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. 2020 Dec 4;5(49):31665–31672. doi: 10.1021/acsomega.0c04074

Removal of Chlorine Ions from Desulfurization Wastewater by Modified Fly Ash Hydrotalcite

Liqiang Qi 1,*, Kunyang Liu 1, Ruitao Wang 1, Jingxin Li 1,*, Yajuan Zhang 1, Lan Chen 1
PMCID: PMC7745446  PMID: 33344818

Abstract

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The effective removal of chlorine ion from the desulfurization slurry is of great significance to the stable operation of the desulfurization system. Modified fly ash hydrotalcites were prepared by alkali/acid-combined roasting and microwaving and used as an adsorbent for chlorine ion in desulfurized wastewater. The specific surface area and porosity of different adsorbents were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The impacts of pH, temperature, adsorbent dosage, and adsorption shaking time on adsorption performance were investigated. Results showed the alkali-combined roasting-modified fly ash hydrotalcite has the optimum removal effect on Cl–. The optimal adsorption performance was achieved when the pH was 8, the adsorption temperature was 60 °C, the mass concentration of adsorbent was 10 g/L, the adsorption shaking time was 180 min, and the removal percentage of Cl– was 68.1%. The adsorption isotherm was consistent with the Langmuir isotherm model, and the adsorption saturation was 694.4 mg/g, which belonged to monolayer adsorption.

1. Introduction

Desulfurization wastewater contains a considerable amount of suspended solids (e.g., gypsum particles, SiO2, aluminum, and iron hydroxide), inorganic salts, and trace heavy metals, such as arsenic, cadmium, chromium, and mercury, thus seriously harming the environment if directly discharged.1 The dissolution of chlorides in the flue gas will increase the chloride ion concentration in the desulfurization absorbent. This increase will decrease the desulfurization rate and affect the gypsum quality, resulting in the corrosion of desulfurization systems. After the triple box process of “neutralization, coagulation, and precipitation”, the content of heavy metals and suspended solids in desulfurization wastewater is reduced but that of chlorine remains high. The 2017 guidelines on feasible technologies for the prevention and control of pollution in thermal power plants (HJ2301-2017) indicated that the key to achieving a near-zero discharge of wastewater is to realize a zero discharge of desulfurization wastewater.2−4 The main methods currently used to remove Cl– from wastewater include electric coagulation, ion exchange, and adsorption.5−7 Adsorption is regarded as one of the effective ways to uptake Cl– from wastewater due to its advantages of simple operation, recyclability, etc.

Fly ash is a byproduct of coal-fired power plants. China is a large producer and user of coal. The coal-fired power generation of China can produce hundreds of millions of tons of fly ash yearly.8−10 Fly ash is characterized by its low cost, easy acquisition, porous physical tissue, large specific surface area, and high adsorption activity.11−13 Therefore, the treatment of harmful substances in wastewater using fly ash has been widely investigated. Studies on the removal of phosphorus from wastewater by fly ash began in 1980 when Kuziemska applied the water extract of brown fly ash as a coagulant to treat phosphorus in wastewater.14 Mohan15 used fly ash as a cheap adsorbent to treat heavy metal ions in urban solid waste leachates. Studies have shown that modified fly ash has a larger specific surface area and a stronger adsorption capacity than those of unmodified fly ash.16 Therefore, using modified fly ash to treat some harmful substances is possible due to its strong adsorption performance. Wang17 used the H2SO4 impregnation method to modify raw coal fly ash (RCFA) and used the modified RCFA (ACFA) as a Fenton-like catalyst to treat polymer flooding wastewater (PW) under microwave prestrengthening conditions. The fly ash was modified by nitric acid at room temperature, and the adsorption performance of the modified fly ash to methylene blue was significantly improved.18 Nguyen19 used 2-mercaptobenzothiazole (MBT) and sodium dodosulfate (SDS) as surfactants and treated fly ash with sodium hydroxide to investigate the morphology, composition, and structural changes of modified and unmodified fly ash as well as the adsorption behavior of Cd2+ and Hg2+. Sahoo20 studied the removal of heavy metals from acidic mine wastewater by alkali-modified fly ash. Research by Li and others found that the acid-modified fly ash method has the best effect, with the chemical oxygen demand (COD) removal rate reaching more than 90% and the wastewater after degradation meeting the discharge standard.21 Malarvizhi22 used 4 mol/L NaOH and fly ash that were mixed and stirred at 90 °C for 1 h, washed with deionized water, and then dried. The adsorption of heavy metals in wastewater indicates that alkali can cause the dissolution and precipitation of fly ash. Specific surface area and activity of fly ash increased due to the dissolution of fly ash acidic oxides, and the adsorption performance of heavy metals in wastewater is enhanced. Fly ash, as a water treatment chemical, is mostly used to remove impurities in water, heavy metals, or decolorization experiments. Two or more modification methods are often combined to modify fly ash and improve its adsorption performance.23 The fly ash modified by microwave combined with alkali had excellent adsorption properties for Hg2+ and Cr6+ in aqueous solutions.24,25 Shi26 used hydrotalcite and modified fly ash to adsorb Cl– of wastewater and found certain removal effects. Alonso-de-Linaje27 investigated the sorption of chlorinated hydrocarbons from synthetic and natural groundwater by organohydrotalcites. However, studies on using fly ash as a Cl– adsorbent are currently limited.

