Modification of Zeolite Derived from Fly Ash and Its Application in Coomassie Brilliant Blue G250 Removal

ABSTRACT:

The utilization of waste sources such as fly ash has been of great interest to scholars to generate high-value products. In this study, zeolite was synthesized from fly ash via the hydrothermal method followed by alkaline fusion, which was employed for the adsorption of Coomassie Brilliant Blue G250 (CBB) in aqueous solution. The physicochemical properties of fly ash and zeolite were analyzed by SEM and BET methods. The CBB dye removal using zeolite was investigated in various conditions such as a pH value of 2 to 9 in a series of reaction times from 5 to 300 minutes, to evaluate the dye adsorption capacity. Following the investigation of influenced parameters and the calculation of kinetic models, the results show that the adsorption capacity of CBB dye on zeolite reached 1186.07 mg g-1 in optimizing conditions with pH 2, an initial dye concentration of 300 mg L^-1 for 3 h. The pseudo-second-order model is well-fitted with the removal of CBB dye onto zeolite. Zeolite-modified fly ash was a potential application for dye removal in wastewater.

Keywords: Zeolite, fly ash, Coomassie Brilliant Blue G250, wastewater, adsorption.

1. Introduction

In the recent year, the widespread issue of water pollution is increasing by the discharge of hazardous pollutants, including heavy metals, dyes and antibiotics. Among them, dye composition is one of the most common substances released from textile, paper, cosmetic industries. There are three main types of dye, like cationic, anionic, and non-ionic. Coomassie brilliant blue G250 (CBB) dye is anionic dye, which contains complex aromatic compounds [1]. In high concentration, it has negative impact on cancer, respiratory tract, and red eye [2]. In addition, the presence of CBB dye can make aesthetic quality reduced and water muddy, inhibiting the transmission of sunlight and lowering photosynthesis quality [3]. Therefore, it is necessary to remove CBB dye before discharging into ecology using more effective techniques. Photodegradation, coagulation-flocculation, adsorption, and membrane separation are conventional approaches for dye treatment from water effluent. Adsorption is considered as favorable removal method because of its reasonable cost, ease of operation, and no secondary pollution [4]. However, adsorbent plays a significant role in this technique, which is interested in not only high efficiency but also economic value.

Fly ash is byproduct derived from the coal combustion in power plant. However, the discharge of fly ash is highly cost in landfill, low reusability, and environmental pollution because of its hazardous components. On the other hand, fly ash is also comprised of main compositions, such as silica, alumina, and ferric oxide as well as high porous, large specific surface area [5].

Thereby, many researchers studied and modified fly ash into high-value products. In 2019, Darmayanti et al. [6] successfully synthesized geopolymer using fusion method to adsorb Cu²⁺ ion in aqueous solution. Another finding is the influence of NaOH, KOH, NaOH+Na₂SiO₃, and KOH+Na₂SiO₃ on the surface of adsorbent material. Sivalingam et al. [7] generated zeolite X from fly ash and its application to remove crystal violet dye. The dye efficiency reached at 99.52 % in the optimizing conditions, including pH 2 for 60 min at 50^oC with initial concentration of 100 mg L^-1 and adsorbent dosage of 1.0 g L^-1. Recently, many synthesis techniques was used to convert fly ash into zeolite, like hydrothermal, microwave-irradiation, sonication, and fusion-assisted hydrothermal synthesis [8]. Depending on the physicochemical properties of the material, the appropriate method is selected to achieve optimal processing performance. In this study, the authors will focus on using a simple, no toxic chemical, environmentally friendly synthesis method, using hydrothermal and alkalization to synthesize zeolite from fly ash. The combination of hydrothermal and alkalization methods makes the process of forming the structural framework of the material easy, besides alkalizing with NaOH also greatly affects the pore structure of the material to increase the adsorption capacity and dye removal [9-10]. Thus, the application of zeolite materials for removing CBB dye through the evaluation of operating conditions and the calculation of kinetic models.

2. Material and method

2.1. Material

Fly ash was collected from the coal combustion process in the factory at VISIP II industrial park, Binh Duong province, Vietnam. Chemicals are used in this work included sodium hydroxide (NaOH, 97%), hydrochloric acid (HCl, 37-38%), anhydrous silica gel (SiO₂), and Coomassie brilliant blue G250 (C₅₅H₄₄N₃NaO₇S₂) purchased from the Xilong Company in China.

2.2. Synthesis of zeolite adsorbent

First, fly ash was pretreated with HCl concentrate in a 100 mL volumetric flask at 80^oC for 2 hrs with 600 rpm, then the mixture was filtered and washed with deionized water several times and dried 16 hrs at 80^oC. Next, the obtained sample is ground into a fine powder and then mixed with anhydrous NaOH and SiO₂ according to the mass ratio (fly ash: NaOH:SiO₂ is 8:8:1) and calcined at 700^oC for 2 hrs. Finally, 10 g of sample after calcination and 80 mL of deionized water were aged for 4 h before hydrothermally heating at 100^oC for 24 hrs. After hydrothermal, the sample was adjusted to the neutral pH value with deionized water, and dried for 16 h at 80^oC to obtain zeolite.

