an effect of a natural zeolite on the characteristics … · useful action of the electrochemically...

Stoyan Djambazov, Albena Yoleva

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AN EFFECT OF A NATURAL ZEOLITE ON THE CHARACTERISTICS OF SPRING OR ELECTROCHEMICALLY ACTIVATED WATER


ABSTRACT

The aim of the present experimental investigation is to trace the change of some general characteristics (pH, electro conductivity, mineralization and chemical composition) of spring water from Rila mountain in Bulgaria, as well as of electrochemically activated water after different periods in contact with a natural zeolite from Haskovo region, Bulgaria. The chemical and phase compositions of the zeolite are determined by means of ICP-AES and XRD. The effect of the zeolite-water contact time of 24 h, 48 h, 72 h and 168 h on the ion exchange process in presence of 10 mass % natural zeolite concentration is followed. The experiments are carried out with two types of a zeolite - a non thermally treated zeolite at 25°С and a thermally treated one for 2 h at a maximal temperature of 300°С and 550°С. Electrochemically activated water of different рН values is obtained through electrolysis carried out for time intervals ranging from 5 min to 20 min. The treated waters of different рН values are used for 48 h treatment at 550°С. The chemical composition, the pH changes, the electro conductivity and the mineralization are determined using ICP-AES and Combo pH/Conductivity/TDS meter (Low Range, HANNA instruments HI98129 multiparameter, 14pH, 3999us/cm, 2000 ppm). The optimal conditions of the ion exchange process between the natural zeolite and the spring water are established. The extended ion exchange process and the higher heat treatment temperature of the zeolite result in a higher amount of transmitted К+and Na+ cations improving thus the ion exchange. It is proved that alkaline water has an activating action stimulating the ion exchange of both cations and anions in the water systems.

Keywords: natural zeolite, spring water, electrochemically activated water, ion exchange.

Received 15 November 2017Accepted 15 June 2018

Journal of Chemical Technology and Metallurgy, 53, 6, 2018, 1195-1202

Department of Silicate Technology University of Chemical Technology and Metallurgy 8 Kliment Ohridski, 1756 Sofia, BulgariaE-mail: [email protected]

INTRODUCTION

Because of their unique ion exchange and adsorption properties, high porosity and excellent thermal stabil-ity, the zeolites are convenient materials for various applications. They are also used for water purification and activation. Their effectiveness through pollutant concentration decrease (heavy metals, anions and or-ganic substances), water softening (decrease of Ca2+ and Mg2+ cations in the water) and activation with K+ and Na+ cations [1 - 5] is proved by different investigations.

The zeolites can interact with hydrogen or hydroxyl ions available in the solutions and as a result some physicochemical phenomena can take place. They re-

fer to hydrolyzation of solid substances, degradation, dissolution and even phase transformations. All these phenomena depend on the structural characteristics and on the chemical composition of the zeolites used. In order to find new possibilities for their application, it is necessary to understand the behavior of the zeolites and their ion exchange in water media. Natural zeolites possess some advantages in comparison with other often used cation exchanged materials. They are cheap and show excellent selectivity towards different cations, which in turn is accompanied by exemption of non-toxic exchange cations (К+, Na+, Са2+ and Mg2+). They allow an easy and cheap use in all spectrums of applications. The effectiveness of water purification by natural and

Journal of Chemical Technology and Metallurgy, 53, 6, 2018

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modified zeolites depends on the type and amount of the zeolite used, on the size distribution of the zeolite particles, on the original concentration of the pollutants (cation/anion), on the рН and the ionic strength of the solution, the temperature, the pressure, the time of the zeolite/solution contact and the presence of other organic compounds and anions. The heat treatment depending on the solid substance and the temperature used can increase the pore volume by elimination of water and organic molecules from the channels of the pores. The water in the cavities of the zeolite network reaches 10 % - 25 % of its total weight. It is important to know the properties referring to zeolite minerals dehydration and structural stability aiming their effective application to water modification [6 - 17]. Investigations related to the useful action of the electrochemically activated (ECA) water on the human health are in progress. For this reason, the study of ion exchange of a zeolite in water activated by electrolysis presents a definite interest. Many parameters, as conductivity, pH, purified water temperature, its ionic strength, the cations and anions concentration in the solution, the zeolite amount and size of its particles [19 - 22] can influence the water modification.

The purpose of the present work is to investigate the exchange of cations and anions of a natural zeolite in spring and ECA water and to follow the changes of water general characteristics as pH, electro conductivity, mineralization, a chemical composition, etc. following the contact with a zeolite.

