Comparison of Nature and Synthetic Zeolite for Waste Battery Electrolyte Treatment in Fixed-Bed Adsorption Column

Abstract

To support a sustainable energy development, CO₂ reduction for carbon neutralization and water-splitting for hydrogen economy are two feasible technical routes, both of which require a significant input of renewable energies. To efficiently store renewable energies, secondary batteries will be applied in great quantity, so that a considerable amount of energy needs to be invested to eliminate the waste battery electrolyte pollution caused by heavy metals including Cu²⁺, Zn²⁺ and Pb²⁺. To reduce this energy consumption, the removal behaviors of these ions by using clinoptilolite and zeolite A under 5, 7 and 10 BV h⁻¹ in a fixed-bed reactor were investigated. The used zeolites were then regenerated by a novel NH₄Cl solution soaking, coupled with the ultrasonication method. Further characterizations were carried out using scanning electron microscopy, N₂ adsorption and desorption test, and wide-angle X-ray diffraction. The adsorption breakthrough curves revealed that the leaching preference of clinoptilolite was Pb²⁺ > Cu²⁺ > Zn²⁺, while the removal sequence for zeolite A was Zn²⁺ > Cu²⁺ > Pb²⁺. The maximum removal percentage of Zn²⁺ ions for clinoptilolite under 5 BV h⁻¹ was 21.55%, while it was 83.45% for zeolite A. The leaching ability difference was also discussed combining with the characterization results. The fact that unit cell stayed the same before and after the regeneration treatment approved the efficacy of the regeneration method, which detached most of the ions while doing little change to both morphology and crystallinity of the zeolites. By evaluating the pH and conductivity changes, the leaching mechanisms by adsorption and ion exchange were further studied.

1. Introduction

Sustainable energy development is of key importance to the human society, which is especially the case when facing the fossil fuel depletion and the associated global warming issues. To tackle this, great efforts have been made to achieve the carbon neutralization via CO₂ reduction to hydrocarbon fuels [1,2]. Alternatively, the hydrogen fuel can be utilized instead in order to totally eliminate the carbon-related issue, which can be produced simply via the water-splitting reaction [3,4]. In both ways, a significant amount of energy is required to facilitate the reduction reaction, which has to be coming from various renewable sources such as solar, wind, geothermal and nuclear energy in order to ensure the sustainability. On the other hand, the urge to preserve renewable energies or smoothly couple them with electrical grids requires an effective large-scale energy storage/conversion system, such as batteries and electrolyzers [5]. Batteries are well-known for their high energy efficiency and fast response. Among them, the commercial lithium-ion battery is already very mature in technology, but it still needs further improvement in cost and safety before being applied into the large-scale electrical grid [6]. On the other hand, the rechargeable metal-air battery such as aqueous Zn-air battery is also promising for this mission considering its great cost-efficiency and high safety level [7]. As for electrolyzers, they can convert the renewable energy into stable chemicals such as hydrogen gas, which have unique advantages such as negligible self-discharge for long-term storage, low-cost expansion of storage capacity and high energy density. However, the energy efficiency would be lower due to the overpotential loss.

For both batteries and electrolyzers, the electrode is one of the most important components where the electrochemical reaction takes place. Its active surface area, catalytic capability as well as stability, strongly determine the device performance, including power density, energy efficiency and long-term durability. Therefore, significant research has been conducted in exploring new catalysts, catalyst structures and synergistic catalyst combinations, among which the nanostructured electrode is more advanced than conventional monolithic electrodes. On the other hand, the electrolyte is also a prerequisite component which determines the ohmic resistance of the energy device. In general, it contains a large extent of heavy metal ions, which can be a very serious environmental problem considering the ever-increasing demand for energy storage. For instance, as the mostly used heavy metal in daily applications, the high concentration and the high toxicity of the Cu²⁺ made it urgent to be removed from the water system [8]. Hence, the heavy metal ions in the waste electrolyte need to be removed efficiently, especially for preventing the water pollution resulted from copper, lead, zinc, mercury and manganese ions that have been reported to be increasingly serious in the estuarine floodplain areas [9,10,11]. Heavy metals including Pb²⁺ in the sediment can accumulate through the food chain and eventually enter the human body [12], causing damage to the kidney, red blood cells and even DNA damage, eventually leading to conformational changes [13]. These are likely to result in cell-cycle modulation, carcinogenesis, or apoptosis, even at very low concentrations [14,15].

