clinoptilolite–Na composite nanoparticles

Accepted Manuscript A study on magnetic removal of sodium, calcium and potassium ions from seawater using magnetite / clinoptilolite–Na composite nanoparticles M.-E. Kouli, G. Banis, P. Tsarabaris, A. Ferraro, E. Hristoforou PII: DOI: Reference:

S0304-8853(18)30765-0 https://doi.org/10.1016/j.jmmm.2018.06.064 MAGMA 64084

To appear in:

Journal of Magnetism and Magnetic Materials

Received Date: Revised Date: Accepted Date:

15 March 2018 12 June 2018 21 June 2018

Please cite this article as: M.-E. Kouli, G. Banis, P. Tsarabaris, A. Ferraro, E. Hristoforou, A study on magnetic removal of sodium, calcium and potassium ions from seawater using magnetite / clinoptilolite–Na composite nanoparticles, Journal of Magnetism and Magnetic Materials (2018), doi: https://doi.org/10.1016/j.jmmm. 2018.06.064

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

A study on magnetic removal of sodium, calcium and potassium ions from seawater using magnetite / clinoptilolite–Na composite nanoparticles Kouli M.-E.1, Banis G.1, Tsarabaris P.2, Ferraro A.1, Hristoforou E.1 1

School of Electrical and Computer Engineering, Laboratory of Electronic Sensors National T U of Athens, Iroon Polytechniou 9, 15780, Zografou, Attiki, Greece 2 School of Electrical and Computer Engineering, High Voltages and Electric Measurements Laboratory National T U of Athens, Iroon Polytechniou 9, 15780, Zografou, Attiki, Greece [email protected]; [email protected]; [email protected]; [email protected]; [email protected]

ABSTRACT: Ion removal from sea and brackish water is essential for desalination process. A similar process takes also place after tertiary treatment of municipal and industrial waste water as a final treatment before discharge to the recipient. The ion removal from sea and brackish water using Reverse Osmosis (R.O.) technique is a certified and well-proven technology that can provide high-quality water supply; however it is relatively expensive. In this paper a study on the effectiveness of cation adsorbing behavior of a common zeolite takes place when combined with magnetite nanoparticles for facile magnetic removal from the bulk of water. The feasibility of selective removal of ions and the ability of producing directly potable water without the need for further enrichment is the basic subject of elaboration in this research. Key words: magnetite; clinoptilolite; composite nanoparticles; ion removal; Introduction Ion removal (commonly known as desalination) is a method of water treatment which has been in the forefront in recent decades. The term desalination, however, does not mean the treatment of seawater and the removal of sodium chloride from it particularly. It is broader and finds several technological applications. Desalination can be carried out in water to remove any salt [1]. The water resulting from desalination can be used either for drinking, irrigation or enrichment of a groundwater or as deionized water, all of which is in the context of reuse [2]. Nevertheless, it is a very expensive method due to constant membranes replacement. The R.O. membranes are in fact nanofiltration membranes [3] which are easily blocked by ions stacking on the surface and the pores. Moreover, difficulties can be spotted in the effective cleaning of the membranes for their full reuse; the entire system demands high energy consumption as well [4]. In this study an alternative cost-effective way for ion trapping is investigated by using magnetite/clinoptilolite–Na composite nanoparticles as adsorbing material. Metallic nanomaterials are well known for their exceptional electromagnetic properties and their high energy absorbing [5], photocatalytic [6] and ion trapping ability [7]. The adsorbing material investigated in this research is clinoptilolite-Na and magnetite

nanoparticles are bound to it in order to recover the material magnetically. Clinoptilolite-Na is a very commonly found zeolite. In previous research, the zeolitic adsorbing ability of toxic ion trapping (such as arsenate [8], nitrate [9], chromium VI [10], phosphates [11]) or drug delivery [12], had been investigated. Zeolites are aluminosilicate minerals whose dried up crystals possess a honeycomb-like structure consisting of openings or pores of the order of a few atoms in width (~2–10 Å) [1315]. Zeolite chemical composition can be generally described by the following empirical molecular formula [16-18]: (, , ) ( , , ) [( ) ( )  ] ∙    where, p is the number of monovalent metal ion, q is the number of divalent metal ions, n is the half of the number of oxygen atom and m is the number of water molecules. A simple criterion for distinguishing zeolites and zeolite-like materials from the densest silicate materials is the FD, the number of tetrahedral coordinated frame atoms (T atoms) per 1000 Å3. A gap is clearly identifiable between zeolite-type materials and dense tetrahedral frame structures. The maximum FD value for zeolite ranges from 19 to over 21 T atoms per 1000 Å3, depending on the type of smaller ring available, while the minimum for dense structures ranges from 20 to 22 atoms [19]. In the crystalline lattice of zeolites, each aluminum atom generates an excess of negative charge which is equilibrated by several interchangeable cations, such as H+, Na+, K+, Ca2+ and Mg2 +. These free cations as well as water molecules are held loosely and can be moved and exchanged with other cations of the environment without substantial alteration of the crystal structure [20]. Thus, Brønsted acidic domains (proton donors) are created and scattered within the frame. Zeolites exhibit selective adsorption ability due to their molecular dimensions and channels [21], large special surface because of their microporous structure, as long as structural and thermal ability up to 1000oC. Clinoptilolite is a zeolite with a HEU (Heulandite) frame type as presented in Fig. 1. The crystalline structures of clinoptilolite are mainly described as monoclinic [22-31] although lower symmetries have been reported [32-36]. Clinoptilolite-Na appears in a wide range of environments, including the transgenic replacement of rhyolite volcanic rocks, active hydrothermal systems and cracks and cavities in volcanic rocks. It is a material that is not expensive to be acquired, for it can be easily found in nature and thus, its effectiveness in ion trapping is studied in this research.

