Description:BACKGROUND

FIELD OF THE DISCLOSURE
[0001] Various embodiments of the disclosure relate generally to modified zeolites. More specifically, various embodiments of the disclosure relate to modified zeolites comprising chelating agents covalently bound to an aminated zeolite derivative and application of the modified zeolites for adsorption of metal ions from an aqueous solution.
DESCRIPTION OF THE RELATED ART
[0002] Water pollution is a major environmental concern, especially the contamination of water bodies by metal ions. Industrial activities, such as mining, electroplating, and chemical manufacturing, often discharge heavy metals like lead, mercury, cadmium, and chromium into water sources. The heavy metal ions are highly toxic, non-biodegradable, and can accumulate in living organisms, leading to severe health hazards, including neurological damage, kidney failure, and even cancer. Alkaline earth metal ions such as calcium (Ca), magnesium (Mg), strontium (Sr), and barium (Ba) are also of particular concern. The alkaline earth metals are commonly found in natural water sources due to geological formations and their concentrations are further elevated due to industrial discharges. Calcium and magnesium metal ions contribute to water hardness, which can lead to scale formation in pipes, boilers, and other water-handling equipment causing economic losses due to increased energy consumption and maintenance costs.
[0003] Several methods have been developed to address the removal of metal ions from water. Chemical precipitation is one method involving the addition of chemical reagents in water to form insoluble metal compounds, which may be removed through filtration or sedimentation. However, chemical precipitation may require high chemical usage leading to secondary pollution.
[0004] Ion-exchange is another method where specific metal ions are replaced with less harmful ions. For example, heavy metal ions which are present in the water may be replaced with more benign sodium or potassium ions. However, prolonged exposure to sodium or potassium ions at concentrations exceeding the recommended human intake could potentially be fatal. Filtration using semi-permeable membrane is another method to separate metal ions. However, filtration methods involve high energy consumption and operational costs.
[0005] Adsorption, a purely surface phenomenon is another method for removal of metal ions. Adsorption is highly effective at removing even trace amounts of metal ions from water, making it suitable for treating low-concentration pollutants. Further, adsorption does not typically generate harmful by-products or secondary pollution, and the adsorbents can often be regenerated and reused.
[0006] Zeolites are natural or synthetic materials having a crystalline structure. A typical zeolite has a tetrahedral crystal structure formed as TO4, where T can be silicon, or aluminum surrounded by oxygen atoms. They exhibit a distinctive three-dimensional framework with well-organized pores and channels containing water (H2O) molecules and cations such as potassium ions, sodium ions, calcium ions, and magnesium ions. The zeolites vary in structures, and chemical compositions, hence their adsorption properties.
[0007] The zeolites are known to adsorb metal ions through molecular sieving whereby small molecules pass through the pores and channels and get adsorbed while large molecules cannot pass through and are discarded. Additionally, zeolites can preferentially remove heavier metal ions and ammonia through ion exchange by cation exchange with other ions present in the zeolite structure.
[0008] Modifying zeolites by treatment with various reagents has recently gained considerable interest. It is known that zeolites on treatment with an acid, base, or salt have higher cation adsorption and heavy metal removal efficiency. However, an excess amount of acid, base, or salt can affect a crystallinity of the zeolite and consequently, lower the adsorption capacity.
[0009] Zeolites have been modified with cationic surfactants which convert the zeolites into multifunctional adsorbents suitable for cations, anions, and molecular species. The interaction between the zeolites and the cationic surfactants occurs through the exchange of organic cations of the surfactant and the inorganic cations of the zeolite, thus forming a positive surface on the zeolite and hence is weak compared to chemical bonding. Further, the cationic surfactants may alter the pore volume, pore diameter, and surface area of the natural zeolites.
[0010] In “New hybrid adsorbent based on APTES functionalized zeolite W for lead and cadmium ions removal: Experimental and theoretical studies” by Prócoro Gamero-Melo et. al.; Chemical Engineering Journal, Volume 499, 2024, 156056, the zeolite W surface was functionalized chemically using aminopropyltriethoxysilane (APTES). The adsorption of metal ions was found to be highly pH dependent. Further, the adsorption of metal ions proceeded through weak interactions such as electrostatic interaction, ion exchange, and hydrogen bonding between the surface APTES group and the metal ions.
