Login In
2017 Volume 75 Issue 6
2017, 75(6): 519-520
doi: 10.6023/A1706E001
Abstract:
2017, 75(6): 529-537
doi: 10.6023/A17020051
Abstract:
Heavy metals are nonbiodegradable and bioaccumulative contaminants with high toxicity, thus heavy metal contamination and treatment have been hot research topics in recent years. Nanoscale zero-valent iron (nZVI) has received considerable attentions for its potential as a remedial agent for heavy metal sequestration and immobilization. In this paper, an overview is provided highlighting recent research progress on heavy metal-nZVI reactions, both laboratory studies and engineering applications are discussed. The core-shell structure with the core being metallic and the shell being iron oxides and the surface chemistry properties endow nZVI with unique and multifaceted functions for heavy metal removal including sorption, reduction and precipitation. Particle size of nZVI is in the range of nanoscale that imparts it with large specific surface area, high surface activity, and high density of reactive surface sites. A hybrid of effects, including instant separation, isolation, immobilization, and toxicity reduction can be achieved at the same time, making nZVI an effective remedial reagent for various heavy metals. Recent progress in instrumental analysis, especially the development of high-resolution electron microscopy, offers much-enhanced capability and new insights into the core-shell nature of nZVI and mechanisms of the heavy metal-nZVI reactions on a single nanoparticle. Research results obtained from a spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) integrated with high sensitive X-ray energy dispersive spectroscopy (EDS) provide detailed information on the fine structural features of nZVI and the intraparticle reactions with individual nanoparticles. Technical feasibility and operational advantages of using nZVI for the treatment of industrial wastewater are assessed through systematic laboratory and pilot scale studies. Based on the encouraging results of bench-scale experiments, we have successfully applied nZVI for large scale applications of nZVI for treatment of industrial wastewater containing heavy metals such as Cu, As, Pb and Zn. The long-term operation results show tremendous potentials of nZVI-based process as an efficient method for heavy metal treatment.
Heavy metals are nonbiodegradable and bioaccumulative contaminants with high toxicity, thus heavy metal contamination and treatment have been hot research topics in recent years. Nanoscale zero-valent iron (nZVI) has received considerable attentions for its potential as a remedial agent for heavy metal sequestration and immobilization. In this paper, an overview is provided highlighting recent research progress on heavy metal-nZVI reactions, both laboratory studies and engineering applications are discussed. The core-shell structure with the core being metallic and the shell being iron oxides and the surface chemistry properties endow nZVI with unique and multifaceted functions for heavy metal removal including sorption, reduction and precipitation. Particle size of nZVI is in the range of nanoscale that imparts it with large specific surface area, high surface activity, and high density of reactive surface sites. A hybrid of effects, including instant separation, isolation, immobilization, and toxicity reduction can be achieved at the same time, making nZVI an effective remedial reagent for various heavy metals. Recent progress in instrumental analysis, especially the development of high-resolution electron microscopy, offers much-enhanced capability and new insights into the core-shell nature of nZVI and mechanisms of the heavy metal-nZVI reactions on a single nanoparticle. Research results obtained from a spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) integrated with high sensitive X-ray energy dispersive spectroscopy (EDS) provide detailed information on the fine structural features of nZVI and the intraparticle reactions with individual nanoparticles. Technical feasibility and operational advantages of using nZVI for the treatment of industrial wastewater are assessed through systematic laboratory and pilot scale studies. Based on the encouraging results of bench-scale experiments, we have successfully applied nZVI for large scale applications of nZVI for treatment of industrial wastewater containing heavy metals such as Cu, As, Pb and Zn. The long-term operation results show tremendous potentials of nZVI-based process as an efficient method for heavy metal treatment.
2017, 75(6): 538-543
doi: 10.6023/A17020047
Abstract:
Nano zero-valent iron (nZVI) is a special kind of iron with large specific surface area, strong reduction activity, and the environmental friendliness. nZVI was usually used to reductively degrade organic pollutants, but its long-term performance was poor and the organic pollutants could not be mineralized. Nano zero-valent iron can reductively activate molecular oxygen to generate reactive oxygen species for oxidation or even mineralization of organic pollutants. Recently, we found the core-shell structure dependent aerobic degradation of organic pollutants by nZVI and proposed a new physical insight into the molecular oxygen activation mechanism of the aerobic nZVI process, where the outward electrons transfer from the iron core initiate the two-electron molecular oxygen activation and surface bound ferrous ions on iron oxide shell favor the single-electron molecular oxygen activation. Several strategies have also been proposed to enhance the production of reactive oxidants by nZVI-induced oxygen activation. We confirmed that addition of extra ferrous ions into the nZVI/O2 system could generate more surface bound ferrous ions for significantly enhancing the generation of reactive oxygen species. Meanwhile, the introduction of some inorganic or organic ligands in the aerobic nZVI system could also improve the active oxygen species generation efficiency. Finally main typical environmental factors including of the pH value, coexisting ions, natural organic matter on the organic pollutants degradation with the aerobic nZVI were discussed. By the way, we also investigated the anoxic Cr(Ⅵ) removal with nZVI. It was found the Cr(Ⅵ) removal rate constant was mainly attributed to the reduction of Cr(Ⅵ) by the surface bound Fe(Ⅱ) besides the reduction of Cr(Ⅵ) adsorbed on the iron oxide shell via the electrons transferred from the iron core. We also demonstrated that the presence of oxygen molecule can inhibit Cr(Ⅵ) removal with nZVI, which was attributed to that the oxygen molecular activation could compete with Cr(Ⅵ) for the consumption of surface bond Fe(Ⅱ) and donor electrons transferred from Fe0 core.
Nano zero-valent iron (nZVI) is a special kind of iron with large specific surface area, strong reduction activity, and the environmental friendliness. nZVI was usually used to reductively degrade organic pollutants, but its long-term performance was poor and the organic pollutants could not be mineralized. Nano zero-valent iron can reductively activate molecular oxygen to generate reactive oxygen species for oxidation or even mineralization of organic pollutants. Recently, we found the core-shell structure dependent aerobic degradation of organic pollutants by nZVI and proposed a new physical insight into the molecular oxygen activation mechanism of the aerobic nZVI process, where the outward electrons transfer from the iron core initiate the two-electron molecular oxygen activation and surface bound ferrous ions on iron oxide shell favor the single-electron molecular oxygen activation. Several strategies have also been proposed to enhance the production of reactive oxidants by nZVI-induced oxygen activation. We confirmed that addition of extra ferrous ions into the nZVI/O2 system could generate more surface bound ferrous ions for significantly enhancing the generation of reactive oxygen species. Meanwhile, the introduction of some inorganic or organic ligands in the aerobic nZVI system could also improve the active oxygen species generation efficiency. Finally main typical environmental factors including of the pH value, coexisting ions, natural organic matter on the organic pollutants degradation with the aerobic nZVI were discussed. By the way, we also investigated the anoxic Cr(Ⅵ) removal with nZVI. It was found the Cr(Ⅵ) removal rate constant was mainly attributed to the reduction of Cr(Ⅵ) by the surface bound Fe(Ⅱ) besides the reduction of Cr(Ⅵ) adsorbed on the iron oxide shell via the electrons transferred from the iron core. We also demonstrated that the presence of oxygen molecule can inhibit Cr(Ⅵ) removal with nZVI, which was attributed to that the oxygen molecular activation could compete with Cr(Ⅵ) for the consumption of surface bond Fe(Ⅱ) and donor electrons transferred from Fe0 core.
