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Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Phosphate removal from aqueous solutions by nanoscale zero-valent iron a
a
a
a
a
a
Donglei Wu , Yanhong Shen , Aqiang Ding , Mengyu Qiu , Qi Yang & Shuangshuang Zheng a
College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China Accepted author version posted online: 15 Mar 2013.Published online: 07 Jun 2013.
To cite this article: Donglei Wu, Yanhong Shen, Aqiang Ding, Mengyu Qiu, Qi Yang & Shuangshuang Zheng (2013) Phosphate removal from aqueous solutions by nanoscale zero-valent iron, Environmental Technology, 34:18, 2663-2669, DOI: 10.1080/09593330.2013.786103 To link to this article: http://dx.doi.org/10.1080/09593330.2013.786103
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Environmental Technology, 2013 Vol. 34, No. 18, 2663–2669, http://dx.doi.org/10.1080/09593330.2013.786103
Phosphate removal from aqueous solutions by nanoscale zero-valent iron Donglei Wu∗ , Yanhong Shen, Aqiang Ding, Mengyu Qiu, Qi Yang and Shuangshuang Zheng College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China
Downloaded by [The University Of Melbourne Libraries] at 09:07 15 September 2014
(Received 23 November 2012; final version received 8 March 2013 ) In this study, nanoscale zero-valent iron (NZVI) was synthesized by conventional liquid-phase chemical reduction methods without a support material and then characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effect of NZVI particles on phosphate removal from aqueous solutions was examined. The results showed that the phosphate removal efficiency increased from 34.49% to 87.01% as the dosage of nanoscale iron particles increased from 100 to 600 mg L−1 with an initial phosphate concentration of 10 mg L−1 , and the phosphate removal efficiency decreased from 72.89% to 51.39% as the initial phosphate concentration increased from 10 to 90 mg L−1 , with 400 mg L−1 NZVI. Phosphate removal efficiencies of 99.41% and 95.09% were achieved at pH values of 2 and 4, respectively, with an initial phosphate concentration of 20 mg L−1 and 400 mg L−1 NZVI. The use of NZVI particles synthesized in a carboxymethyl cellulose (CMC)–water solution significantly enhanced phosphate removal from an aqueous solution compared with the use of NZVI synthesized in an ethanol–water solution. NZVI particles achieved 71.34% phosphate removal, which was remarkably higher than that of microscale zero-valent iron (MZVI) particles (16.35%) with 10 mg L−1 of phosphate and 400 mg L−1 iron. Based on the removal mechanism analysis performed in this study, we recommend that phosphate removal be accomplished by simultaneous adsorption and chemical precipitation. The XRD patterns of the NZVI before and after the reactions indicated the formation of crystalline vivianite (Fe3 (PO4 )2 · 8H2 O) during the procedure. Keywords: phosphate removal; nanoscale zero-valent iron; mechanism; adsorption; chemical precipitation
1. Introduction Phosphorous is considered a limiting element and is a major contributor to the eutrophication of water bodies. Therefore, removal of phosphorus from wastewater can be an effective method of controlling eutrophication in water.[1] The Chinese primary discharge standard (GB8978-1996) for phosphorus from municipal wastewater treatment plants has become increasingly stringent to restrict the concentration of phosphorus in wastewater and to reduce the negative effects of phosphorus discharged to receiving water bodies. Phosphorus removal can be accomplished either biologically or by chemical precipitation. Biological processes rely on biomass growth (bacteria, microalgae or plants) or intracellular bacterial polyphosphate accumulation and sorption.[2] Biological treatment has the advantage of avoiding the use of chemicals and excessive sludge production.[3] However, it tends to be a sensitive process, and fluctuations in the chemical composition and temperature of wastewater often make its implementation not feasible and lead to a failure to meet water quality standards. In contrast, chemical precipitation has been widely applied for phosphate removal. The main chemical additives used to remove phosphorus include alum, ion salts and lime.[4,5] However, despite its ease of operation and effectiveness, ∗ Corresponding
author. Email: [email protected]
© 2013 Taylor & Francis
