A novel anion exchange resin, quaternary ammonium–Chlorella vulgaris (QACV), was prepared by introducing quaternary ammonium groups onto dried Chlorella vulgaris as base material. Degrees of epoxy, amine and quaternary ammonium groups of QACV were measured. Water retention, optical microscopy, and Fourier transform infrared spectrometry were used to characterize QAVC. The adsorption behavior of QACV towards Ag(CN)2 in different conditions was studied carefully. The results showed that QAVC was efficient to adsorb Ag(CN)2 at pH 9–11, and adsorption equilibrium was almost reached in 30 min. Both kinetics and isotherm parameters in the adsorption process were obtained. The data indicated that the pseudo-second-order model provided a good correlation for adsorption of Ag(CN)2 on QACV and the calculated rate constant of the adsorption was 3.51 g/(mmol min). The equilibrium data fitted well in the Langmuir isotherm and the estimated maximum adsorption capacity qm was 1.96 mmol/g. The dimensionless separation factor RL was between 0 and 1, suggesting that the adsorption process of Ag(CN)2 using QACV was favorable. The QACV could be used successively three times without significantly affecting its adsorption efficiency. Chlorella vulgaris was a potential base material to be modified with quaternary ammonium groups to prepare an adsorbent for adsorption of Ag(CN)2.

INTRODUCTION

In the metallurgical process, cyanidation is the dominant method (Habashi 1967; Parga et al. 2014). As an extremely toxic substance, discharge of large quantities of cyanide-containing wastewater can cause severe pollution (Boening & Chew 1999). Additionally, cyanide can be generated from electroplating, metal finishing, chemical and mechanical polishing (Allison & Benson 1955; Blair 1999; Petzow 1999; Abbott et al. 2007). The wastewater also contains significant amounts of heavy metals, namely copper, nickel, zinc, silver, and iron (Dash et al. 2009). Owing to the highly reactive nature of cyanide ions, metal complexes of variable stability and toxicity are readily formed (Sharpe 1976). Since the formation of metal-cyanide complexes does not eliminate the toxicity of cyanide, these must be removed from wastewater prior to their discharge in the environment.

Many methods have been performed for the removal of metal-cyanide complexes, such as precipitation, solvent extraction, adsorption with activated carbon, and ion exchange with resins (Dai et al. 2010; Sherwood et al. 2013; Ok & Jeon 2014; Zhang et al. 2014). Among these technologies, activated carbon is often used to treat cyanide wastewater in the metallurgical industry, but its obvious disadvantage is that the adsorption process is time-consuming (McDougall et al. 1980; Dai et al. 2010). Ion exchange has unique advantages of application with relatively dilute metal solution, shorter equilibrium time, and environmental acceptability (Jha et al. 2008). Most commercial resins used in adsorption of metal cyanide are anion exchange resins (Dai et al. 2010; Ok & Jeon 2014). They contain a lot of quaternary ammonium groups that play a major role in adsorbing metal cyanide, but these quaternary ammonium groups need to be introduced onto some base material, such as ethylstyrene copolymer, divinlbenzene copolymer, and vinylethylbenze copolymer (Zhang & Dreisinger 2002; Dai et al. 2010; Ok & Jeon 2014). These base materials are costly and their synthetic process is difficult to control.

Chlorella vulgaris (C. vulgaris) is a low-cost material on account of its wide distribution in aquatic environments, easy collection, and mass cultivation. It has been used as a biosorbent to adsorb cyanide (Gurbuz et al. 2004; Çalik 2007; Gök & Küçükçongar 2013). However, there were some disadvantages such as long equilibrium time and requiring some nutrients to be added during the process of biosorption. Therefore, in the present study, the authors have tried to use C. vulgaris as base material modified with quaternary ammonium groups to prepare a novel adsorbent. Chlorella vulgaris contains a large amount of reactive hydroxyl groups on cell walls (Thompson & Preston 1967; Domozych et al. 2012), which provides the possibility of introducing quaternary ammonium groups.