In this paper, modified fly ash hydrotalcites were prepared by alkali/acid-combined roasting and microwaving and used as adsorbents for chlorine ion in desulfurized wastewater. The optimal preparation conditions and adsorption isotherms of adsorbents were studied, and the influence of various preparation conditions on the removal rate was analyzed.

2. Results and Discussion

2.1. Determination of the Optimum Modification Method

2.1.1. Adsorbent Characterization

Figure 1 shows the surface morphology of the original fly ash hydrotalcite and the scanning electron microscopy (SEM) diagram of the fly ash hydrotalcite modified by four modification methods. Figure 1a shows raw ash, and Figure 1b–e is the SEM diagrams of alkali-combined roasting, acid-combined roasting, alkali-combined microwave, and acid-combined microwave modification. Figure 1 shows that the surface of modified fly ash hydrotalcite is rougher than that of the original fly ash. The porous structure is also more obvious, greatly changing its original surface morphology, and the specific surface area and pore volume are greatly improved. In addition, the SEM diagrams corresponding to different modification methods are different. The surface of the particle is smoother, and picture b is the roughest, followed by c, d, and e. The specific surface area from large to small is b > c > d > e > a (see Table 1). Therefore, the adsorption capacity is also different. The alkali-combined roasting modification method has a more evident removal percentage of Cl– compared with that of other modification methods. Thus, the SEM surface of this method is rough and its porous structure is evident. Therefore, the adsorption effect of this method is better.

Figure 1.

Figure 1

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SEM diagram of the raw fly ash hydrotalcite and four modification adsorbents.

Table 1. Specific Surface Area and Pore Volume Analysis.
species specific surface area (m2/g) pore volume (cc/g)
the original gray 5.310 0.007
alkali + roasting modification 24.579 0.075
acid + roasting modification 19.899 0.033
alkali + microwave modification 14.155 0.040
acid + microwave modification 11.767 0.011
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Table 1 shows the specific surface area and pore volume of fly ash and modified fly ash hydrotalcite. The specific surface area of the adsorbent modified by alkali roasting was 24.579 m2/g, which was considerably larger than that of the original fly ash and increased by approximately fivefold. The OH– dissolved from fly ash and Na+ and K+ in alkaline modifier destroyed Si–O and Al–O bonds in the fly ash vitreous body, depolymerized the silicate glass network, promoted the formation of zeolite skeleton from fly ash, and increased many new active points in alkali modification, as shown in Figure 2; thus, the physical and chemical adsorption performances of fly ash are improved.28,29

Figure 2.

Figure 2

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Aircraft layout of alkali-modified fly ash.

The volume and the surface area of fly ash increased during high-temperature roasting and modification. This increase could be attributed to the melting of fusible substances in fly ash, the destruction of the glass network structure, the depolymerization of the original high polymer silicate network, and the loose and porous fly ash particles. Simultaneously, the water on the surface of fly ash particles at the beginning of high-temperature roasting modification was evaporated as temperature increased; this phenomenon exposed additional adsorption activity points on the fly ash surface and promoted the improvement of the adsorption capacity of fly ash.30

2.1.2. Removal Percentage of Cl– by Four Adsorbents

Figure 3 shows that the removal percentages of Cl– using the four modified methods were 56.9, 45.2, 39.7, and 19.2%. These results showed that adsorbent A had the optimum removal effect on Cl– in the desulfurization wastewater. Strong alkali can destroy the Si–O–Si and Si–O–Al network structure in depolymerized fly ash and can act as an activator to increase the activity of fly ash and improve the physical and chemical adsorption properties of fly ash, The high-temperature roasting makes the moisture inside the fly ash evaporate, and more pores are formed on the fly ash surface, which increases the surface active site of the fly ash. Therefore, the alkali-combined roasting-modified fly ash hydrotalcite was used in the subsequent optimization experiments of adsorption conditions.

