Removal behaviour of a thiazine, an azo and a triarylmethane dyes from polluted kaolinitic soil using electrokinetic remediation technology

Accepted Manuscript Title: Removal behaviour of a thiazine, an azo and a triarylmethane dyes from polluted kaolinitic soil using electrokinetic remediation technology Author: Effendi Mohd Yusni Shunitz Tanaka PII: DOI: Reference:

S0013-4686(15)30049-9 http://dx.doi.org/doi:10.1016/j.electacta.2015.06.153 EA 25320

To appear in:

Electrochimica Acta

Received date: Revised date: Accepted date:

6-1-2015 27-6-2015 28-6-2015

Please cite this article as: Effendi Mohd Yusni, Shunitz Tanaka, Removal behaviour of a thiazine, an azo and a triarylmethane dyes from polluted kaolinitic soil using electrokinetic remediation technology, Electrochimica Acta http://dx.doi.org/10.1016/j.electacta.2015.06.153 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.

Removal behaviour of a thiazine, an azo and a triarylmethane dyes from polluted kaolinitic soil using electrokinetic remediation technology Effendi a,b, Shunitz Tanaka a, ,* a

Division of Environmental Science Development , Graduate School of Environmental Science ,

Hokkaido University, North 10 West 5 Kita-ku, Sapporo 060-0810, Japan b

Department of Chemistry, Faculty of Mathematics and Natural Science, State University of

Padang, Air Tawar Padang, West Sumatera, 25131 , Indonesia

*Corresponding Author Tel: +81 11 706 2219 E-mail: [email protected] Abstract In this study, we investigated the potentiality of the electro-kinetic remediation (EKR) technique for the removal of organic dyes polluted soil. Methylene blue (MB), methyl orange (MO), and phenol red (PR) are representing a thiazine, an azo, and a tryarilmethane dye respectively, which was spiked with kaolinite were selected as a model for pollutant dyes tests. An EKR tool (15 cm length) equipped with a DC electric current with the maximum values of 30 V. Graphite electrodes were used for both anode and cathode was set up for two weeks operation. 1

As a result, only 40-55 % of dye was removed from the soil sections by using distilled water. However, by the addition of some electrolytes; the percentage of dyes removed from the soil increased from 73- 76 % and 85 - 89 % for sodium sulphate, and monosodium dihydrogen phosphate, respectively. It resulted that 55-64 % of dyes was removed without controlling the pH. The significant improvement was achieved by controlling the pH of the system. By controlling the pH in the cathode chamber, only 23 % of MB, 25 % of MO, and 18 % of PR dyes remain in the soil sections, respectively. While by controlling the pH in the anode chamber, almost 90 % of tested dyes could be removed from the kaolinite chamber effectively. The movement of a thiazine dye, from the anode to the cathode chamber was controlled by electro-migration and electro-osmosis phenomena. An azo dye transported from the cathode to the anode chamber by a similar process. However, a triarylmethane dye was removed from the soil sections by only electro-osmosis process. For three kinds of tested dyes, it were found that electro-osmotic flow moving from the anode to the cathode directions. The ageing of dye affects the removal percentage of the dye. Keywords :electro-kinetic remediation, kaolinite, electro-migration, electro-osmotic, pH controlling, thiazine dye, azo dye, triarylmethane dye. 1.

Introduction Nowadays, environmental pollution, especially soil pollution has been trending topics

and obtaining serious consideration around the world since it appeared as an environmental problem. In terms of soil contamination, there are two kinds of soil contaminant, inorganic contaminants such as, metal and heavy metals, and organic contaminants such as polyaromatic hydrocarbon (PAH), oil, pesticides, and dyes. Dyes are organic colorants used in

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textile, pharmaceutical, cosmetic, food, and other industries for imparting different shades of colors. As for the textile industries, billion litres of dyes are produced every day around the world. Most of the dye manufacturers and users, particularly in the textile industries, release massive quantities of wastewater containing dye to the extent of 0.001- 0.7 % w/v [1]. Dye wastes, even in low concentrations, are visually detected, affect aquatic life, the food cycle, which become harmful to human health. Methylene Blue (MB), 3,7-bis (Dimethylamino9-phenotiazin-5-ium chloride), C16H18N3SCl is a thiazine dye which is most commonly used substances for dyeing cotton, wood, and silk. MB give rise to harmful effects for breathing, vomiting, severe headache, diarrhea, painful micturation, and methemeglobinea. Methyl

orange

(MO),

(Sodium

4-[(4-dymethylamino

phenylazo)]