Fig. 1: The crystalline structure of clinoptilolite-Na with cationic sites from the refinement of Koyama and Takéuchi [23]. Usually clinoptilolite contains 4 to 7 cations per cell unit [37]

Materials and methods Materials The materials used for the preparation of nanoparticles were: iron chloride (II) tetrahydrate 99% (Merck), iron chloride (III) heptahydrate 99% (RS), acetic acid 99 – 100% (Sigma Aldrich), natural commercial powdered clinoptilolite – Na 90% with particle size 50 µm (Zeolithos Ellada), synthetic zeolite 99% with particle size < 10 µm (Sigma Aldrich), ammonia hydrated 30 – 33% (Sigma Aldrich), PVA 99% (Sigma Aldrich), glycerol 98% (Chembiotin), absolute ethanol 99,99% (Fisher Scientific) and deionized water Methods Synthesis of Fe3O4 nanoparticles In a beaker with 40 ml deionized water, 1 g of Polyvinyl Alcohol and 7 ml of 0.8 M aqueous NH4OH are added (solution A). PVA is used as a surfactant and ammonia is used as a pH regulator to maintain the pH slightly near to 9. In a beaker with 40 ml deionized water, ferric chloride (FeCl3·6H2O) and ferrous chloride (FeCl2·4H2O) are added in a 2:1 ratio and mixed (solution B). Ferric and ferrous chloride are the precursors on the basis of which the reaction will take place to form Fe3O4. Solution B is added to solution A and forms solution C. Solution C enters the microwave furnace and is heated for 2.5 minutes at minimum power (approx. 400W). The resulting product is an aqueous three-phase solution in which the magnetite nanoparticles are present in the aqueous and residual organic phase. Synthesis of Fe3O4 composite nanoparticles / clinoptilolite-Na In a beaker with 100 ml deionized water, 7.5g of natural Clinoptilolite-Na powder, 50 ml of glycerol and 50 ml of 99.8% acetic acid are added to form solution D. Then, solution C is added to solution D to form the final solution E. The container with

solution E enters the microwave furnace to complete the particle synthesis process by assisted microwave co-precipitation. The heating time in microwaves is 7.5min at minimum power. When the composition is completed, the nanoparticles are removed magnetically and washed five times with deionized water and alcohol successively to remove the remaining organic and unbounded clinoptilolite. Finally, the nanoparticles are left to dry at 70°C, in a vacuum atmosphere, for 18-24 hours. The nanoparticles were structurally characterized by an X-ray diffractometer (2θ = 0-70°) and visualized in grain size by SEM. Their magnetic response was studied via VSM (Vibrating Sample Magnetometer). The determination of the percentage of each ion in water samples was performed by flame metering for untreated seawater and for treated seawater at the 1st and 6th hours of zeolite treatment for each different amount of clinoptilolite-Na and for each different temperature Sea salt ion adsorption study by salinity change and control of the removal mechanism of the nanoparticles from the solution In order to ascertain the probability of adsorption of ions from Fe3O4 / clinoptiloliteNa nanoparticles, salinity measurements were made in sea water before and after the administration of the composite nanoparticles thereto, at room temperature and for t = 1-6 h. In particular, 2 gr of composite Fe3O4 / clinoptilolite-Na nanoparticles were added to a vessel with 100 ml sea water, under 200 rpm constant stirring, and then magnetically removed by applying an external magnetic field from a permanent magnet. The procedure was occurring once per hour, and the salinity was being measured. At second time and if a change in salinity was observed, salinity change measurements were made on samples containing sea water and clinoptilolite-Na powder, with stirring of 200 rpm, so that the removal mechanism of the ions from the solution by adsorbing them from the zeolite. To conduct the experiments three influence parameters were taken into account: temperature, time and amount of zeolite. Table 1 shows the three influence parameters. Table 1: Influence parameters for conducting experimental measurements

PARAMETER

EXPERIMENTAL CHANGE

Time

1–6h

Temperature

5 C, 25 C, 50oC, 70oC, 90oC

Clinoptilolite-Na mass

0.1g, 0.5g, 1g, 2g

ο

o

The value of each experimental conductivity and salinity measurement comes as an average of a set of 5 measurements for each case which ensures the reliability of the measurement. The experimental measurements performed are presented in Table 2.