Conventional methods have been used to remove the heavy metal ions from contaminated water, including chemical precipitation [16], electrochemical methods [17], membrane filtration [18] and ion exchange and adsorption. These either require extra electricity input or create additional slurry that demands further treatment. Among these methods, ion exchange and adsorption stand out for its considerable treatment capacity, high removal efficiency, fast response and low energy consumption [14,19]. Moreover, adsorption was considered to be a cost-efficient, easy, flexible and durable process [20]. Due to their abundant resources, renewable property and relatively low cost, zeolites were massively applied in the fields of adsorption, catalysis and ion exchange [21,22]. Zeolites are microporous crystalline aluminosilicates minerals with cage-like structures [23]. The primary building unit of zeolite is based on TO₄ tetrahedra, where T is aluminum or silicon atom, and this structure makes zeolite a suitable material for ion exchange [24]. Some silicon cations are substituted by aluminum cations, yielding a net negative charge in the tectosilicate framework, which gives zeolites a cation exchangeability [25]. Several pieces of literature proved that natural zeolite such as clinoptilolite has been widely applied into the fields of catalytic activities [26] and electrodes [27]. Meanwhile, it was also implemented globally over the years as the most widespread adsorbent to remove heavy metals from wastewater [28,29,30,31]. Zeolite A is usually synthesized and used as the carrier for basis of catalyst [32] or selective electrode [33]. Zeolites received the spotlight because of the high catalytic adsorption capacity, controlled acidity, confinement effects and high stability when applied as the catalyst [34].

Many studies have been conducted for leaching heavy metals from contaminated water [35,36] in batch mode. On the other hand, using zeolite for the removal of heavy metals in a fixed-bed column has been attracting attention due to the fact that it can better mimic the real contaminated water treatment process [37,38,39]. In fixed-bed studies, most of them focus on the selectivity of a certain type of zeolite towards different ions, while little attention is paid to the difference in the leaching performances among different zeolites. Therefore, in this work, we examined clinoptilolite and also zeolite A in the fixed-bed column to compare their leaching performances as well as their corresponding selectivity towards copper, lead and zinc ions.

The reactivation of used adsorbents is also important in industrial applications. Usually, acid, including nitric acid [40], base or salts were utilized in the regeneration process. However, zeolite is material with aluminol groups at the edge; when zeolite is put under a low pH value (pH < 4) environment, the gibbsite edge begins to dissolve [41]. Thus, harsh treatment should be avoided. Herein, the combination of soaking and ultrasonic bathing method was proposed as a novel regeneration method. It has been proved that most natural zeolites in their exchanged form are selective for NH₄⁺ experimentally [42] and theoretically [43]. Therefore, the combination of NH₄Cl solution soaking and ultrasonic bathing is likely to enhance regeneration efficiency, which has never been reported before to the best of our knowledge. In general, this work will provide a sustainable treatment method with low energy consumption for waste battery electrolyte by reusing the zeolites, which will contribute to the achievement of clean water and sanitation (goal 6), responsible consumption and reproduction (goal 12), protecting the life on land (goal 15) as well as the life below water (goal 14) of the 17 Sustainable Development Goals (SDGs).

2. Materials and Methods

2.1. Adsorption Experiment Raw Materials

Lead (II) nitrate (Pb(NO₃)₂, 99%), copper (II) sulphate pentahydrate (CuSO₄⋅5H₂O), zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl ≥ 99.5%) were purchased from Sigma-Aldrich with analytical grade. Heavy metal bulk solutions at a concentration of 0.5 g L⁻¹ were prepared by dissolving the corresponding salts in the deionized water to mimic the waste battery electrolyte. A 0.01 M nitric acid (HNO₃) was used to adjust the initial solution pH to 4 in order to avoid precipitation during all ion exchange experiments. The average size of clinoptilolite was in the range of 9–16 mm, while that of zeolite A is approximately 5 mm. All zeolites were washed with distilled water five times to remove residue dust on the surface and then dried at 60 °C for 3 days.

2.2. Fixed-Bed Adsorption

The fixed-bed adsorption column was designed as shown in Figure 1. The solution with a specific concentration (C) was injected at a constant volumetric rate (Q) through a peristaltic pump from the bottom of the column, and then the liquid samples were collected from the top of the column. To gain more precise breakthrough curves, samples were taken out every 10 min at the beginning of the experiment for 1 h. After that, the sampling time was set to be 20 min. The diameter and the length of the column were 4.2 cm and 21 cm, respectively, and the empty bed volume (BV) was calculated to be 291 mL.