[0011] “Comparative study of the absorption of active zeolite and ethylenediamintetraacetate (EDTA) modified zeolite as absorbent in a mixture of Copper (II), Nickel (II), and Zinc (II) ions”, by H Marpaung et al, Journal of Chemical Natural Resources Vol. 2, No. 01, 2020, 58-65 disclosed natural zeolite activation using 15% hydrochloric acid (HCl) to remove impurities and regulate the location of the ions in the zeolite. The HCl-treated activated zeolite was modified using EDTA. However, the interaction between the zeolite and EDTA is purely a physical interaction and not a chemical one. As a result, the EDTA is loosely bound on the zeolite surface.
[0012] Limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of described systems with some aspects of the present disclosure, as set forth in the remainder of the present application and with reference to the drawings.
SUMMARY
[0013] According to embodiments of the present disclosure, a modified zeolite is provided. The modified zeolite comprises an aminated zeolite derivative derived from an aminated zeolite obtained by amination of a zeolite. The modified zeolite further comprises a chelating agent covalently bound to the aminated zeolite derivative.
[0014] In another embodiment, a system for adsorbing metal ions from an aqueous solution is provided. The system comprises the modified zeolite.
[0015] In yet another embodiment, a process for adsorbing metal ions from an aqueous solution comprising contacting the modified zeolite with the aqueous solution is provided. The modified zeolite adsorbs metal ions from the aqueous solution.
[0016] In yet another embodiment, a method of preparing a modified zeolite is provided. The method comprises treating a zeolite with an aminating agent to obtain an aminated zeolite. The method further comprises treating the aminated zeolite with a chelating agent to obtain the modified zeolite.
BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1 is a flow chart that illustrates a method of preparing a modified zeolite, in accordance with an exemplary embodiment of the disclosure;
[0018] FIG. 2 is a bar chart displaying concentrations of metal ions plotted against type of materials; and
[0019] FIG. 3 is a bar chart of percentage removal of calcium ions plotted against number of cycles.
[0020] Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description of exemplary embodiments is intended for illustration purposes only and is, therefore, not intended to necessarily limit the scope of the present disclosure.
DETAILED DESCRIPTION OF EMBODIMENTS
[0021] The following description illustrates some exemplary embodiments of the disclosed disclosure in detail. Those of skill in the art will recognize that there are numerous variations and modifications of this disclosure that are encompassed by its scope. Accordingly, the description of a certain exemplary embodiment should not be deemed to limit the scope of the present disclosure.
[0022] The term “comprising” as used herein is synonymous with “including,” or “containing,” and is inclusive or open-ended and does not exclude additional, unrecited elements, or process steps.
[0023] All numbers expressing quantities of ingredients, property measurements, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained.
[0024] These and other features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout.
[0025] As used throughout this disclosure, “zeolites” may refer to micropore-containing, and/or mesopore-containing inorganic materials with regular intra-crystalline pores and channels. As used herein, the term “micropore” refers to pores in a structure with a diameter of less than or equal to 2 nanometers (nm), and greater than or equal to 0.1 nm. As used herein, the term “mesopore” refers to pores in a structure with a diameter greater than 2 nm and less than or equal to 50 nm. Unless otherwise described herein, the “pore size” of a material refers to the average pore size, but materials may additionally include mesopores having a particular size that is not identical to the average pore size.
[0026] As used herein, the term “adsorption” generally refers to processes of adhesion of metal ions onto the surface of an adsorbent through various mechanisms including surface-complex formation (complexation), electrostatic interactions, ion-exchange, molecular sieving, diffusion, and similar processes. However, when referring to modified zeolites, “adsorption” primarily denotes the mechanism of complexation.
[0027] As used herein, the term "aqueous solution" refers to a solution in which water is the solvent. The solution may contain dissolved substances such as salts, acids, bases, or other solutes. Unless otherwise specified, the term encompasses solutions of varying concentrations, pH levels, and ionic compositions.
[0028] FIG. 1 is a flow chart 100 that illustrates a method of preparing a modified zeolite through exemplary steps 102 to 104, according to embodiments of the present disclosure. At step 102, a zeolite is treated with an aminating agent to obtain an aminated zeolite.