Table 2: The experimental measurements performed for water samples treated with clinoptilolite-Na based on the influence factors

Clinoptilolite-Na mass (g) 0,1

0.5

1

2

Temperature (oC)

Time (h)

5 25 50 70 90 5 25 50 70 90 5 25 50 70 90 5 25 50 70 90

1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6 1–6

Results and Discussion Structural analysis By Scanning Electron Microscopy (SEM) the final product was studied macroscopically and microscopically as illustrated in Fig. 2b and 2c. As mentioned before, the nanoparticles were synthesized by the microwave assisted co-precipitation method [38-41]. The resulting powder color was gray-green (Fig. 2a), as opposed to pure magnetite whose color is bright black, indicating the complexation of magnetite with clinoptilolite-Na to form a composite particle.

Fig. 2: a) Composite nanoparticles Fe3O4 / clinoptilolite-Na synthesized by the assisted microwave co-precipitation method; b) Image of the composite nanoparticles from SEM; c) White areas are rich in iron and indicate the intense complexation of magnetite

The magnetite nanoparticle size synthesized was in the range of 15 – 25 nm while the size of the composite particles synthesized was calculated from 50 µm to 100 µm and the morphology of the granules was mainly spheroidal with some angular expressions. That particle size range, especially for the case of the composite nanoparticles, occurs as a result of unavoidable agglomeration of the nanoparticles in environmental

conditions due to air humidity and prolonged storage time, given that zeolites can absorb humidity. The crystalline structure of the nanoparticles produced was analyzed by XRDiffraction. XRD patterns were obtained with a BRUKER-binary V3 (RAW) diffractometer using CuKα radiation. The crystallite sizes were estimated from the line broadening of the (311) / 35,5o – for the magnetite – and at the 22.5o – for the composite nanoparticle – peaks obtained using a scan rate in 2θ of 0.6° min-1. The crystallite size D was calculated from the Scherrer equation: 

 = !∗#$%& (1) Where K= 0.91, λ is the wavelength of the X-rays 2, Θ is the Bragg diffraction angle (Θ=2θ/2), and β is the full width at half-maximum (FWHM) of the X-ray diffraction peak in radians. So for magnetite the equation (1) is: =

.(∗).*+, Å .( /01∗#$%)2.2*

= 15 nm (2)

And for the clinoptilolite-Na the equation (1) transforms to: =

.(∗).*+, Å .* /01∗#$%)).*

= 110 nm (3)

In the following figures the microstructure analysis for magnetite, and composite nanoparticles synthesized are presented. Fig. 3 illustrates the magnetite synthesized. The peaks at 30°, 35°, 37°, 43°, 57° and 62°, indicating the cubic structure of the inverse spinel, are apparent in this diagram, which confirms the successful composition of pure magnetite by the microwave assisted co-precipitation method.

Fig. 3: XRD pattern for magnetite synthesized

The XRD chart for the composite magnetite / clinoptilolite-Na nanoparticle synthesized is illustrated in Fig. 4. In the chart, the 22°, 22.5°, 24°, 28°, 30°, 35°, 36° 1

K is a dimensionless shape factor, with a value close to unity. The shape factor has a typical value of about 0.9 2 1.54060 Å for Cu K-Alpha1 radiation

and 44° peaks indicate the presence of clinoptilolite-Na. The peaks at 30°, 35°, 37°, 43°, 57° and 62°, indicating the cubic structure of the inverse spinel, are also apparent in this diagram, which confirms the successful binding of magnetite nanoparticles to clinoptilolite-Na by microwave assisted co-precipitation method.

Fig. 4: XRD pattern of Fe3O4 / clinoptilolite-Na composite nanoparticles synthesized

Mass magnetization saturation was determined by the magnetometer of a vibrating sample-VSM at room temperature, since temperature is a factor that highly affects the hysteresis loop of magnetic nanoparticles, metals and metallic alloys [42-45]. Two representative magnetization curves of the nanoparticles prepared with and without clinoptilolite-Na are illustrated in Fig. 5.

Fig. 5: Saturation loop of the nanoparticles produced

It is observed that both samples show similar magnetic behavior. MNPs without clinoptilolite-Na exhibit a 70 Am2kg-1 saturated mass magnetization which is reached in lower magnetic fields than 1.5 T, while MNPs with clinoptilolite-Na exhibit a 27 Am2kg-1 saturated mass magnetization which is reached in higher magnetic fields than

1.5 T. The lower magnetic susceptibility of the composite MNPs is an outcome of the complexation of pure mangetite with clinoptilolite as the latter reduces the magnetic properties of the former. The magnetization loops obtained at room temperature exhibit absence of hysteresis and residual magnetization within the limits of our experimental uncertainty, which is the main characteristic of superparamagnetic behavior of a few nanometers particle size [46-49]. Needing to check macroscopically (visually) the magnetic response of the synthesized nanoparticles, a permanent external magnet was placed in contact with the solution of the container of Fig. 6, containing water and a certain amount of composite nanoparticles. As it was expected, the nanoparticles were attracted to the magnetic field created by the magnet and touch the glass wall thereby achieving separation of the solid from the liquid phase.