Figure 3.

Figure 3

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Cl– removal percentages by the four modification adsorbents.

2.2. Optimization of Adsorption Conditions

2.2.1. Influence of pH

The wastewater with an initial mass concentration of 10 g/L Cl– was prepared, and the pH of the wastewater was adjusted to 5, 6, 7, 8, 9, and 10.  A total of 1 g of adsorbent was added to 100 mL of desulfurization wastewater, which was shaken for 2 h at a constant temperature of 40 °C in the water bath and then filtered. Figure 4 shows the removal percentage of Cl– at different pH values.

Figure 4.

Figure 4

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Effect of pH on adsorption rate.

The points of zero charge (pHPZC) of fly ash, hydrotalcite, and the alkali-combined roasting-modified fly ash hydrotalcite are 4.86, 11.21, and 8.52, respectively.31,32 As can be seen from Figure 4, initially, the removal percentage of Cl– increased significantly with pH. The removal percentage reached the maximum at pH 8 and then decreased with the increase in pH. Because fly ash hydrotalcite is alkaline. In an acidic environment, fly ash can react chemically and destroy the porous structure. The pH value of modified fly ash hydrotalcite adsorbent cannot be less than 4 because its interlayer structure is destroyed and its adsorption performance is reduced. In a strongly alkaline environment, the OH– in the solution combines with part of the adsorption point when the pH is considerably high, and competitive adsorption occurs with Cl–, reducing the dechlorination rate.

2.2.2. Influence of Temperature

Figure 5 shows that 1 g of adsorbent was placed in 100 mL of desulfurization wastewater with an initial mass concentration of 10 g/L of Cl–, and the pH of the waste solution was adjusted to 8. The solution was shaken in a water bath at 20, 30, 40, 50, 60, 70, and 80 °C for 2 h and then filtered. The results show that the removal percentage of Cl– increased first and then decreased as the oscillation temperature increased. The removal percentage reached the maximum value at 60 °C. This result shows that the removal percentage of ions increases with the temperature. This finding may be attributed to the physical adsorption at low temperatures and the temperature increase for easy desorption, thereby decreasing the removal percentage. The chemical adsorption, adsorption site activity, and removal percentage will all increase at 30–60 °C. The molecular thermal movement will be violent when the oscillation temperature continues to rise. This phenomenon results in the easy desorption of adsorbed particles, which are not conducive to adsorption and decreases the removal percentage.

Figure 5.

Figure 5

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Effect of temperature on the adsorption rate.

2.2.3. Influence of Input and Dosage

Modified fly ash hydrotalcite at 0, 0.2, 0.4, 0.6, 0.8, 1, 1.2, and 1.4 g was added to 100 mL of wastewater containing the initial mass concentration of 10 g/L Cl– at pH 8. The water bath was maintained at a constant temperature of 60 °C for 2 h and then filtered. Figure 6 shows the effect of different amounts of fly ash on Cl– removal percentages in desulfurization wastewater.

Figure 6.

Figure 6

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Effect of adsorbent dosage on the adsorption rate.

Figure 6 shows that with the increase in modified fly ash additive quantity, the Cl– removal percentage continues to rise with the additional mass concentration of 10 g/L modified fly ash. The removal percentage no longer increased when the adsorbent additive mass concentration continued to increase to 14 g/L. This phenomenon may be observed when the Cl– concentration in the water for the reduction of the concentration gradient is no longer evident and the diffusion flux is close to 0. Thus, modified fly ash adsorbent adsorption reaches an equilibrium of Cl–.

2.2.4. Influence of Shaking Time

A total of 1 g of adsorbent was added to 100 mL of desulfurization wastewater with 10 g/L initial mass concentration of Cl– at pH 8, and the shaking time was set as 60, 120, 180, 240, and 300 min at an oscillation temperature of 60 °C. Figure 7 shows the effect of different shaking times on the Cl– removal percentages in desulfurization wastewater.

Figure 7.

Figure 7

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Effect of shaking time on adsorption rate.