chemical precipitation requires expensive metal salts and produces large amounts of sludge, which can result in secondary pollution. Thus, more innovative approaches are required to overcome the challenges of phosphorus removal from wastewater. Phosphate adsorption is one potential solution that could be satisfactory from an economic perspective. Considerable attention has been given to a variety of cost-effective solid sorbents in recent years such as fly ash,[6,7] active red mud,[6,8] natural wollastonite,[9] iron humate,[10] biogenic iron oxides [11] and other waste materials.[12,13] In recent years, magnetic iron-containing sorbents have been widely applied for the phosphate removal. Zeng et al. [14] used iron oxide tailings as en effective adsorbent for phosphate removal; hydroxide-containing iron also worked effectively for phosphate removal.[15] The most appropriate sorbent should not only meet economic and convenience requirements and have the best sorption capacity, but also accommodate the diverse pH values present in wastewater.[6] Nanoscale zero-valent iron (NZVI) particles have attracted interest in recent years because of their large surface areas and high surface reactivity. Remediation with NZVI has been applied to various pollutants such as chlorinated organic contaminants,[16–18] nitroaromatic
Downloaded by [The University Of Melbourne Libraries] at 09:07 15 September 2014
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compounds,[19] nitrate [20,21] and heavy metal ions.[22, 23] NZVI’s large surface area also make it an excellent sorbent. Previous research has focused on NZVI’s reduction effect, but few studies have focused on its sorption capacity. Kim and Carraway [24] showed that the removal of pentachlorophenol from aqueous solutions by zero valent iron (ZVI) can be achieved by both dechlorination reactions and adsorption. NZVI has certain advantages over other phosphate sorbents because it can simultaneously remove phosphates by chemical precipitation due to the Fe2+ generated by its anaerobic corrosion.[25] Noubactep [26] has discussed the plausibility of contaminant co-precipitation with iron corrosion products as a contaminant removal mechanism. This study investigated the simultaneous adsorption and chemical precipitation of inorganic phosphate anions from aqueous solutions by NZVI. Batch experiments were conducted using different NZVI particle dosages, initial phosphate concentrations, pH values and dispersing agent conditions to investigate the influence of these factors on phosphate removal with NZVI. The mechanism of phosphate removal by the NZVI particles was also studied. 2.
Materials and methods
2.1. Materials Analytical grade sodium borohydride (NaBH4 ), ferrous sulfate heptahydrate (FeSO4 ·7H2 O), ethanol, potassium dihydrogen phosphate (KH2 PO4 ) and ascorbic acid were purchased from the Shanghai Chemical Reagents Company. Iron powder (>400 mesh, >98%) and carboxymethyl cellulose (CMC) were obtained from the Aladdin Chemical Company. Deionized water was deoxygenated by bubbling argon (Ar) gas through it for 30 min. 2.2. Preparation of NZVI particles A total of 100 mL of alcohol was placed in a three-neck flask before 200 mL of ferrous solution (0.2 M) was added to the solution under Ar gas protection. Finally, 200 mL of NaBH4 (0.4 M) solution was added dropwise to the ferrous solution with magnetic stirring. The final concentration of NZVI was 0.08 M (4480 mg L−1 ). The reduction process of the entire aqueous solution was performed under a flow of Ar gas. Ferrous iron was reduced according to the following equation: − 0 Fe(H2 O)2+ 6 + 2BH4 → Fe ↓ +2B(OH)3 + 7H2 ↑
2.3. Batch experiments The batch experiments were conducted in a 250 mL serum bottle maintained in a rotary shaker at 200 rpm under anaerobic conditions. To each bottle, 200 mL of a solution containing a certain amount of KH2 PO4 (as P) and a fixed concentration of NZVI was added. The entire process was
performed in an Ar atmosphere to remove residual oxygen and the solvents were also saturated with Ar gas before being used. Samples from the batch experiments were taken at certain time intervals with a 10 mL syringe and filtered through a 0.22 μm membrane filter prior to analysis. Duplicate bottles were established and the results were averaged for each treatment. The effects of certain variations were investigated in this study. The concentration of NZVI was varied between 100, 200, 400 and 600 mg L−1 while the initial phosphate concentration was maintained at 10 mg L−1 . The initial phosphate concentration was set at 10, 20, 50 and 90 mg L−1 while the concentration of NZVI was maintained at 400 mg L−1 . The initial pH was varied between 2.0, 4.0, 6.0 and 9.0, respectively, and the effects of different dispersing agents were studied. A sample of 400 mg L−1 NZVI particles and microscale iron particles were also tested under the same conditions for comparison purposes.