2.3. Coomassie brilliant blue G250 dye removal

Coomassie brilliant blue G250 adsorption on zeolite was carried out in batch experiments. 40 mL of the dye solution with a concentration of 300 mg L^-1 containing the adsorbent into a polyethylene centrifuge tube placed in a shaker at 200 rpm at room temperature. Besides, the factors of pH (2 - 9), contact time (5 - 300 minutes) are the parameters that need to be investigated. The dye solution after adsorption was filtered by a nylon filter with a diameter of 0.45 µm and analyzed by a UV-Vis machine (Agilent Cary 60, US).

The adsorption capacity of zeolite was calculated according to equation (1):

Whereas Co: the initial concentration of dye solution (mg L^-1); Ce: the concentration of dye solution after adsorption equilibrium (mg L^-1); V: The initial volume (mL); m: the dosage of adsorbent (g).

Based on previous research by Tran et al. [11] showed that the kinetic model in non-linear form was performed in Equation (2) and (3).

Non-linear first order model: q_t = q_e1 (1 - e^-k1t)                       (2)

Non-linear second order model:

         Whereas qe: The equilibrium adsorption capacity (mg g^-1); qt: The adsorption capacity at time t (mg g^-1); t: the time of adsorption (min); k₁, k₂: the pseudo first-order and pseudo second-order kinetic adsorption rate constant.

3. Results and discussions

3.1. Characterization of zeolite

Figure 1: SEM image of (a) fly ash and (b) zeolite

Morphological characteristics of fly ash and zeolite were analyzed by SEM measurement technique. Figure 1 demonstrates that the fly ash is almost spherical in shape, with a smooth surface with an average pore diameter of 4.83 nm. In addition, fly ash (Figure 1a) contains irregularly shaped active minerals and unburnt carbon components. Moreover, the size and shape of fly ash components are not uniform due to the temperature difference in cooling and burning process [12]. Meanwhile, the formed zeolite (Figure 1b) has a cubic shape, the edges become sharper, the spherical forms are shifted into irregular crystalline. The change in the morphology of zeolite materials caused by the aging stage in the hydrothermal process, and the alkalization process with NaOH in the presence of anhydrous SiO₂ helped a structural framework for the material form [10].

The physicochemical attributes of the materials were analyzed and calculated by the BET and BHJ methods. As can be seen in the results, the total specific surface area of fly ash was SBET = 11 m2 g^-1, while the average pore diameter and volume were only 4.83 nm and 0.01 cm3 g-1, respectively. However, after modification, the total specific surface area of the zeolite material increased by 9-folds compared to that of fly ash (SBET = 90 m2 g^-1), the pore volume and pore diameter also increased to approximately 8-folds and 1.5-folds, respectively. This is because NaOH is activated on the surface of the material and the synthesis conditions impact the material morphology [6, 9, 13].

3.2. Effect of dye adsorption by zeolite

3.2.1. Effect of pH value

Figure 2: Effect of pH value

pH value is parameter in the determination of dye adsorption capacity and reaction mechanism between adsorbent and adsorbate in solution. The effect of pH on the dye adsorption behavior of zeolite was demonstrated in Figure 2, which was investigated in the range of 2-9 with an initial CBB dye concentration of 300 mg L^-1 for 3 hrs. As can be seen from the below line graph, the maximum adsorption capacity was 237.7 mg g^-1 at pH 2. After that, a significant reduction was observed in adsorption capacity from pH 2 to pH 4, to about 120 mg g-1 and then there was relatively stable. This tendency can be explained by the filling of the binding vacancy and the presence of electrostatic attraction between the color molecules and the material [14-15]. More specifically, the CBB dye is an anionic dye, so the adsorption behavior was higher in the acidic environment due to the interaction between SO₃^2- ions present in the color molecule and H+ ions in the acidic environment, which meant that promoted the diffusion of dye molecules into the zeolite material. On the contrary, when the pH increased, the concentration of OH- also increased, so the competition between SO₃^2- and OH- ions appeared, causing the adsorption capacity to markedly decrease. Therefore, pH 2 was the greatest medium to adsorb CBB dye on zeolite, which would be studied in the investigation of the remaining conditions.