Figure 7 shows that the general trend of the Cl– removal percentage increased after the first reduction as the adsorption time increased and reached the maximum at 180 min. The removal percentage slightly dropped after 180 min. The results show that increasing the stirring time can raise the contact time and improve the adsorption effect. However, the adsorption amount reached saturation due to a long time. At this temperature, increasing the stirring time will not increase the adsorption rate. Thus, the removal percentage is reduced. Prolonged adsorption time is not conducive to the removal of Cl–. Thus, the optimum shaking time is 180 min.

Therefore, the optimum preparation conditions are as follows: modification method using alkali-combined roasting (the ratio of fly ash to hydrotalcite is 2:1), mass concentration of fly ash of 10 g/L, constant-temperature shaking time of water bath of 180 min, initial mass concentration of Cl– of 10 g/L, oscillation temperature of 60 °C, waste liquid pH of 8, and adsorption rate of up to 68.1%.

2.3. Adsorption Isotherm

Adsorption isotherm refers to a curve that reflects the relationship of the amount of solute Qe adsorbed on the unit mass by adsorbents at constant temperatures in a certain volume of solution and the corresponding equilibrium concentration of the solution Ce. Adsorption isotherms can be used to describe the adsorption characteristics of the adsorbents. The Freundlich and Langmuir adsorption isotherms are two widely used adsorption isotherms in environmental chemistry.

(1) Freundlich empirical formula

2.3. 1

where Qe is the adsorption capacity of the adsorbent, mg/g; Ce is the equilibrium concentration, mg/L; 1/n is the nonlinear coefficient (1/n is a constant describing the adsorption strength); 0.1 < 1/n < 0.5 is easily adsorbed, 1/n > 2 is difficult to adsorb; and k is the Freundlich constant.

The above equation is usually expressed as a logarithmic equation of a line.

2.3. 2

(2) Langmuir empirical formula

2.3. 3

where Qe is the adsorption capacity of the adsorbent, mg/g; Ce is the equilibrium concentration, mg/L; Xm is the saturated adsorption of adsorbent, mg/g; and b is the constant related to adsorption energy.Figure 8 shows the adsorption isotherms of modified fly ash and hydrotalcite at 25 °C. Figures 9 and 10 show the Freundlich and Langmuir adsorption isotherms, respectively. The Langmuir model represents monolayer adsorption at specific homogeneous sites, while the Freundlich equation applies to multilayer adsorption. Both models reflect a certain temperature in a certain solution volume and the amount of solute Qe by adsorbent adsorption on the unit mass solution corresponding to the equilibrium concentration of Ce. The adsorption characteristics of modified fly ash hydrotalcite at 25 °C were analyzed. According to the slope and intercept, the Freundlich constant 1/n at 25 °C is 0.67325.1/n and exceeds the range of 0.1–0.5. This result indicates that the modified fly ash hydrotalcite at 25 °C does not easily adsorb high concentrations of Cl–, which is consistent with the single-factor variables discussed above. Figures 9 and 10 show that the correlation coefficient R2 was 0.9826 and 0.9931, respectively. The adsorption isotherm was consistent with the Langmuir isotherm model. The Langmuir model represents the monolayer adsorption at specific homogeneous sites, while the Freundlich equation applies to multilayer adsorption. Moreover, the adsorption characteristics of modified fly ash hydrotalcite are more consistent with the Langmuir isotherm model, indicating that the adsorption of Cl– by modified fly ash belongs to monolayer adsorption. The adsorption saturation is 694.4 mg/g. Table 2 shows the Brunauer–Emmett–Teller (BET) surface areas and the adsorption capacity of different adsorbents.33,34

Figure 8.

Figure 8

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Adsorption isotherm of Cl– by the modified adsorbent.

Figure 9.

Figure 9

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Freundlich isotherm model.

Figure 10.

Figure 10

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Langmuir isotherm model.

Table 2. BET Surface Areas and Adsorption Capacity of Different Adsorbents.

adsorbents specific surface area (m2/g) adsorption capacity (mg/g)
alkali + roasting-modified fly ash hydrotalcite 24.58 694.4
OBC1000-3-10 62.26 4.34
OBC1000-3-15 86.52 6.76
KOBC15 303.59 11.13
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3. Conclusions

The increase in chloride ion concentration in the desulfurization absorbent will decrease the desulfurization efficiency and affect the gypsum quality. The effective removal of chlorine ion from the desulfurization slurry is of great significance for the stable operation of the desulfurization system. Modified fly ash hydrotalcites were prepared by alkali/acid-combined roasting and microwaving and used as adsorbents of chlorine ion in the desulfurized wastewater. The optimum preparation conditions for modifying fly ash hydrotalcite adsorbent are as follows: joint alkali-roasting modification method (fly ash and hydrotalcite ratio is 2:1), adsorbent concentration of 10 g/L, water bath temperature shaking time of 180 min, Cl– initial mass concentration of 10 g/L, oscillation temperature of 60 °C, liquid optimum pH of 8, and adsorption rate reaching 68.1%.