2017, 75(6): 544-551
doi: 10.6023/A17010007
Abstract:
Zero-valent iron (ZVI), a simple but amazingly versatile material, has low intrinsic reactivity toward various contaminants as documented from laboratory studies as well as field demonstrations, which poses potential limitations to its practical application in environmental remediation. Although many methods have been developed to improve the reactivity of ZVI in the literature, high costs, significant work-load, and complex operations may inhibit the application of these methods. We pioneered the research in employing weak magnetic field (WMF) to accelerate the removal of various metal(loid)s, including Se(Ⅳ)/Se(Ⅵ), As(V)/As(Ⅲ), Sb(V), Cu(Ⅱ)/EDTA-Cu(Ⅱ), and Cr(Ⅵ) by pristine ZVI (Pri-ZVI) and/or aged ZVI. The rate constants of metal(loid)s sequestration by Pri-ZVI or aged ZVI were increased by 1.1~383.7 folds due to the application of WMF. Furthermore, WMF could be employed to improve the removal of organic contaminants by ZVI activated H2O2 or persulfate because of the accelerated ZVI corrosion in the presence of WMF. The superimposed WMF had negligible influence on the apparent activation energy of metal(loid)s removal by ZVI, indicating that WMF accelerated metal(loid)s removal by ZVI but did not change the mechanisms. The XAFS, XRD, and XPS analysis confirmed that the application of WMF did not change the mechanisms of metal(loid)s removal but accelerated the transformation (reduction or oxidation) of contaminants. Electrochemical analysis showed that the accelerated ZVI corrosion in the presence of WMF was ascribed to the enhanced mass transfer. We further identified the relative contribution of Lorentz force (FL) and magnetic gradient force (FΔB) in the enhancing effect of WMF. It suggested that FΔB rather than FL was the major driving force for the observed WMF effect on the enhanced reactivity of ZVI. Moreover, we proposed to apply premagnetization to increase the reactivity of ZVI toward As(Ⅲ) sequestration taking advantage of the magnetic memory of ZVI, i.e., the remanence of ZVI. In addition, the premagnetized ZVI (Mag-ZVI) samples from different origins were applied to enhance the removal of various oxidative contaminants[such as azo dyes, As(Ⅲ), Pb(Ⅱ), Cu(Ⅱ), Se(Ⅳ), Ag(Ⅰ) and Cr(Ⅵ)] under well-controlled experimental conditions. The rate constants of contaminants removal by premagnetized ZVI samples were 1.2~12.2 folds greater than those by Pri-ZVI samples. As a chemical-and energy-free method, improving the reactivity of ZVI by either WMF superimposition or premagnetization treatment is novel and promising.
Zero-valent iron (ZVI), a simple but amazingly versatile material, has low intrinsic reactivity toward various contaminants as documented from laboratory studies as well as field demonstrations, which poses potential limitations to its practical application in environmental remediation. Although many methods have been developed to improve the reactivity of ZVI in the literature, high costs, significant work-load, and complex operations may inhibit the application of these methods. We pioneered the research in employing weak magnetic field (WMF) to accelerate the removal of various metal(loid)s, including Se(Ⅳ)/Se(Ⅵ), As(V)/As(Ⅲ), Sb(V), Cu(Ⅱ)/EDTA-Cu(Ⅱ), and Cr(Ⅵ) by pristine ZVI (Pri-ZVI) and/or aged ZVI. The rate constants of metal(loid)s sequestration by Pri-ZVI or aged ZVI were increased by 1.1~383.7 folds due to the application of WMF. Furthermore, WMF could be employed to improve the removal of organic contaminants by ZVI activated H2O2 or persulfate because of the accelerated ZVI corrosion in the presence of WMF. The superimposed WMF had negligible influence on the apparent activation energy of metal(loid)s removal by ZVI, indicating that WMF accelerated metal(loid)s removal by ZVI but did not change the mechanisms. The XAFS, XRD, and XPS analysis confirmed that the application of WMF did not change the mechanisms of metal(loid)s removal but accelerated the transformation (reduction or oxidation) of contaminants. Electrochemical analysis showed that the accelerated ZVI corrosion in the presence of WMF was ascribed to the enhanced mass transfer. We further identified the relative contribution of Lorentz force (FL) and magnetic gradient force (FΔB) in the enhancing effect of WMF. It suggested that FΔB rather than FL was the major driving force for the observed WMF effect on the enhanced reactivity of ZVI. Moreover, we proposed to apply premagnetization to increase the reactivity of ZVI toward As(Ⅲ) sequestration taking advantage of the magnetic memory of ZVI, i.e., the remanence of ZVI. In addition, the premagnetized ZVI (Mag-ZVI) samples from different origins were applied to enhance the removal of various oxidative contaminants[such as azo dyes, As(Ⅲ), Pb(Ⅱ), Cu(Ⅱ), Se(Ⅳ), Ag(Ⅰ) and Cr(Ⅵ)] under well-controlled experimental conditions. The rate constants of contaminants removal by premagnetized ZVI samples were 1.2~12.2 folds greater than those by Pri-ZVI samples. As a chemical-and energy-free method, improving the reactivity of ZVI by either WMF superimposition or premagnetization treatment is novel and promising.