2.4.
Analysis methods
The phosphate was determined at 700 nm using an ultraviolet–visible (UV-Vis) spectrophotometer (UV2802 Shanghai) by the colorimetric method of reduction with ascorbic acid. The morphology of the NZVI particles was observed with an FEI SIRON SEM operated at 25 kV and a JEOL JEM-1230 TEM operated at 80 kV. The specific surface area was measured with a Micromeritics Tristar 3020 analyser at 77 K using the Brunauer–Emmett–Teller (BET) nitrogen gas sorption method. X-ray diffraction (XRD) analysis of the nanoscale iron particles before and after the reaction was performed using an X’Pert PRO X-ray diffractometer with Cu Kα radiation in the 2θ range from 5◦ to 90◦ . The surface functional groups on the NZVI particles were studied by Fourier transform infrared (FT-IR) analysis (NICOLET AVA TAR370 FT-IR spectrometer). Prior to scanning and measuring, the samples were obtained by washing the wet precipitates three times with alcohol and drying them in a vacuum oven at 80◦ C for 24 h.
3. Results and discussion 3.1. Characterization of synthesized NZVI particles The NZVI particles prepared in this study had a BET specific surface area of 20.92 m2 g−1 . The specific surface area of these NZVI particles was not as large as that of the nanoscale iron particles (37.83 m2 g−1 ) used in the kinetics and pathways study on nitrate reduction by Yang and Lee,[20] but it was 24 times larger than that of commercially available fine iron powder (Aladdin Chemical Company >98%,
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Phosphate removal from aqueous solutions by nanoscale zero-valent iron a
a
a
a
a
a
Donglei Wu , Yanhong Shen , Aqiang Ding , Mengyu Qiu , Qi Yang & Shuangshuang Zheng a
College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China Accepted author version posted online: 15 Mar 2013.Published online: 07 Jun 2013.
To cite this article: Donglei Wu, Yanhong Shen, Aqiang Ding, Mengyu Qiu, Qi Yang & Shuangshuang Zheng (2013) Phosphate removal from aqueous solutions by nanoscale zero-valent iron, Environmental Technology, 34:18, 2663-2669, DOI: 10.1080/09593330.2013.786103 To link to this article: http://dx.doi.org/10.1080/09593330.2013.786103
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Environmental Technology, 2013 Vol. 34, No. 18, 2663–2669, http://dx.doi.org/10.1080/09593330.2013.786103
Phosphate removal from aqueous solutions by nanoscale zero-valent iron Donglei Wu∗ , Yanhong Shen, Aqiang Ding, Mengyu Qiu, Qi Yang and Shuangshuang Zheng College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, China
Downloaded by [The University Of Melbourne Libraries] at 09:07 15 September 2014
(Received 23 November 2012; final version received 8 March 2013 ) In this study, nanoscale zero-valent iron (NZVI) was synthesized by conventional liquid-phase chemical reduction methods without a support material and then characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effect of NZVI particles on phosphate removal from aqueous solutions was examined. The results showed that the phosphate removal efficiency increased from 34.49% to 87.01% as the dosage of nanoscale iron particles increased from 100 to 600 mg L−1 with an initial phosphate concentration of 10 mg L−1 , and the phosphate removal efficiency decreased from 72.89% to 51.39% as the initial phosphate concentration increased from 10 to 90 mg L−1 , with 400 mg L−1 NZVI. Phosphate removal efficiencies of 99.41% and 95.09% were achieved at pH values of 2 and 4, respectively, with an initial phosphate concentration of 20 mg L−1 and 400 mg L−1 NZVI. The use of NZVI particles synthesized in a carboxymethyl cellulose (CMC)–water solution significantly enhanced phosphate removal from an aqueous solution compared with the use of NZVI synthesized in an ethanol–water solution. NZVI particles achieved 71.34% phosphate removal, which was remarkably higher than that of microscale zero-valent iron (MZVI) particles (16.35%) with 10 mg L−1 of phosphate and 400 mg L−1 iron. Based on the removal mechanism analysis performed in this study, we recommend that phosphate removal be accomplished by simultaneous adsorption and chemical precipitation. The XRD patterns of the NZVI before and after the reactions indicated the formation of crystalline vivianite (Fe3 (PO4 )2 · 8H2 O) during the procedure. Keywords: phosphate removal; nanoscale zero-valent iron; mechanism; adsorption; chemical precipitation