[0029] The zeolites, as described herein include, for example, aluminosilicates, silicates, or combinations thereof, having a tetrahedral structure of TO4, where T stands for aluminum, and/or silicon surrounded by oxygen atoms. The silicon and aluminum tetrahedra, SiO4 and AlO4, respectively, linked by oxygen atoms form a crystalline, three-dimensional framework. The crystalline, three-dimensional framework consists of pores and channels having well-defined pore sizes. Suitable zeolites for amination include, but are not limited to, zeolite 3A, zeolite 4A, zeolite 5A, zeolite 13X, zeolite Y, clinoptilolite zeolite, zeolite Beta, zeolite ZSM-5, or combinations thereof. Due to the substitution of some silicon atoms with aluminum atoms, the suitable zeolites acquire a net negative charge, which can be balanced by the adsorption of cations through electrostatic interactions.
[0030] The cations inherently present in zeolites are exchangeable and can be replaced with other cations through ion-exchange during metal ion adsorption. In mechanisms such as molecular sieving or electrostatic interactions, the structure or physical properties of the zeolite such as surface area, pore size, and pore volume play a crucial role in determining the types of cations that can be adsorbed. For example, in adsorption through electrostatic interactions, an increase in negatively charged surface of the zeolite can enhance the adhesion of cationic metal ions. Due to the presence of pores and channels, the zeolites possess a high internal surface area for adsorption. Each of the zeolites differs in pore size, framework type, and silicon (Si) to aluminium (Al) ratio, and hence may have distinct adsorption behaviors. Modifying the structure or physical properties of zeolites can further alter their adsorption characteristics. Additionally, zeolites are mechanically strong, exhibit excellent thermal stability, and resist chemical degradation, making them ideal for applications such as the adsorption of metal ions from aqueous solutions.
[0031] Suitable aminating agents include, but are not limited to, 3-aminopropyltriethoxysilane (APTES), 3-aminopropyltrimethoxysilane (APTMS), N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS), N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAPTES), (3-Aminopropyl)methyldiethoxysilane (APMDES), (3-aminopropyl)methyldimethoxysilane (APMDMS), triethoxysilylpropylamine (TESPA), N-(6-aminohexyl)aminomethyltriethoxysilane, hexamethylenediamine (HMDA), ethylenediamine (EDA), or combinations thereof. In some embodiments, the aminating agent is aminopropyltriethoxysilane (APTES).
[0032] As will be appreciated, the aminating agent adds at least one amine functionality or amine functional group(s) (amine group) to the zeolite. The term “at least one” as used herein refers to having one amine group, or more than one amine group. The amination of the zeolite may be performed using two different methods, grafting and impregnation. The grafting method involves attaching an amine functional group (-NH2) to the zeolite surface via covalent bonds. The grafting method typically results in a higher degree of functionalization and more stable amine groups as they are bound to the zeolite structure. The grafting method may alter the physical properties of the zeolite. In one embodiment, grafting may enhance a surface area, porosity, and pore size of the zeolite.
[0033] The impregnation method is easier to implement when compared to the grafting method. The impregnation method involves immersing the zeolite in a solution containing the desired aminating agent to adsorb the aminating agent on its surface. After impregnation, the zeolite is washed and dried to remove unattached aminating agent. Impregnation method of amination may result in lower levels of amine functionalization and less stable amine groups compared to the grafting method of amination.
[0034] In one preferred embodiment, the step 102 of amination is performed using the grafting method. In a representative reaction [I], as shown below, zeolite [A] on reaction with aminopropyltriethoxysilane (APTES) [B], the silicon atom of an individual APTES molecule binds to the oxygen atoms that are available mostly on a surface, or accessible within the pores of the zeolite thus providing at least one amine functional groups to the aminated zeolite [C].
Reaction [I]

A B C

[0035] The amination may result in an addition of one amine group (-NH2) on zeolite or more than one amine group on zeolite. For example, the ethoxysilane groups of 3-aminopropyltriethoxysilane (APTES) can form hydrogen bonds with hyroxyl groups present in zeolites leading to nucleophilic attack of the hydroxyl group on silicon atom of the ethoxysilane group. The nucleophilic attack can lead to the breaking of Si-OEt bond of the ethoxysilane group with the release of ethanol to form the aminated zeolite. Similarly, non-silane aminating agents such as ethanolamine (EA) can form hydrogen bonds with hydroxyl groups present in zeolites leading to nucleophilic attack of the hydroxyl group on carbon atom of ethanol group. The nucleaophilic attack can lead to the breaking of Et-OH bond of the ethanolamine with the release of ethanol to form the aminated zeolite.