Fixed bed experiments were carried out in order to compare the leaching performances of zeolite A and clinoptilolite. Three different heavy metal ions (Cu²⁺, Pb²⁺ and Zn²⁺) and three different volumetric flowrates (5 BV h⁻¹ = 24.25 mL min⁻¹, 7 BV h⁻¹ = 33.95 mL min⁻¹ and 10 BV h⁻¹ = 48.5 mL min⁻¹) were investigated in this project, and each experiment lasted for 3 h to ensure that the leaching process reached a stable state.

2.3. Characterization of the Zeolites Associated with Heavy Metal Adsorption Ions

The samples were dried under 60 °C for 3 days and then reserved for the following characterizations: Scanning electron microscopy (FEI Quanta 200 Environmental SEM) was used to study the surface morphology of zeolite samples before and after the adsorption and regeneration. Energy Dispersive X-ray Spectroscopy (EDX) was used to analyze the elemental composition of the adsorbent. The dried samples were further ground into powders and sent for characterizations including N₂ adsorption and desorption test, also called Brunauer, Emmett and Teller (BET) test, for the measurement of the pore size and the surface area of the samples. An XRD diffractometer (PANalytical XRD5 (Phillips)) was also used to investigate the crystal phases and the mineral identity of these samples. The X-ray source was generated by copper Kα radiation, the scanning range started from 15° to 100° at a rate of 5°/min, 0.02°/step.

The heavy metal concentrations in the liquid samples were measured by inductively coupled plasma optical emission spectrometry (ICP-OES). The exit relative metal concentration (C_t/C₀) was defined by the following equation:

$${\mathit{C}}_{\mathit{t}}{/\mathit{C}}_0=\frac{\left({\mathit{C}}_0-{\mathit{C}}_{\mathit{R}}\right)}{{\mathit{C}}_0}\times 100\%$$

(1)

where C₀ is the initial solution concentration, C_t is the solution concentration at time t, C_R represents the removed solution concentration. Therefore, the smaller the C_t/C₀ value, the more the corresponding contaminants are removed. By plotting C_t/C₀ versus bed volume, the breakthrough curves were then obtained. Meanwhile, the pH and the conductivity of the samples were measured simultaneously by the pH meter (Eutech PC 2700, Thermo Scientific, Waltham, MA, USA).

2.4. Regeneration Experiments

The used zeolites were washed 5 times with distilled water and placed in an oven at 60 °C for 3 days to be fully dried. Then, they were weighed and poured into a 500 mL beaker before adding 300 mL regeneration solution (NH₄Cl at the concentration of 1 g L⁻¹), and the mixture was ultrasonicated at room temperature for 2 h. The regenerated zeolite was also washed 5 times with distilled water and placed in an oven at 60 °C for 3 days to be fully dried.

3. Results

3.1. Heavy Metal Ions Leaching Experiments

The adsorption behavior of both zeolites toward 0.5 g L⁻¹ Cu²⁺, Zn²⁺ and Pb²⁺ was studied under 5 BV h⁻¹, 7 BV h⁻¹ and 10 BV h⁻¹ in a fixed-bed adsorption column. As shown in Figure 2, the leaching speed of Cu²⁺, Zn²⁺ and Pb²⁺ ions via both zeolites gradually decreased over time. The lower flow rate of the feed solution in the column provided a longer contact time for the adsorption process between the heavy metal ions and the adsorbents. Therefore, 5 BV h⁻¹ flow rate provided the longest contact time, hence enhancing the leaching performance.

Overall, Zn²⁺ has more affinity to Zeolite A, while Pb²⁺ was more prone to be adsorbed by clinoptilolite. The corresponding pH and conductivity evaluations were also illustrated in Figure 3 and Figure 4. After the Zn²⁺ solutions passed through the fixed-bed adsorption column with clinoptilolite, the pH increased from 4 to 6.5 (on average) and there were negligible changes during the whole experiment time. This indicates that the amount of H⁺ ion in the solution decreased due to the H⁺/Na⁺ exchange according to Kurtoğlu and Atun [44]. In the case of zeolite A, the pH increased to 8 (on average) and then decreased to 6.5 (on average), which could be attributed to the increased concentration of heavy metal ions in the effluent solution. The ions bounded with the H₂O molecular, leading to the hydrolysis effect and resulting in a decrease of pH value [45].