Fly ash hydrotalcite adsorbent modified using joint alkali roasting demonstrated the following: a large surface area and pore volume, a strong adsorption capability, consistent Cl– adsorption isotherm with the Freundlich and Langmuir adsorption isotherms, and correlation coefficient R2 of 0.9826 and 0.9931.

4. Materials and Methods

4.1. Preparation of Modified Fly Ash Hydrotalcite

The fly ash used in the experiment was obtained from the Baoding power plant. The chemical composition of the samples was determined using the test method for the analysis of the coal ash according to the Chinese standard GB/T 1574-2007, as shown in Table 3.

Table 3. Chemical Composition of Fly Ash.

chemical composition content (%)
SiO2 54.1
Fe2O3 17.5
Al2O3 11.6
CaO 11.3
TiO2 2.69
K2O 1.18
MgO 0.192
BaO 0.162
MnO 0.126
others 1.15
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Table 3 shows that the contents of SiO2, Fe2O3, and Al2O3 in fly ash account for 80%. Fly ash contains a large number of irregular and closed pores rich in active vitreous particles, such as SiO2– and Al2O3. These vitreous particles contain many small active channels, thus providing a large specific surface area and good activity and increasing their adsorption capacity. The typical molecular composition of talc in the experiment is Mg6Al2(OH)16CO3·4H2O, also known as layered bimetallic hydroxide, which is a kind of anion clay with a layered structure similar to the regular octahedral structure of brucite Mg(OH)2.3535

Fly ash and hydrotalcite are taken as raw materials in the present study. After mixing fly ash and hydrotalcite in the 2:1 ratio, four modification methods are adopted to produce four required adsorbents to determine the optimal scheme, as shown in Table 4.

Table 4. Preparation Schemes of Four Adsorbents.

adsorbent modification methods specific steps
A alkali-combined roasting modification Fly ash hydrotalcite was placed into 10 wt % sodium hydroxide solution to shake for 1 h and then filtered and roasted in a muffle furnace at 450 °C for 2 h to obtain adsorbent A.
B alkali combined with microwave modification Fly ash hydrotalcite was placed into 10 wt % sodium hydroxide solution to shake for 1 h and then filtered. Microwave irradiation was conducted at 600 W, 60 °C for 10 min and then maintained at room temperature for 2 h. Adsorbent B was obtained after cooling to room temperature.
C acid-combined roasting modification Fly ash hydrotalcite was placed into 10 wt % sulfuric acid solution to shake for 1 h and then filtered and roasted in a muffle furnace at 450 °C for 2 h to obtain adsorbent C.
D acid combined with microwave modification Fly ash hydrotalcite was placed into 10 wt % sulfuric acid solution to shake for 1 h and then filtered. Microwave irradiation was conducted at 600 W, 60 °C for 10 min and then maintained for 2 h at room temperature. Adsorbent D was obtained after cooling to room temperature.
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4.2. Feature Analysis

The wastewater used in the experiment was simulated wastewater, which was dissolved in 1 L of deionized water with 10 g of NaCl, and the mass concentration of Cl– was 10 g/L. The main instruments used in this experiment are listed in Table 5. The specific surface area and pore volume of the adsorbent were tested by the porous physical adsorption instrument of the American Canta EVO. The SEM images were obtained by field emission scanning electron microscopy and manufactured by JEOL Electronics in Japan.

Table 5. Main Experimental Instruments.

the instrument model manufacturer
microwave synthesis reaction apparatus XH-MC-1 Beijing Xianghu Technology Development Co., Ltd.
muffle furnace SA2-9-17TP Nanyang Xinyu Furnace Industry Co., Ltd.
vacuum drying oven ZDF6050 Shanghai Qixin Scientific Instrument Co., Ltd.
speed-regulating multipurpose oscillator HY-4 Changzhou Runhua Electric Appliance Co., Ltd.
ion meter PXS-270 Shanghai Electronic Science Instrument Co., Ltd.
electronic balance FA2004B Shanghai Youke Instrument Co., Ltd.
thermostatic magnetic stirrer HJ-6AB Changzhou Runhua Electric Appliance Co., Ltd.
BET (porous physical adsorption instrument) QUANTACHROME Conta EVO
SEM (field emission scanning electron microscope) JSM-7800F Prime Japanese Electronic JEOL
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4.3. Adsorption Experiment

A total of 100 mL of simulated waste liquid was added to 250 mL of the tapered flask. A total of 1 g of prepared adsorbent was also added, and the tapered flask was placed onto a speed-regulating multipurpose oscillator to vibrate for 60 min and then stopped. The simulated waste liquid was allowed to stand for a period and then filtered. The clear liquid was taken to determine the content of Cl–. The concentration of Cl– was identified through the ion-selective electrode method.