Fig. 6: External magnetic field effect of permanent magnet on a liquid solution with magnetite / clinoptilolite-Na complex nanoparticles

Salinity measurements Initially, the seawater salinity chart with composite Fe3O4 / clinoptilolite-Na nanoparticles is presented, as a result of a series of measurements carried out at 25°C for a period of 1 to 6 hours. Salinity measurements for composite Fe3O4 / clinoptilolite-Na nanoparticles at 25°C were performed to determine whether changes appeared in sea water salinity when the nanoparticles were induced and to confirm operation of the ion sequestrant and particle removal. At this point, it needs to be clarified that the objective of this work is solely the adsorption properties of clinoptilolite-Na considering the Na, Ca and K cation removal from saline water. Magnetite is merely used as a strong magnetic core and serves only magnetic removal purposes. The measurements presented in the following chart were performed as a preliminary test in order to prove that the entire system mechanism operates.

Fig. 7 : Salinity versus time measurements for composite Fe3O4 / clinoptilolite-Na nanoparticles at 25°C

As shown in Fig. 7, a reduction of the salinity by 4 psu at the first time of nanoparticles application is first observed, and then stabilization takes place with slight fluctuations. These measurements form solid evidence that interaction happens among the ions of clinoptilolite and the free ions exist in the treated solution. In order to investigate the optimum concentration of clinoptilolite -Na, different concentrations of the zeolite were used to treat seawater. The charts, which will be presented next, illustrate the salinity alternations for different concentrations of clinoptilolite-Na at different temperatures and times in seawater solution.

Fig. 8: Salinity versus time fluctuation chart for seawater treated with 1 g/L clinoptilolite-Na at different temperatures for hours 1-6

As presented in Fig. 8, water samples which were treated with 1 g/L of clinoptiloliteNa, a relatively repetitive state is observed with conductivity and salinity maintaining an almost constant value fluctuation for all temperatures with a greater salinity decrease of 2 psu at the 1 hour processing time for sample at 25°C and an increase in

salinity of 1 and 2 psu at 1 hour processing time for specimens at 70°C and 90°C respectively.

Fig. 9: Salinity versus time fluctuation chart for seawater treated with 5 g/L clinoptilolite - Na at different temperatures

In Fig. 9, water samples with 5 g/L clinoptilolite-Na, exhibit relevant characteristics. For temperatures of 5°C, 25°C and 50°C, salinity is followed by a downward trend of 5, 7 and 4.5 psu respectively, up to 1 hour. Then, for the following hours (1-6), salinity shows continuous fluctuations indicating the clinoptilolite ion exchange capability. For temperatures of 70°C and 90°C, conductivity and salinity show consistent fluctuations which are induced at values higher than the original accompanied with an initial steady increase of up to 1 hour. Although in the environment, the particular mineral exhibits high stability and relatively low ion exchange capacity at high temperatures. Charts prove that if the aforementioned mineral under the same conditions comes into contact with freely dissolved ions, it tends to become unstable, allowing for easier ion exchange. It is noted that when the samples are treated at elevated temperatures, the ions of the material itself become more agile and outgassed instead of adsorbing the water ions until equilibrium takes place.

Fig. 10: Salinity versus time fluctuation chart for seawater treated with 10 g/L clinoptilolite - Na at different temperatures

In the case of seawater treated with 10 g/L of clinoptilolite-Na, as presented in Fig. 10, a decrease of salinity is observed by 1 psu, 3 psu, at 25 oC and 50 oC respectively at 1 hour and then increase and stabilization of the salinity up to the 6th hour. At 5°C increase was observed at the 1st hour followed by stabilization, while at 70°C reduction of 3 psu was observed for the 1st hour and then abrupt increase of 10 psu at the 4th hour of treatment. At 90°C the salinity was abruptly increased by 6 psu at the 3rd hour and then stabilized. Such abrupt increases of salinity at higher temperatures and clinoptilolite-Na concentration probably occur due to the increased mobility of the ions when the temperatures increase and the bonds between the molecules are looser.

Fig. 11: Salinity versus time fluctuation chart for seawater treated with 20 g/L clinoptilolite - Na at different temperatures

For water samples treated with 20 g/L clinoptilolite-Na the salinity chart of Fig. 11 illustrates slight salinity reduction rate for 5oC and 25oC for the 1st hour of treatment and then minimal increase. After the 1st hour for the 5oC an increase in the salinity value appears while an equilibrium occurs for the 25oC. Water samples at 50oC and 70oC exhibit the same behavior with decrease of salinity value by 6 psu at the 2nd hour and then stabilization. At 90oC there is a constant increase in the salinity value with higher fluctuation value 48.4 psu at the 5th hour. These values practically render the particular amount of clinoptilolite-Na inappropriate and prove that for high concentrations of clinoptilolite-Na occurs intense ion exchange and even transfer of ions from the adsorbent to the water until equilibrium is reached. Ion analysis The ion analysis, as presented in Table 3, was performed for the water samples for each concentration of clinoptilolite-Na, at 25°C for the 1st and the 6th hour of treatment, at ambient temperature and at the times of extreme treatments. The pH of seawater was about 7.5-8 while after treatment with clinoptilolite-Na was reduced to 5.3-5.5 (slightly acidic) which is a result of the clinoptilolite-Na ion exchangeability behavior [50]. Table 3: Ionic analysis of water before and after treatment with different concentrations of clinoptilolite-Na at 25oC for the first and sixth hour of treatment and correlation with the respective salinity value

