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ISSN 0321-2653 ИЗВЕСТИЯ ВУЗОВ. СЕВЕРО-КАВКАЗСКИЙ РЕГИОН._ТЕХНИЧЕСКИЕ НАУКИ. 2018. № 4
ISSN 0321-2653 IZVESTIYA VUZOV. SEVERO-KAVKAZSKIYREGION. TECHNICAL SCIENCE. 2018. No 4
УДК 541.183 DOI: 10.17213/0321-2653-2018-4-124-131
EFFECTS OF PULSE ELECTROMAGNETIC FIELD ON THE NUCLEATION QUANTITY AND CRYSTAL GROWTH OF CALCIUM CARBONATE IN WATER
© 2018 г. Wang Xingguo
Changchun Institute of Technology, Changchun, Republic of China
ВЛИЯНИЕ ИМПУЛЬСНОГО МАГНИТНОГО ПОЛЯ НА ОБРАЗОВАНИЕ ЦЕНТРОВ КРИСТАЛЛИЗАЦИИ И ДИНАМИКУ РОСТА КРИСТАЛЛОВ КАРБОНАТА КАЛЬЦИЯ В ВОДНЫХ РАСТВОРАХ
Ван Синго
Чанчуньский инженерно-технологический институт, г. Чанчунь, Китайская Народная Республика
Wang Xingguo - Associate Professor, Changchun Institute of Ван Синго - доцент, Чанчуньский инженерно-технологический
Technology, Changchun, Republic of China. институт, г. Чанчунь, Китайская Народная Республика.
The nucleation and growth rate of crystals is vital for the crystallization speed. This study investigated the effects of pulse electromagnetic field (PEMF) on the nucleation and growth rate of freshly-formed calcium carbonate under dynamic conditions. The results revealed that the influences of PEMF on the crystallization of calcium carbonate varied with the ratio of Ca2+/CO32~. The application of PEMF considerably reduced the quantity offormed crystals at low ratios of Ca2+/CO32- while the application of PEMF increased the amount offormed crystals at high ratios of Ca2+/CO32~. However, the presence of PEMF slowed crystal agglomeration and extended the precipitation time and made the quasi-stable structure more stable. Zeta potential analysis showed that the application of PEMF increased the positive surface charge carried by the crystals as the ratio of Ca2+/CO32-was larger than 1 while made the surface charge of crystals more negative in the case of the ratio of Ca2+/CO32-less than 1.
Ключевые слова: PEMF; precipitated calcium carbonate; crystal growth; nucleation; Zeta potential.
Скорость кристаллизации определяется образованием ядра и скоростью роста кристаллов. В данной статье рассмотрены результаты исследования влияния электромагнитных полей на образование ядра и скорость роста кристаллов карбоната кальция в динамичных условиях. Доказано, что степень воздействия электромагнитных полей на кристаллизацию карбоната кальция зависит от соотношения Ca2+/CO32~. Так, воздействие электромагнитного поля значительно сокращает количество сформированных кристаллов при низких значениях соотношения Ca2+/CO32, одновременноувеличивая размеры сформированных кристаллов. В присутствии электромагнитного поля снижается скорость агломерации кристаллов и увеличивается время образования осадка, делая его структуру более стабильной. Анализ полученных значений дзета-потенциала показывает, что в присутствии электромагнитного поля увеличивается положительный заряд кристаллической поверхности при соотношении Ca2+/CO32~более 1.
Keywords: импульсное электромагнитное поле; кристаллизация карбоната кальция; рост кристаллов; дзета-потенциал.
ISSN 0321-2653 IZVESTIYA VUZOV. SEVERO-KAVKAZSKIYREGION.
1. Introduction
The build up of scale deposits is a common and costly problem in many industrial processes using natural water supplies (Baker and Judd, 1996). As estimated by Davill (1993) that in Britain alone the formation of scales in industrial process plant where water is heated or used as a coolant cost 1 billion pounds per year (Darvill, 1993). Such costs can be attributed to cleaning (i.e. descaling) or the poor thermal conductivity of scaled surface; heat transfer is decreased by 95 % with a CaCO3 scale layer of 25 mm in thickness (Glater et al., 1980) whereas an SiO2 scale layer of 0.5 mm in thickness results in a 90 % decrease in heat transfer (Grutsch and McClintock, 1984). The effects of external engergy, like high frequency electric or magnetic field interacting on a dispersed system, although still somewhat controversial, have attracted increasing attention in so-called non-chemical methods of wastewaters treatment or to prevent the hard scale formation in industrial installations (Hoiysz et al., 2003).