The objective of this research was to study C. vulgaris's potential as base material modified with quaternary ammonium groups to prepare an adsorbent for adsorption of silver-cyanide complex Ag(CN)2. Quaternary ammonium–C. vulgaris (QACV) was prepared through three substitution reactions. The dried C. vulgaris was modified by epichlorohydrin (EPC), triethylenetetraamine (TETA), and 2,3-epoxypropane trimethyl ammonium chloride (GTA) successively. The substitution degree of each reaction and water retention of QACV were analyzed. In addition, optical microscopy and Fourier transform infrared (FTIR) spectroscopy were used to characterize QACV. The adsorption properties of the resin for Ag(CN)2 were investigated at different conditions, including pH, contact time, and initial concentration of Ag(CN)2. Adsorption kinetics of pseudo-first-order and pseudo-second-order kinetics and isotherm models of Langmuir and Freundlich were used to evaluate the adsorption process. The effect of regeneration of QACV using NaCl solution on its adsorption capacity was also studied.

METHODS

Preparation of QACV

Chlorella vulgaris (the strain was bought from Type Culture Collection, Chinese Academy of Freshwater Algae Species Library Commission, and numbered FACHB-1072) used in this study was produced by fermentation in a 10 L bioreactor (Bioq-6010, China) with a working volume of 6 L. At the end of fermentation, C. vulgaris was centrifuged at 2,000 rpm for 10 min and then dried at 60 °C to produce dried C. vulgaris powder.

The anion exchange resin quaternary ammonium–C. vulgaris was prepared as shown in Figure 1 (Zhang et al. 2014). First, 5 g of dried C. vulgaris powder was incubated with 10 mL EPC, 10 mL 1 mol/L NaOH solution, and 10 mL dimethyl sulfoxide (DMSO) at 40 °C for 3 h to synthesize epoxy C. vulgaris (CV1). Second, the CV1 was reacted with a mixture of 10 mL TETA, 10 mL 1 mol/L Na2CO3 solution, and 45 mL deionized water at 60 °C for 16 h to synthesize aminated C. vulgaris (CV2). Finally, QACV was synthesized by suspending the CV2 in a mixture of 25 g GTA, 25 mL DMSO, and 25 mL deionized water at 60 °C for 6 h. Each reaction was conducted with magnetic stirring and each production was vacuum-filtrated with a sintered glass funnel (pore 1.5–2.5 μm) and rinsed three times with deionized water. In addition, the final product was further washed with 1 mol/L NaCl solution and then washed with deionized water and dried at 60 °C for 12 h.

Figure 1

Synthesis route of QACV.

Figure 1

Synthesis route of QACV.

Characterization of QACV

The substitution degree of each reaction was determined successively. The epoxy substitution degree of CV1 was obtained as follows (China 2008): 0.200 g dried CV1 was treated with a 25 mL mixture of hydrochloric acid and acetone for 0.5 h. The mixed solution was titrated with 0.15 mol/L NaOH solution after separating. The epoxy value was calculated according to Equation (1): 
formula
1
The degree of amine of CV2 was determined by measuring the quantity of introduced basic functional groups according to the method of retro-titration. For this, 0.100 g of CV2 was treated with 100 mL of 0.01 mol/L HCl solution for 1 h with magnetic stirring. Then the solution was titrated with 0.01 mol/L NaOH solution after separation. The concentration of amine groups was calculated by Equation (2): 
formula
2
In Equations (1) and (2), CNaOH is the concentration of NaOH solution (mol/L), VNaOH and are the volumes of NaOH solution spent in the titration of non-reacted acid's excess (mL) of blank sample and test sample, respectively, m1 and m2 are the weight of CV1 and CV2 (g).
The degree of quaternization of QACV was determined by measuring the quantity of chloride ions by the method of AgNO3 titration. For this, 0.100 g dried QACV was packed into a 300 mm × 19 mm column and washed by 100 mL of 0.5 mol/L sodium sulfate solution at a speed of 2–3 mL/min. The effluent was collected and titrated with 0.01 mol/L AgNO3 solution. This procedure was conducted in triplicate. The concentration of ammonium groups, C-NR4+, was calculated according to Equation (3): 
formula
3
where is the concentration of AgNO3 solution (mmol/L), and are the consumed volumes of AgNO3 solution of blank sample (mL) and test sample, respectively, m3 is the weight of QACV (g).
The water retention of QACV was measured. One thousand grams of dried QACV was immersed in 40 mL of distilled water for 24 h, and then centrifuged at 2,000 rpm for 10 min to determine the water retention capacity, which was calculated by Equation (4): 
formula
4
where V is the volume of wet QACV (mL), m4 is the weight of QACV. Morphology of QACV was measured on an optical microscope (Nikon ECLIPSE E600).