Sample

Concentration (gr/L)

Time (h)

Seawater 1 5 Clpt 10 20

1 6 1 6 1 6 1 6

Na+ (mg/L) 13.680

K+ (mg/L) 480

Ca2+ (mg/L) 1.290

12.870 12.900 12.750 13.080 14.880 12.960 14.220 12.930

450 480 480 600 600 510 600 540

990 1.050 1.020 1.020 1.200 990 1.170 1.110

Salinity (psu) 35,5 33,3 39,9 28,3 29,7 34,4 33,6 34,3 33,4

For the 1st hour of treatment of the seawater sample with clinoptilolite-Na of 1 g/L, there is a decrease in the concentration of all three metal ions with a markedly higher reduction in sodium ions, a decrease of 1000 mg/L. For the 6th hour, it is also observed to be less than the initial concentration for Na, K and Ca ions but higher than that recorded for the 1 hour sample. It is observed that total salinity appeared to be 4 psu greater, which is attributable to a possible deviation of the salinity value or to the possibility of ion exchange of the ions inherent in raw clinoptilolite-Na as impurities and released into the solution. For the 1st hour of treatment of the seawater sample with clinoptilolite-Na of 5g/L, there is a decrease in Na and Ca ion concentration with a markedly higher reduction in Na ions, a decrease of 1000 mg/L in this case. For the 6th hour, the concentrations

of Na and Ca ions are also observed to be less than the initial concentrations, but higher than those recorded for the 1st hour sample. Also, the concentration of K was increased by 120 mg/L, relatively to the original sample. It is observed that total salinity appeared to be significantly lower than the initial in both cases, which is in agreement with the values of the individual dissolved ions found. For the 1st hour treatment of the seawater sample with clinoptilolite-Na 10 g/L, a small decrease in calcium ion concentration and an increase in sodium and potassium ion concentration occurred, with a more pronounced increase in sodium ions, an increase of 1000 mg/L. For the 6th hour, the concentration of Na and Ca is also less than the initial concentration of them. A decrease in the K value occurs, in respect to the K value of the 1st hour but greater than the initial one. It is observed that the salinity value for the 1st hour appeared higher than the initial one, which is probably attributed to a possible deviation of the salinity meter or the possibility of ion exchange of ions inherent in native clinoptilolite-Na as impurities and were released in the solution but in ion analysis are not apparent. Therefore it is evident is that increasing the concentration of clinoptilolite-Na by 5 g/L implies a sharp increase in Na and Ca ions. This increase is probably observed due to the ion exchange occurring during the 1st hour due to the increased load in water related to the increase in the concentration of clinoptilolite-Na and the ions trapped in its vicinity and then released into the solution. At 6th hour the seawater – clinoptilolite-Na solution shows that the adsorption of ions from the solution has occurred and the solution itself has now become more balanced. For the 1st hour of treatment for the seawater sample with clinoptilolite-Na 20 g/L, there is an increase in Na and K ion concentration with a significantly higher Na ion increase of 1000 mg/L. For the 6th hour of treatment, a value of concentration lower than the initial concentration of the Na and Ca ions is observed. Moreover, the concentration of K was reduced by 60 mg/L in comparison to the 1st hour sample, but remained higher than the initial sample. It was observed that the total salinity did not peak higher than the initial one in either of the two cases, even during the 6th hour it appeared 2 psu lower, which is in agreement to the values of individual dissolved ions found only for the 6th hour of treatment. Na values in the 1st hour of treatment are quite high but salinity is reduced by 1 psu. This increase of Na and K ions in the primary stage of treatment shows practically how Na and K ions move from the adsorbent to the water solution. For the reason mentioned above, the possibility of a financially advantageous electrophoretic assistance unit with magnetic particle retention field which would increase the adsorption capacity of the zeolite and improve the ability of the same amount of composite nanoparticles to be reused with negligible losses, should be investigated. Such a unit could consist of a magnet and electrodes, where the composite nanoparticles are stabilized by the magnet on one side of an inert aqueous solution and the cations encased in the zeolite frame are captured by the charge electrodes, creating in this way empty grid positions. At the same time, the specific

surface area of the composite nanoparticles should be increased by decreasing their size. By creating a larger particle surface, more active cation adsorbing centers will be created, leading to higher ion removal rates. Conclusions Magnetic ion trapping is the method which is studied in the current work and can possibly be carried out in water to remove any salt present in the form of dissolved ions. The dominant salts in sea water, which also determine the salinity value, are mainly sodium, at a concentration of 3.5% and, secondly, calcium and potassium in much lower concentrations. From the data acquainted from the current study the following conclusions were drawn: For the Fe3O4/clinoptilolite-Na nanoparticle production, microwave assisted coprecipitation proved an effective method for the synthesis of the composite nanoparticles which were used to trap the seawater ions and be magnetically removed. The nanoparticles were successfully tested for their susceptibility to magnetization via VSM and optically by applying an external magnet to an aqueous solution containing magnetic nanoparticles. The nanoparticles were tested for ion adsorption from seawater solution and magnetic removal in order to obtain preliminary results of the method’s effectiveness. The salinity of the solution was reduced by 4 psu from the first application time, and then the solution reached equilibrium. The nanoparticles were easily removed from the solution by applying an external magnet. Then, the study was focused on the adsorbing abilities of the clinoptilolite-Na. The adsorbance and ion exchange capability of clinoptilolite-Na was determined through a set of measurements of the adsorbent concentration in seawater solution related to the temperature and residence time of the adsorbent in the solution. Thus, the following were observed: •