A large number of investigations have been carried out related to the effect of magnetic field on aqueous solutions and suspensions (Oshitani et al, 1999; Coey et al, 2000), scale formation (Wang et al., 1997; Rebecca et al, 1998; Chibowski et al,2003) and biological systems. The existence of the effects of magnetic field on them has been confirmed by various experimental evidences.
Higashitani et al. (1992; 1993; 1995; 1996; 1999; 2000) conducted a series of well-controlled experiments to quantify the effects of magnetic field on solutions and suspensions. They reported the results related to the effects of magnetic exposure on particle formation and deposition of CaCO3, zeta potential and diffusivity of colloid particles and fluorescence probe emission intensity in solution. Recently, they examined the short-range interaction force between a mica surface and an AFM probe tip in electrolyte solutions by atomic force microscopy. Their studies revealed that magnetic exposure could reduce the agglomeration rate, surface potential and diffusivity of colloidal particles in suspension.
Colic and Morse (1998) investigated the effects of radiofrequency electromagnetic field (RF EMF) with different amplitudes on calcium carbonate precipitation and found that the treatment of water with RF of high amplitude reduced nuclei and led to the formation of larger particles. On the other hand, RF treatment with low amplitude resulted in the production of more smaller nuclei and particles.
Wang et al. (1997) studied the effects of an external magnetic field on the formation of calcium
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carbonate from super-saturated solution and their results indicated that under certain conditions in the presence of an external magnetic field, the nuclea-tion rate can be greatly increased and the resultant crystals are greater in number, with smaller sizes and irregular shapes. Dalas and Koutsoukos (1989) investigated the influences of a static magnetic field with the B value of 18T on the crystallization of calcium carbonate and found that the presence of this magnetic field could reduce the crystallization rate by 40 %. Later, Higashitani et al (1993) examined the same system and reported that the nuclea-tion rate was reduced and the growth rate was increased markedly as the B of the magnetic field was about 0.3T. Anyway, most of the previous studies focused on the effects of static magnetic field and the results from the these studies suggested that magnetic field had very complex effects on the crystallization process of CaCO3 and were often in conflict with each other. The discrepancy may be due to the differences of experimental conditions at different laboratories.
Higashitani at al. (1999) examined the contribution of the pulse and alternating magnetic fields on the precipitation of CaCO3 and compared with that of the static field and observed that the substantial time required to reach the maximum magnetic effect in the pulse and alternating fields was much smaller than the time achieved in the static field and the magnetic effect depended on the frequency of magnetic field. Therefore, it is possible that the pulse magnetic field is much more effective in changing the crystallization process of calcium carbonate than the static field. However, very few studies have been carried out to examine the effects of pulse electromagnetic field (PEMF) on the nuclea-tion and growth in crystallization process under dynamic conditions.
In the present study, we determined the distribution of crystal granularity with a particle size analyzer at different saturation condition and compared the crystal granularity distributions with or without the presence of PEMF to analyze the behavior of calcium carbonate crystals. In addition, we explored the possible mechanisms of PEMF by measuring the zeta potential of freshly-formed Ca-CO3 and online microscope observation.
2. Materials and methods
2.1. Materials. Reagent-grade chemicals were used to prepare all of the solutions used in this study. The water used was a Milli-Q Water (17.3 MQ cm). CaCh and N2CO3 solutions of equal molar concen-
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tration were employed following Chibowski et al. (2003). The concentration of CaCh and Na2CO3 solutions was 6x10"3 M. The solutions were filtered through 0.45-^m membrane filters made of cellulose acetate (MFS) and then kept in a temperature-controlled bath of 25±0.5oC.
