluoride ions of the solution, as shown in Figure 9. When the initial level of fluoride ions in the solution was 126.2 mg/L, the adsorption rate reached the maximum value of 98.6%. When the fluoride ion level in the solution was less than 126.2 mg/L, it can be basically removed by adsorption. This is because at lower initial fluoride concentrations, the active sites on the adsorbent surface remain unoccupied, and as the initial concentration increases, the available active sites on the adsorbent surface decrease rapidly [37]. After adsorption equilibrium, the residual fluoride ion concentration in the solution was lower than 2 mg/L. Then, the adsorption process tends to be saturated with the gradual increase in the fluoride ion level in the solution, and at the same time, due to the adsorption reaching saturation, the residual fluoride ions in the solution gradually increase, increasing the fluoride ion concentration.

3.3. Adsorption Isotherms

The adsorption isotherm was plotted at optimum experimental conditions, as shown in Figure 10a. In this work, the adsorption isotherms based on three well-established fundamental models, such as the Langmuir, Freundlich, and Temkin models, were investigated in order to describe the adsorption mechanism and the adsorption process at equilibrium conditions, as shown in Figure 10a. These models can be expressed by Supplementary Equations (S3)–(S5) [38,39]. The adsorption isotherm of the Langmuir model, Freundlich model, and Temkin model was plotted in Figure 10b–d, respectively. Figure 10a shows that the adsorption capacity gradually increases with the increase in fluoride ions in the solution. After adsorption equilibrium, the fluoride ion level in the solution is less than 10 mg/L, and the adsorption capacity increases at a large rate and then gradually tends to equilibrium.
The linear fitting parameters of the Langmuir, Freundlich, and Temkin adsorption isothermal models are revealed in Table 2. Compared with the other two models, the R2 of the Langmuir model is greater than 0.9998, while the R2 of Freundlich model and Temkin model is only 0.9301 and 0.9617, respectively. This indicates that the fluoride ions’ adsorption via the synthesized lanthanum–zirconium composite adsorbent was more consistent with the Langmuir adsorption model, and the adsorption of fluoride ions in solution was mainly in the form of monolayer and homogeneous adsorption. The maximum adsorption capacity at 25, 35, and 45 °C is 204.50, 232.02, and 239.23 mg/g, respectively. The adsorption capacity gradually increases with the increase in temperature, which is consistent with the previous conclusions, indicating that the adsorption process was an isothermal reaction, and increasing the temperature was conducive to the fluoride ions’ adsorption. Thereby, as the temperature increased from 25 °C to 45 °C, the interaction between fluoride ions and the active sites of the adsorbent was enhanced, promoting the adsorption process—a behavior consistent with chemisorption. Therefore, 45 °C was selected as the optimal adsorption temperature to ensure effective removal of fluoride ions from the leaching solution of spent LIB.
Compared to other adsorbents, the La@Zr adsorbent has a higher fluoride adsorption capacity, as shown in Table 3. This shows that there is an efficient and potential application in defluorination.