For FTIR analysis, samples were prepared by mixing 1 mg of material with 100 mg of spectroscopy grade KBr. The FTIR spectra were recorded using Nicolet 6700 equipment with detector at 4 cm−1 resolution from 400 cm−1 to 4,000 cm−1 and 32 scans per sample.

Adsorption experiments

All adsorption experiments were performed with 0.02 g QACV with 20 mL solution in 100 mL Erlenmeyer flasks stoppered with rubber stoppers and placed in a rotary shaking incubator at 180 rpm at the desired concentration of , pH, ambient temperature, and reaction time. The pH was controlled by different concentrations of NaOH and HNO3 solution. The samples were separated by vacuum filtration with a sintered glass funnel (pore 1.5–2.5 μm) and the concentration of remaining Ag(CN)2 in the filtrate was detected by atomic absorption spectrophotometry (AA32DCRT/GA3201, China). Each adsorption experiment was conducted in triplicate and the average value presented. The adsorption capacity of QACV for is calculated by Equation (5): 
formula
5
where qe is the adsorption capacity for of QACV (mmol/g), C0 is the initial concentration of in the solution (mmol/L), Ce is the concentration of in the solution at equilibrium (mmol/L), V is the volume of solution (L), and m is the weight of QACV (g).

To investigate the effect of pH of solution on qe of , pH was controlled in the range of 9–14. To investigate the effect of reaction time on the qe of , the reaction time was incrementally increased from 10 s to 240 min. In addition, the qe of QACV for different initial concentrations was investigated.

Regeneration of QACV

Regeneration of from QACV was examined in a 0.1 mol/L NaCl solution. One gram of QACV was first equilibrated with 1,000 mL solution with an initial concentration of 2.56 mmol/L at pH 11. The QACV with adsorbed was added into 100 mL of desorption solution. The mixtures were placed in a rotary shaking incubator at 180 rpm at ambient temperature for 1 h. After the regeneration, the QACV was separated and washed with deionized water, and reused in the next cycle of adsorption and desorption experiments. The adsorption–desorption experiments were conducted for four cycles.

RESULTS AND DISCUSSION

Characterization of QACV

Figure 1 illustrates the synthesis route to prepare QACV. In general, the epoxy group is liable to react with the amine group rather than the hydroxyl group because of the stronger nucleophilicity of the amine group. This explains why hydroxyl groups were not chosen as the main reaction sites for epoxy groups of GTA, although hydroxyl was abundant on C. vulgaris. In addition, the design of tentacle-type ligands could offer a large amount of reaction sites (amine group) for GTA, improving the density of function groups (Zhang et al. 2014). The substitution degree of epoxy, amine, and quaternary ammonium groups of each reaction are presented in Table 1. The C. vulgaris was activated with EPC by reaction between the hydroxyl group of C. vulgaris and chlorine of EPC, and the epoxy value of CV1 was 0.91 mmol/g. The epoxy groups in CV1 were used to anchor TETA with C. vulgaris to produce aminated derivatives, and the concentration of amine was 2.36 mmol/g. QACV was eventually obtained by functionalizing CV2 with quaternary ammonium groups, and the degree of quaternization was 2.37 mmol/g. These results indicated the success of the synthesis methodology applied in this work.

Table 1

The substitution degree of each reaction

Material Cepoxy (mmol/g) CNH,NH2 (mmol/g) C-NR4+ (mmol/g) 
CV1 0.91 – – 
CV2 – 2.36 – 
QACV – – 2.37 
Material Cepoxy (mmol/g) CNH,NH2 (mmol/g) C-NR4+ (mmol/g) 
CV1 0.91 – – 
CV2 – 2.36 – 
QACV – – 2.37 

The water retention capacity of QACV was 6.8 mL/g, higher than some full-synthesized ion exchange resins, such as AV-17-10P with 4.6 mL/g (Kononova et al. 2007) and strong base acrylic anion exchanger with 5.7 mL/g (Wójcik et al. 2011); this strong hydrophilic characteristic made the resin more suitable to be used in aqueous solution.