2.2. Experimental setup. The schematic of the experimental setup used in this study is presented in Fig. 1. The pulse electromagnetic field device, which can operate continuously, is composed of a self-made pulse electromagnetic field generator (frequency: 2 ± 0.2 kHz, amplitude: 10V ± 0.3 V) and exterior-connected ferromagnetic winding set (200 loops, O = 0.5mm). Containers, Bi, B2 and B3, for storing reagents were all sealed, and a filtering device was installed at the gas-inlet of Bi and B2 for the removal of CO2 and other granular impurities. An overflow device L is equipped with container B3 to ensure a constant volume of solution in B3.
2.3. Experimental procedure. Each experiment was repeated for six times and the mean values were presented. After each experiment, the experimental setup was cleaned according to the following procedures: i) immerged in 1:1 HCl for 10 min; ii) rinsed with tap water for at least five times; iii) washed with distilled water for three times; iv) rinsed with Milli-Q water and dried.
2.3.1. PEMF-treatment of Na2CO3 solution. According to the conclusions drawn by Highashitani et al. (1993), the pretreatment of Na2CO3 solution with magnetic field had more pronounced effects on the crystallization of CaCO3 than the pretreatment of CaCl2 solution with magnetic field. Therefore, we pretreated Na2CO3 solution with PEMF before mixing Na2CO3 solution with CaCl2 solution. Therefore, a volume of 250 ml Na2CO3 solution (6x10-3 M) was circulated at 25 ± 0.5oC continuously for 30 min before it was mixed with CaCl2 solution by the peristaltic pump C3, whose flowrate is 125 mL/min, through a rubber hose with a diameter of 3 mm, outside which the PEMF was applied via the loops wrapped around the rubber hose.
2.3.2. Dynamic experiments. To examine the effect of CaCl2/Na2CO3 ratios on the particle size distribution of the formed crystals, CaCl2 solution was pumped with the peristaltic pump C2, whose flowrate was 5 mL/min, to mix with the PEMF-treated Na2CO3 solution to achieve different CaCh/Na2CO3 ratios. The mixing was carried out under the condition of continuous circulation of the mixture with and without PEMF exposure. The mixture was taken out immediately for particle size analysis as the ratios of CaCh/Na2CO3 being 1:10,
1:5, 2:5 and 1:1 were achieved at 5, 10, 20 and 50 min, respectively. The quantity and size of the freshly-formed calcium carbonate crystals were measured with a HIAC/ROYCO particle size analyzer.
D4
A _
ЁЗ]
Fig. 1 Experimental setup: А: Filter for filtering out CO2
and other dusts in the air; B1, B2, B3 is Double-layer automatic temperature-constant glass container, wherein,
B1: CaCl2 6x10"3 M solution; B2: Na2CO3 6x10"3 M solution; B3: Mixed reactor; C1, C2, C3: Peristaltic pumps; Di, Di, D3, D4, D5, De: Ball-valves; E: Winding coil; F: Pulse electromagnetic generator; G: Micro-camera; H1, H2: Computers; I: Light dispersion detector; J: Spectrophotometer; K: Granularity analyzer; L: Overflowing device / Рис. 1. Принципиальная схема
экспериментальной установки: А: фильтрующee устройство для удаленияя CO2 и пылевидных частиц из воздуха; B1, B2, Bз-стеклянный контейнер с автоматическим двухуровневым регулированием температуры, где B1: раствор CaCh концентрацией 6х10"3 M; B2: раствор Na2CO3 концентрацией 6x10-3 M; B3: контейнер для смешивания и реакции; C1, C2, C3:
перистальтический насос; D1, D2, D3, D4, D5, De: шаровой клапан; E: обмотки; F: устройство генерации электромагнитного импульса; G: иикрокамера; H1, H2: компьютер; I: установка для измерения рассеяния
оптического рассеяния; J: спектрофотометр; K: анализатор частиц; L: перепускное устройство
Different amounts of CaCh solution was pumped with the peristaltic pump C2, whose flowrate was adjusted to ensure that the CaCh solution was finished pumping in 5 min, to mix with a 250 ml PEMF-treated Na2CO3 solution. The mixture was circulated in the PEMF train for another 1 h and during this period the mixture was sampled at different time for particle size distribution analysis to investigate the variation of the properties of CaCO3 crystals formed with PEMF treatment time and with varying ratio of CaCh/Na2CO3. To compare the adhesion characteristics of calcium carbonate crystals, formed on solid wall with or without PEMF exposure, a method similar to that used by Emil Chibowski (2003) was adopted. A quartz glass sheet of 3 cm2 (3cmx1cm) was washed carefully with acetone and methanol and then rinsed with double distilled water, which was filtered with 0.45 цш filter paper, for three times. The quartz glass sheet was then stored in a temperature-controlled dryer for
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later use. This glass sheet was placed at the bottom of the glass container B3 just before the experiments were carried out. When each experiment was completed, the mixture of CaCh and N2CO3 solutions and the quartz glass sheet were left in container B3 for another 12 hr. Then the quartz glass sheet was taken out and carefully rinsed with double distilled water for three times to remove the floated particles and then placed in a dryer for 24 hours. The morphology of the crystals deposited on the quartz glass sheet was recorded with a micro-camera.