As shown in Figure 4, the conductivity values decreased for all the experiments as a function of time, except for clinoptilolite leaching Pb²⁺. This indicates that the number of movable electrolyte ions in the solution decreased, which may be resulted from the adsorption mechanism. The existing ions in the bulk were adsorbed into the zeolite matrix, leading to a decrease in the conductivity of the effluent solution. It is worth noting that in the experiment of clinoptilolite leaching Pb²⁺, another removal behavior appeared. The conductivities in the effluent solutions nearly stayed at the same level around 400 μS (the conductivity of raw solution was 404 μS), revealing that there might be only ion exchange in the removal process [38].

As shown in Figure 5, at the end of experiments when using clinoptilolite, the removal percentage of Pb²⁺ was the most (62.4%), followed by Cu²⁺ (32.7%), and the removed Zn²⁺ was the least (21.55%). Under the same experimental conditions, zeolite A adsorbed the most amount of Zn²⁺ and the least Pb²⁺. This shows that the selectivity sequence among these three ions for clinoptilolite is: Pb²⁺ > Cu²⁺ > Zn²⁺, while it was Zn²⁺ > Cu²⁺ >Pb²⁺ for zeolite A. In addition, the removal percentage for zeolite A towards Pb²⁺ is the least among all three ions, which can be explained by the Hard-Soft interaction theory: the harder the cations, the higher the charge density they have, and their d-orbitals do not participate in π-bond formation. This led to the higher possibility to conduct the electrostatic interaction [46,47]. However, as a soft cation, Pb²⁺ was least adsorbed by the zeolite A.

3.2. Regeneration Experiments

As can be seen from Figure 6a, the regenerated clinoptilolite followed a similar adsorption behavior with the clean clinoptilolite at the beginning of the experiment. However, as the adsorption proceeded, the regenerated clinoptilolites showed a weaker leaching ability than the pristine clinoptilolites. At the end of the adsorption, the removal percentage (1 − C_t/C₀) × 100% dropped from 23.91% to 16.63% after the regeneration. This phenomenon also occurred frequently in other studies [12,48], illustrating two facts: 1. The regeneration method was effective, which detached most of the Zn²⁺ ions that had been bound to the zeolite adsorption sites; 2. Some of the residue Zn²⁺ ions were not completely removed from the zeolite matrix and still occupied part of the adsorption sites, resulting in a decrease in the removal percentage after regeneration.

The removal performance was represented by the removal percentage of Zn²⁺ ions in the solution at the end of the experiment. The corresponding removal percentages are listed in

Table 1. The removal performances of the clean zeolites used to remove the heavy metal ions for the first time (Original experiment) and the regenerated zeolites used to remove the heavy metal ions (Regeneration experiment).

		Removal Percentage (%)
Clinoptilolite leach Zn2+ at 5 BV h−1	Original experiment	23.91
	Regeneration experiment	16.63
Zeolite A leach Zn2+ at 5 BV h−1	Original experiment	84.44
	Regeneration experiment	74.99

. Our findings suggest that the adsorption ability of each zeolite was similar after the regeneration, and the regeneration method to reactivate the used zeolite was effective. This work is a novel empirical example of the application of ultrasonication to treat contaminated zeolites. Our results encourage further research to investigate the processes and mechanisms using different classes of adsorbents and contaminants.

3.3. Supportive Characterization of the Zeolites Associated with Heavy Metal Adsorption

3.3.1. SEM and EDX

SEM-EDX analysis was conducted on clean and post-treatment samples of each zeolite. Clinoptilolite is a kind of material with a rough surface as shown in Figure 7a, and the ultrasonic bath did not change much on its morphology. As shown in Figure 7b, there are some plate-like coagulations on the surface. Additionally, smaller cubic-structured particles were formed on zeolite A after the adsorption process in Figure 7d, which indicates that there existed some substances on the surface after the adsorption of zinc ions.

In terms of the EDX analysis, the elements present in each zeolite sample and their atomic percentages were displayed in

Table 2. Elemental analysis of clean clinoptilolite, zinc-contaminated clinoptilolite, clean zeolite A and zinc-contaminated zeolite A.