At 25οC occurs maximization of the adsorption of clinoptilolite-Na. At the same time, there is a decrease in the ion exchange capability among of the material and the free solution ions

•

As optimal concentration of clinoptilolite-Na, in terms of adsorption and ion exchange, 5gr/lt was determined, based on salinity and ion analysis. For this concentration, the response of the adsorber is observed the first correspondent (at 1st of treatment) before the solution is finally equilibrated.

•

Ion analysis detected ion exchange not only among Na, K and Ca of clinoptilolite-Na and the seawater solution, but also probably among the impurities of clinoptilolite-Na and the aqueous solution. This hypothesis resulted from a comparison of salinity measurements and ion analysis. The former were either increasing or remained unchanged, while the latter exhibited decrease. The optimum ion removal ratio was calculated 7% for the case of 5g/L clinoptilolite-Na for the 1st hour of treatment as 25 oC, which

stands far from a satisfying. However it can be possibly improved with further study to reach a rate of even 90% of ion removal in continuous cycles of application. As aforementioned, and since zeolites seem very promising raw materials with good adsorbing properties and as their cation exchangeability seems to be the only obvious obstacle for the effective use of them in ion trapping procedures it is strongly recommended the electrophoretic assistance unit with magnetic particle retention field be designed and tested as for the ability of the same amount of composite nanoparticles to be reused, to be improved, with negligible losses, in multiple cycles of water treatment.

ACKNOWLEDGMENTS - The author Maria-Elisavet Kouli would like to thank the General Secretariat for Research and Technology (GSRT) and the Hellenic Foundation for Research and Innovation (HFRI) of the Greek Ministry of Education for supporting her PhD fellowship. - This paper is part of a project that has received funding from the Bio Based Industries Joint Undertaking under the European Union's Horizon 2020 research and innovation program under grant agreement No 745695. REFERENCES [1] Talbert N. Eisenberg and E. Joe Middlebrooks (Auth.), Reverse Osmosis Treatment of Drinking water, Butterworth-Heinemann, 1986, ISBN: 978-0-25040617-3, 0-250-40617-9 [2] Victor Augusto Yangali Quintanilla, Rejection of emerging organic contaminants by nanofiltration and reverse osmosis membranes: effects of fouling, modelling and water reuse, CRC Press; Balkema, Leiden, The Netherlands, 2010, ISBN: 9780203093368, 0203093364, 978-0-415-58277-3 [3] American Water Works Association, Reverse Osmosis and Nanofiltration, (Awwa Manual M46), 2007, ISBN: 1-58321-491-7, 978-1-58321-491-6 [4] Puretec, Basics of Reverse osmosis/reverse-osmosis-systems

Osmosis,

http://puretecwater.com/reverse-

[5] A. Ghasemi, A. Hossienpour, A. Morisakod, A. Saatchia, M. Salehia, Electromagnetic properties and microwave absorbing characteristics of doped barium hexaferrite, Journal of Magnetism and Magnetic Materials 302 (2006) 429– 435

[6] B. Safizade, S. M. Masoudpanah, M. Hasheminiasari and A. Ghasemi, Photocatalytic activity of BiFeO3/ZnFe2O4 nanocomposites under visible light irradiation, Royal Society of Chemistry Advances, DOI: 10.1039/C7RA13380D, 2018, 8, 6988-6995 [7] Nikhat Neyaz, Mohd Sadiq S. Zarger, Weqar A Siddiqui: Synthesis and characterisation of modified magnetite super paramagnetic nano composite for removal of toxic metals from ground water, International Journal of Environmental Sciences, Volume 5, No 2, 2014 [8] Carmen Pizarro, María A. Rubio, Mauricio Escudey, María F. Albornoz, Daniela Muñoz, Juliano Denardinb, and José D. Fabrisd: Nanomagnetite-Zeolite Composites in the Removal of Arsenate from Aqueous Systems, J. Braz. Chem. Soc., Vol. 26, No. 9, 1887-1896, 2015 [9] Xu Chen, Tielong Li: Reduction of nitrate in water by nanoscale zero-valent iron particles and zeolite, Bioinformatics and Biomedical Engineering, 2009. ICBBE 2009, 3rd International Conference [10] Karna Nicole Barquist: Synthesis and environmental adsorption applications of functionalized zeolites and iron oxide/zeolite composites, PhD Thesis, University of Iowa, fall 2009 [11] Lili Gan, Jiane Zuo, Bangmi Xie: Peng Li, Xia Huang, Zeolite (Na) modified by nano-Fe particles adsorbing phosphate in rainwater runoff, Journal of Environmental Sciences 2012, 24(11) 1929–1933 [12] Manuel Arruebo, Rodrigo Fernandez – Pacheco, Silvia Irusta, Jordi Arbiol, M Ricardo Ibarra and Jesus Santamarıa: Sustained release of doxorubicin from zeolite– magnetite nanocomposites prepared by mechanical activation, Nanotechnology 17 (2006) 4057–4064 [13] Database of Zeolites Structures. http://www.iza-structure.org. Accessed 22 June 2014 [14] Gattardi, G., Crystal chemistry of natural zeolite,. Pure Appl. Chem. 58, 343–349 (1986) [15] The Mineral Group Zeolite. http://www.minerals-n-more.com. Accessed 10 July 2013 [16] Zeolites. http://www.encyclopedia.com. Accessed 20 June 2012 [17] Shigemoto N., Hayashi H.: Selective formation of Na-X zeolite from coal fly ash by fusion with sodium hydroxide prior to hydrothermal reaction, J. Mater. Sci. 28, 4781–4786 (1993)