The same procedure but without the magnetic exposure was repeated to examine the effects of PEMF treatment on the properties of calcium carbonate crystals formed in this process.
2.3.3. Static experiments. Static experiments were carried out to compare the settleability and surface charge of CaCO3 crystals formed by the PEMF-treated Na2CO3 solution or non-treated Na2CO3 solution with CaCl2 solution. The variations of the UV-vis absorbance at 543.2 nm and zeta potential of the mixture with time were recorded immediately after CaCl2 solution was dosed into the PEMF-treated N2CO3 solution or non-treated Na2CO3 solution. The zeta potential of the mixture was performed with a JS94G+ zeta potential analyzer.
3.Results and discussions
3.1. Effect of PEMF on CaCO3 crystallization at different ratios of CaCl2/Na2CO3.
The effects of PEMF treatment and the ratio of CaCl2/Na2CO3 on the crystallization of CaCO3 were investigated by measuring the particle size distribution of freshly-formed CaCO3 crystals immediately as a per-determined ratio of CaCl2/Na2CO3 was achieved, as demonstrated in Fig. 2. PEMF exposure decreased the formation of CaCO3 crystals of various granularities when the ratio of CaCl2/Na2CO3 was as low as 1:10. As more CaCl2 solution was added to the Na2CO3 solution and the ratio of CaCl2/Na2CO3 increased to 1:5, more precipitates with a size of 2 ^m were observed in the PEMF-treated system. A further increase in the amount of added CaCl2 and the PEMF application resulted in a significant increase in the formation of crystals with particle size varying from 2 to 13 ^m. There were more crystals with a size of 2 ^m in the reference system at a ratio of CaCh/Na2CO3 being 2:5. Furthermore, the PEMF treatment favored the formation of crystals with a size of 3 ^m as more calcium carbonate precipitates with particle size of 3 ^m were formed than those of other sizes in PEMF-treated system. This phenome-
non was also observed in both the PEMF-treated system and the reference system when there were equal molar concentrations of CaCh and Na2CO3 in the mixture. Under this condition, the PEMF treatment enhanced the formation of the crystals with granularity of 3 ^m by over 50 %.
140-,
120-
0
100 -
Ш
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£ 80-
3
с
Ф 60-
о
Ё га 40-
о.
га 20-
Ü5
0-
о
2
14
4 6 8 10 12 crystal particle size (10-3 mm)
Fig. 2 Crystal particle quantity in different sizes granularities formed when CaCl2 was added in different
quantities:----Reference sample without PEMF
exposure;--- Sample with PEMF exposure. The added
CaCl2 : ■ 0,15 mmol; • 0,3 mmol; A0,60 mmol;
1,5 mmol (Temperature: 25±0,5 °С, Concentration of CaCO3 and CaCl2 solution 6x10"3mol/l).
Рис. 2. Зависимость образования кристаллов от
концентрации хлорида кальция, где:----контрольные
образцы без воздействия ЭМП; -: образцы после
воздействия ЭМП в присутствии хлорида кальция в количестве: ■ 0,15 ммоль; • 0,3 ммоль; ▲ 0,60 ммоль; ^1,5 ммоль (температура: 25±0,5 °С, концентрация раствора CaCO3 и CaCl2 6х10-3моль/л).