NaCl standard solution of 10–1, 1, 5, and 10 g/L was configured to draw the Cl– standard curve. The abscissa of the standard curve is the potential value, and the ordinate is the logarithm of Cl– concentrations. The determination coefficient R2 is ≥0.999 based on the illustrated standard curve. The parameters of the standard curve are shown in Figure 1. The line equation in the standard curve illustration is obtained as follows: y = kx + b, where y is the potential value and x is the logarithm of Cl– concentrations, as shown in Figure 11.

Figure 11.

Figure 11

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Chloride ion standard curve.

The linear regression equation is y = −53.835x + 89.157. The correlation coefficient R2 = 0.9999.

The concentration of simulated waste solution C0 was determined in the adsorption experiment, and the residual amount of Cl– in the solution Ce was measured after the adsorption of modified fly ash. The adsorption amount of modified fly ash to Cl– can be calculated by the following formula

4.3. 4

where Qe is the equilibrium adsorption capacity, mg/g; C0 is the initial concentration, mg/L; Ce is the equilibrium concentration, mg/L; m is the adsorbent mass, g; and V is the solution volume, L.

Acknowledgments

This work was supported by the Natural Science Foundation of Hebei Province (Grant No. B2019502067) and the Fundamental Research Funds for the Central Universities (Grant No. 2020MS152).

The authors declare no competing financial interest.