2017, 75(6): 552-559
doi: 10.6023/A17020058
Abstract:
Biomineralization, a ubiquitous phenomenon found in nature, is a process of the formation of mineral crystal mediated biologically. However, little information is available on how to consciously regulate and strengthen this biomineralization process with an aim to treat effectively wastewater. Here we develop a novel passive biomineralization-limestone ditch treatment system (PBDTS) for purifying toxic metal-containing acid mine drainages (AMD) generated in many mines. It is well documented that the treatment of AMD by traditional passive limestone ditch treatment system (PLDTS) consume a large amount of lime and consequently produce many toxic residue to be treated due to high concentration of dissolved iron and sulphate in AMD. In the paper, Acidithiobacillus ferrooxidans biofilm formed in elastic filler packed in AMD will oxide Fe2+in AMD into Fe3+ and subsequently form biogenic schwertmannite[Fe8O8(OH)6SO4]. Newly formed schwertmannite as a crystal seed will grow by self and scavenge, to a great extent, most of toxic metalloid As and a few of heavy metal cation through co-precipitation and/or adsorption processes. The remaining non-mineralized Fe3+ is reduced to Fe2+ by Acidiphilic iron-reducing bacterial (Acidiphilium sp.) immobilized in slow-release organic carbon-source material filled in next stage of AMD ditch. The resulting Fe2+ from the biological reduction of Fe3+ are re-oxidized by Acidithiobacillus ferrooxidans and hydrolyzed to form schwertmannite through several oxidizing-reducing cycles. As a result, most of soluble Fe and sulphate in AMD can be removed and recovered in the form of schwertmannite in acidic AMD environment. The effluent of AMD pretreated by biomineralization could be neutralized and easily reach a water quality standard by China only with a few of lime. The results from simulation test showed that such a novel PBDTS could save more than 80% of lime requirement amount and produce less than 10% of toxic neutralized residues with comparison to traditional PLDTS. Moreover, the levels of nonferrous metals in the neutralized residues obtained in PBDTS are more than 10 times higher than that in PLDTS. Therefore, the neutralized residues obtained in PBDTS could be considered as nonferrous metal mine to be exploited. Undoubtedly, more attention should be paid to the role of biomineralization in wastewater treatment. Finally, future research needs are proposed in the paper.
Biomineralization, a ubiquitous phenomenon found in nature, is a process of the formation of mineral crystal mediated biologically. However, little information is available on how to consciously regulate and strengthen this biomineralization process with an aim to treat effectively wastewater. Here we develop a novel passive biomineralization-limestone ditch treatment system (PBDTS) for purifying toxic metal-containing acid mine drainages (AMD) generated in many mines. It is well documented that the treatment of AMD by traditional passive limestone ditch treatment system (PLDTS) consume a large amount of lime and consequently produce many toxic residue to be treated due to high concentration of dissolved iron and sulphate in AMD. In the paper, Acidithiobacillus ferrooxidans biofilm formed in elastic filler packed in AMD will oxide Fe2+in AMD into Fe3+ and subsequently form biogenic schwertmannite[Fe8O8(OH)6SO4]. Newly formed schwertmannite as a crystal seed will grow by self and scavenge, to a great extent, most of toxic metalloid As and a few of heavy metal cation through co-precipitation and/or adsorption processes. The remaining non-mineralized Fe3+ is reduced to Fe2+ by Acidiphilic iron-reducing bacterial (Acidiphilium sp.) immobilized in slow-release organic carbon-source material filled in next stage of AMD ditch. The resulting Fe2+ from the biological reduction of Fe3+ are re-oxidized by Acidithiobacillus ferrooxidans and hydrolyzed to form schwertmannite through several oxidizing-reducing cycles. As a result, most of soluble Fe and sulphate in AMD can be removed and recovered in the form of schwertmannite in acidic AMD environment. The effluent of AMD pretreated by biomineralization could be neutralized and easily reach a water quality standard by China only with a few of lime. The results from simulation test showed that such a novel PBDTS could save more than 80% of lime requirement amount and produce less than 10% of toxic neutralized residues with comparison to traditional PLDTS. Moreover, the levels of nonferrous metals in the neutralized residues obtained in PBDTS are more than 10 times higher than that in PLDTS. Therefore, the neutralized residues obtained in PBDTS could be considered as nonferrous metal mine to be exploited. Undoubtedly, more attention should be paid to the role of biomineralization in wastewater treatment. Finally, future research needs are proposed in the paper.
2017, 75(6): 560-574
doi: 10.6023/A17010039
Abstract:
With the widespread using of nuclear energy, the nuclear technology is developed rapidly and the radionuclide pollution such as uranium has become the serious problem for human health. Nanoscale Zero-Valent Iron (nZVI) has become the excellent adsorbent for the removal of uranium ions from environment because of its low cost, easy preparation, high surface-activity and excellent performance for adsorption of uranium. Due to synergistic effect of each monomer, the nZVI nanocomposites have been applied to remove radionuclides and the adsorption capacity of nZVI nanocomposites are improved to a further level. Hence, the preparation of nZVI and its nanocomposites for the efficient removal of radionuclides is one of the hot issues in the field of environmental science. The aim of this review is to summarize and outlook the recent research on the application of nZVI nanocomposites for the efficient removal of radioactive uranium from environment. The preparation of nZVI and its composites, the removal efficiency and removal mechanism has been summarized, and the application of the nZVI nanocomposites in environmental pollution cleanup has also been discussed, expecting for the reference of practical application and future research.
With the widespread using of nuclear energy, the nuclear technology is developed rapidly and the radionuclide pollution such as uranium has become the serious problem for human health. Nanoscale Zero-Valent Iron (nZVI) has become the excellent adsorbent for the removal of uranium ions from environment because of its low cost, easy preparation, high surface-activity and excellent performance for adsorption of uranium. Due to synergistic effect of each monomer, the nZVI nanocomposites have been applied to remove radionuclides and the adsorption capacity of nZVI nanocomposites are improved to a further level. Hence, the preparation of nZVI and its nanocomposites for the efficient removal of radionuclides is one of the hot issues in the field of environmental science. The aim of this review is to summarize and outlook the recent research on the application of nZVI nanocomposites for the efficient removal of radioactive uranium from environment. The preparation of nZVI and its composites, the removal efficiency and removal mechanism has been summarized, and the application of the nZVI nanocomposites in environmental pollution cleanup has also been discussed, expecting for the reference of practical application and future research.
2017, 75(6): 575-582
doi: 10.6023/A17020045
Abstract:
Nanoscale zero-valent iron (NZVI), an environmental remediation agent derived from wide range of raw materials, has been extensively applied in the field of remedying polluted water environment such as groundwater and wastewater. Although NZVI possesses some advantages such as excellent reaction activity, low cost and low toxicity, the limitation of in-situ remediation and storage concerning this kind of material has not been completely overcome yet. Among methods to improve the practical application of NZVI in water environment, sulfidation has become a research hotspot over recent decade. This means that the focus of modifying NZVI has shifted from reaction activity to electron selectivity. Most of the preparation methods of sulfidated NZVI belong to the chemical approach. These sulfidated materials have been heavily used to degrade organic pollutants and remove heavy metals in water to test their practical reactivity. Reaction mechanisms of pollutants and sulfidated NZVI in different environmental systems have also been extensively investigated. Hereinto, according to the species of organic pollutants and the reaction conditions, these reaction mechanisms can be roughly divided into three categories, including adsorption, reduction, and oxidation. In recent years, it is noted that sulfidated NZVI has made great progress to enhance the reaction activity and electrons selectivity, though it still has some limitations in the practical application. It is necessary to thoroughly review recent research progress about the reaction activities of sulfidated NZVI and its reaction mechanisms with pollutants in water, because it can clearly figure out new directions towards future development of sulfidated NZVI application. Due to the superior properties of sulfidated zero-valent iron, this material and relevant iron sulfide-based materials are going to belong to the most important functional materials in the field of environmental remediation with promising development prospect.