3.4. Adsorption Kinetics

The change in adsorption capacity with adsorption time was explored via adsorption kinetics. The adsorption kinetics curves of the La@Zr adsorbent for the fluorine ion solutions of 100, 200, and 280 mg/L are presented in Figure 11a, at an initial pH of three, an adsorbent dose of 1 g/L, and a reaction temperature 45 °C. In order to further explore the adsorption mechanism of fluoride ions, pseudo-first-order model, pseudo-second-order model, and intra-particle diffusion models were used to analyze the adsorption data. These models are expressed by Supplementary Equations (S6)–(S8) [40,41,42]. The adsorption kinetics simulated by Supplementary Equation (S6) are showed in Figure 11b–d, respectively.
Figure 11a shows that the adsorption capacity increased rapidly with the extension of time in the first 30 min of the reaction; the corresponding adsorption capacities of 100, 200, and 280 mg/L fluoride ion solution are 92.90, 168.20, and 192.93 mg/g at 30 min, respectively, and the adsorption capacities are 93.93, 176.36, and 202.55 mg/g as the reaction time is extended to reach the adsorption equilibrium. Indicating that the fluoride adsorption process on the La@Zr adsorbent is composed of two steps, specifically, approximately 95% of the adsorption capacity is achieved within the initial 30 min, followed by a gradual approach to equilibrium. This behavior is attributed to the saturation of active sites on the adsorbent surface, resulting in a diminished driving force for subsequent adsorption [43]. The adsorption capacity also gradually increases with the increase in the fluoride ions’ concentration in the solution, because the adsorption of fluoride ions in the solution by the adsorbent is dependent on the dynamic adsorption equilibrium; the equilibrium adsorption capacity becomes larger with the increase in fluoride ions in the solution.
Table 4 shows the kinetic parameters of the pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. Compared to the other two models, the linear correlation coefficients (R2) of the pseudo-second-order model is higher than 0.95, indicating that the pseudo-second-order model was the best-fit model in expressing the fluorine adsorption process. Moreover, the amount of adsorbed fluoride at equilibrium calculated by the pseudo-second-order model was 93.61, 179.61, and 204.50 mg/g at different initial fluoride ion concentrations, which is similar to the experimental data (93.93, 176.36, and 202.55 mg/g), indicating that the adsorption process was well expressed by the pseudo-second-order model. Furthermore, as the initial fluoride concentration increases, the rate constant K2 decreases, indicating a negative correlation between adsorption rate and initial fluoride concentration, with the lower concentration resulting in the weaker competition of the adsorption surface sites.

3.5. Desorption and Regeneration

The saturated adsorbent was desorbed and regenerated via NaOH solution with 0.5, 1, 2, and 3 mol/L, and the regenerated adsorbent was then adsorbed and desorbed four times to investigate the regeneration performance of the adsorbent. The experimental conditions were as follows: fluoride ion concentration of 200 mg/L, initial pH of three, reaction temperature of 45 °C, adsorbent dosage of 1 g/L, and adsorption time of 1 h. Figure 12 depicts the fluoride adsorption efficiency of regeneration for four different NaOH concentrations. Under the conditions of desorption with different NaOH concentrations, the adsorption rate of fluoride ions remains above 95% after four cycles of adsorption and regeneration, indicating that the La@Zr adsorbent synthesized in the experiment is a kind of fluoride removal material that can be reused.

4. Conclusions

This investigation into a lanthanum–zirconium composite adsorbent for eliminating fluoride ions from spent ternary lithium-ion battery leachate has led to the following key findings:
(1)
The La@Zr composite adsorbent prepared using the hydrothermal synthesis method has microporous structure with a specific surface area of 67.41 m2/g and a pore size of 2–50 nm, and its pore size distribution is mesoporous.
(2)
In acidic solutions, the adsorbent has the maximum adsorption capacity of 193.4 mg/g. Moreover, it can selectively adsorb fluoride in mixed solution containing Li, Ni, Co, Mn, and other metal ions.
(3)
The adsorption of fluoride ions by adsorbents is more consistent with the Langmuir model, the secondary adsorption process is mainly chemical adsorption, and the adsorption reaction is a multi-stage control process. The adsorption by adsorbents is a monolayer adsorption, and the adsorption process is an endothermic reaction, and increasing temperature is conducive to the adsorption reaction.
(4)
The recycling and regeneration of the adsorbent is a vital index when measuring its practical performance. The fluoride removal performance of the adsorbent can be restored after alkali washing and regeneration, and the adsorption rate of fluoride ions can still reach 95% after four cycles of use.
(5)
Through the development of new adsorbents and optimization of adsorption processes, clean production of waste lithium batteries has been achieved.
This study provides a novel approach for the advanced removal of fluoride from spent cathode material leachates.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/inorganics13110369/s1.

Author Contributions

Literature search, B.L. and Z.C.; study design, B.L. and F.L.; investigation, J.W. and T.Z.; funding acquisition, F.L.; data collection, B.L. and F.C.; data analysis, B.L., C.L. and Z.C.; data interpretation, B.L. and F.C.; writing, Z.C. and B.L.; review and editing, F.L., C.L. and S.X. All authors have read and agreed to the published version of the manuscript.