EXPERIMENTAL

Zeolites from Haskovo region in Bulgaria (Fig. 1) were used for the experiments carried out. Their chemi-cal and phase composition were determined by ICP-AES and XRD analysis (DRON 3M, Co-Ka radiation).

ICP-AES was used for a chemical analysis, while Combo pH/Conductivity/TDS meter (Low Range, HANNA instruments HI98129 multiparameter, 14 pH, 3999 us/cm, 2000 ppm) was applied to determine the general characteristics of spring and ECA water after its contact with the zeolite - рН, electroconductivity, TDS, mineralization (a concentration of the ions dis-solved in water).

The effect of the contact time between the zeolite present at 10 mass % and spring water from Rila moun-tain region, Bulgaria, on the ion exchange process was investigated. Its values referred to 24 h, 48 h, 72 h and 168 h. The experiments were carried out with non-ther-mally treated zeolite at 25°С and thermally treated one for 2 h at a maximal temperature of 300°С and 550°С.

The zeolite used was crushed to a size ranging from 1 mm to 5 mm. Its concentration in the water amounted to 10 mass %. Plastic containers of 200 ml volume were used. Each sample contained 20 g of zeolite in 200 ml of water.

ECA water of a different рН value was obtained by electrolysis carried out within different time periods ranging from 5 min to 20 min. The zeolite initially heated for 48 h at 550°С was used for the experiments with ECA water. The changes of the latter chemical composition, pH, conductivity and mineralization were determined.

RESULTS AND DISCUSSION

The chemical composition of the zeolite shown in Table 1 proves that it has a high content of SiO2 of K-Ca clinoptilolite type.

The result from XRD analysis of the zeolite shows that its main phase is clinoptilolite. Its amount is 83 mass %. Some small quantities of anorthoclase and opal are also found as secondary phases. Fig. 2 presents XRD data referring to the zeolite used.

The measured values of pН, electro conductivity and mineralization of the spring water are given in Table 2. The results show that the values of these parameters increase with the water contact with the zeolite. The Fig. 1. A natural zeolite from Haskovo region.


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Table 1. A chemical composition of the zeolite from Kralevo field, East Rodope mountain.

Oxides SiO2 Al2O3 TiO2 Fe2O3 MgO CaO Na2O K2O ΣH2O

Weight % 71,35 12,72 0.20 0.90 0.94 2,20 0.94 3,94 12,79

N Type of water рН Elecrto conductivity (μS/cm)

TDS, рpm (mg/l)

0 0 – Pure spring water 7,45 31 15

1 Water after 24 hours contact with natural zeolite

7,62 40 20


7,57 36 18


7,75 37 18


7,92 52 26

5 Water after 24 hours contact with natural zeolite heated at 300оС

7,21 92 46


7,46 97 48


7,80 95 47


8,32 100 50


7,33 140 70


8,25 154 77


8,34 168 84


9,0 193 96

Table 2. Change of spring water pH, electro conductivity and mineralization with increase of the time of contact with the zeolite.


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changes are very significant when the zeolite is heated at 550°С. The time of contact also influences the change of these parameters. The latter values increase with this time increase. The water becomes alkaline (рН reaches a value of 9, while that of the spring water is 7,45). The electroconductivity of pure spring water increases from 31 μS/cm to 193 μS/cm after a contact with a zeolite heated for 168 h at 550°С.

The change of Na+ and K+ cations concentration in the water in dependence on the time of contact with the zeolite and the temperature of its heat treatment are illus-

trated in Fig. 3. It is found that Na+ cations concentration in pure spring water amounting to 1,18 mg/l increases to 44,85 mg/l after one week of contact with a zeolite thermally treated for 2 h at 550°С.

An analogous tendency is found for К+ cations. The latter concentration in pure water is equal to 1,49 mg/l/, while after treatment it increases to 5,68 mg/l. There-fore, the increase of the duration of the activation and the temperature of the heat treatment leads to a higher amount of К+ and Na+ cations transmitted to the water. An opposite dependence is observed for Ca2+, Mg2+, F-,

Fig. 2. XRD patterns of the zeolite from Haskovo region.

Fig. 3. Change of Na+ and K+ cation concentration in water after its contact with non-thermally treated zeolite (Na 25) and thermally treated one at 300°С (Na 300) and 550°С (Na 550) for different periods of time.


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Fig. 4. Change of Ca2+ and Mg2+ cation concentrations in water after its contact with a non- thermally treated zeolite (Ca 25 and Mg 25) and a thermally treated one at 300°С (Ca 300 and Mg 300) and 550°С (Ca 550 and Mg 550) for differ-ent periods of time.