1. Introduction Phosphorous is considered a limiting element and is a major contributor to the eutrophication of water bodies. Therefore, removal of phosphorus from wastewater can be an effective method of controlling eutrophication in water.[1] The Chinese primary discharge standard (GB8978-1996) for phosphorus from municipal wastewater treatment plants has become increasingly stringent to restrict the concentration of phosphorus in wastewater and to reduce the negative effects of phosphorus discharged to receiving water bodies. Phosphorus removal can be accomplished either biologically or by chemical precipitation. Biological processes rely on biomass growth (bacteria, microalgae or plants) or intracellular bacterial polyphosphate accumulation and sorption.[2] Biological treatment has the advantage of avoiding the use of chemicals and excessive sludge production.[3] However, it tends to be a sensitive process, and fluctuations in the chemical composition and temperature of wastewater often make its implementation not feasible and lead to a failure to meet water quality standards. In contrast, chemical precipitation has been widely applied for phosphate removal. The main chemical additives used to remove phosphorus include alum, ion salts and lime.[4,5] However, despite its ease of operation and effectiveness, ∗ Corresponding
author. Email: [email protected]
© 2013 Taylor & Francis
chemical precipitation requires expensive metal salts and produces large amounts of sludge, which can result in secondary pollution. Thus, more innovative approaches are required to overcome the challenges of phosphorus removal from wastewater. Phosphate adsorption is one potential solution that could be satisfactory from an economic perspective. Considerable attention has been given to a variety of cost-effective solid sorbents in recent years such as fly ash,[6,7] active red mud,[6,8] natural wollastonite,[9] iron humate,[10] biogenic iron oxides [11] and other waste materials.[12,13] In recent years, magnetic iron-containing sorbents have been widely applied for the phosphate removal. Zeng et al. [14] used iron oxide tailings as en effective adsorbent for phosphate removal; hydroxide-containing iron also worked effectively for phosphate removal.[15] The most appropriate sorbent should not only meet economic and convenience requirements and have the best sorption capacity, but also accommodate the diverse pH values present in wastewater.[6] Nanoscale zero-valent iron (NZVI) particles have attracted interest in recent years because of their large surface areas and high surface reactivity. Remediation with NZVI has been applied to various pollutants such as chlorinated organic contaminants,[16–18] nitroaromatic
Downloaded by [The University Of Melbourne Libraries] at 09:07 15 September 2014
2664
D. Wu et al.
compounds,[19] nitrate [20,21] and heavy metal ions.[22, 23] NZVI’s large surface area also make it an excellent sorbent. Previous research has focused on NZVI’s reduction effect, but few studies have focused on its sorption capacity. Kim and Carraway [24] showed that the removal of pentachlorophenol from aqueous solutions by zero valent iron (ZVI) can be achieved by both dechlorination reactions and adsorption. NZVI has certain advantages over other phosphate sorbents because it can simultaneously remove phosphates by chemical precipitation due to the Fe2+ generated by its anaerobic corrosion.[25] Noubactep [26] has discussed the plausibility of contaminant co-precipitation with iron corrosion products as a contaminant removal mechanism. This study investigated the simultaneous adsorption and chemical precipitation of inorganic phosphate anions from aqueous solutions by NZVI. Batch experiments were conducted using different NZVI particle dosages, initial phosphate concentrations, pH values and dispersing agent conditions to investigate the influence of these factors on phosphate removal with NZVI. The mechanism of phosphate removal by the NZVI particles was also studied. 2.