Funding

This paper has been financially supported by the Jiangxi Ganpo Talent Plan Innovative High end Talent Project (gpyc20240066), Training Plan for Academic and Technical Leaders of Major Disciplines in Jiangxi Province (20225BCJ23009), the Natural Science Foundation for Distinguished Young Scholars of Jiangxi Province (No. 20232ACB214006); Major Science and Technology Research Projects in Yichun City (2023ZDKJGG01), Unveiling the List and Commanding the Lead Project in Yichun City (2024JBGSXMO7), and Jiangxi Provincial Key Laboratory of High-Performance Steel and Iron Alloy Materials (No. 2024SSY05041).

Data Availability Statement

The data presented in this study are available upon request from the corresponding author. The data are not publicly available due to privacy.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, investigation, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Inorganics 13 00369 g001
Figure 1. The flow chart of preparation process of La@Zr composite adsorbent.
Figure 1. The flow chart of preparation process of La@Zr composite adsorbent.
Inorganics 13 00369 g001
Inorganics 13 00369 g002
Figure 2. SEM images of the surface of La@Zr adsorbent at magnifications of (a) 10,000X and (b) 30,000X.
Figure 2. SEM images of the surface of La@Zr adsorbent at magnifications of (a) 10,000X and (b) 30,000X.
Inorganics 13 00369 g002
Inorganics 13 00369 g003
Figure 3. Characterization of the isotherm of N2 for La@Zr adsorbent.
Figure 3. Characterization of the isotherm of N2 for La@Zr adsorbent.
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Inorganics 13 00369 g004
Figure 4. Characterization of porosity distribution of La@Zr adsorbent.
Figure 4. Characterization of porosity distribution of La@Zr adsorbent.
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Inorganics 13 00369 g005
Figure 5. Selective adsorption of fluoride ions by La@Zr adsorbent.
Figure 5. Selective adsorption of fluoride ions by La@Zr adsorbent.
Inorganics 13 00369 g005
Inorganics 13 00369 g006
Figure 6. FTIR analysis before and after adsorption by La@Zr adsorbent.
Figure 6. FTIR analysis before and after adsorption by La@Zr adsorbent.
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Inorganics 13 00369 g007
Figure 7. Effect of initial pH on the fluoride adsorption.
Figure 7. Effect of initial pH on the fluoride adsorption.
Inorganics 13 00369 g007
Inorganics 13 00369 g008
Figure 8. Effect of temperature on the fluoride adsorption.
Figure 8. Effect of temperature on the fluoride adsorption.
Inorganics 13 00369 g008
Inorganics 13 00369 g009
Figure 9. Effect of initial fluoride ion concentration on the fluoride adsorption.
Figure 9. Effect of initial fluoride ion concentration on the fluoride adsorption.
Inorganics 13 00369 g009
Inorganics 13 00369 g010
Figure 10. (a) Fluoride adsorption isotherms of La@Zr adsorbent at different temperatures of 25 °C, 35 °C, and 45 °C, and adsorption isotherm models of (b) Langmuir, (c) Freundlich, and (d) Temkin fitting curve of fluoride by La@Zr adsorbent.
Figure 10. (a) Fluoride adsorption isotherms of La@Zr adsorbent at different temperatures of 25 °C, 35 °C, and 45 °C, and adsorption isotherm models of (b) Langmuir, (c) Freundlich, and (d) Temkin fitting curve of fluoride by La@Zr adsorbent.
Inorganics 13 00369 g010
Inorganics 13 00369 g011
Figure 11. (a) Adsorption kinetic of fluoride on La@Zr adsorbent with different initial fluoride concentration of 100 mg/L, 200 mg/L, and 280 mg/L and (b) pseudo-first-order, (c) pseudo-second-order, and (d) intra-particle diffusion kinetic fitting for fluoride removal by La@Zr adsorbent.