Element Content (%)	Si	Al	K	Na	Ca	Mg	O	Zn
Clean clinoptilolite	62.59	15.11	7.01	0	3.59	3.38	8.31	0
Zn2+-contaminated clinoptilolite	61.69	12.26	5.31	0	5.21	2.65	11.55	1.33
Clean zeolite A	46.97	25.57	3.88	5.43	2.12	3.7	12.33	0
Zn2+-contaminated zeolite A	45.53	24.77	3.27	6.17	3.05	3.49	11.69	2.03

. Zinc was absent from the clean zeolites, and after the adsorption reaction, the zinc content increased to 1.33% for clinoptilolite, and it increased to 2.03% for zeolite A. These results directly proved that the adsorption was successful. Plus, the ratio of Si/Al of clean clinoptilolite was around 4.14, which was similar to reported data 4.84 by Nezamzadeh-Ejhieh and Moeinirad [49,50].

3.3.2. BET

The BET was also conducted for the aforementioned samples, and the results are shown in

Table 3. BET results of 4 samples (1: clean clinoptilolite; 2: Zn²⁺-contaminated clinoptilolite; 3: clean zeolite A; 4: Zn²⁺-contaminated zeolite A).

	1	2	3	4
BET surface area (m2 g−1)	30.99	44.17	40.69	301.48
Micropore Volume (×10−2 cm3 g−1 STP)	0.17	0.31	1.07	1.40
Micropore Area (m2 g−1)	2.74	5.23	18.68	244.28
External Surface Area (m2 g−1)	28.26	38.95	22.01	57.20

below. After the adsorption, the surface area of clinoptilolite increased from 30.99 m² g⁻¹ to 44.17 m² g⁻¹. Similarly, the surface area of zeolite A drastically increased from 40.69 m² g⁻¹ to 301.48 m² g⁻¹, indicating that a more complex structure was formed.

3.3.3. XRD

The lattice parameters of the zeolites are also listed in the

Table 4. The lattice parameters of zeolites before and after the adsorption of Zn²⁺.

	1	2	3	4
Major Phase	HEU (Heulandite)	CHA (Chabazite)	Sodium Aluminum Silicate	Sodium Zinc Aluminum Silicate
a (Å)	17.536	8.845	24.9506	12.152
b (Å)	17.277	16.607	24.9506	12.152
c (Å)	7.409	9.746	24.9506	12.152
α	90°	90°	90°	90°
β	116.62°	123.19°	90°	90°
γ	90°	90°	90°	90°

below, where a, b and c represent the size of the unit cells, while α, β and γ represent the angles of these unit cells. The tested samples include: 1. clean clinoptilolite; 2. Zn²⁺-contaminated clinoptilolite; 3. clean zeolite A; 4. Zn²⁺-contaminated zeolite A. Clinoptilolite unit cell has a wider β angle, while the α and γ angles are 90°. The heavy metal removal procedure reduced the overall size of the unit cell and transferred the lattice structure of clinoptilolite from the HEU phase-type to CHA phase-type. This phenomenon also happened to zeolite A. The lattice size of the zeolite A was decreased by half from that of the previous state. The detailed matching spectra was shown in the Supporting Information, where typical XRD peaks of ZnO were assigned at 31.84 (100), 34.51 (002), 47.63 (102), 56.71 (110), 62.69 (103), 69.18 (201) which agree with JCPDS PDF No. 88-0287 [51].

3.4. Leaching Mechanism

The charge deficit, which was resulted from the replacement of Si⁴⁺ by Al³⁺, enabled the tridymite structure to adsorb cations. Hence, both the adsorption and ion exchange happened simultaneously during the leaching process [52,53,54]. The leaching mechanisms can be summarized by the following equations:

$${\mathrm{nSi}–\mathrm{OH}+\mathrm{M}}^{\mathrm{n}+} \stackrel{ }{\leftrightarrow }{ (\mathrm{Si}–\mathrm{O})}_{\mathrm{n}}{–\mathrm{M}+\mathrm{nH}}^{+}$$

(2)

$${\mathrm{SiO}}^{-}{+\mathrm{MOH}}^{+} \to \mathrm{SiOMOH}$$

(3)

$${\mathrm{nSiO}}^{-}{+\mathrm{M}}^{\mathrm{n}+} \stackrel{ }{\leftrightarrow }{ (\mathrm{Si}–\mathrm{O})}_{\mathrm{n}}–\mathrm{M}$$