Nanoscale zero-valent iron (NZVI), an environmental remediation agent derived from wide range of raw materials, has been extensively applied in the field of remedying polluted water environment such as groundwater and wastewater. Although NZVI possesses some advantages such as excellent reaction activity, low cost and low toxicity, the limitation of in-situ remediation and storage concerning this kind of material has not been completely overcome yet. Among methods to improve the practical application of NZVI in water environment, sulfidation has become a research hotspot over recent decade. This means that the focus of modifying NZVI has shifted from reaction activity to electron selectivity. Most of the preparation methods of sulfidated NZVI belong to the chemical approach. These sulfidated materials have been heavily used to degrade organic pollutants and remove heavy metals in water to test their practical reactivity. Reaction mechanisms of pollutants and sulfidated NZVI in different environmental systems have also been extensively investigated. Hereinto, according to the species of organic pollutants and the reaction conditions, these reaction mechanisms can be roughly divided into three categories, including adsorption, reduction, and oxidation. In recent years, it is noted that sulfidated NZVI has made great progress to enhance the reaction activity and electrons selectivity, though it still has some limitations in the practical application. It is necessary to thoroughly review recent research progress about the reaction activities of sulfidated NZVI and its reaction mechanisms with pollutants in water, because it can clearly figure out new directions towards future development of sulfidated NZVI application. Due to the superior properties of sulfidated zero-valent iron, this material and relevant iron sulfide-based materials are going to belong to the most important functional materials in the field of environmental remediation with promising development prospect.
2017, 75(6): 583-593
doi: 10.6023/A17010021
Abstract:
Iron-bearing minerals are widespread in soil and subsurface environment where they support microbial growth and metabolisms by serving as the terminal electron acceptors for microbial anaerobic respiration; the electron donors and energy sources for microbial autotrophic growth; the conductors for mediating electron transfer between microbial cells and the electron storage materials. Because microbial cell envelope is neither permeable to iron-bearing minerals nor electrical conductive, microorganisms have evolved capabilities to exchange electrons between the microbial cytoplasmic membrane and the minerals external to the microbial cells (i.e., microbial extracellular electron transfer). Microbial extracellular electron transfer differs fundamentally from the microbial electron transport chain for aerobic respiration. In this review, we discussed the molecular underpinnings of microbial extracellular electron transfer with iron-bearing minerals and applications of the related microorganisms in remediation of environmental contaminants, production of novel nano-materials, biomining and bioenergy production.
Iron-bearing minerals are widespread in soil and subsurface environment where they support microbial growth and metabolisms by serving as the terminal electron acceptors for microbial anaerobic respiration; the electron donors and energy sources for microbial autotrophic growth; the conductors for mediating electron transfer between microbial cells and the electron storage materials. Because microbial cell envelope is neither permeable to iron-bearing minerals nor electrical conductive, microorganisms have evolved capabilities to exchange electrons between the microbial cytoplasmic membrane and the minerals external to the microbial cells (i.e., microbial extracellular electron transfer). Microbial extracellular electron transfer differs fundamentally from the microbial electron transport chain for aerobic respiration. In this review, we discussed the molecular underpinnings of microbial extracellular electron transfer with iron-bearing minerals and applications of the related microorganisms in remediation of environmental contaminants, production of novel nano-materials, biomining and bioenergy production.
2017, 75(6): 594-601
doi: 10.6023/A17030099
Abstract:
Arsenic (As(Ⅲ/Ⅴ)) and selenium (Se(Ⅳ/Ⅵ)) are toxic inorganic contaminants in groundwater and industrial wastewater. The pollution caused by As and Se has become an environmental concern throughout the world. A variety of treatment technologies have been applied for As and Se removal from aqueous solutions. Among them, nanoscale zero-valent iron (nZⅥ) has been found to have a remarkable capability to remove As and Se from waters. Although lots of studies on the process of As and Se removal with nZⅥ are published, a systematic comparative study is still limited. In this study, the removal capacities of As(Ⅲ), As(Ⅴ), Se(Ⅳ) and Se(Ⅵ) with nZⅥ in a single-specie system were compared. The performances of nZⅥ for As(Ⅲ), As(Ⅴ), Se(Ⅳ) and Se(Ⅵ) were investigated on different conditions (including dissolved oxygen, nZⅥ dosage, contact time, and initial solution pH). The morphology and structure of fresh and spent nZⅥ were also examined by spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) intergrated with energy-dispersive X-ray spectrometry (XEDS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The batch experiments were conducted at room temperature in the 50-mL glass vials sealed with screwcaps. According to the speciation diagram, H3AsO30 and H2AsO4- are the respective predominant dissolved As(Ⅲ) and As(Ⅴ) species respectively at pH 5.0; while HSeO3- and SeO42- are the predominant dissolved Se(Ⅳ) and Se(Ⅵ) species respectively at pH 5.0. The results showed that the removal capacities of As and Se investigated generally followed the order of Se(Ⅳ)> As(Ⅲ)> Se(Ⅵ)> As(Ⅴ). Dissolved oxygen (DO) was found no apparent effects on the removal of As(Ⅲ) and Se(Ⅳ), while the removal performance of As(Ⅴ) and Se(Ⅵ) was inhibited at high dissolved oxygen level (>14 mg/L). The removal of As and Se were enhanced with increasing nZⅥ dosage. Initial solution pH had no significant effect on Se(Ⅳ) removal, whereas the removal of As(Ⅲ), As(Ⅴ), and Se(Ⅵ) appeared to be strongly dependent on the initial solution pH. The spent nZⅥ were different due to the different mechanisms of As(Ⅲ/Ⅴ) and Se(Ⅳ/Ⅵ) reactions with nZⅥ. The results will be useful for the application of nZⅥ to the treatment of As/Se-containing wastewater.