References

  1. Deng X.; Qi L. Q.; Zhang Y. J. Experimental Study on Adsorption of Hexavalent Chromium with Microwave-Assisted Alkali Modified Fly Ash. Water, Air, Soil Pollut. 2018, 229, 17–22. 10.1007/s11270-017-3679-8. [DOI] [Google Scholar]
  2. Gitari W. M.; Petrik L. F.; Etchebers O.; Key D. L.; Okujeni C. Utilization of fly ash for treatment of coal mines wastewater: Solubility controls on major inorganic contaminants. Fuel 2008, 87, 2450–2462. 10.1016/j.fuel.2008.03.018. [DOI] [Google Scholar]
  3. Jiang D. N.; Sha H. W.; Gong G. H.; Song J.; Xu H. T.; Zhou C. C.; Shen K. Fundamental Research and Demonstration Project of Evaporation Treatment of Wastewater from FGD in Flue Gas Duct. Adv. Mater. Res. 2014, 864–867, 434–437. 10.4028/www.scientific.net/AMR.864-867.434. [DOI] [Google Scholar]
  4. Ma S.; Chai J.; Chen G. D.; Yu W. J.; Zhu S. J. Research on desulfurization wast-ewater evaporation: Present and future perspectives. Renewable Sustainable Energy Rev. 2016, 58, 1143–1151. 10.1016/j.rser.2015.12.252. [DOI] [Google Scholar]
  5. Qi L. Q.; Li J. T.; Yao Y.; Zhang Y. J. Heavy Metal Poisoned and Regeneration of Selective Catalytic Reduction Catalysts. J. Hazard. Mater. 2019, 366, 492–500. 10.1016/j.jhazmat.2018.11.112. [DOI] [PubMed] [Google Scholar]
  6. Nduta K. G.; Mwangi I. W.; Wanjau R. W.; Ngila J. C. Removal of Chlorine and Chlorinated Organic Compounds from Aqueous Media Using Substrate-Anchored Zero-Valent Bimetals. Water, Air, Soil Pollut. 2016, 227, 10. 10.1007/s11270-015-2685-y. [DOI] [Google Scholar]
  7. Peretyazhko T. S.; Ralston S. J.; Sutter B.; Ming D. W. Evidence for Adsorption of Chlorine Species on Iron (III) (Hydr)oxides in the Sheepbed Mudstone, Gale Crater, Mars. J. Geophys. Res. 2020, 125, e2019JE006220 10.1029/2019JE006220. [DOI] [Google Scholar]
  8. Wang X. X.; Shen X. D. Experimental study on strength of lightweight aggregate concrete with different amounts of fly ash. Silicate Bull. 2011, 30, 69. [Google Scholar]
  9. Zhang P.; Li M. Y.; Lv C. J.; Zhang Y. J.; Wang L. M.; Fu D. Effect of partial pressure on CO2 absorption performance in piperazine promoted 2-diethylaminoethanol and 1-dimethylamino-2-propanol aqueous solutions. J. Chem. Thermodyn. 2020, 150, 106198 10.1016/j.jct.2020.106198. [DOI] [Google Scholar]
  10. Qi L. Q.; Yao Y.; Han T. Y.; Li J. T. Research on the electrostatic characteristic of coal-fired fly ash. Environ. Sci. Pollut. Res. 2019, 26, 7123–7131. 10.1007/s11356-019-04166-6. [DOI] [PubMed] [Google Scholar]
  11. Shi D. Z.; Ma J. Y.; Wang H. L.; Wang P.; Hu C. Y.; Zhang J. L.; Gu L. Detoxification of PCBs in fly ash from MSW incineration by hydrothermal treatment with composite silicon-aluminum additives and seed induction. Fuel Process. Technol. 2019, 195, 106157 10.1016/j.fuproc.2019.106157. [DOI] [Google Scholar]
  12. Ma L. J.; Han L. N.; Chen S.; Hu J. L.; Chang L. P.; Bao W. R.; Wang J. C. Rapid synthesis of magnetic zeolite materials from fly ash and iron-containing wastes using supercritical water for elemental mercury removal from flue gas. Fuel Process. Technol. 2019, 189, 39–48. 10.1016/j.fuproc.2019.02.021. [DOI] [Google Scholar]
  13. Wang T. F.; Fan H. M.; Yang W. P.; Meng Z. Stabilization mechanism of fly ash three-phase foam and its sealing capacity on fractured reservoirs. Fuel 2020, 264, 116832 10.1016/j.fuel.2019.116832. [DOI] [Google Scholar]
  14. Wang S. B.; Ma Q.; Zhu Z. H. Characteristics of coal fly ash and adsorption application. Fuel 2008, 87, 3469–3473. 10.1016/j.fuel.2008.05.022. [DOI] [Google Scholar]
  15. Mohan S.; Gandhimathi R. Removal of heavy metal ions from municipal solid waste leachate using coal fly ash as an adsorbent. J. Hazard. Mater. 2009, 169, 351–359. 10.1016/j.jhazmat.2009.03.104. [DOI] [PubMed] [Google Scholar]
  16. Chatterjee A.; Hu X. J.; Lam F. L. Y. Modified coal fly ash waste as an efficient heterogeneous catalyst for dehydration of xylose to furfural in biphasic medium. Fuel 2019, 239, 726–736. 10.1016/j.fuel.2018.10.138. [DOI] [Google Scholar]
  17. Wang N.; Sun X. Y.; Zhao Q.; Wang P. Treatment of polymer-flooding wastewater by a modified coal fly ash-catalysed Fenton-like process with microwave pre-enhancement: System parameters, kinetics, and proposed mechanism. Chem. Eng. J. 2021, 406, 126734 10.1016/j.cej.2020.126734. [DOI] [Google Scholar]