benzenesulfonate,

C14H14N3NaO3S, is an azo dye. The reductive cleavage of an azo linkage produces aromatic amines which can possibly lead to intestinal cancer. In addition, high concentrations of MO can be dangerous to human life. Phenol Red (PR), also known as Phenolsulfonpthalein, PSP, C19H14O6S, is a tryarilmethane dye attributed with some harmful effects to humans due to the inhibition effect to the growth of renal ephitelial cells. Direct or indirect contact with PR leads to irritations of the eye, respiratory system, and skin. This compound is also toxic to the muscle fibres and has mutagenic effects [2]. Even though there is insufficient records about the real number of victims due to dye pollution, but in terms of scientific relevance, this is a great chance to explore and study more on the removal of dye from contaminated soil for environmental safety. Several methods can be used to remove dyes from the soil through biological, physical, and chemical processes with different advantages and disadvantages of each methods [3-10]. Previous researchers reported about the removal of MB by using carbon derived from peach

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stones [11], coir pith activated carbon [12], photocatalytic [13], and electrochemical degradation [14]. Even though the application of electro-kinetic remediation has been listed as one of the most promising methods for decontamination of soils polluted from organic and inorganic compounds [15,16]. However, only a few reports of studies on the removal of dyes were found in the literature. Therefore, it is a great opportunity to develop an effective method of soil remediation using cost-effective and eco-friendly technologies for future applications. Electro-kinetic remediation is a method for extracting and removing heavy metal ions and organic pollutants from the soil. This technique allows for the in situ removal of contaminants from the soil, so the cost operation and destruction of the soil matrix can be minimized [17]. The application of electro-kinetic remediation for organic and inorganic contaminants has been reported by previous researchers [18-23]. . The basic principle of the electro-kinetic remediation system is the application of low intensity direct voltage or current between anode and cathode through the soil compartment. Contaminants are migrated towards the electrodes by a couple of phenomena. Firstly, by electro-migration process; in which positively charged organic compounds are transported to the cathode sites, and in vice versa, negatively charged organic compounds are migrated to the anode sites. Secondly, by electro-osmosis forces, it was a relative movement of a liquid containing ions with respect to a stationary charged surface [24, 25]. During the removal process of organic compounds including dyes in contaminated soil by electro-kinetic remediation, the dye pollutant will be migrated towards the anode or cathode site depending on the charge of the dye. This study demonstrated the trend and behaviour of the removal of three dyes from polluted soils by EKR. Since the results significantly depends on the operating conditions and the chemical structure of the dyes, thus several parameters such as, pH, the initial concentration

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of dye, the addition of electrolyte into the system, and ageing effect of the dye in the soil were investigated. The transportation and the distribution of pollutant dyes and the directions of electro-osmotic flow for each dye after EKR process was also studied.

2.

Experimental

2.1.

Materials Kaolinite clay soil used in this study with the the precipitation volume of 4.0 – 6.5 ml/g

was obtained from Wako Pure Chemical Industries, Ltd., Japan. The soil contains 82 % of clay and 18 % of silt. A thiazine dye (MB) was purchased from Kanto Chemical Co. Inc., Japan, while an azo dye (MO), a triarylmethane dye (PR), sodium sulphate, and monosodium dyhidrogen phosphate were purchased from Wako Pure Chemical Industries, Ltd., Japan.

2.2.

Kaolinite sample preparation Polluted kaolinite samples in this study were prepared by the mixing process. One

hundred and twenty grams of kaolinite clay minerals were mixed with 40 ml of MB, MO, or PR 300 mgL-1 dyes solution thoroughly, and a mixture of 100 mg dye/kg dry kaolinite was obtained. The mixture stands up for 24 h for the drying procedure. The molecular structure of dyes are shown in Figure 1. The initial pH of the mixtures was around 4.1-4.3, and the moisture content of the mixtures was around 32 % in all experiments. Kaolinite clay mineral was selected as a model of soil matrix due to the suitable parameters such as lower buffering capacity, and cation exchange capacity compared with other clay minerals [26].

2.3.

Electro-kinetic Remediation (EKR) Cell 5

The EKR system used in this study was set up as shown in Figure. 2. It consists of a soil compartment, two electrode chambers, a peristaltic pump, a power supply and a data recorder . Graphite electrodes with the length of 8-10 cm and a diameter of 4-6 mm were purchased from CZ Republic and were used for both the anode and cathode. The sample, 120 g of dyes polluted kaolinite was loaded to the soil chambers. The processing fluid or electrolyte was inserted to the electrode chamber solution to enhance the electrical conductivity of the system, improving desorption of dye from kaolinite particles, and to increase the transportation rate of the pollutants from kaolinite. The pH in both chambers was controlled by 0.1 M of hydrochloric acid or sodium hydroxide solution. A DC voltage of 30 V was applied between the anode and cathode and monitoring data was taken periodically by using a midi logger(GL2000, Graphtec).