Fig. 5. Change of water conductivity after its contact with a zeolite heated at 25 оС, 300 оС and 550оС.

Fig. 6. Change of water рН after its contact with a zeolite for different periods of time


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HCO3- and SO3

-. The changes оf Са2+ and Mg2+ cations concentrationс are given in Fig. 4. A more pronounced decrease is registered for Ca2+ cations when compared to that of Mg2+ cations.

The change of the water conductivity after its contact with the zeolite is shown in Fig. 5. The water conductiv-ity increases, while the greatest value is observed in case

of a contact with a zeolite heated at 550°С. A similar trend is valid for the change of water рН shown in Fig. 6.

ECA water of different рН values is obtained by electrolysis carried out for different periods of time rang-ing from 5 min to 20 min (Fig. 7). The change of ECA water рН and conductivity with a contact with a zeolite of 48 h is shown in Fig. 8. It is seen that рН stays con-stant but the electro conductivity increases significantly. The same is valid for water mineralization because it is related to its conductivity.

Fig. 9 shows the change of the concentration of К+, Na+, Са2+ and Mg2+ in ECA water of a different рН after 48 h contact with a zeolite heated at 550°С. The change of НСОз anions concentration is present in Fig. 10, while that of F-, С1-, РO4

3- and SO42- is shown in Fig. 11.

CONCLUSIONS

The present work describes the effect of the contact time between a natural zeolite from Haskovo region,

Fig. 7. ECA water рН values as a function of electrolysis duration.

Fig. 8. Change of ECA water рН and electroconductivity after its contact with a zeolite for 48 h.

Fig. 9. Changes of the concentration of К+, Na+, Са2+ and Mg2+ in ECA water of a different рН after its 48 hour contact with a zeolite heated at 550°С.

Fig. 10. Change of the concentration of НСО- in ECA water of a different рН after its 48 h contact with a zeolite heated at 550°С.

Fig. 11. Changes of the concentration of F-, Сl-, РO43-,

SO42- in ECA water of a different рН after its 48 h contact

with a zeolite heated at 550°С.


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Bulgaria and spring water from Rila mountain region, Bulgaria on the main characteristics of the water as рН, electroconductivity and mineralization. It is proved that the ion exchange increases with contact time increase. Na+ and K+ penetrate the water and the nano-sized rings of the zeolite but they are replaced by Са2+ and Mg2+. A significant change is found referring to НСОз

- con-centration, which increases from 16,6 mg/1 to 97,63 mg/1 in the activated water. Irrespectively of their low concentration, SO4

-, РО4-, Сl- and F- are exchanged. This

results in increase of water electroconductivity from 31 µS/cm to 200 µS/cm, of water mineralization from 15 mg/1 to 96 mg/1 and рН from 7,4 to 9,0 in case of the longest contact time .

The effect of the thermal treatment of the zeolite on the ion exchange between the zeolite and water is studied experimenting with a non-thermally treated zeolite at 25°С and a zeolite heated at 300°С and 550°С. The high-est values of the ion exchange level and the water param-eters followed are observed in experiments with a zeolite heated for 2 h at 550°С. The increased ion exchange is attributed to the dissolution of the horizontal and vertical rings of the zeolite structure during the thermal treatment.

Optimal conditions are found for the ion exchange between a zeolite and water. The highest concentra-tion of Na cations (in the spring water it is 1,18 mg/1) transferred to the spring water from the zeolite is 45 mg/1. This increase is observed in case of one-week contact time and thermal treatment of the zeolite for 2 h at 550°С. Analogous trend is observed for К cations (in the spring water it is 1,49 mg/1) where after treatment the concentration reaches a value of 5,68 mg/1. Conse-quently, the longer ion exchange process and the higher heat treatment temperature lead to a higher amount of transmitted К and Na cations in the water and improve-ment of the ion exchange process.

The effect of the initial рН value of water activated by the electrolysis on its characteristics is studied for a zeolite heated at 550°С being in contact with the water for 48 h. pH dependence of the ion exchange, water conductivity and mineralization is found. The water рН increase brings about increase not only of the concentra-tion of the dissolved cations and anions but also of the conductivity and the mineralization. Water рН value stays in the range from 7 to 8 because of the equilibrium between the cations and anions concentrations.

It is proved that the alkaline water possesses an

activating action, stimulates the ion exchange towards the extraction of cations and anions from the water sys-tems leading thus to strong increase of the conductivity at decreased рН in the range of its neutral values. The process studied is analogous to those of human body purification from toxins and radicals.

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