Figure 2 shows the morphology of C. vulgaris and QACV. Clearly, the QACV retained excellent spherical cell morphology relative to C. vulgaris and the diameter was about 3–8 μm. The perfect spherical shape would benefit the adsorbent with suitable fluid dynamics for adsorption.

Figure 2

Optical microscope images of (a) C. vulgaris and (b) QACV.

Figure 2

Optical microscope images of (a) C. vulgaris and (b) QACV.

FTIR spectroscopy characterized the chemical structure of untreated C. vulgaris, QACV, and QACV with absorbed , and the spectra are presented in Figure 3. As seen, the band located at 3,424 cm−1 in C. vulgaris was attributed to –OH stretching vibration. The stretching vibration of C-H in both –N+(CH3)3 and -CH2-NH-CH2- of QACV made the band located at 2,925 cm−1 and 2,853 cm−1 broad. Another difference in the FTIR spectra of QACV in relation to C. vulgaris was observed at the band located at 1,478 cm−1 that corresponds to the C-N vibration of –N+(CH3)3Cl. In the spectrum of QACV with absorbed , the sharp bands appear at 2,134 cm−1, which was the characteristic peak of –CN in (Jones & Penneman 1954). The appearance of these bands indicated the success of preparation of QACV and its adsorption of . As shown in Figure 1, the functional group of QACV was quaternary amine, and chloride ions were adsorbed into the ammonium groups through electrostatic interactions. In the process of adsorption, the ions were adsorbed on the resin while chloride ions were released to the solution, which follows (Zhang et al. 2014): 
formula
Figure 3

FTIR spectra of untreated C. vulgaris, QACV, and QACV with absorbed Ag(CN)2.

Figure 3

FTIR spectra of untreated C. vulgaris, QACV, and QACV with absorbed Ag(CN)2.

Effect of pH on adsorption

To avoid the formation of volatile HCN, which is highly toxic, the adsorption experiment was conducted under basic conditions. The effect of pH on the adsorption of onto QACV is shown in Figure 4. The initial concentration of was 2.56 mmol/L, adsorption time was 30 min, and temperature was 28 °C. The adsorption of on the QACV was insensitive to pH in the range of 9–11. The adsorption capacity of QACV for decreased under the condition of pH ≥ 12. The quaternary ammonium group is a strong electrolyte that can completely ionize in the solution, so ion exchange sites did not vary in the solution with pH 9–14. Thus, the result might be explained by competition existing between OH and . In this work, the concentration of OH (≥10 mmol/L at pH ≥ 12) was higher than the initial concentration of (2.56 mmol/L) in the solution; therefore in the later experiments, the solution pH in the adsorption test was adjusted to about 11.

Figure 4

Effect of pH on the adsorption of Ag(CN)2 onto QACV (experimental conditions: Ag(CN)2 concentration 2.56 mmol/L, contact time 30 min, temperature 28 °C). Average of triplicate samples with error bars showing one standard deviation.

Figure 4

Effect of pH on the adsorption of Ag(CN)2 onto QACV (experimental conditions: Ag(CN)2 concentration 2.56 mmol/L, contact time 30 min, temperature 28 °C). Average of triplicate samples with error bars showing one standard deviation.

Effect of contact time on adsorption

Figure 5 depicts the effect of contact time on the adsorption of onto QACV. The initial concentration of was 2.56 mmol/L, pH was 11, and temperature was 28 °C. As shown, qe sharply increased during the first 10 min (93% of total amount adsorbed for ), and the equilibrium was almost reached after 30 min (99% of total amount adsorbed for ). After this equilibrium period, the amount of adsorbed did not significantly change with time. Based on this result, adsorption time was determined to be 30 min for the remaining adsorption experiments. It is a faster adsorption process in relation to the gold-cyanide adsorption onto Dowex 21 K XLT resin (1 h: the initial concentration of gold was 0.39 mmol/L, the resin concentration was 10 g/L) (Ok & Jeon 2014) and Kuraray QA6/12HAH (>24 h: the initial concentration of gold was 9 mmol/L, the resin concentration was 10 g/L) (Dai et al. 2010), and copper cyanide adsorption onto Purolite A500/2788 resin (4 h: the concentration of copper was 9 mmol/L, the resin concentration was 10 g/L) (Dai et al. 2010). The rapid adsorption is promising regarding economic feasibility because equilibrium time plays a major role in the adsorption process.