2.4.

Remediation process After the completion of the EKR treatment, the soil was taken from the soil chambers

carefully, divided into five sections, and labelled as S1,S2,S3,S4, and S5 from the anode to the cathode direction. The sample soil was left all day for the drying procedure. The samples then were analyzed for pH, electrical conductivity, and dyes concentrations for each section. Determination of the pH for all sections was done by adding potassium chloride solution of 1.0 M with ratio 2-3 ml of solution per 1 g of dry sample. The sample of soil was shaken for 3 hours to get the homogeneous mixtures. The pH and electrical conductivity of each section were measured by pH meter, and Conducto meter, respectively. For the determination of dye amount in soil, 4 g of soil samples were added into 32 ml of 0.1 M sodium sulphate or monosodium dihydrogen phosphate solution at pH 8-12, shaked for 3 hours at 150 rpm and then centrifuged at

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4000 rpm for 10-15 minutes. Finaly, the dye concentrations were determined by absorbance measurements using UV-Visible Spectrophotometer at the 665 nm, 440 nm, and 560 nm as the maximum wavelength for a thiazine (MB), an azo (MO), and a triarylmethane (PR) dye respectively.

3.

3.1.

Results and Discussion

Effect of adding electrolyte as a fluid processing This study aims to investigate the feasibility of the electro-kinetic remediation treatment

for kaolinite polluted with three tested dyes, methylene blue (MB), methyl orange (MO) and phenol red (PR). Therefore, a certain amount of kaolinite sample contaminated with dyes was inserted to the electro-kinetic chamber. All equipments were set up and run for two weeks. Mobilization of dye, pH value and distribution of dye remained in all sections after the electro-kinetic process were determined. To study the electrolyte influences on the electro-kinetic remediation of kaolinite polluted with dyes, several electrolytes were added as fluid processing materials into the chamber. The distribution of MB and its pH values in all sections after the EKR treatment are shown in Fig. 3. When distilled water was used as a migrating media, around 43 % of dyes still remained in soil sections (Figure.3a). The concentration distribution of MB in the all sections varied from 5 to 15 %. The lowest concentration remaining in section 1 was 5 % . This concentration was increased in section 2 and section 3. The highest concentration of MB achieved in section 4 was 15 %, almost three times the amount in section 1. However, in section 5, the MB concentration was decreased again by 5 %. Most of MB was accumulated in the

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cathode and in the EOF receiver in the amount of 27.8 % and 28.6 % respectively. It was found clearly that MB migrates from the anode toward the cathode chamber since it has a positive charge. The EOF moved also from the anode to the cathode directions. The pH of soil sections after the EKR process were also described in Figure 3a. The main reaction which takes places during this process was the electrolysis of water. Water oxidation in the anode chamber resulted in the production of H+, and water reduction resulted in OH- at the cathode chamber. Therefore, the pH tendency was to be acidic (around pH 2) near the anode in Section 1, and almost alkaline (around 9) in the cathode chamber. No significant differences of increasing pH in section 2, section 3, and section 4 was recorded. The H+ produced in the anode chamber was moved toward the cathode chamber and yields an acid condition in the sites, thus producing acidification of the kaolinite. From the distribution of MB concentration and the pH value during the process, it was clearly found that the removal direction of MB was from the anode to cathode.The EOF also moved from anode to cathode chamber directions. To study the effect of electrolyte on the electro-kinetic process, sodium sulphate and monosodium dihydrogen phosphate were added to the chamber. Figure 3b depicts the electro-kinetic remediation of MB removal by adding sodium sulphate as an electrolyte. The direction of MB removal was found from anode to cathode. This direction was just the same as previously explained for the pH effect (which was created as pH 4.2 in anode chamber and pH 9.3 in the cathode chamber). However, the percentage of MB removal was increased where a total of 25.6 % of MB remained in the soil sections. Here, 37.8 % MB was found in the cathode chamber and 38.3 % in the EOF receiver. A more significant effect on the pH value was produced when monosodium dihydrogen phosphate was used for fluid processing (Figure 3c). The pH 3.8 was almost acidic in the anode chamber and pH 10.2 an almost strong alkaline in the