[18] Berkgaut V., Singer A.: High capacity cation exchanger by hydrothermal zeolitization of coal fly ash, App. Clay. Sci. 10, 369–378 (1996) [19] Ch. Baerlocher, Lynne B. McCusker, D.H. Olson: Atlas of Zeolite Framework Types, Elsevier Science (2007) [20] Cejka J. and H. van Bekkum (Editors): Zeolites and ordered Mesoporous materials: progress and prospects, Elsevier, 2005 [21] Maesen T., Marcus B.: Introduction to Zeolite Science and Practice, 2nd completely revised and expanded edition, eds: H. Van Bekkum, E.M. Flanigen, P.A. Jacobs, J.C. Jansen Elsevier, Amsterdam, Stud. Surf. Sci. Catal., 137, 2001 [22] Alberti, A.: The crystal structure of two clinoptilolites. Tschermaks Mineral. Petrogr. Mitt. 22, 25-37, 1975 [23] Koyama, K. and Takéuchi, Y.: Clinoptilolite: the distribution of potassium atoms and its role in thermal stability. Z. Kristallogr. 145, 216-239, 1977 [24] Bresciani-Pahor, N., Calligaris, M., Nardin, G., Randaccio, L., Russo, E., and Comon-Chiaromonti, R.: Crystal structure of a natural and partially Ag-exchanged heulandite. J. Chem. Soc., Dalton Trans. 1980, 1511-1514, 1980 [25] Alberti, A. and Vezzalini, G.: The thermal behavior of heulandites: A structural study of the dehydration of the Nadap heulandite. Tschermaks Mineral. Petrogr. Mitt. 31, 259-270, 1983 [26] Hambley, T.W., and Taylor, J.C.. Neutron diffraction studies on natural heulandite and partially dehydrated heulandite. J. Solid State Chem. 54, 1-9, 1984 [27] Smyth, J.R., Spaid, A.T., and Bish, D.L.: Crystal structures of a natural and a Cs-exchanged clinoptilolite. Am. Mineral. 75, 522-528, 1990 [28] Armbruster, T. and Gunter, M.E.: Stepwise dehydration of heulanditeclinoptilolite from Succor Creek, Oregon, U.S.A.: A single crystal X-ray study at 100 K. Am. Mineral. 76, 1872-1883, 1991 [29] Armbruster, T.: Dehydration mechanism of clinoptilolite and heulandite: Singlecrystal X-ray study of Na-poor, Ca-, K-, Mg-rich clinoptilolite at 100 K. Am. Mineral. 78, 260-264, 1993 [30] Gunter, M.E., Armbruster, T., Kohler, T., and Knowles, C.R.: Crystal structure and topical properties of Na- and Pb-exchanged heulandite-group zeolites. Am. Mineral. 79, 675-682, 1994 [31] Cappelletti, P., Langella, A., and Cruciani, G.: Crystal-chemistry and synchrotron Rietveld refinement of two different clinoptilolite from volcaniclastics of North-Western Sardinia. Eur. J. Mineral. 11, 1051-1060, 1999