Materials and methods
2.1. Materials Analytical grade sodium borohydride (NaBH4 ), ferrous sulfate heptahydrate (FeSO4 ·7H2 O), ethanol, potassium dihydrogen phosphate (KH2 PO4 ) and ascorbic acid were purchased from the Shanghai Chemical Reagents Company. Iron powder (>400 mesh, >98%) and carboxymethyl cellulose (CMC) were obtained from the Aladdin Chemical Company. Deionized water was deoxygenated by bubbling argon (Ar) gas through it for 30 min. 2.2. Preparation of NZVI particles A total of 100 mL of alcohol was placed in a three-neck flask before 200 mL of ferrous solution (0.2 M) was added to the solution under Ar gas protection. Finally, 200 mL of NaBH4 (0.4 M) solution was added dropwise to the ferrous solution with magnetic stirring. The final concentration of NZVI was 0.08 M (4480 mg L−1 ). The reduction process of the entire aqueous solution was performed under a flow of Ar gas. Ferrous iron was reduced according to the following equation: − 0 Fe(H2 O)2+ 6 + 2BH4 → Fe ↓ +2B(OH)3 + 7H2 ↑
2.3. Batch experiments The batch experiments were conducted in a 250 mL serum bottle maintained in a rotary shaker at 200 rpm under anaerobic conditions. To each bottle, 200 mL of a solution containing a certain amount of KH2 PO4 (as P) and a fixed concentration of NZVI was added. The entire process was
performed in an Ar atmosphere to remove residual oxygen and the solvents were also saturated with Ar gas before being used. Samples from the batch experiments were taken at certain time intervals with a 10 mL syringe and filtered through a 0.22 μm membrane filter prior to analysis. Duplicate bottles were established and the results were averaged for each treatment. The effects of certain variations were investigated in this study. The concentration of NZVI was varied between 100, 200, 400 and 600 mg L−1 while the initial phosphate concentration was maintained at 10 mg L−1 . The initial phosphate concentration was set at 10, 20, 50 and 90 mg L−1 while the concentration of NZVI was maintained at 400 mg L−1 . The initial pH was varied between 2.0, 4.0, 6.0 and 9.0, respectively, and the effects of different dispersing agents were studied. A sample of 400 mg L−1 NZVI particles and microscale iron particles were also tested under the same conditions for comparison purposes.
2.4.
Analysis methods
The phosphate was determined at 700 nm using an ultraviolet–visible (UV-Vis) spectrophotometer (UV2802 Shanghai) by the colorimetric method of reduction with ascorbic acid. The morphology of the NZVI particles was observed with an FEI SIRON SEM operated at 25 kV and a JEOL JEM-1230 TEM operated at 80 kV. The specific surface area was measured with a Micromeritics Tristar 3020 analyser at 77 K using the Brunauer–Emmett–Teller (BET) nitrogen gas sorption method. X-ray diffraction (XRD) analysis of the nanoscale iron particles before and after the reaction was performed using an X’Pert PRO X-ray diffractometer with Cu Kα radiation in the 2θ range from 5◦ to 90◦ . The surface functional groups on the NZVI particles were studied by Fourier transform infrared (FT-IR) analysis (NICOLET AVA TAR370 FT-IR spectrometer). Prior to scanning and measuring, the samples were obtained by washing the wet precipitates three times with alcohol and drying them in a vacuum oven at 80◦ C for 24 h.
3. Results and discussion 3.1. Characterization of synthesized NZVI particles The NZVI particles prepared in this study had a BET specific surface area of 20.92 m2 g−1 . The specific surface area of these NZVI particles was not as large as that of the nanoscale iron particles (37.83 m2 g−1 ) used in the kinetics and pathways study on nitrate reduction by Yang and Lee,[20] but it was 24 times larger than that of commercially available fine iron powder (Aladdin Chemical Company >98%,