8

cathode chamber. However, there is no large change in pH and the buffering effect was observed in sections 3-5. The total percentage of MB removed from the kaolinite sections was around 84.5 %. The amount of MB almost accumulated in cathode and EOF receiver as 42 % and 42,3 % respectively. For the thiazine dye represented by MB with a positive charge, the increasing of distribution concentration was similar for each sections. The dye start moving from anode chamber, to the section 1, 2 and 3 with increasing dye remains, reach the highest remains in section 4 and finally decreased again in section 5. The directions of the removal for the positive dye was recorded from anode to the cathode chamber. The moving of electroosmotic flow was also found moved from the anode toward the cathode . Figure.4 depicts the distribution of MO and the changing of pH values during the EKR treatment in all soil sections. When distilled water was used as fluid processing, around 48 % of dyes still remain in soil sections (Figure 4a). Around 50 % of MO was found in the anode chamber and in the EOF receiver. In contrary to MB, a different trend of MO removal resulted. MO dye starts moving from the cathode to the anode chamber since MO has a negative charge. Therefore, the highest concentration was reached in section 2 and decreased in section 1 near the anode chamber due to the acidic conditions. The pH condition was almost acidic in all sections of the anodic chamber ranging from 4.2 to 5.2, while in the cathode chamber it was increased by 9.5. A similar trend resulted for another treatment including the presence of electrolyte of sodium sulphate (Figure 4b). All sections were almost at a pH from 2.4 to 3.2, and the highest concentration of dye in section 2 was 9.0 %. Here, around 27 % of dye remained in the soil chamber, which is almost 35 % in the cathode chamber and 36 % in the EOF receiver. The dye

9

remains in soil sections were decreased drastically when monosodium dihydrogen phosphate was used for

fluid processing (Figure 4c). Here, 42.8% of MO was found in the cathode chamber

and 43.5 % in the EOF receiver, and totally 86 % of the MO pollutant was removed from the soil sections. The pH was recorded at 3.6 in the anode chamber, increased at section 2 and became neutral in section 3 by electrolyte reactions. The alkaline condition started in section 4 and increased in section 5 at pH around 10.2. Even though the direction of the MO removal was really different with MB removal, electro-migration and electro-osmosis occurred in the kaolinite sections during the EKR process. For the azo dye represented by MO with a negative charge, the increase of distribution concentration was found similar for each section. The dye start moving from the anode chamber, to the section 1. The directions of the removal for the negative dye was recorded from cathode to the anode chamber. However, the electro-osmotic flow transported by the opposite direction, from the anode toward the cathode chamber. To complete the investigation about the trend of dye removal instead of the positive (MB) and negative (MO) dyes charged, the study concerning the removal of neutral dyes was conducted. Phenol Red (PR) was selected as a tested dye representing the triarylmethane group of dye. PR has both a positive charge and negative charge as shown in Figure 1, however the net charge of the whole molecule is neutral. It means that the PR dye movement during the electro-kinetic process under the electric field was restricted to the electro-osmosis phenomena. Therefore, the operating conditions to achieve the optimum value of electro-osmotic flow (EOF) should be adjusted. As mentioned in Figure 5a, 40 % of PR still remains in soil sections when distilled water was used in the process. Twenty nine percent of PR accumulated in cathode chamber and 30 %

10

in the EOF receiver. The concentration distribution of PR shows the analog trend with the removal of the positive dye. The dye movement will be started from the anode chamber in acidic conditions to the cathode chamber in alkaline condition. PR dye had the highest concentration in section 4 when sodium sulphate (Figure 5b) and monosodium dihydrogen phosphate (Figure 5c) were used as an electrolyte in this process. By previous conditions, the amount of dyes removed from soil sections were increased to 76% ( 74 % in cathode and EOF receiver) and 90 % (almost 88 % in cathode and EOF receiver) by using sodium sulphate and monosodium dihydrogen phosphate, respectively. Both of them showed a similar trend of concentration distribution of PR removal and pH values, since PR dye moved from the anode to cathode chamber, and the highest concentration was achieved in section 4. The soil was acidified in section 1 and section 2, and alkalined in section 5, but in sections 3 and 4 reached neutral pH around 6.5 to 7.5. For the triarylmethane dye represented by PR with a positive and negative charge and the net charge of the whole molecule is neutral, the distribution of dye amounts was also found similar for each section. The dye start moving from the anode chamber to section 1. The amount of PR was found increased in section 2, section 3, and section 4, but finally decrease in section 5. The directions of the removal for the neutral charge of dye was from anode to the cathode chamber, which is similar with the EOF moving direction. As already mentioned above, the main reactions which occured in the electrokinetic prosess for the dyes removal was the electrolysis of water that produced H+ in the anode and OHin the cathode . This condition yields an acidified kaolinite. The current intensity, which fixes the rate around the ions, was created, and it depends on the amount of current voltage applied and also the electrical conductivity of the electro-kinetic treatment solution [27] .The amount of dye which remains in each section is affected by electrical conductivity. The higher the electrical

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conductivity the bigger the amount of dye removed. The electrical conductivities of each section of the three tested dyes are shown in Table 1. These results show a similar trend with the other dyes already reported [28].