It was also observed that PEMF exposure led to the earlier formation and slow settlement of Ca-CO3 precipitates in the mixture of Na2CO3 and CaCh. Therefore, a pre-determined amount of CaCh solution was dosed into a PEMF-treated 250 mL of Na2CO3 solution of 6x10-3 mol/L in 5 min and the mixture was circulated in the PEMF for 1 hr to examine the variation of the crystal sizes formed in the mixture of N2CO3 and CaCh with time. Same experiments were repeated without the application of PEMF to work as the reference. The results obtained at different ratios of CaCl2/Na2CO3 were shown in Fig. 3, 4 and Fig.5.
When 0.15 mmol CaCh was added to the Na2CO3 solution (CaCh/Na2CO3 ratio=1:10), much more CaCO3 crystal particles with size of 2 or 3 ^m, were formed in the reference system than in the PEMF-treated system, as demonstrated in Fig. 3. Similar quantity of crystals with a size of 5 or 7^m was observed in two systems at the end of circulation. With the commencement of circulation, the amount of crystals with a size of 2 or 3^m in the
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reference system increased rapidly and reached maximum at 10 min. Hereafter, their quantity decreased rapidly in 5 min and then decreased slowly with time. There was a minor fluctuation in the quantity of CaCO3 crystals with a size of 5 or 7^m in the first 15 min after circulation in the reference system. However, the quantity of CaCO3 crystals of various sizes increased slightly in the first 20 min and then kept almost constant in the following time.
о
t: m о.
о / ri
, о
, п.
о
-
— о - □
А-
-ù-
-Д ~(г
10
50
60
20 30 40 cycle time (min)
Fig. 3 Relationship between crystal particle quantity and circulation treatment time in the system, when 1,2 mmol of calcium chloride was added. In the figure, broken line refers
to reference sample without PEMF exposure, solid line refers to sample treated by PEMF, ■□ - 2 ^m; o^ - 3 ^m;
▲ Д - 5 ^m; - 7 ^m (Temperature: 25 ± 0,5 °С, concentration of Na2CO3 and CaCh 6x10-3 mol/l) / Рис. 3. Взаимосвязь между количеством кристаллических частиц и временем циркуляции в системе при добавлении 1,2 ммоль хлорида кальция. На рисунке ломаная линия относится к эталонному образцу без воздействия ЭМП, сплошная линия относится к образцу, подвергнутому воздействию ЭМП: ■ □ - 2 ммоль; o^ - 3 ммоль; ▲ Д - 5 ммоль; - 7 ммоль (температура: 25 ± 0,5 °С, концентрация Na2CO3 и CaCl2 6x10"3 моль/л)
At the beginning of circulation as the ratio of CaCh/Na2CO3 was increased to 2:5, the CaCO3 crystals of various granularities appeared in much higher quantity in the PEMF-treated system than in the reference system, as shown in Fig. 4. Without the application of PEMF, the quantity of crystals with a size of 2 or 3 ^m reached its maximum value in about 15 min and then decreased with time. For the crystals with larger size in the reference system, their amount increased with time. With the case of exposure to PEMF, the amount of CaCO3 precipitates decreased slowly with circulation. At the end of circulation, PEMF exposure resulted in only a minor increase in the amount of precipitates with a size of 5 or 7^m.
Fig. 5 illustrates that the variation of the quantity of the crystals with a size of 2 or 3 ^m with time in the reference system at a ratio of CaCl2/Na2CO3 being 1:1 has similar trend as those observed at the ratio of CaCh/Na2CO3 being 1:10 or 2:5.