Figure 11. (a) Adsorption kinetic of fluoride on La@Zr adsorbent with different initial fluoride concentration of 100 mg/L, 200 mg/L, and 280 mg/L and (b) pseudo-first-order, (c) pseudo-second-order, and (d) intra-particle diffusion kinetic fitting for fluoride removal by La@Zr adsorbent.
Inorganics 13 00369 g011
Inorganics 13 00369 g012
Figure 12. The effect of regeneration of the La@Zr adsorbent the after four cycles.
Figure 12. The effect of regeneration of the La@Zr adsorbent the after four cycles.
Inorganics 13 00369 g012
Table 1. Main chemical composition of leachate from spent lithium-ion batteries.
Table 1. Main chemical composition of leachate from spent lithium-ion batteries.
ElementLiNiCoMnF
Concentration(mg/L)606524,780956514,195200
Table 2. Isotherm models of La@Zr adsorbent.
Table 2. Isotherm models of La@Zr adsorbent.
Langmuir IsothermFreundlich IsothermTemkin Isotherm
C e q e = C e q m + 1 q m K L ln q e = ln K F + ln C e n q e = B ln K T + B ln C e
T (°C)KLqm (mg/g)R12KFnR22KTBR32
250.22204.500.999180.574.420.91345.6834.060.9347
350.36232.020.9989102.594.630.880210.4737.070.9066
450.54239.230.9998120.645.330.930131.6832.980.9617
Table 3. Comparison of fluoride adsorption on various adsorbents.
Table 3. Comparison of fluoride adsorption on various adsorbents.
AdsorbentsMaximum qe(mg/g)pHReferences
Al-CPCM resin5.687[23]
LDH-BCF15.215.71[25]
Al2O3 nanoparticles13.704[26]
Zeolite hydroxyapatite composite0.36[27]
HAP34.527.5[28]
Zr-PZI183.57.0[29]
MCH-La136.787.0[30]
Mg-Al-Zr composite22.97.0[31]
La@Zr composite239.233.0Present study
Table 4. Parameters of the kinetics study for fluoride adsorption onto La@Zr adsorbent.
Table 4. Parameters of the kinetics study for fluoride adsorption onto La@Zr adsorbent.
Pseudo-First-Order Kinetic ModelPseudo-Second-Order Kinetic ModelIntra-Particle Diffusion Model
ln ( q e − q t ) = ln q e − K 1 t ( t / q t ) = 1 / K 2 q e 2 + ( t / q e ) q t = K p t 1 / 2 + C
C0 (mg/L)Qe,exp (mg/g)K1qe,calcd (mg/g)R12K2qe,calcd (mg/g)R22KpR32C
10093.931.0293.040.74830.068193.610.95850.240.558791.11
200176.360.25171.030.92290.0027179.610.98873.960.5454134.79
280202.550.28195.630.90350.0025204.500.98964.080.5498158.68
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Chen, Z.; Liu, F.; Liao, B.; Zhang, T.; Chen, F.; Wang, J.; Liao, C.; Xu, S. Deep Removal of Fluoride Ions from Spent Ternary Lithium-Ion Batteries Leachate Using Porous La@Zr Adsorbent. Inorganics 2025, 13, 369. https://doi.org/10.3390/inorganics13110369

AMA Style

Chen Z, Liu F, Liao B, Zhang T, Chen F, Wang J, Liao C, Xu S. Deep Removal of Fluoride Ions from Spent Ternary Lithium-Ion Batteries Leachate Using Porous La@Zr Adsorbent. Inorganics. 2025; 13(11):369. https://doi.org/10.3390/inorganics13110369

Chicago/Turabian Style

Chen, Zaoming, Fupeng Liu, Bin Liao, Tao Zhang, Feixiong Chen, Jie Wang, Chunfa Liao, and Shengming Xu. 2025. "Deep Removal of Fluoride Ions from Spent Ternary Lithium-Ion Batteries Leachate Using Porous La@Zr Adsorbent" Inorganics 13, no. 11: 369. https://doi.org/10.3390/inorganics13110369

APA Style

Chen, Z., Liu, F., Liao, B., Zhang, T., Chen, F., Wang, J., Liao, C., & Xu, S. (2025). Deep Removal of Fluoride Ions from Spent Ternary Lithium-Ion Batteries Leachate Using Porous La@Zr Adsorbent. Inorganics, 13(11), 369. https://doi.org/10.3390/inorganics13110369

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