3.2.

Effect of controlling pH during the electrokinetic remediation process The purpose of controlling the pH in the cathode chamber was to prevent the formation

of an alkaline environment at the cathode side by using an acid solution. In this experiment, sulphuric acid 0.1 M at pH around 7 was used in the anode chamber to avoid the pH jumping. The controlling pH in the anode chamber will avoid the formation of H+ ions and the acid front by using a base solution such as sodium hydroxide 0.1 M at a pH of almost 7. By this condition, the basic front was generated at the cathode sites, and penetrated into the soil sections so that there was an increase in the pH of the fluid processing. Also, due to the lower mobility of the OH- ions, the electrical resistance of the system was slightly higher [29]. For the MB, without controlling pH, it was found that the distribution of concentration migrated towards the cathode, and the highest concentration of MB dye was in section 4. The MB dye remains in the soil section by 42 % which was accumulated by 27.6 % and 28.9 % in the cathode chamber and in the EOF receiver respectively (Figure 6a). However, when the controlling pH was applied in the cathode, the total MB concentration remains will decrease by 23 % (Figure 6b). Here, around 38 % of MB was found in the cathode chamber and 39 % in the EOF receiver. The distribution concentration was decreased from the cathode to the anode chamber and the MB dye was present in section 1. The pH was increased from 4.0 in section 1 to around 9.8 in section 5. While, when the controlling pH was made in the anode chamber, the MB dye remains in kaolinite sections was really decreased to 11 % wich is almost 41.7 % of MB

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accumulated in the cathode chamber and 42.7 % was found in the EOF receiver (Figure 6c). The trend of the distribution concentration and pH was similar to that with the controlling pH in the cathode chamber For the MO as an azo dye that has a negative charge, without controlling the pH it was found that the distribution amount of the day migrated towards the anode (Figure 7a). MO dye had its highest concentration in section 4 and the MO dye remained in the soil section at 43 %. (25 % in the cathode and 25.6 % in the EOF receiver). When the controlling pH was applied in the cathode chamber (Figure 7b), the total MB concentration remains decreased to 24.2 % (37 % in the cathode chamber and 38 % in the EOF receiver). The distribution concentration decreased from the cathode to the anode chamber and the MB dye was present in its highest concentration in section 1. The same trend was found when controlling pH in the anode was conducted. Thus, the MO dye which remained in the kaolinite sections really decreased to 9.5 % (Figure 7c). Here almost 44.6 % and 45.3 % of MO were found accumulated in the cathode chamber and the EOF receiver, respectively. Finally, for the PR as a neutral molecule representing the triarylmethane group of dye, it was found a similar trend of the dye moving directions and the pH value. Without controlling the pH, the dye migrated towards the cathode, which is concentrated in section 4 at 16 % from the total percentage of removal (Figure 8a). Here, 29 % of PR was accumulated in the cathode chamber and 30 % in the EOF receiver, and 59 % of PR was removed from the soil. The percentage of the PR removal decreased significantly by 18.3 % which is 40 % and 41.3 % of the dye found in the cathode chamber and the EOF receiver respectively (Figure 8b). Finally, almost 42.5 % of PR was found in the cathode chamber, 43.3 % was accumulated in the EOF receiver, and in total total 87 % of the PR dye was removed from the soil sections when the controlling pH was done

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in the cathode chamber (Figure 8c). As mentioned above, the amount of dye remains in each sections controlled by the electrical conductivity through to the each kaolinite sections. The higher the electrical conductivity the larger the amount of dye which was removed. The electrical conductivities of each section of tested dyes with respect to the uncontrolled pH, controlled pH in the cathode, and controlled pH in the anode chamber are shown in Table 2.

3.3.