Figure 5

Effect of contact time for the adsorption of Ag(CN)2 onto QACV (experimental conditions: Ag(CN)2 concentration 2.56 mmol/L, pH = 11, temperature 28 °C). Average of triplicate samples with error bars showing one standard deviation.

Figure 5

Effect of contact time for the adsorption of Ag(CN)2 onto QACV (experimental conditions: Ag(CN)2 concentration 2.56 mmol/L, pH = 11, temperature 28 °C). Average of triplicate samples with error bars showing one standard deviation.

Adsorption kinetics

The kinetics of adsorption is used to describe the mechanism of adsorption and potential rate controlling steps such as mass transport and chemical reaction processes. The kinetics of adsorption of onto QACV was analyzed by pseudo-first-order and pseudo-second-order equations (Lagergren 1898; Ho & McKay 1999). The non-linear forms of the two kinetic models are shown as follows.

Pseudo-first-order model: 
formula
6
Pseudo-second-order model: 
formula
7
where qe and qt are the amounts of adsorbed (mmol/g) at equilibrium and at time t (min), respectively. k1 (min−1) and k2 (g/(mmol min)) are the rate constants of first-order and second-order adsorption, respectively.

The experimental data were fitted with the curves of non-linear forms of pseudo-first-order and pseudo-second-order equations, and the estimated parameters are listed in Table 2. The R2 value and F value of the pseudo-first-order model were found to be lower than those of the pseudo-second-order model. In addition, the theoretical qe2,cal (0.90 mmol/g) value is closer to the experimental qe,exp (0.91 mmol/g) value than qe1,cal (0.88 mmol/g). Moreover, the experimental value of qe,exp is not in good agreement with the theoretical value calculated for qe1,cal from Equation (5). Based on these results, it can be concluded that the pseudo-second-order model was more likely to predict kinetic behavior of adsorption of on QACV. Therefore, the adsorption process was inferred to be a chemical process, because the pseudo-second-order model assumes the rate-limiting step of the adsorption process is chemical sorption involving sharing or exchange of electrons between the adsorbents and adsorbates (Ho & McKay 1999). Conversely, the pseudo-first-order model assumes that the adsorption is controlled by diffusion (Lagergren 1898). The rate constant of the adsorption calculated by fitting the pseudo-second-order model was 3.51 g/(mmol min).

Table 2

Comparison of pseudo-first-order and pseudo-second-order adsorption rate constants, calculated and experimental qe values, R2 values and F values for Ag(CN)2 adsorption onto QACV

  Pseudo-first-order
 
Pseudo-second-order
 
Model qe mmol/g k1 min−1 qe1,cal mmol/g R2 F value k2 g/(mmol min) qe2,cal mmol/g R2 F value 
Non-linear 0.91 2.05 0.88 0.961 1345 3.51 0.90 0.994 9018 
  Pseudo-first-order
 
Pseudo-second-order
 
Model qe mmol/g k1 min−1 qe1,cal mmol/g R2 F value k2 g/(mmol min) qe2,cal mmol/g R2 F value 
Non-linear 0.91 2.05 0.88 0.961 1345 3.51 0.90 0.994 9018 

Adsorption isotherm

The adsorption isotherm describes how adsorbates interact with adsorbents and is important in optimizing the use of the latter. The Langmuir isotherm equation can be theoretically derived based on some fundamental assumptions. The Freundlich isotherm equation is an empirical model mainly deriving from the Langmuir isotherm equation. Non-linear forms of the Langmuir and Freundlich isotherms are expressed as follows.

Langmuir isotherm: 
formula
8
Freundlich isotherm: 
formula
9
where qe is the equilibrium adsorption capacity (mmol/g). qm is the maximum adsorption capacity (mmol/g). Ce is the concentration of adsorbate at equilibrium (mmol/L). KL is the the Langmuir constant related to the affinity of binding sites (L/mmol). KF and n are the Freundlich constants, which represent adsorption capacity and adsorption intensity, respectively.