[0036] A weight percent of the aminating agent to the total weight of the zeolite used for amination is in a range of 2 weight percent (wt %) to 25 weight percent.
[0037] Before amination, the zeolite is washed thoroughly with deionized water to remove impurities. In one embodiment, at step 102, the aminating agent is dissolved in a solvent to form a solution. The solvent may be selected based on the solubility of the aminating agent. Further, the aminating agent should not undergo any adverse reactions with the solvent. Suitable solvents include dichloromethane. The zeolite is added to the above solution with continuous stirring for a period of time in a range of 10 hours to 22 hours to form the aminated zeolite. The amination is performed at room temperature. As used herein, the term “room temperature” refers to a temperature in a range of 20 degrees Celsius (°C) to 35 °C. The aminated zeolite is washed with the solvent to remove any unreacted aminating agent and dried under vacuum at high temperature in a range of 70 °C to 90 °C for 7 to 12 hours.
[0038] At step 104, the aminated zeolite is treated with a chelating agent to form the modified zeolite. The chelating agent comprises at least one carboxylic acid group. The term “at least one” as used herein refers to having one carboxylic acid group, or more than one carboxylic acid group.
[0039] The chelating agent comprises ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), cis-1,2-cyclohexanediaminetetraacetic acid (CDTA), nitrilotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), or combinations thereof. In one embodiment, the chelating agent is EDTA.
[0040] In one embodiment, the chelating agent is activated using an activating agent to form an activated chelating agent. Examples of activating agents for EDTA include a combination of N-hydroxysuccinimide (NHS) and 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC). As known in the art, EDC activates the carboxyl group of EDTA but forms a highly unstable intermediate which is stabilized using NHS. The combination of EDC and NHS ensures efficient activation of the carboxyl groups of EDTA for bond formation with an amine group. The activating agent and the chelating agent are dissolved in a suitable solvent with stirring for a period of time in a range of 1 hour to 2 hours to form an activated chelating agent solution. Examples of solvents include dichloromethane (DCM), dimethyl formamide (DMF), dimethyl sulphoxide (DMSO), or combinations thereof.
[0041] At step 104, the aminated zeolite obtained from step 102, is provided in a solution of the chelating agent and stirred for a period of time in a range of 2 hours to 7 hours to form the modified zeolite. The solution of the chelating agent is prepared in a solvent such as dichloromethane (DCM), dimethyl formamide (DMF), dimethyl sulphoxide (DMSO), or combinations thereof. In another embodiment, the aminated zeolite is provided in the activated chelating agent solution and stirred for a period of time in a range of 2 hours to 7 hours to form the modified zeolite. The modified zeolite formed is isolated from the solution, washed with deionized water, and dried under vacuum at room temperature. The modified zeolite obtained may be in the form of beads, or in powdered form which may be compounded further to obtain a desired shape.
[0042] The concentration of the chelating agent to the total weight of the modified zeolites is in a range of 2 weight percent (wt %) to 25 weight percent.
[0043] According to embodiments of the present disclosure, a modified zeolite for adsorption of metal ions is provided. The modified zeolite comprises an aminated zeolite derivative derived from an aminated zeolite. The modified zeolite further comprises a chelating agent covalently bound to the aminated zeolite derivative. The modified zeolite is a reaction product of an aminated zeolite and a chelating agent produced using the method illustrated in FIG. 1.
[0044] The aminated zeolite derivative of the modified zeolite is derived from an aminated zeolite (for example, by following step 102 of FIG. 1) and has a structure, [II];

[II]
[0045] The aminated zeolite derivative [II] is obtained when the amine group of the aminated zeolite (structure C as illustrated in reaction scheme [I]) reacts with the carboxylic acid group of the chelating agent to form an amide, where -NH of structure [II] arises from the amine group on reaction with the carboxylic acid group of the chelating agent to form the modified zeolite. If the chelating agent has more than one carboxylic acid group, it can bind with other amine groups present in the zeolite framework to form a 3-dimensional network, as shown in structure [III].

[III]

[0046] In some embodiments, the modified zeolite has a desired pore diameter. The modified zeolite has a pore diameter in a range of 1.6 nanometers (nm) to 3 nm.
[0047] The modified zeolite of the present disclosure can adsorb metal ions from an aqueous solution. In one embodiment, the metal ions present in the aqueous solution can complex with the chelating agent moiety of the modified zeolite to form a modified zeolite-metal ion complex as shown in structure [IV].