Effect of dye ageing on the removal percentage of the dye We also studied about the other consideration related with the ageing effect on the

removal process of pollutants in the EKR system. All of dyes in this study were polluted in one day or 24 hours. There are many types of ageing such as physical, biological , and chemical aging [30] as well as photochemical degradation, thermal degradation, chemical attack, and mechanical stress [31]. It will be interesting point to conduct the experiment by considering the effect of aging of dye in the soil. It has been hypothesized that aging involves diffusion into soil micropores, portioning into soil organic matter, strong surface adsorption, or a combination of these processes [32]. Since the aging effect of the dye in the soil is important factor, a study should be conducted to determine whether the time that a compound remains in the soil affects the removal ability of the dye in the EKR system. After doing some experiments, we obtained the following results as shown in Figure 9. From these figures it can be seen that after ageing of 30 days, the removal percentage of dyes decreased when compared with the 1 day ageing treatment. By uncontrolling the pH (Figure 9a), it was found that only 42 % MO was removed from the soil chamber. It was also found that 63% and 76 % of MO removed from the soil sections by controlling the pH in the Cathode and the Anode chamber respectively. These results decreased if we compared with removal of MO by

14

only 1 day ageing treatment as shown in the Table 3. It can be seen that the removal percentage of MO with 30 days ageing treatment, if compared with MO with 1 day aging, decreased as 16, 24, and 26 % for uncontrolling pH, controlled pH in the cathode, and controlled pH in the anode chamber respectively.The time that a compound remains in the soil affects a biodegradability, adsorption behaviour and the ease of extraction [33]. It can be concluded that the ageing of dye affects the removal percentage of the dye. The longer the time of ageing treatment, the smaller the removal percentage of dye. From the results mentioned above, it can be seen that by using sodium sulphate as an electrolyte, the removal percentage of dyes increased as 16.7 %, 21.6 %, and 16.3 % for MB, MO, and PR, respectively. As an average, by using sodium sulphate as an electrolyte, the removal percentage increased as 18.2%. While, by using monosodium dihydrogen phosphate as an electrolyte, the removal percentage of dyes increased as 28.3 %, 34.7 %, and 29.7 % for MB, MO, and PR, respectively. As an average, by using monosodium dyhidrogen phosphate as an electrolyte, the removal percentage increased by 30.9 %. The use of both electrolytes, increased the electro-osmotic flow, improved the desorption of dye from the surface of kaolinite particles, and prevented the acidification of the medium. In this system, methylene blue which has a positive charge was transported by electromigration and electroosmosis phenomena from anode to cathode direction. Methyl Orange which has a negative charge was transported by electromigration from cathode to anode. While, Phenol Red was transferred from the kaolinite section by only electroosmosis process due to the neutral charge. The removal velocity of three dyes was different for different kinds of treatment . It was found that the EOF rate of methylene blue (positive charged dye) more higher than methyl orange (negative charged dye) and phenol red (neutral charged dye). Controlling pH in cathode will be favoured the advance of acid front. It will avoid the formation of alkaline environment in the cathode sites. Moreover, the jumping pH formation will be avoided. The soil sample was acidified and so that the pH profile , from section 1 to section 5 was almost flat and the electrical resistance of the system was kept lower than that of the previous system. As a result, the data in Fig.6b,7b and 8b were different with data in Fig.6a,7a, and 8a, whithout controlling pH, especially in section 4 and section 5. It resulted that 15

by controlling the pH in Cathode, the removal percentage of dyes increases as 20.4 % (Fig.6b), 8.8 % (Fig.7b), and 22.4 % (Fig.8b) for MB, MO, and PR respectively. As an average, by controlling pH in Cathode chamber, the removal percentage of dyes sample increased as 20.5 %. While, the controlling pH on the Anode chamber aims to avoid the formation of hydrogen ions and the acid front. The basic front generated at the cathode chamber, penetrated in to the soil system, and increasing the pH of fluid processing and so that pH profile were almost flat in the end of the experiment. And more amount of dyes were transported. By controlling the pH in Anode, the removal percentage of dyes increased by 27.8 % (Fig.6c), 39.2 % (Fig.7c), and 26.9 % (Fig.8c) for MB, MO, and PR, respectively. As an average, by controlling pH in Anode, the removal percentage increased by 31.3 %. From all treatments in this experiment, it can be seen that by controlling the pH in the anode chamber, the better removal of dyes was achieved indicating the high effectiveness of this treatment.

4.