The experimental data were fitted with the curves of non-linear forms of Langmuir and Freundlich isotherm equations (Figure 6), and the estimated parameters are listed in Table 3. It was found that the maximum adsorption capacity of Ag(CN)2 is 1.96 mmol/g, lower than the theoretical maximum concentration of active sites (, 2.37 mmol/g), which may be explained by the fact that the steric hindrance on the cell surface of C. vulgaris inhibited the adsorption of to some extent (Hu et al. 2009). As shown, the values of R2 and F for the Langmuir isotherm model were higher than those of the Freundlich isotherm model, which indicates that the Langmuir isotherm model had more validity in fitting experimental data. The qm of QACV fitted with the Langmuir isotherm was 1.96 mmol/g, higher than those obtained from Purolite A500/2788 adsorption of copper cyanide (1.20 mmol/g) (Dai et al. 2010) and Dowex 21 K XLT resin adsorption of cold cyanide (0.162 mmol/g) (Ok & Jeon 2014); thus anion exchange resin QACV has great potential in adsorption capacity.

Table 3

Isotherm constants and values of R2 and F for Ag(CN)2 adsorption onto QACV

  Freundlich
 
Langmuir
 
Isotherm model KF R2 F value qm mmol/g KL L/mmol R2 F value 
Non-linear 2.81 0.71 0.953 575 1.96 0.49 0.991 3014 
  Freundlich
 
Langmuir
 
Isotherm model KF R2 F value qm mmol/g KL L/mmol R2 F value 
Non-linear 2.81 0.71 0.953 575 1.96 0.49 0.991 3014 
Figure 6

Adsorption isotherm of the adsorption of Ag(CN)2 onto QACV (experimental conditions: contact time 30 min, pH = 11, temperature 28 °C). Average of triplicate samples with error bars showing one standard deviation.

Figure 6

Adsorption isotherm of the adsorption of Ag(CN)2 onto QACV (experimental conditions: contact time 30 min, pH = 11, temperature 28 °C). Average of triplicate samples with error bars showing one standard deviation.

The Langmuir parameters given in Table 3 can be used to predict affinity between adsorbate and adsorbent using the dimensionless separation factor RL (Hall et al. 1966; McKay et al. 1987): 
formula
10

where C0 is the initial concentration of adsorbents in aqueous solution. The RL value implies that adsorption is unfavorable (RL > 1), linear (RL = 1), favorable (0 < RL < 1), or irreversible (RL = 0). The smaller the value of RL, the smoother the adsorption process is. The values of RL for adsorption of on QACV are between 0 and 1 and are shown in Figure 7. Also, RL values decreased as the initial concentration of increased, which suggests that the adsorption process is more favorable at higher initial concentration than at a lower one.

Figure 7

The dimensionless separation factor RL for the adsorption of Ag(CN)2 ions onto QACV.

Figure 7

The dimensionless separation factor RL for the adsorption of Ag(CN)2 ions onto QACV.

Regeneration of QACV

For potential practical application, it is important to examine the possibility of regeneration of the resin. NaCl solution was used to desorb and regenerate the QACV adsorbed with (Table 4). The effect of four adsorption–desorption consecutive cycles on the efficiency of the adsorption of on QACV was studied. In the second cycle, the adsorption capacity could reach 96.7% of that of the first adsorption. Also, the adsorption capacity reduced significantly in the fourth cycle. The adsorption capacity of QACV was kept above 90% relative to the first adsorption in three repetitions of the adsorption–desorption cycles.

Table 4

Regeneration efficiencies of Ag(CN)2 on QACV from four adsorption–desorption cycles

Cycle number 
Adsorption capacity (mmol/g) 0.91 0.88 0.82 0.63 
Cycle number 
Adsorption capacity (mmol/g) 0.91 0.88 0.82 0.63 

CONCLUSIONS

This study indicates that dried C. vulgaris is a potential base material when modified with quaternary ammonium groups to prepare an adsorbent for adsorption of . QACV was synthesized and characterized by FTIR. The best adsorption performance of QACV for was at pH 9–11. Adsorption equilibrium was quickly almost reached in 30 min. The adsorption kinetics closely followed the pseudo-second-order kinetic model. The experimental adsorption isotherm data were well fitted with the Langmuir model and the estimated maximum adsorption capacity of by QACV was 1.96 mmol/g, in a solution of pH 11. The dimensionless separation factor RL showed that QACV could be used for adsorption of from aqueous solution. The prepared QACV could be reused three times without significantly decreasing its adsorption capacity. Real wastewater contains a number of contaminants that may affect the performance of the material. Thus, further studies should be conducted to assess the potential of the material in the removal of from industrial wastewater.

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