3.2.2. Effect of contact time

Figure 3: Effect of contact time

Figure 3 shows the influence of contact time for CBB removal on fly ash with an initial concentration of 300 mg L^-1 with pH value of 2 at room temperature. The investigation of contact time was of paramount importance in the evaluation of adsorption kinetics. The adsorption capacity rapidly increased in the first 60 minutes in the dye adsorption uptake on zeolite. After 120 minutes, the adsorption process almost reached saturation. This was because many available vacancies existed in the pore structure of the zeolite for the first time. Afterward, the competitive interaction between CBB dye molecules entering the zeolite pore, the adsorption process will form a film that hinders the subsequent adsorption. However, the survey time was extended to evaluate the adsorption capacity of the material. The results showed that 180 minutes is the best time for the process to reach steady state with the adsorption capacity of 1186.07 mg g^-1 [16].

3.3. Adsorption kinetics

The data of CBB dye adsorption were fitted with different kinetic model studies. The pseudo first-order and pseudo second-order models were used to calculate the adsorption capacity of materials and investigate the agreement between experiment and theory.

Figure 4: Kinetics plot of dye adsorption on zeolite

Figure 4 shows the dye adsorption kinetic curve by zeolite. Based on the above experimental data, we can express the relationship between adsorption capacity (qt) versus time (t) for nonlinear first- and second-order kinetic models.

From the graph, the pseudo-second-order kinetic model was consistent with the calculated data of dye adsorption process on zeolite. In addition, the correlation coefficient of the pseudo-second-order kinetic model reached R² = 0.95, which was higher than that of pseudo-first-order kinetic model. This proved that the initial solution concentration did have no effect on the removal of CBB on zeolite, but only the zeolite loading affected the adsorption process. This result was the same as previous studies, Munagapati et al. [17] used turkey tail fungus (Trametes versicolor) to remove Congo Red, Vigneshwaran and his colleagues [18] removed Malachite Green and Rhodamine B with tapioca skin. The research conditions of these works are different, so the similarity is only relative. However, this study shows that fly ash is also a promising material for adsorbent in water treatment.

4. Conclusions

In this research, zeolite was successfully synthesized from fly ash through a hydrothermal method combined with alkali fusion and its application in the removal of CBB dye. the adsorption capacity of CBB dye on zeolite reached 1186.07 mg g-1 in optimizing conditions with pH 2, initial dye concentration of 300 mg L^-1 for 3 h. Moreover, the pseudo-second-order kinetic model is well-fitted with the CBB dye adsorption process. Therefore, fly ash can be considered a promising adsorbent for dye treatment.

Acknowledgements: This research is funded by Nguyen Tat Thanh University, Ho Chi Minh City, Vietnam (No. 2022.01.106/Hđ-KHCN).

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TỔNG HỢP VẬT LIỆU HẤP PHỤ

TỪ QUÁ TRÌNH BIẾN TÍNH TRO BAY ỨNG DỤNG TRONG

XỬ LÝ MÀU COOMASSIE BRILLIANT BLUE G250

• NGUYỄN THỊ HỒNG HÀ¹

• TS. TRẦN THỊ TƯỜNG VI¹

¹Viện Ứng dụng Công nghệ và Phát triển bền vững

Trường Đại học Nguyễn Tất Thành

TÓM TẮT:

Tro bay là chất thải có nguồn gốc từ quá trình đốt than trong nhà máy điện đã được nhiều nhà nghiên cứu sử dụng để tạo ra các sản phẩm có giá trị cao. Việc sử dụng tro bay để tổng hợp vật liệu có khả năng loại bỏ thuốc nhuộm đang được quan tâm. Nghiên cứu này đã tổng hợp Zeolite từ tro bay thông qua phương pháp thủy nhiệt kết hợp với phản ứng kiềm hóa, để loại bỏ màu Coomassie Brilliant Blue G250 (CBB) trong nước thải. Tính chất hóa lý của tro bay và zeolite được phân tích bằng phương pháp SEM và BET. Quá trình loại bỏ màu nhuộm CBB bằng zeolite được nghiên cứu ở các điều kiện khác nhau như môi trường pH từ 2 đến 9 trong khoảng thời gian phản ứng từ 5 đến 300 phút để đánh giá khả năng hấp phụ thuốc nhuộm. Sau khi nghiên cứu các thông số ảnh hưởng và tính toán mô hình động học, kết quả cho thấy rằng khả năng loại bỏ màu nhuộm đạt đến 1186.07 mg g^-1 tại môi trường pH 2, trong 3h và mô hình biểu kiến bậc hai hoàn toàn phù hợp với quy trình loại bỏ thuốc nhuộm CBB bằng zeolite. Zeolite là vật liệu có tiềm năng ứng dụng trong xử lý màu nhộm trong nước thải.

Từ khóa: Zeolite, tro bay, Coomassie Brilliant Blue G250, nước thải, hấp phụ.

[Tạp chí Công Thương - Các kết quả nghiên cứu khoa học và ứng dụng công nghệ, Số 23 tháng 10 năm 2023]