Arsenic (As(Ⅲ/Ⅴ)) and selenium (Se(Ⅳ/Ⅵ)) are toxic inorganic contaminants in groundwater and industrial wastewater. The pollution caused by As and Se has become an environmental concern throughout the world. A variety of treatment technologies have been applied for As and Se removal from aqueous solutions. Among them, nanoscale zero-valent iron (nZⅥ) has been found to have a remarkable capability to remove As and Se from waters. Although lots of studies on the process of As and Se removal with nZⅥ are published, a systematic comparative study is still limited. In this study, the removal capacities of As(Ⅲ), As(Ⅴ), Se(Ⅳ) and Se(Ⅵ) with nZⅥ in a single-specie system were compared. The performances of nZⅥ for As(Ⅲ), As(Ⅴ), Se(Ⅳ) and Se(Ⅵ) were investigated on different conditions (including dissolved oxygen, nZⅥ dosage, contact time, and initial solution pH). The morphology and structure of fresh and spent nZⅥ were also examined by spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) intergrated with energy-dispersive X-ray spectrometry (XEDS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The batch experiments were conducted at room temperature in the 50-mL glass vials sealed with screwcaps. According to the speciation diagram, H3AsO30 and H2AsO4- are the respective predominant dissolved As(Ⅲ) and As(Ⅴ) species respectively at pH 5.0; while HSeO3- and SeO42- are the predominant dissolved Se(Ⅳ) and Se(Ⅵ) species respectively at pH 5.0. The results showed that the removal capacities of As and Se investigated generally followed the order of Se(Ⅳ)> As(Ⅲ)> Se(Ⅵ)> As(Ⅴ). Dissolved oxygen (DO) was found no apparent effects on the removal of As(Ⅲ) and Se(Ⅳ), while the removal performance of As(Ⅴ) and Se(Ⅵ) was inhibited at high dissolved oxygen level (>14 mg/L). The removal of As and Se were enhanced with increasing nZⅥ dosage. Initial solution pH had no significant effect on Se(Ⅳ) removal, whereas the removal of As(Ⅲ), As(Ⅴ), and Se(Ⅵ) appeared to be strongly dependent on the initial solution pH. The spent nZⅥ were different due to the different mechanisms of As(Ⅲ/Ⅴ) and Se(Ⅳ/Ⅵ) reactions with nZⅥ. The results will be useful for the application of nZⅥ to the treatment of As/Se-containing wastewater.
2017, 75(6): 602-607
doi: 10.6023/A17010004
Abstract:
As a persistent chlorinated organic pollutant, Atrazine (2-chloro-4-(ethylamino)-6-isopropylamino-s-triazine) in the environment brings harm to natural environment as well as the human health. Since Atrazine is difficult to be degraded biologically, various strategies have been developed to realize efficient and environmentally-friendly removal of Atrazine. Recently, nanoscaled iron has been extensively applied for the remediation/treatment of wastewater contaminated with various organic and inorganic pollutants and exhibits superior activity than that of bulk iron. But its removal efficiency would decrease along with reaction time. In this study, we report that copper ions could efficiently promote atrazine degradation with Fe@Fe2O3 nanowires via the molecular oxygen activation processes. As indicated by the electron spin resonance analysis (ESR) and X-ray photoelectron spectroscopic analysis (XPS) results, the addition of Cu2+ ions could promote the release of dissolved Fe(Ⅱ) from Fe@Fe2O3. During the degradation process, the concentration of Fe(Ⅱ) in the solution with Cu2+ ions is maintained at a much higher level than that without Cu2+ ions. At the same time, Cu2+ ions were reduced to low valence states (Cu0), which further promoted the release of Fe2+. The generated Fe2+ would then activate the molecular oxygen via the single-electron or double-electron transfer route. As a result, more reactive oxygen species such as ·OH were generated to degrade atrazine. Under room temperature and aerobic condition, the Atrazine removal rate constant in Fe@Fe2O3/Cu2+ system was 0.694 h-1, which was almost 23 times that in Fe@Fe2O3 system. Moreover, the Fe@Fe2O3/Cu2+ catalytic system also remains superior activity in the pH range of 2~5. The intermediates of atrazine degradation were detected and the atrazine degradation in the Fe@Fe2O3/Cu2+ catalytic system was accompanied with alkylic oxidation, dealkylation and dechlorination. This study provides a new way to enhance molecular oxygen activation by core-shell Fe@Fe2O3 nanowires, and also deepens our understanding of the molecular oxygen activation processes by Fe@Fe2O3 for the aerobic pollutant degradation.
As a persistent chlorinated organic pollutant, Atrazine (2-chloro-4-(ethylamino)-6-isopropylamino-s-triazine) in the environment brings harm to natural environment as well as the human health. Since Atrazine is difficult to be degraded biologically, various strategies have been developed to realize efficient and environmentally-friendly removal of Atrazine. Recently, nanoscaled iron has been extensively applied for the remediation/treatment of wastewater contaminated with various organic and inorganic pollutants and exhibits superior activity than that of bulk iron. But its removal efficiency would decrease along with reaction time. In this study, we report that copper ions could efficiently promote atrazine degradation with Fe@Fe2O3 nanowires via the molecular oxygen activation processes. As indicated by the electron spin resonance analysis (ESR) and X-ray photoelectron spectroscopic analysis (XPS) results, the addition of Cu2+ ions could promote the release of dissolved Fe(Ⅱ) from Fe@Fe2O3. During the degradation process, the concentration of Fe(Ⅱ) in the solution with Cu2+ ions is maintained at a much higher level than that without Cu2+ ions. At the same time, Cu2+ ions were reduced to low valence states (Cu0), which further promoted the release of Fe2+. The generated Fe2+ would then activate the molecular oxygen via the single-electron or double-electron transfer route. As a result, more reactive oxygen species such as ·OH were generated to degrade atrazine. Under room temperature and aerobic condition, the Atrazine removal rate constant in Fe@Fe2O3/Cu2+ system was 0.694 h-1, which was almost 23 times that in Fe@Fe2O3 system. Moreover, the Fe@Fe2O3/Cu2+ catalytic system also remains superior activity in the pH range of 2~5. The intermediates of atrazine degradation were detected and the atrazine degradation in the Fe@Fe2O3/Cu2+ catalytic system was accompanied with alkylic oxidation, dealkylation and dechlorination. This study provides a new way to enhance molecular oxygen activation by core-shell Fe@Fe2O3 nanowires, and also deepens our understanding of the molecular oxygen activation processes by Fe@Fe2O3 for the aerobic pollutant degradation.