[32] Alberti, A.: On the crystal structure of the zeolite heulandite. Tschermaks Mineral. Petrogr. Mitt. 18, 29-146, 1972 [33] Merkle, A.B. and Slaughter, M.: Determination and refinement of the structure of heulandite. Am. Mineral. 53, 1120-1138, 1968 [34] Yang, P. and Armbruster, T.: Na, K, Rb, and Cs exchange in heulandite single crystals: X-ray structure refinements at 100 K. J. Solid State Chem. 123, 140-149, 1996 [35] Sani, A., Vezzalini, G., Ciambelli, P., and Rapacciuolo, M.T.: Crystal structure of hydrated and partially NH4-exchanged heulandite. Microporous Mesoporous Materials 31, 263-270, 1999 [36] Stolz, J., Yang, P., and Armbruster, T.: Cd-exchanged heulandite: Symmetry lowering and site preference. Microporous Mesoporous Materials 37, 233-242, 2000a [37] Deer, A., Howie, R., Wise, W.S., and Zussman, J.: Rock Forming Minerals. vol. 4B.Framework Silicates: Silica Minerals, Feldspathoids and the Zeolites. The Geological Society, London, (2004) [38] Microwaves in Nanoparticle Synthesis, First Edition. Edited by Satoshi Horikoshi and Nick Serpone.© 2013 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH & Co. KGaA [39] Ferry Iskandar , Pipit Fitriani , Shanty Merissa , Rino R. Mukti , Khairurrijal , and Mikrajuddin Abdullah, Fe3O4/Zeolite Nanocomposites Synthesized by Microwave Assisted Coprecipitation and Its Performance in Reducing Viscosity of Heavy Oil, 5th Nanoscience and Nanotechnology Symposium (NNS2013) AIP Conf. Proc. 1586, 132-135 (2014); doi: 10.1063/1.4866746 [40] S. S. Pati, S Kalyani, V Mahendran, John Philip, Microwave Assisted Synthesis of Magnetite Nanoparticles, Journal of Nanoscience and Nanotechnology, Vol. 14, 5790-5797, 2014 [41] S Kalyani, J. Sangeetha, John Philip, Microwave Assisted Synthesis of Ferrite Nanoparticles: Effect of Reaction Temperature on Particle Size and Magnetic Properties, Journal of Nanoscience and Nanotechnology, Vol. 15, 5768-5774, 2015 [42] M. Ghezelbash, S. M. R. Darbani, A. E. Majd, A. Ghasemi, Temperature Dependence of Magnetic Hysteresis Loop of NdFeB with Uniaxial Anisotropy by LIBS Technique, Journal of Superconductivity and Novel Magnetism (2017) 30:1893– 1898 DOI 10.1007/s10948-017-3984-x [43] Takuma Sato, Kaori Nagaoka, Satoru Kobayashi, Jayappa Manjanna, and Takeshi Murakami, Temperature dependence of magnetic hysteresis scaling for cubic Fe3O4 nanoparticles, AIP ADVANCES 7, 056319 (2017)

[44] Yongjae Yu and Lisa Tauxe, Temperature dependence of magnetic hysteresis, Geochemistry Geophysics Geosystems, Volume 5, Number 6, 19 June 2004, Q06H11, doi:10.1029/2003GC000685 [45] I. Kong, S.H. Ahmad, M.H. Abdullah, A.N. Yusoff, The Effect Of Temperature On Magnetic Behavior Of Magnetite Nanoparticles And Its Nanocomposites, Nanoscience and Nanotechnology, International Conference on Nanoscience and Nanotechnology, (NANO-Sci-Tech 2008), © 2009 American Institute of Physics 9780-73 54-0673-5/09/$25.00 [46] Ali Ghasemi, Particle size dependence of magnetic features for Ni0.6xCuxZn0.4Fe2O4 spinel nanoparticles, Journal of Magnetism and Magnetic Materials 360 (2014) 41–47 [47] Xuemin He, Wei Zhong, Chak-Tong Au and Youwei Du, Size dependence of the magnetic properties of Ni nanoparticles prepared by thermal decomposition method, Nanoscale Research Letters20138:446 [48] Thanh Quang Bui, Suong Nu-Cam Ton, Anh Trong Duong, Hoa Thai Tran, Sizedependent magnetic responsiveness of magnetite nanoparticles synthesised by coprecipitation and solvothermal methods, Journal of Science: Advanced Materials and Devices 3, 2018, 107-112 [49] E. Ranjith Kumar, Ch. Srinivas, M. S. Seehra, M. Deepty, I. Pradeep, A. S. Kamzin, M. V. K. Mehar, N. Krisha Mohan, Particle size dependence of the magnetic, dielectric and gas sensing properties of Cosubstituted NiFe2O4 nanoparticles, Sensors and Actuators A: Physical 279 (2018) 10-16 [50] Cejka J. and H. van Bekkum (Editors): Zeolites and ordered Mesoporous materials: progress and prospects, Elsevier, 2005

HIGHLIGHTS

Magnetic ion trapping can possibly be carried out in water to remove any salt present in the form of dissolved ions. The dominant salts in sea water, which also determine the salinity value, are mainly sodium, at a concentration of 3.5% and, secondly, calcium and potassium in much lower concentrations. Microwave assisted co-precipitation proved an effective method for the synthesis of the composite nanoparticles Fe3O4/clinoptilolite-Na The composite nanoparticles were used to trap the seawater ions and be magnetically removed. The nanoparticles were successfully tested for their susceptibility to magnetization via VSM and optically by applying an external magnet to an aqueous solution containing magnetic nanoparticles. Their structural characterization occurred via XRD and SEM. The nanoparticles were tested for ion adsorption from seawater solution and magnetic removal in order to obtain preliminary results of the method’s effectiveness. The nanoparticles were easily removed from the solution by applying an external magnet. The study was mainly focused on the adsorbing abilities of the clinoptilolite-Na. The adsorbance and ion exchange capability of clinoptilolite-Na was determined through a set of measurements of the adsorbent concentration in seawater solution related to the temperature and residence time of the adsorbent in the solution.