Conclusions The obtained results of this research clearly showed that the addition of electrolyte and

controlling the pH value during the treatment could reveal the optimum condition for the electro-kinetic remediation process. Furthermore, the dye removal was really increased from the kaolinite sections. More over, the process was improved by addition of adequate electrolytes since their presence in the anode and cathode chambers favoured the electrical conductivity and desorption of pollutants or contaminants from the soil or from the surface of the soil. Moving directions of dye, pH value changes, the electrical conductivity, concentration after the EKR process, for the five sections( section 1 to section 5) from the anode site to the cathode site, were different for any kind of dye contaminant . The characteristic and behaviour of the removal system was different among all tested dye contaminants, since there were differences of the dye structures and the charge of the dyes. Thus, it can be concluded that the operating conditions, especially the pH value into the kaolinite chamber soil sample, are decisive parameters to 16

achieve the best remedation process. It also can be concluded that the ageing of dye affects the removal percentage of the dye. The longer the time of ageing treatment, the smaller the removal percentage of dye. Considering the achieved results in this study, the EKR technique could be a promising option for the remediation method for soil and sediments polluted with organic compounds including dyes.

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[14] M.Pianizza, A.Barbucci, R.Ricotti, G.Cerisola, Sep.Purif.Technol, 54 (2007) 382-387. [15] A. Sanroman, M.A, Pazos. M.T. Ricart, C. Cameselle, Chemosphere 57 (2004) 233. [16] R.E. Saichek, K.R. Reddy, Crit. Rev. Environ. Sci. Technol, 35 (2005) 115. [17] M. Page, C.L. Page, J. Environ. Eng. 128 (2002) 208. [18] Vyrkutyte, J. Sillanpaa, M. Latostenmaa, P, Sci. Total. Environ. 289 (2002) 97. [19] A. Altin, and Degirmenci, M, Sci. Total Environ 337 (2005) 1. [20] H. Sarahney, J. Wang, A.N. Alshawabkeh, Environ. Eng. Sci. 22 (2005) 642. [21] P.E. Jensen, L.M. Ottosen, T.C. Harmon, Environ. Eng. Sci. 24 (2007) 234. [22] A.P. Khodadoust, K.R. Reddy, K. Maturi, Environ. Eng. Sci 21 (2004) 691. [23] R.S. Putra, S. Tanaka, Sep. Purif. Technol. 79 (2011) 208-215. [24] A.T. Yeung, Environ. Eng. Sci 23 (2006)202. [25] Y.B. Acar, A.N. Alshawabkeh, Environ.Sci.Technol 27 (1993) 2638. [26] S. Pamukcu, Electron.J.Geotech. Eng 2 (2007) [27] R.E. Hicks, S. Tondorf, Environ. Sci. Technol. 28 (1994) 2203. [28] M.Pazos, C.Cameselle, M.A.Sanroman, Environ. Sci. 25 (2008) 419-426. [29]

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Table 1. Electrical conductivity of soil samples (mS cm-1 . 10-1) after the removal process of dye polluted kaolinite soil by using electrokinetic remediation system with respect to the different fluid processing.

Dye

Thiazine dye (MB)

Azo dye (MO)

Triarylmethane dye (PR)

H20

Na 2SO 4

NaH2PO 4

H20

Na 2SO 4

NaH2PO 4

H20

Na2SO 4

NaH2PO 4

S1

3.1

3.2

2.9

5.7

7.4

4.5

1.2

1.1

0.7

S2

3.4

3.6

3.5

6.8

1.23

7.7

1.8

1.3

1.1

S3

3.6

3.8

3.9

6.6

9.2

8.6

2.9

1.4

1.5

S4

3.9

4.1

4.3

6.2

3.4

7.6

3.3

1.7

2.2

S5

2.6

2.2

2.8

3.5

2.3

6.8

1.9

0.8

0.8

Section

19

Table 2. Electrical conductivity of soil samples (mS cm-1 . 10-1) after the removal process of dye polluted kaolinite soil by using electrokinetic remediation system with respect to the controlling of pH.

Dye

Thiazine dye (MB)

Azo dye (MO)

Triarylmethane dye (PR)

Uncontr pH

Controlling pH in Cat

Controlling pH in Anode

Uncontr pH

Controlling pH in Cat

Controlling pH in Anode

Uncontr pH

Controlling pH in Cat

Controlling pH in Anode

S1

3.1

2.6

2.3

5.7

5.1

6.8

1.2

2.7

1.7

S2

3.4

2.4

2.2

6.8

4.8

6.6

1.8

2.5

1.5

S3

3.6

2.3

2.1

6.6

4.3

6.4

2.9

2.1

1.4

S4

3.9

2.1

2.0

6.2

4.1

6.1

3.3

1.6

1.3

S5

2.6

1.9

2.8

3.5

3.8

5.8

1.9

1.4

1.9

Section

Table 3. Effect of dye ageing on the removal percentage of an azo dye (methyl orange), after electrokinetic remediation process with respect to the controlling of pH.