Fig. 4. Relationship between crystal particle quantity and circulation treatment time in the system, when 3,6 mmol of calcium chloride was added. In the figure, broken line refers to reference sample without PEMF exposure, real line refers to sample treated by PEMF, ■□ - 2 mmol; o^ - 3 mmol; ▲ Д - 5 mmol; - 7 mmol; (temperature: 25 ± 0,5 °С, concentration of Na2CO3 and CaCl2 6x10-3 mol/l) / Рис. 4 Взаимосвязь между количеством кристаллических частиц и временем циркуляции в системе при добавлении 3,6 ммоль хлорида кальция. На рисунке ломаная линия относится к эталонному образцу без воздействия ЭМП, сплошная линия относится к образцу, подвергнутому воздействию ЭМП: ■ □ - 2 ммоль; o^ - 3 ммоль; ▲ Д - 5 ммоль; - 7 ммоль (температура: 25 ± 0,5 °С, концентрация Na2CO3 и CaCl2 6x10-3моль/л)
Fig. 5. Relationship between crystal particle quantity and circulation time in the system, when 7,2 mmol of calcium chloride was added. In the figure, broken line refers to reference sample without PEMF exposure, real line refers to
sample treated by PEMF, ■□ - 2 mmol; o^ - 3 mmol; ▲ △ - 5 mmol; - 7 mmol (Temperature: 25 ± 0,5 °С, concentration of Na2CO3 and CaCl2 6x10-3 mol/l) / Рис. 5. Взаимосвязь между количеством кристаллических частиц и временем циркуляции в системе при добавлении 7,2 ммоль хлорида кальция. На рисунке ломаная линия относится к эталонному образцу без воздействия ЭМП, сплошная линия относится к образцу, подвергнутому воздействию ЭМП: ■ □ - 2 ммоль; o^ - 3 ммоль; ▲ Д - 5 ммоль; - 7 ммоль, (температура: 25 ± 0,5 °С, концентрация Na2CO3 и CaCl2 6x10-3моль/л)
0
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However, PEMF exposure resulted in a minor decrease in the first 10 min and then a slight increase in the amount of the crystals with a size of 2 or 3 ^m. The CaCO3 crystals of 2 or 3 ^m in diameter obtained in the PEMF-exposed system at the end of circulation were in a similar amount as those at the beginning of circulation. The quantity of the precipitates with a size of 5 or 7 ^m kept almost stable with circulation in both PEMF-treated system and reference stystem. Anyway, much more CaCO3 crystals were formed in the PEMF-exposed system than in the reference system.
The experimental results (vide supra) indicated that the PEMF treatment inhibits the nucleation at low super-saturation, resulting in less quantity of crystal particles in suspension. Under high saturation conditions, the nucleation is facilitated by PEMF treatment and there are much more small crystals in the PEMF-treated sample than that without PEMF application. For both cases, it should be pointed out that the small crystals present in the PEMF-treated sample can be kept very stable without agglomeration or deposition. However, the crystals in non-PEMF-treated sample undergo agglomeration and settlement quickly and the suspension becomes clear accordingly. These phenomena suggested that the crystals induced by PEMF treatment are not easy to agglomerate or settle, which is consistent with the conclusions made by Higashitani et al. (1992; 1993; 1995).
.S
с ß
о а а -10-и
N
Big I
----------------- ;......................в
•
.............A.............
................................1................ ■
Ca/ CO 1.2*10"2/ 6*10"' -■- PEMF .....□.....no PEMF
6*10"'/ 6*10 —•— PEMF .....О.....no PEMF
Ca2*/ CO 6*10"'/1.2*10"2 -■- PEMF .....no PEMF
а b
Fig. 6. The morphology of crystals deposited on the quartz glass sheet under different operating conditions: a - with
PEMF-treatment; b - without PEMF-treatment / Рис. 6. Морфология кристаллов, нанесенных на лист кварцевого стекла при различных условиях: a - после воздействия ЭМП; b - в отсутствии ЭМП
The morphology of the crystals deposited on the quartz glass sheet in the dynamic experiment was recorded with a micro-camera, as shown in Fig. 7. Obviously, fewer crystals were deposited on the quartz glass sheet and they were dispersed if Na2CO3 underwent PEMF-treatment before mixing with CaCl2. On the other hand, much more crystals were observed on the quartz glass sheet and they agglomerated when no PEMF was applied. This observation indicated that PEMF treatment enhanced the dissolution of CaCO3 in water.
0 20 40 60 80 100 120 140 160 Time,min.