2017, 75(6): 608-616
doi: 10.6023/A17020046
Abstract:
Green rusts can coexist with As(Ⅴ) in some anoxic environments, such as soils, sediments, and groundwater, the interaction between them will affect the transformation of green rusts and the environmental behaviors of As(Ⅴ), but the influences of As(Ⅴ) on the processes and mechanisms of green rust transformation have not been fully understood. In this study, the effects of As(Ⅴ) concentration, pH, temperature, and air rate on hydrosulfate green rust (GR2(SO42-), GR) transformation have been systematically studied by solution chemistry methods combined with spectroscopic analysis, including synchrotron based X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and As K-edge X-ray absorption near edge structure (XANES) spectroscopy. GR shows extremely strong removal capability of As(Ⅴ) via adsorption and co-precipitation during its transformation, meanwhile the presence of As(Ⅴ) increases the stability of GR and significantly affects the crystallinity and phases of the transformation products and the transformation mechanisms. With increasing the As(Ⅴ) concentration (0~20 mmol/L As) at pH 7.3 and 25℃ under open and stirring conditions, the mechanisms change from dissolution-oxidation-precipitation (DOP) to solid state oxidation (SSO), and the transformation products of GR change from mixed phases of goethite and lepidocrocite to pure lepidocrocite to mixed phases of poorly crystalline lepidocrocite, ferrihydrite, and ferric GR, and their crystallinity gradually decreases. The transformation processes of GR exhibit strong accumulation capability towards As(Ⅴ), leading to the formation of amorphous FeAsO4 surface precipitation at high As(Ⅴ) concentrations (Fe/As molar ratio < 24). When the molar ratio of Fe/As=24, lepidocrocite is the main product at the conditions of pH 6.5~9, temperature of 5~45℃, and air rate of 0~0.05 m3/h, its crystallinity decreases with increasing pH and air rate or decreasing temperature. High pH and air rate, and low temperature favors the formation of ferric GR (same structure with GR but only contains Fe(Ⅲ)) and ferrihydrite, while high temperature favors the formation of goethite. These new insights provide important implications for understanding the formation and transformation mechanisms of various iron oxides and the environmental behaviors of As(Ⅴ).
Green rusts can coexist with As(Ⅴ) in some anoxic environments, such as soils, sediments, and groundwater, the interaction between them will affect the transformation of green rusts and the environmental behaviors of As(Ⅴ), but the influences of As(Ⅴ) on the processes and mechanisms of green rust transformation have not been fully understood. In this study, the effects of As(Ⅴ) concentration, pH, temperature, and air rate on hydrosulfate green rust (GR2(SO42-), GR) transformation have been systematically studied by solution chemistry methods combined with spectroscopic analysis, including synchrotron based X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and As K-edge X-ray absorption near edge structure (XANES) spectroscopy. GR shows extremely strong removal capability of As(Ⅴ) via adsorption and co-precipitation during its transformation, meanwhile the presence of As(Ⅴ) increases the stability of GR and significantly affects the crystallinity and phases of the transformation products and the transformation mechanisms. With increasing the As(Ⅴ) concentration (0~20 mmol/L As) at pH 7.3 and 25℃ under open and stirring conditions, the mechanisms change from dissolution-oxidation-precipitation (DOP) to solid state oxidation (SSO), and the transformation products of GR change from mixed phases of goethite and lepidocrocite to pure lepidocrocite to mixed phases of poorly crystalline lepidocrocite, ferrihydrite, and ferric GR, and their crystallinity gradually decreases. The transformation processes of GR exhibit strong accumulation capability towards As(Ⅴ), leading to the formation of amorphous FeAsO4 surface precipitation at high As(Ⅴ) concentrations (Fe/As molar ratio < 24). When the molar ratio of Fe/As=24, lepidocrocite is the main product at the conditions of pH 6.5~9, temperature of 5~45℃, and air rate of 0~0.05 m3/h, its crystallinity decreases with increasing pH and air rate or decreasing temperature. High pH and air rate, and low temperature favors the formation of ferric GR (same structure with GR but only contains Fe(Ⅲ)) and ferrihydrite, while high temperature favors the formation of goethite. These new insights provide important implications for understanding the formation and transformation mechanisms of various iron oxides and the environmental behaviors of As(Ⅴ).
2017, 75(6): 617-620
doi: 10.6023/A17030082
Abstract:
Organic carbon (OC) stability in tropical soils is strongly affected by the mutual interactions of OC, kaolinite and the Fe(Ⅲ) cation. Low molecular weight organic acids (LMWOAs) represent the most biodegradable constituent of OC in soils. Therefore, investigating retention mechanisms of LMWOAs in kaolinite-Fe(Ⅲ)-LMWOAs systems are of significant importance in understanding the sequestration and cycling of OC in tropical soils. However, retention mechanisms of LMWOAs in the kaolinite-Fe(Ⅲ)-LMWOAs system remains unclear, and there is a lack of direct evidence at the molecular level. In this study, citric acid (CA) was chosen as a model compound for LMWOAs and a sorption sample was collected after batch experiment using kaolinite, Fe(Ⅲ), and CA as reagents at pH 3.5 and at an initial Fe/CA molar ratio of 2.0. Synchrotron-based scanning transmission X-ray microspectroscopy (STXM) was applied to characterize the distribution of carbon (C), iron (Fe) and silicon (Si), representing CA, Fe(Ⅲ) cation/Fe hydroxides and kaolinite respectively, at the submicron scale in the sorption sample. After that, the hot spots of C and Fe were selected and further probed by STXM coupled with Near-edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy at the C and Si K-edge and the Fe L3-edge, respectively, to reveal the molecular structures of C, Si and Fe. Our results indicated the similar correlation of C-Fe (R2=0.965) to C-Si (R2=0.960) in the sorption sample, which implied a close relationship between CA and Fe hydroxides as well as kaolinite. We also found two Fe species as ferrihydrite and kaolinite-Fe(Ⅲ)-citrate complex coexisted in the Fe-enriched hot spots probed by STXM coupled with Fe L3-edge NEXAFS spectroscopy. These results provide direct evidence of the contribution of CA retention through ferrihydrite-induced adsorption/coprecipitation and ternary complexation of CA and kaolinite via an Fe bridge in the investigated ternary system. This study will enhance our understanding of the stability of CA and the sequestration and cycling of LMWOAs in tropical soils.
Organic carbon (OC) stability in tropical soils is strongly affected by the mutual interactions of OC, kaolinite and the Fe(Ⅲ) cation. Low molecular weight organic acids (LMWOAs) represent the most biodegradable constituent of OC in soils. Therefore, investigating retention mechanisms of LMWOAs in kaolinite-Fe(Ⅲ)-LMWOAs systems are of significant importance in understanding the sequestration and cycling of OC in tropical soils. However, retention mechanisms of LMWOAs in the kaolinite-Fe(Ⅲ)-LMWOAs system remains unclear, and there is a lack of direct evidence at the molecular level. In this study, citric acid (CA) was chosen as a model compound for LMWOAs and a sorption sample was collected after batch experiment using kaolinite, Fe(Ⅲ), and CA as reagents at pH 3.5 and at an initial Fe/CA molar ratio of 2.0. Synchrotron-based scanning transmission X-ray microspectroscopy (STXM) was applied to characterize the distribution of carbon (C), iron (Fe) and silicon (Si), representing CA, Fe(Ⅲ) cation/Fe hydroxides and kaolinite respectively, at the submicron scale in the sorption sample. After that, the hot spots of C and Fe were selected and further probed by STXM coupled with Near-edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy at the C and Si K-edge and the Fe L3-edge, respectively, to reveal the molecular structures of C, Si and Fe. Our results indicated the similar correlation of C-Fe (R2=0.965) to C-Si (R2=0.960) in the sorption sample, which implied a close relationship between CA and Fe hydroxides as well as kaolinite. We also found two Fe species as ferrihydrite and kaolinite-Fe(Ⅲ)-citrate complex coexisted in the Fe-enriched hot spots probed by STXM coupled with Fe L3-edge NEXAFS spectroscopy. These results provide direct evidence of the contribution of CA retention through ferrihydrite-induced adsorption/coprecipitation and ternary complexation of CA and kaolinite via an Fe bridge in the investigated ternary system. This study will enhance our understanding of the stability of CA and the sequestration and cycling of LMWOAs in tropical soils.