Treatment

Removal percentage of MO by 1 day ageing (%)

Removal percentage of MO by 30 days ageing (%)

Uncontrolling pH

51

42

Controlling pH in Cathode

75

63

Controlling pH in Anode

89

76

20

Fig. 1 Chemical structure of tested dyes (a) methylene blue, C16H18N3SCl, (a thiazine dye), ( b) methyl orange, C14H14N3NaO3S (an azo dye), and (c ) phenol red C19H14O5S, (a triarylmethane dye).

Fig. 2 Schematic diagram of electro-kinetic cell equipment set-up ; soil sections (S1, S2, S3, S4,S5), anode chamber, cathode chamber, electrolyte , peristaltic pump, power supply, EOF receiver and data recorder.

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Fig. 3 Amount of distribution (mg) of a thiazine dye (methylene blue), which remains in the equipment chamber after the electro-kinetic remediation process using ; (a) distilled water, (EOF rate of 0.031 mlmin-1) (b) sodium sulphate, (EOF rate of 0.039 mlmin-1) and (c ) monosodium dihydrogen phosphate, (EOF rate of 0.043 mlmin-1), for fluid processing. Initial concentration of MB is 100 mg /kg, with direct constant voltage of 30 V, and the processing time of 15 days.

22

Fig. 4 Amount of distribution (mg) of an azo dye (methyl orange) which remains in the equipment chamber after the electro-kinetic remediation process using ; (a) distilled water, (EOF rate of 0.025 mlmin-1) (b) sodium sulphate, (EOF rate of 0.032 mlmin-1) and (c ) monosodium dihydrogen phosphate, (EOF rate of 0.036 mlmin-1), for fluid processing. Initial concentration of MO is 100 mg /kg, with direct constant voltage of 30 V, and the processing time of 15 days.

23

Fig. 5 Amount of distribution (mg) of a triarylmethane dye (phenol red) which remains in the equipment chamber after the electro-kinetic remediation process using ; (a) distilled water, (EOF rate of 0.028 mlmin-1) (b) sodium sulphate, (EOF rate of 0.034 mlmin-1) and (c ) monosodium dihydrogen phosphate, (EOF rate of 0.038 mlmin-1), for fluid processing . Initial concentration of PR is 100 mg /kg, with direct constant voltage of 30 V, and the processing time of 15 days.

Fig. 6 Amount of distribution (mg) of a thiazine dye (methylene blue) which remains in the equipment chamber after the electro-kinetic remediation process by different treatment ; (a) by un-controlling of pH, (EOF rate of 0.031 mlmin-1) (b) by controlling of pH in the cathode chamber, (EOF rate of 0.042 mlmin-1) and ( c) by controlling of pH in the anode chamber, (EOF rate of 0.05 mlmin-1), during the treatment. Initial concentration of MB is 100 mg /kg, with direct constant voltage of 30 Volt, and the processing time of 15 days.

24

Fig. 7 Amount of distribution (mg) of an azo dye (methyl orange) which remains in the equipment chamber after the electro-kinetic remediation process by different treatment ; (a) by un-controlling of pH (EOF rate of 0.025 mlmin-1), (b) by controlling of pH in the cathode chamber, (EOF rate of 0.035 mlmin-1) and (c) by controlling of pH in the anode chamber, (EOF rate of 0.041 mlmin-1), during the treatment. Initial concentration of MO is 100 mg /kg, with direct constant voltage of 30 Volt, and the processing time of 15 days.

25

Fig. 8 Amount of distribution (mg) of a triarylmethane dye (phenol red) which remains in the equipment chamber after the electro-kinetic remediation process by different treatment ; (a) by un-controlling of pH, (EOF rate of 0.028 mlmin-1) (b) by controlling of pH in the cathode chamber, (EOF rate of 0.035 mlmin-1) and (c) by controlling of pH in the anode chamber, (EOF rate of 0.038 mlmin-1), during the treatment. Initial concentration of PR is 100 mg /kg, with direct constant voltage of 30 Volt, and the processing time of 5 days.

Fig. 9 Amount of distribution (mg) of an azo dye (methyl orange) which remains in the equipment chamber after the electro-kinetic remediation process by 30 days ageing treatment; (a) by un-controlling of pH, (b) by controlling of pH in the cathode chamber, and (c) by controlling of pH in the anode chamber, during the treatment. Initial concentration of MO is 100 mg /kg, with direct constant voltage of 30 V. The processing time of 15 days, and the EOF rate are 0.015, 0.019, and 0.023 mlmin-1 for (a), (b), and (c) respectively.

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