Fig. 7. Zeta potentials of deposits formed during in circulation for 30 minutes in solution of CaCl2 and Na2CO3 at a temperature of 25±1 °С / Рис. 7. Значения дзета-потенциала отложений, образованных в процессе перемешивания в течение 30 мин в растворах CaCl2 и Na2CO3 при температуре 25±1 °С
The zeta potentials of CaCO3 crystals formed in static experiments with or without PEMF treatment at different times were determined and the results are demonstrated in Fig. 7. At the beginning and at the end of precipitation, the surface charges carried by the precipitates were only dependent on the ratio of CaCl2/Na2CO3 in the mixture and has no relationship with or without PEMF treatment. Ca-CO3 crystals carried positive charge (~9 mV) at the end of crystallization as there were excessive CaCl2 in the mixture and they had negative charge (-5— 10 mV) when there were excessive Na2CO3 in the mixture. PEMF application was found to have little effect on the zeta potential of CaCO3 crystals in the process of crystallization as there were equal amounts of CaCh and Na2CO3 in the mixture. However, PEMF treatment affected the zeta potential of CaCO3 crystals in the process of precipitates formation when surplus Ca2+ or CO32" were in the mixture. PEMF exposure resulted in more positive surface charge of calcium carbonate deposits when excessive Ca2+ cations were present in the mixture and more negative zeta potential of CaCO3 crystals as there were excessive CO32" anions in the mixture. This finding is consistent with that reported by Chibowski at al. (2003). Obviously the effects of magnetic field on CaCO3 crystallization process was dependent on the amount of excessive Ca2+ and CO32- in the reaction process.
UV absorbance of the mixtures of CaCh and PEMF-treated or non-treated Na2CO3 at different ratios of CaCh/Na2CO3 (1:2, 1:1 and 2:1) was recorded with time, as shown in Fig. 8, to observe the nucleation and crystal growth of calcium carbonate
0
0
Ca/ CO
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with time. In the first 3-4 minutes after mixing, the turbidity of the mixture containing non-treated Na2CO3 increased due to nucleation.
Time ,min
Fig. 8. Na2CO3 solution and CaCl2 solution of different quantities was mixed, and then the absorbance relationship
with time was immediately determined X = 543,2 nm / Рис. 8. Зависимость оптической плотности растворов Na2CO3 и CaCl2 от времени перемешивания при длине волны X = 543,2 нм
Thenturbidity decreased significantly because of the sedimentation of the precipitates and the turbidity finally decreased as the larger particles precipitated, and then the nucleation rate diminished. However, the turbidity of the mixture with PEMF-treated Na2CO3 experienced a jump, then decrease, then increase and then slow decrease with time. Compared with the non-treated sample, it took much longer time for the precipitates in the PEMF-treated sample to settle down.
4. Conclusions
Under dynamic conditions, we studied the effect PEMF treatment on the particle size distribution of newly-formed calcium carbonate cystals and its variation with time. The results showed that PEMF had marked effects on crystallization process of calcium carbonate, depending on the ratio of Ca2+/CO32- in the mixture. At low ratio of Ca2/CO32-, PEMF treatment suppressed the production of Ca-CO3 crystals. Under high saturation conditions
nucleation is facilitated by PEMF treatment and there are much more small crystals in the PEMF-treated sample than that without PEMF application. For both cases, the small crystals present in the PEMF-treated sample can be kept stable without agglomeration or deposition. Furthermore, PEMF exposure resulted in more positive surface charge of calcium carbonate deposits when excessive Ca2+ cations were present in the mixture and more negative zeta potential of CaCO3 crystals as there were excessive CO32" anions in the mixture.
Литература
1. Baker J.S., Judd S.J., Magnetic Amelioration of Scale Formation. Water Res. 30. 1996. Р. 247 - 249.
2. Higashitani K., Okuhara K., Hatade S. Effects of Magnetic Fields on Stability of Nonmagnetic Ultrafine Colloidal Particles. J. Colloid Interface Sci. 152. 1992. 125 р.
3. Higashitani K., Kage A., Katamura S., Imai K., Hatade S. Effects of magnetic field on formation of CaCO3 particles. J.Colloid Interface Sci. 156. 1993. 90 р.
4. Higashitani K., Iseri H., Okuhara K., Kage A., Hatade S. Magnetic Effects on Zeta Potential and Diffusivity of Nonmagnetic Colloidal Particles.J. Colloid Interface Sci. 172. 1995. Р. 383 - 388.
5. Higashitani K., Oshitani J., Ohmura N. Effects of magnetic field on water investigated with fluorescent probes. Colloids Surf. A 109. 1996. 167 р.