[IV]

[0048] In prior art, the chelating or complexing agents are known for metal ion removal from an aqueous solution through complexation. However, the chelating agents, such as EDTA, form water-soluble metal complexes on complexation as a result the metal ions remain in the aqueous solution. The terms ‘chelation” or “complexation”, as used herein refer to multiple coordination bonds between chelating agents and metal ions leading to sequestration of the metal ions. The chelating agent of the modified zeolite is chemically bound to the zeolite. It is an advantage of the present disclosure by covalently binding the chelating agent on an insoluble adsorbent (zeolite), the metal ions on chelating with the modified zeolite are easily adsorbed from the aqueous solution.
[0049] The terms “removal efficiency” (RE) or “metal ion removal efficiency”, as used herein refers to a percentage of metal ions removed from an aqueous solution and is calculated as a percentage of difference between an initial concentration (Co) of ions in solution and final concentration (Cf) of ions in solution to the final concentration of ions in solution. In the present disclosure, the metal ions are removed from an aqueous solution through adsorption on the modified zeolite primarily by complexation with the chelating agent.
[0050] In some embodiments, a system for adsorbing metal ions from an aqueous solution comprising the modified zeolite is provided. In one embodiment, the system is a water filtration unit, where the water filtration unit comprises the modified zeolite in the form of beads, or in the form of powder. In one embodiment, the modified zeolites are loaded in a vertical column where the water containing metal ions flows in from the top and the modified zeolite adsorbs the metal ions present in the water. In another embodiment, the system comprises a horizontal filtration bed comprising the modified zeolite where the water containing metal ions flows over the bed to adsorb the metal ions from the water.
[0051] In one embodiment, the metal ion is a heavy metal ion. Examples of heavy metal ions include ions of metals including lead, zinc, mercury, nickel, manganese, copper, chromium, iron, cadmium, cobalt, tin, and combinations thereof. In some embodiments, the metal ion is an alkaline earth metal ion that may contribute to the hardness of the water. Examples of alkaline earth metal ions include ions of calcium (Ca), strontium, barium, and magnesium (Mg). In preferred embodiments, the metal ion is calcium, magnesium or combinations thereof.
[0052] The inventive modified zeolites have a net negative charge to adsorb the positively charged (cationic) metal ions. However, chelation or complexation is the major driving force for the adsorption of metal ions. Prior art un-modified zeolites remove metal ions through primarily ion-exchange mechanism. However, in the ion-exchange mechanism, sodium and/or potassium ions inherently present in the zeolite structure are replaced with heavier metal ions. As a result, sodium and/or potassium leach into the solution. Prolonged exposure to sodium and/or potassium ions at concentrations exceeding the recommended human intake could potentially be fatal.
[0053] The modified zeolites have larger surface area, and pore diameter due to amination and covalent bonding with the chelating agent when compared to zeolites without any modification. The adsorption of metal ions is further enhanced by having the desired pore diameter that allows for the diffusion of water into the modified zeolite structure. The pore diameter and the swelling of the modified zeolite increase a contact time and a contact surface available for adsorption thereby enhancing the adsorption of metal ions. Thus, the pore diameter, the overall negative charge on the modified zeolite, and the chelating abilities of the chelating agent contribute to its strong affinity for metal ions.
[0054] In prior art zeolites, the adsorption of metal ions is pH dependent and they function effectively only at a pH of 6 or below, or under acidic conditions. The inventive modified zeolites can function in neutral pH for metal ion adsorption. As used herein, the term “neutral pH” refers to a pH in a range of 6.5 to 7.5. It is an advantage of the modified zeolites that they function efficiently to remove metal ions from natural water sources, municipal water sources, and the like, where the pH ranges between 6.5 and 8.5.
[0055] In another embodiment, a process for water softening comprising contacting the modified zeolite produced using the method illustrated in FIG. 1 is provided. The term “water softening”, as used herein refers to the removal of dissolved calcium or magnesium ions from water. The term “water softening” is also termed as “hardness removal”, and relates to removal of calcium ions, or magnesium ions, or both. The water containing more than 200 milligrams per litre (mg/L) of dissolved calcium ions or magnesium ions is termed as hard water. The portable water or drinking water should have a minimum total hardness of 150 mg/L. The process comprises contacting the modified zeolite with an aqueous solution to remove metal ions from the aqueous solution.