2017, 75(6): 621-628
doi: 10.6023/A17030093
Abstract:
Aqueous Fe(Ⅱ) (Fe(Ⅱ)aq)-catalyzed recrystallization of iron (hydr)oxides is the important chemical reaction of iron cycle in anaerobic environments, which poses significant effects on the environmental behavior of heavy metals in soils and sediments. Ferrihydrite is the initial iron mineral phase during the ferrous mineralization and has relatively unstable crystal structure. The structure transformation behavior of ferrihydrite is active and also poses important effects on environmental behavior of soil heavy metals. However, the Fe(Ⅱ)aq-catalyzed phase transformation of ferrihydrite has been rarely reported, especially with the coexisting metal ions. In the present study, the effects of coexisting heavy metal of Pb(Ⅱ) on the Fe(Ⅱ)aq-catalyzed phase transformation of ferrihydrite coupling the environmental behavior of Pb(Ⅱ) were systematically studied. The results show that ferrihydrite underwent efficient phase transformation rates when catalyzed by Fe(Ⅱ)aq whenever with or without the effect of Pb(Ⅱ). Compared with the reaction system that without Pb(Ⅱ), the adsorption of Fe(Ⅱ) on the surface of ferrihydrite was inhibited due to the competition of Pb(Ⅱ) when with the coexistence of Pb(Ⅱ), which further decreased the rates of Fe atom exchange between Fe(Ⅱ)aq and structural Fe(Ⅲ) of ferrihydrite. With the inhibited Fe atom exchange reaction, the phase transformation rates were relatively decreased and transformation products were changed during the Fe(Ⅱ)aq-catalyzed phase transformation of ferrihydrite. Goethite and magnetite were found to be the final transformed products of iron (hydr)oxides when without Pb(Ⅱ), while lepidocrocite was determined to be the main transformed product with little goethite and magnetite as the other transformed products when with Pb(Ⅱ). During the Fe(Ⅱ)aq-catalyzed phase transformation of ferrihydrite with the coexistence of Pb(Ⅱ), some Pb were stabilized through being incorporated into the structure of ferrihydrite transformed products with the possible mechanisms of occlusion by the crystal lattice and structural incorporation, so as to decrease the activity of the polluted heavy metal of Pb. The obtained results in the present study are expected to provide further insights for understanding the iron cycle coupling with the environmental behavior of heavy metals in soils and sediments.
Aqueous Fe(Ⅱ) (Fe(Ⅱ)aq)-catalyzed recrystallization of iron (hydr)oxides is the important chemical reaction of iron cycle in anaerobic environments, which poses significant effects on the environmental behavior of heavy metals in soils and sediments. Ferrihydrite is the initial iron mineral phase during the ferrous mineralization and has relatively unstable crystal structure. The structure transformation behavior of ferrihydrite is active and also poses important effects on environmental behavior of soil heavy metals. However, the Fe(Ⅱ)aq-catalyzed phase transformation of ferrihydrite has been rarely reported, especially with the coexisting metal ions. In the present study, the effects of coexisting heavy metal of Pb(Ⅱ) on the Fe(Ⅱ)aq-catalyzed phase transformation of ferrihydrite coupling the environmental behavior of Pb(Ⅱ) were systematically studied. The results show that ferrihydrite underwent efficient phase transformation rates when catalyzed by Fe(Ⅱ)aq whenever with or without the effect of Pb(Ⅱ). Compared with the reaction system that without Pb(Ⅱ), the adsorption of Fe(Ⅱ) on the surface of ferrihydrite was inhibited due to the competition of Pb(Ⅱ) when with the coexistence of Pb(Ⅱ), which further decreased the rates of Fe atom exchange between Fe(Ⅱ)aq and structural Fe(Ⅲ) of ferrihydrite. With the inhibited Fe atom exchange reaction, the phase transformation rates were relatively decreased and transformation products were changed during the Fe(Ⅱ)aq-catalyzed phase transformation of ferrihydrite. Goethite and magnetite were found to be the final transformed products of iron (hydr)oxides when without Pb(Ⅱ), while lepidocrocite was determined to be the main transformed product with little goethite and magnetite as the other transformed products when with Pb(Ⅱ). During the Fe(Ⅱ)aq-catalyzed phase transformation of ferrihydrite with the coexistence of Pb(Ⅱ), some Pb were stabilized through being incorporated into the structure of ferrihydrite transformed products with the possible mechanisms of occlusion by the crystal lattice and structural incorporation, so as to decrease the activity of the polluted heavy metal of Pb. The obtained results in the present study are expected to provide further insights for understanding the iron cycle coupling with the environmental behavior of heavy metals in soils and sediments.
2017, 75(6): 629-636
doi: 10.6023/A17010018
Abstract:
The influence mechanism of natural organic matter (NOM) on the removal of contaminant by iron-based nanomaterials remains controversial. In this study, the effect of humic acid (representing NOM) on the degradation of decabromodiphenyl ether (BDE209) by biochar supported Ni/Fe nanoparticles (BC@Ni/Fe) were investigated, which indicated that the removal of BDE209 by BC@Ni/Fe was inhibited in the presence of HA, and with the increase of HA concentration, the inhibitory effect showed more significant. The interaction between HA and BC@Ni/Fe shown that HA was quickly adsorbed on the BC@Ni/Fe. The results of the Zeta potential and sedimentation experiment of BC@Ni/Fe showed that the stability and surface charge of BC@Ni/Fe were effectively improved with the increase of HA concentration, indicating that the inhibitory effect of HA in the debromination of BDE209 by BC@Ni/Fe was not through inhibiting the performance of nanoparticles by HA. The corrosion capacity of BC@Ni/Fe decreased with the increase of HA, which did positively correlate with the effect of HA on the reactivity of BC@Ni/Fe in the removal of BDE209. Additionally, those typical quinone compounds in HA (lawsone and AQDS), which have the electron transfer function, did not serve as an electron transfer medium to directly participating in the reaction process, on the contrary, those compounds did adversely effect on the removal of BDE209. In the coexisting system of HA and BDE209, the equilibrium adsorption capacity of HA on BC@Ni/Fe was 4.75 mg/g. Conversely, the adsorption quantities of BDE209 on BC@Ni/Fe in the absence of HA was 0.31 mg/g, which was about 1.3 times higher than that of in the presence of HA (the adsorption quantities of BDE209 was 0.23 mg/g). Moreover, in the coexistent system of HA and BDE209, the kinetic rate constants for the adsorption of HA was 0.1854 min-1, which was approximately 45 times greater than that of BDE209 (0.0041 min-1). It was shown from the analyzed results that the adsorption rate of HA on BC@Ni/Fe was much greater than that of BDE209. Therefore, that is to say, HA could be preferentially adsorbed onto the surface of BC@Ni/Fe. The adsorbed HA coated on the surface of BC@Ni/Fe occupied the active sites, which hindered the nanoparticles to contact with H2O, reduced the corrosion of Fe0, thus inhibited the removal of BDE209.