(4)

$${\mathrm{nMOH}}^{+}{+\mathrm{M}}^{\prime }\left(\mathrm{z}\right) \stackrel{ }{\leftrightarrow }{ \mathrm{M}}_{\mathrm{n}}{\left(\mathrm{z}\right)+\mathrm{M}}^{\prime \mathrm{n}+}{+\mathrm{nOH}}^{-}$$

(5)

where Mⁿ⁺ represents the heavy metal ions in the bulk solutions, while M’(z) represents the free ions in the zeolites matrix. Among those equations, Equations (2)–(4) illustrate the adsorption process, while Equation (5) represents the ion exchange mechanism. A similar phenomenon was also found in using clinoptilolite-based electrodes for bromate determination. Electroactive cations in zeolite were exchanged by zeolitic compounds, hence the ion exchange was achieved through replacing the modifier agent to the cations of the supporting electrolyte in solution [55].

During the leaching process, more negatively charged surfaces became available, therefore leading to greater Zn²⁺ uptake [56]. According to the analysis of the characterization, the results of the experiments as well as the literature studies, the leaching procedure mainly consists of 3 steps. Take zeolite A leaching Zn²⁺ as an example; the details are shown in Figure 8.

In Figure 8a, at the beginning of the adsorption, the pH of the bulk solution was 4. According to the cation activity series, H⁺ was also involved in the exchange process. At this time, monovalent H⁺ entered the zeolite matrix and led to the rapid pH rise of the solution. Meanwhile, ions including K⁺ and Ca²⁺ were also substituted, and therefore, a huge increase of conductivity from 915 μS (raw Zn²⁺ solution conductivity) to around 3300 μS under 5 BV h⁻¹ was observed. As the pH was elevated in Figure 8b, more negatively charged surfaces become available, therefore leading to greater metal uptake, even at precipitation pH value [56]. This explained the remarkable leaching behavior of zeolites at the beginning of the experiments. During this stage, some ions were precipitated, while other partial ions entered the zeolite matrix. Both of the activities resulted in a dramatic drop in conductivity. As shown in Figure 8c, after the Zn²⁺ ions entered the lattice structure, the hydrolysis began as:

$${{\left[\mathrm{M}\right(\mathrm{H}}_2{\mathrm{O})}_{\mathrm{x}}]}^{\mathrm{c}+}{+\mathrm{H}}_2\mathrm{O} \stackrel{ }{\leftrightarrow }{ \left[\mathrm{M}\right(\mathrm{H}}_2{\mathrm{O})}^{\mathrm{x}-1}{\left(\mathrm{OH}\right)]}^{(\mathrm{c}-1)+}{+\mathrm{H}}_3{\mathrm{O}}^{+}$$

(6)

Zinc ions combined with water molecules created larger complexes and therefore produced H⁺. This process lowered the pH of the solution back to near neutral. This large complex gathered on the surface of the zeolite, increasing the specific surface area as shown in the BET results. Over time, the leaching process will reach saturation, that is, adsorbents will be exhausted. From then on, the conductivity in the solution will remain at a certain level.

4. Conclusions

In this work, the heavy metal ions leaching performances of natural clinoptilolite and synthesized zeolite A at different flow rates were comprehensively studied in a fixed-bed adsorption column. The removal preference of the two types of zeolites was found to be Pb²⁺ > Cu²⁺ > Zn²⁺ when using clinoptilolite, while it was Zn²⁺ > Cu²⁺ > Pb²⁺ for zeolite A. Among the two zeolites used for adsorption experiments, zeolite A is better for the adsorption of heavy metal ions in water than clinoptilolite. Namely, zeolite A leached 4 times higher Zn²⁺ ions under 5 BV h⁻¹ in comparison to clinoptilolite (83.45% for zeolite A and 21.55% for clinoptilolite). A novel regeneration method was applied by combining the ultrasonication and NH₄Cl solution soaking. The regeneration method was effective without influencing the intrinsic zeolite properties. The unit cell stayed the same before and after the regeneration treatment, while the adsorption process created smaller secondary structures, especially on zeolite A. The surface area of zeolite A before adsorption was 40.69 m² g⁻¹ and it was 301.48 m² g⁻¹ after the adsorption. This was caused by the hydrolysis phenomenon. This study extends the use of zeolite beyond electrical-chemical wastewater treatment and agriculture: our results encourage testing the mentioned mechanisms when the novel regeneration method is applied.