[0056] The process of metal ion adsorption may be a batch process, or a continuous process. For example, a horizontal tank bed may be operated in a batch mode, where a batch of water is made to contact for a period of time to soften the water and is replaced with the next batch of water to be softened.
[0057] The modified zeolites of the present invention can be regenerated once the metal ion removal efficiency falls below accepted range on prolonged use. In one embodiment, the modified zeolite is regenerated by washing in deionized water. In another embodiment, the modified zeolite is regenerated by providing it in a solution comprising the chelating agent.
EXAMPLES
[0058] The present disclosure will now be described in greater detail by the
following non-limiting examples. It is understood that one skill in the art will envision additional embodiments consistent with the disclosure provided herein.
EXAMPLE 1
Preparation of aminated zeolite:
[0059] About 2 grams (g) of 6.819 milliliters (ml) of aminopropyltriethoxysilane (APTES) was dissolved in 90 ml of anhydrous dichloromethane (DCM) to form an aminating agent solution. 10 g of zeolite 3A beads were added to the aminating agent solution and magnetically stirred for 16 hours at room temperature in the dark to form white solids of aminated zeolite. Upon completion of the amination, the white solids were collected by filtering them using a filter paper and washed several times using DCM to remove ungrafted or unattached APTES. The aminated zeolite 3A beads (zeolite-NH2) were vacuum dried at 90° C overnight and stored for further use.
[0060] Fourier transform infrared (FTIR) spectra of aminated zeolite and un-modified zeolite 3A beads were recorded to confirm the formation of the aminated zeolite.
EXAMPLE 2
Preparation of modified zeolites
[0061] 1 g of EDTA was dissolved in 100 mL of deionized water, followed by the addition of 1 g of N-hydroxysuccinimide (NHS) and 0.5 g of 1,2-dichloroethane (EDC) to activate the carboxyl groups in EDTA over 2 hours of stirring. Subsequently, 5 grams of aminated zeolite from Example 1 were immersed in the activated EDTA solution and stirred for 5 hours. The resulting modified zeolite was thoroughly washed with deionized water and vacuum-dried for storage at room temperature.
[0062] A set of modified zeolites were prepared using varying concentrations of EDTA from 1 to 5 grams, and were labeled as zeolite-NH2@EDTA (containing 1 g of EDTA), zeolite-NH2@EDTA-2 (containing 3 g of EDTA), and zeolite-NH2@EDTA-3 (containing 5 g of EDTA), respectively. However, the zeolite-NH2@EDTA sample containing 1 g of EDTA demonstrated the highest efficiency for metal ion removal, attributed to the optimal EDTA concentration. Excessive EDTA deposition beyond this value did not enhance the removal efficiency.
Metal ion removal studies
[0063] The metal ion removal efficiencies of the zeolite (zeolite 3A), and modified zeolite (zeolite-NH2@EDTA) were estimated by providing each of the zeolites in separate solutions of calcium chloride (CaCl2) having an initial concentration of 1000 mg/L and determining metal ion concentrations post-treatment with the zeolites. The metal ion concentration of a solution, post-treatment with the zeolite may be determined from titration with EDTA, or by atomic absorption spectroscopy (AAS). FIG. 2 is a bar chart 200 depicting various metal ion concentrations namely sodium (Na), potassium (K), and calcium (Ca) in the calcium chloride solution post-treatment against type of materials, namely zeolite 3A and zeolite-NH2@EDTA. Bar diagram 202 corresponds to the metal ion concentrations of calcium chloride solution post-treatment with unmodified zeolite (zeolite 3A) and bar diagram 204 corresponds to metal ion concentrations of calcium chloride solution post-treatment with zeolite-NH2@EDTA.
[0064] In zeolite 3A (corresponding to bar diagram 202), calcium ion concentration post-treatment was found to be 26 mg/L, resulting in a 97.4% removal efficiency. The presence of high amount of sodium (Na) and potassium (K) ions in the solution containing zeolite 3A (unmodified zeolite) suggests that the calcium ions were removed mostly through a competing ion exchange process where the sodium ions and potassium ions from zeolite were replaced with calcium ions.