6. Ivan U. Vakarelski, Kazushige Ishimu.ra, Higashitani K. Adhesion between Silica Particle and Mica Surfaces in Water and Electrolyte Solutions. J. Colloid Interface Sci. 227. 2000. Р. 111 - 113.
7. Colic M., Morse D.J. Effects of Amplitude of the Radiofre-quency Electromagnetic Radiation on Aqueous Suspensions and Solutions.Colloid Interface Sci. 200. 1998. Р. 266 - 272.
8. Wang Y., Babchin A.J., Cherny L.T., Chow R.S., Sawatzky R.P. Rapid Onset of Calcium Carbonate Crystallization Under the Influence of A Magnetic Field.Water Res. 31. 1997. 346 р.
9. Dalas E., Koutsoukos P.G. The effect of magnetic fields on calcium carbonate scale formation J. Crystal Growth, 96. 1989. 802 р.
10. Oshitani J., Uehara R., Higashitani K. Magnetic Effects on Electrolyte Solutions in Pulse and Alternating Fields. Colloid and Interface Sci. 209. 1999. Р. 378 - 379.
11. Chibowski E., Hoysza L., Chibowski M. Precipitation of calcium carbonate from magnetically treated sodium carbonate solution. Colloids and Surfaces A. 225. 2003. Р. 63 - 73.
12. Chibowski E., Hotysz L., Szczes A. Time dependent changes in zeta potential of freshlyprecipitated calcium car-bonate.Colloids Surf. A 222. 2003. Р. 41 - 54.
References
1. Baker J.S., Judd S.J. Magnetic Amelioration of Scale Formation. Water Res. 1996, no. 30, pp. 247 - 249.
2. Higashitani K., Okuhara K., and Hatade S., Effects of Magnetic Fields on Stability of Nonmagnetic Ultrafine Colloidal Particles. J. Colloid Interface Sci., 1990, 152, 125.
3. Higashitani K., Kage A., Katamura S., Imai K., and Hatade S. Effects of magnetic field on formation of CaCO3 particles. J. Colloid Interface Sci.1993, 156, 90.
4. Higashitani K., Iseri H., Okuhara K., Kage A., and Hatade S. Magnetic Effects on Zeta Potential and Diffusivity of Nonmagnetic Colloidal Particles. J. Colloid Interface Sci., 1995, no. 172, pp. 383 - 388.
ISSN 0321-2653 IZVESTIYA VUZOV. SEVERO-KAVKAZSKIYREGION. TECHNICAL SCIENCE. 2018. No 4
5. Higashitani K., Oshitani J., and Ohmura N. Effects of magnetic field on water investigated with fluorescent probes. Colloids Surf. 1996, A 109, 167.
6. Ivan U. Vakarelski, Kazushige Ishimu.ra, and Higashitani K., Adhesion between Silica Particle and Mica Surfaces in Water and Electrolyte Solutions. J. Colloid Interface Sci., 2000, no. 227, pp. 111 - 113.
7. Colic M., Morse D., Effects J. of Amplitude of the Radiofrequency Electromagnetic Radiation on Aqueous Suspensions and Solutions. Colloid Interface Sci. 1998, 200, 266, 272.
8. Wang Y., Babchin A.J., Cherny L.T., Chow R.S., Sawatzky R.P. Rapid Onset of Calcium Carbonate Crystallization Under the Influence of A Magnetic Field. Water Res. 1997, 31, 346.
9. Dalas E. and Koutsoukos P.G. The effect of magnetic fields on calcium carbonate scale formation. J. Crystal Growth, 1989, 96, 802.
10. Oshitani J., Uehara R., and Higashitani K. Magnetic Effects on Electrolyte Solutions in Pulse and Alternating Fields. Colloid and Interface Sci. 1999, 209, 378 - 379.
11. Chibowski E., Hoysza L., Chibowski M. Precipitation of calcium carbonate from magnetically treated sodium carbonate solution. Colloids and Surfaces, 2003, A 225, pp. 63 - 73.
12. Chibowski E., Hotysz L., Szczes A. Time dependent changes in zeta potential of freshlyprecipitated calcium carbonate. Colloids Surf. 2003, A 222, pp. 41 - 54.
Поступила в редакцию /Receive 24 сентября 2018 г. /September 24, 2018