  18. Wang S. B.; Boyjoo Y.; Choueib A.; Zhu Z. H. Removal of dyes from aqueous solution using fly ash and red mud. Water Res. 2005, 39, 129–138. 10.1016/j.watres.2004.09.011. [DOI] [PubMed] [Google Scholar]
  19. Nguyen T. C.; Tran T. D. M.; Dao V. B.; Vu Q. T.; Nguyen T. D.; Thai H. Using Modified Fly Ash for Removal of Heavy Metal Ions from Aqueous Solution. J. Chem. 2020, 2020, 8428473 10.1155/2020/8428473. [DOI] [Google Scholar]
  20. Sahoo P. K.; Tripathy S.; Panigrahi M. K.; Equeenuddin Sk. Md. Evaluation of the use of an alkali modified fly ash as a potential adsorbent for the removal of metals from acid mine drainage. Appl. Water Sci. 2013, 3, 567–576. 10.1007/s13201-013-0113-2. [DOI] [Google Scholar]
  21. Li P. L.; Hu Z.; Wang C. X.; Wang C. L.; Hu F. M. Study on the preparation of acid-modified fly ash and its degradation of beneficiation wastewater COD. Multipurp. Util. Miner. Resour. 2019, 02, 103–108. [Google Scholar]
  22. Malarvizhi T. S.; Santhi T. Lignite fired fly ash modified by chemical treatment for adsorption of zinc from aqueous solution. Res. Chem. Intermed. 2013, 39, 2473–2494. 10.1007/s11164-012-0774-8. [DOI] [Google Scholar]
  23. Zhang F.; Ou Y. P.; Zhang X. M.; Chen L. Research progress on modification and adsorption application of fly ash. Appl. Chem. Ind. 2016, 45, 747–750. 10.1109/TIA.2009.2013575. [DOI] [Google Scholar]
  24. Qi L. Q.; Teng F.; Deng X.; Zhang Y. J.; Zhong X. Y. Experimental study on adsorption of Hg(II) with microwave-assisted alkali-modified fly as. Powder Technol. 2019, 351, 153–158. 10.1016/j.powtec.2019.04.029. [DOI] [Google Scholar]
  25. An C. J.; Yang S. Q.; Huang G. H.; Zhao S.; Zhang P.; Yao Y. Removal of sulfonated humic acid from aqueous phase by modified coal fly ash waste: Equilibrium and kinetic adsorption studies. Fuel 2016, 165, 264–271. 10.1016/j.fuel.2015.10.069. [DOI] [Google Scholar]
  26. Shi Y. F.; Wang X. H.; Zhang L. J.; Li Z. H. Study on the removal performance of hydrotalcite and fly ash on Cl– and SO42– in desulfurization wastewater. Bull. Chin. Ceram. Soc. 2015, 34, 1402–1406. [Google Scholar]
  27. Alonso-de-Linaje V.; Mangayayam M. C.; Tobler D. J.; Dietmann K. M.; Rspinosa R.; Rivers V.; Dalby K. N. Sorption of chlorinated hydrocarbons from synthetic and natural groundwater by organo-hydrotalcites: Towards their applications as remediation nanoparticles. Chemosphere 2019, 236, 124369 10.1016/j.chemosphere.2019.124369. [DOI] [PubMed] [Google Scholar]
  28. Li D. X.; Chen Y. M.; Shen J. L.; Wang Y. J.; Su J. H. Effects of alkali on activation and microstructure of fly ash. J. Mater. Sci. Eng. 2000, 01, 52. [Google Scholar]
  29. Fang J. L.; Lu W. X.; Xu C. X. Progress in activiting techniques and mechanism studies of fly ash. J. Shanghai Univ. (Nat. Sci. Ed.) 2002, 8, 255–260. [Google Scholar]
  30. Ou Y. P.; Fan H. Y.; Zhang X. M.; Chen L. Research progress on the mechanism of fly ash modification based on adsorption. J. Mater. Sci. Eng. 2014, 32, 619–624. [Google Scholar]
  31. Karanac M.; Dolic M.; Veljovic D.; Rajakovic-Ognjanovic V.; Velickovic Z.; Pavicevic V.; Marinkovic A. The removal of Zn2+, Pb2+, and As(V) ions by lime activated fly ash and valorization of the exhausted adsorbent. Waste Manage. 2018, 78, 366–378. 10.1016/j.wasman.2018.05.052. [DOI] [PubMed] [Google Scholar]
  32. Shah B. A.; Oluyinka O. A.; Shah A. V. Fly Ash Reuse as Mesoporous Ca- and Mg-Zeolitic Composites for the Seclusion of Aniline from Aqueous Solution. Arab. J. Sci. Eng. 2019, 44, 289–304. 10.1007/s13369-018-3596-1. [DOI] [Google Scholar]
  33. Guan C. H.; Lv X. J.; Han Z. X.; Chen C.; Xu Z. M.; Liu Q. S. The adsorption enhancement of graphene for fluorine and chlorine from water. Appl. Surf. Sci. 2020, 516, 146157 10.1016/j.apsusc.2020.146157. [DOI] [Google Scholar]
  34. Du Z. Y.; Tian W. J.; Qiao K. L.; Zhao J.; Wang L.; Xie W. L.; Chu M. L.; Song T. T. Improved chlorine and chromium ion removal from leather processing wastewater by biocharcoal-based capacitive deionization. Sep. Purif. Technol. 2020, 233, 116024 10.1016/j.seppur.2019.116024. [DOI] [Google Scholar]
  35. Cavani F.; Trifirò F.; Vaccari A. Hydrotalcite-type anionic clays: Preparation, properties and applications. Catal. Today 1991, 11, 173–301. 10.1016/0920-5861(91)80068-K. [DOI] [Google Scholar]

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