[0065] In zeolite-NH2@EDTA (corresponding to bar diagram 204), the sodium ion concentration was reduced by 32%, and the potassium ion concentration was negligible when compared to Bar diagram 202. The calcium ion removal efficiency was greater than 97%. The presence of EDTA on modified zeolite (zeolite-NH2@EDTA) promotes the removal of calcium ions primarily through EDTA-metal-ion chelation rather than ion exchange. This was advantageous for water treatment systems as it ensured that while one contaminant, such as calcium, was removed, other contaminants like sodium and potassium did not leach into the solution. This enhanced the overall treatment process and prevented adverse effects from increased concentrations of sodium or potassium ions.
[0066] FIG. 3 is a bar chart 300 depicting percentage removal of calcium ions plotted against number of cycles the modified zeolite was used for removal of calcium ions. This study is indicative of the mechanical stability, chemical integrity and reusability of the inventive modified zeolites. As seen from the bar chart 300, even after 5 cycles the modified zeolite recorded a calcium ion removal efficiency of 90% thus confirming the reusability.
[0067] The synergistic effect resulting from structural changes due to the modification of zeolite, electrostatic interactions between the negatively charged modified zeolite and the metal ions, and chelation with the chelating agent resulted in excellent adsorption of positively charged metal ions when compared to unmodified zeolite. As the chelating agent was covalently bound in the modified zeolite, chemical integrity and mechanical stability of the modified zeolite structure were not compromised.
[0068] It is to be understood that the above description is intended to be illustrative, and not restrictive. Furthermore, many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure has been described with reference to specific exemplary embodiments, it will be recognized that the disclosure is not limited to the embodiments described, but can be practiced with modification and alteration within the scope of the appended claims.
[0069] The modified zeolitized demonstrates excellent chemical integrity and structural stability, maintaining high removal efficiency for calcium ions from water even after have reuse cycles.
, Claims:We claim,
1. A modified zeolite comprising:
an aminated zeolite derivative derived from an aminated zeolite, wherein the aminated zeolite is obtained by amination of a zeolite; and
a chelating agent covalently bound to the aminated zeolite derivative.
2. The modified zeolite as claimed in claim 1, wherein a concentration of the chelating agent to the total weight of the modified zeolite is in a range of 2 weight percent (wt%) to 25 wt%.
3. The modified zeolite as claimed in claim 1, wherein the chelating agent comprises ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), cis-1,2-cyclohexanediaminetetraacetic acid (CDTA), nitrilotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), or combinations thereof.
4. The modified zeolite as claimed in claim 1, wherein the zeolite comprises zeolite 3A, zeolite 4A, zeolite 5A, zeolite 13X, zeolite Y, clinoptilolite zeolite, zeolite Beta, zeolite ZSM-5, or combinations thereof.
5. The modified zeolite as claimed in claim 1, wherein the amination is performed using an aminating agent, and wherein the aminating agent comprises 3-aminopropyltriethoxysilane (APTES), 3-aminopropyltrimethoxysilane (APTMS), N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS),
N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAPTES),
(3-Aminopropyl)methyldiethoxysilane (APMDES),
(3-aminopropyl)methyldimethoxysilane (APMDMS), triethoxysilylpropylamine (TESPA), N-(6-aminohexyl)aminomethyltriethoxysilane, hexamethylenediamine (HMDA), ethylenediamine (EDA), or combinations thereof.
6. The modified zeolite as claimed in claim 5, wherein the aminating agent comprises 3-aminopropyltriethoxysilane and the chelating agent comprises ethylenediaminetetraacetic acid.
7. The modified zeolite as claimed in claim 1, wherein a pore diameter of the modified zeolite is in a range of 1.6 nanometers (nm) to 3 nm.
8. A system for adsorbing metal ions from an aqueous solution, the system comprising the modified zeolite as claimed in claim 1.
9. The system as claimed in claim 8, wherein the modified zeolite has a calcium ion removal efficiency, a magnesium ion removal efficiency, or both of more than 97% from the aqueous solution in neutral pH.
10. A process for adsorbing metal ions from an aqueous solution comprising contacting the modified zeolite as claimed in claim 1 with the aqueous solution, wherein the modified zeolite adsorbs metal ions from the aqueous solution.
11. A method (100) of preparing a modified zeolite comprising:
treating a zeolite with an aminating agent (102) to obtain an aminated zeolite; and
treating the aminated zeolite with a chelating agent (104) to obtain the modified zeolite.
12. The method of preparing the modified zeolite as claimed in claim 11, wherein treating the aminated zeolite with the chelating agent (104) comprises activating the chelating agent.