The influence mechanism of natural organic matter (NOM) on the removal of contaminant by iron-based nanomaterials remains controversial. In this study, the effect of humic acid (representing NOM) on the degradation of decabromodiphenyl ether (BDE209) by biochar supported Ni/Fe nanoparticles (BC@Ni/Fe) were investigated, which indicated that the removal of BDE209 by BC@Ni/Fe was inhibited in the presence of HA, and with the increase of HA concentration, the inhibitory effect showed more significant. The interaction between HA and BC@Ni/Fe shown that HA was quickly adsorbed on the BC@Ni/Fe. The results of the Zeta potential and sedimentation experiment of BC@Ni/Fe showed that the stability and surface charge of BC@Ni/Fe were effectively improved with the increase of HA concentration, indicating that the inhibitory effect of HA in the debromination of BDE209 by BC@Ni/Fe was not through inhibiting the performance of nanoparticles by HA. The corrosion capacity of BC@Ni/Fe decreased with the increase of HA, which did positively correlate with the effect of HA on the reactivity of BC@Ni/Fe in the removal of BDE209. Additionally, those typical quinone compounds in HA (lawsone and AQDS), which have the electron transfer function, did not serve as an electron transfer medium to directly participating in the reaction process, on the contrary, those compounds did adversely effect on the removal of BDE209. In the coexisting system of HA and BDE209, the equilibrium adsorption capacity of HA on BC@Ni/Fe was 4.75 mg/g. Conversely, the adsorption quantities of BDE209 on BC@Ni/Fe in the absence of HA was 0.31 mg/g, which was about 1.3 times higher than that of in the presence of HA (the adsorption quantities of BDE209 was 0.23 mg/g). Moreover, in the coexistent system of HA and BDE209, the kinetic rate constants for the adsorption of HA was 0.1854 min-1, which was approximately 45 times greater than that of BDE209 (0.0041 min-1). It was shown from the analyzed results that the adsorption rate of HA on BC@Ni/Fe was much greater than that of BDE209. Therefore, that is to say, HA could be preferentially adsorbed onto the surface of BC@Ni/Fe. The adsorbed HA coated on the surface of BC@Ni/Fe occupied the active sites, which hindered the nanoparticles to contact with H2O, reduced the corrosion of Fe0, thus inhibited the removal of BDE209.
2017, 75(6): 637-644
doi: 10.6023/A17020056
Abstract:
Iron oxides and kaolinite are the main sources of variable charges in the red soil. As a result of being protonated and deprotonated under different acid-base conditions, the surface hydroxyl groups can buffer the pH changes of red soil. In this study, iron oxide and kaolinite were titrated by the standard HCl and NaOH solution through the auto potentiometric titration under the controlled pH=2.9~9.5, to study the surface charge of soil minerals. The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and N2 desorption/adsorption isotherms (BET) were used to characterize the crystal structures, surface groups and specific surface areas of soil minerals. Based on the characterization data and titration curves, the acid-base properties of the minerals were analyzed by using 1-site/2-pK surface complexation model. The Gran plot method, commonly used to determine the equivalence points, was applied to calculate the concentration (Hs) and density (Ds) of the surface active sites on the soil minerals. The acid-base equilibrium constants (pKaint) of soil minerals were obtained by extrapolation and the corresponding pHpzc were calculated by the following formula:pHpzc=1/2 (pKa1int+pKa2int). The result of calculated value of pHpzc was nearly equal with the experimental value, which showed that it is feasible to apply this model calculation method on the soil minerals. In addition, the above parameters can explain the acid-base buffer capacity of the minerals quantitatively. The results show that goethite and kaolinite have the higher surface active site concentration. According to the parameters, the surface chemical speciation of minerals at different pH were calculated by Visual Minteq software with the double layer model (DLM) to explain the mechanism of acid-base buffer behavior on the mineral surfaces. Finally, the acid-base titration method and model calculation approach were also used to analyze the acid-base buffer capacity of the natural red soil samples. The feasibility of this method on the red soil was further verified. Then, the surface chemical species (≡SOH2+, ≡SO- and ≡SOH) of the red soil were calculated by surface complex model to further explain their acid-base buffer mechanism.
Iron oxides and kaolinite are the main sources of variable charges in the red soil. As a result of being protonated and deprotonated under different acid-base conditions, the surface hydroxyl groups can buffer the pH changes of red soil. In this study, iron oxide and kaolinite were titrated by the standard HCl and NaOH solution through the auto potentiometric titration under the controlled pH=2.9~9.5, to study the surface charge of soil minerals. The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and N2 desorption/adsorption isotherms (BET) were used to characterize the crystal structures, surface groups and specific surface areas of soil minerals. Based on the characterization data and titration curves, the acid-base properties of the minerals were analyzed by using 1-site/2-pK surface complexation model. The Gran plot method, commonly used to determine the equivalence points, was applied to calculate the concentration (Hs) and density (Ds) of the surface active sites on the soil minerals. The acid-base equilibrium constants (pKaint) of soil minerals were obtained by extrapolation and the corresponding pHpzc were calculated by the following formula:pHpzc=1/2 (pKa1int+pKa2int). The result of calculated value of pHpzc was nearly equal with the experimental value, which showed that it is feasible to apply this model calculation method on the soil minerals. In addition, the above parameters can explain the acid-base buffer capacity of the minerals quantitatively. The results show that goethite and kaolinite have the higher surface active site concentration. According to the parameters, the surface chemical speciation of minerals at different pH were calculated by Visual Minteq software with the double layer model (DLM) to explain the mechanism of acid-base buffer behavior on the mineral surfaces. Finally, the acid-base titration method and model calculation approach were also used to analyze the acid-base buffer capacity of the natural red soil samples. The feasibility of this method on the red soil was further verified. Then, the surface chemical species (≡SOH2+, ≡SO- and ≡SOH) of the red soil were calculated by surface complex model to further explain their acid-base buffer mechanism.
