Effect of Fe(Ⅲ) on the bromate reduction by humic substances in aqueous solution

Humic substances are ubiquitous redox-active organic compounds of environment.In this study,experiments were conducted to determine the reduction capacity of humic acid in the matrix of bromate and Fe(Ⅲ) solutions and the role of Fe(Ⅲ) in this redox process.The results showed that the humic acid regenerated Fe(Ⅱ) and reduced bromate abiotically.The addition of Fe(Ⅲ) could accelerate the bromate reduction rate by forming humic acid-Fe(Ⅲ) complexes.Iron species acts as electron mediator and catalyst for the bromate reduction by humic acid,in which humic acid transfers electrons to the complexed Fe(Ⅲ) to form Fe(Ⅱ),and the regenerated Fe(Ⅱ) donate the electrons to bromate.The kinetics study on bromate reduction further indicated that bromate reduction by humic acid-Fe(Ⅲ) complexes is pH dependent.The rate decreased by 2-fold with the increase in solution pH by one unit.The reduction capacity of Aldrich humic acid was observed to be lower than that of humic acid or natural organic matter of Suwanne River,indicating that such redox process is expected to occur in the environment.     

Effect of organic fractions on sorption properties of organic pollutants in sediments

Humic substrates are a major fraction of sediment organic matters, and the sorption of hydrophobic organic chemicals by humic substrates influences their behavior and fate in sediment. In this paper, organic matters were divided into non-humic substrates and humic substrates. Non-humic substrates include acid leaching fraction, acid extracted fraction, and lipid; humic substrates were fractionated into Ca-binding-FA(fulvic acid), Ca-binding-HA (humic acid), oxide-FA, oxide-HA, and humin. To study the effect of organic fractions on sorption properties, sorption kinetic and equilibrium sorption experiments of phenanthrene and pentachlorophenol(PCP) in five sediments were carried out. The results showed that the contents of acid leaching fraction and oxide-binding-HA were the main fractions to affect the sorption rate constant, and for the sorption capacity of phenanthrene, humin was the major fraction, followed by oxide-binding-HA, oxidebinding-FA, and so on. While for PCP, the factors of influence on sorption capacity were mainly CEC, Ca-binding-FA, and Ca-binding-HA.     

Photo-induced transformations of Hg(Ⅱ) species in the presence of Nitzschia hantzschiana,ferric ion,and humic acid

Effects of algae Nitzschia hantzschiana, Fe(Ⅲ) ions, humic acid, and pH on the photochemical reduction of Hg(Ⅱ) using the irradiation of metal halide lamps (λ 365 nm, 250 W) were investigated. The photoreduction rate of Hg(Ⅱ) was found to increase with increasing concentrations of algae, Fe(Ⅲ) ions, and humic acid. Alteration of pH value affected the photoreduction of Hg(Ⅱ) in aqueous solution with or without algae. The photoreduction rate of Hg(II) decreased with increasing initial Hg(Ⅱ) concentration in aqueous solution in the presence of algae. The photochemical kinetics of initial Hg(Ⅱ) and algae concentrations on the photoreduction of Hg(Ⅱ) were studied at pH 7.0. The study on the total Hg mass balance in terms of photochemical process revealed that more than 42% of Hg(Ⅱ) from the algal suspension was reduced to volatile metallic Hg under the conditions investigated.     

Sorption of Perfluorooctane sulfonate（PFOS） including its isomers on hydrargillite as a function of pH,humic substances and Na2SO4

Perfluorooctane sulfonate（PFOS） is a persistent organic pollutant（POP） and emergent contaminant that are widespread in the environment. Understanding the mechanisms controlling the distribution of PFOS and its isomers between hydrargillite and the water phase is important in order to study their redistribution and mobility in the environment. This study investigated the effects of pH, humic acid, fulvic acid and Na₂SO₄ on sorption of PFOS isomers to hydrargillite. A mixture...     

Preliminary investigation of phosphorus adsorption onto two types of iron oxide-organic matter complexes

Iron oxide(FeO)coated by natural organic matter(NOM)is ubiquitous.The associations of minerals with organic matter(OM)significantly changes their surface properties and reactivity,and thus affect the environmental fate of pollutants,including nutrients(e.g.,phosphorus(P)).In this study,ferrihydrite/goethite-humic acid(FH/GE–HA)complexes were prepared and their adsorption characteristics on P at various p H and ionic strength were investigated.The results indicated that the Fe O–OM complexes showed a decreased P adsorption capacity in comparison with bare Fe O.The maximum adsorption capacity(Q_(max))decreased in the order of FH(22.17 mg/g)FH-HA(5.43 mg/g)GE(4.67 mg/g)GE-HA(3.27 mg/g).After coating with HA,the amorphous FH–HA complex still showed higher P adsorption than the crystalline GE–HA complex.The decreased P adsorption observed might be attributed to changes of the Fe O surface charges caused by OM association.The dependence of P adsorption on the specific surface area of adsorbents suggests that the Fe O component in the complexes is still the main contributor for the adsorption surfaces.The P adsorptions on Fe O–HA complexes decreased with increasing initial p H or decreasing initial ionic strength.A strong dependence of P adsorption on ionic strength and p H may demonstrate that outer-sphere complexes between the OM component on the surface and P possibly coexist with inner-sphere surface complexes between the Fe O component and P.Therefore,previous over-emphasis on the contributions of original minerals to P immobilization possibly over-estimates the P loading capacity of soils,especially in humic-rich areas.     

Dissimilatory Fe(III) reduction characteristics of paddy soil extract cultures treated with glucose or fatty acids

Dissimilatory Fe(Ⅲ) reduction is a universal process with irreplaceable biological and environmental importance in anoxic environments. Our knowledge about Fe(Ⅲ) reduction predominantly comes from pure cultures of dissimilatory Fe(Ⅲ) reducing bacteria (DFRB). The objective of this study was to compare the effects of glucose and a selection of short organic acids (citrate, succinate, pyruvate, propionate, acetate, and formate) on Fe(Ⅲ) reduction via the anaerobic culture of three paddy soil solutions with Fe(OH)3 as the sole electron acceptor. The results showed significant differences in Fe(Ⅲ) reduction among the three paddy soil solutions and suhstrate types. Bacteria from the Sichuan paddy soil responded quickly to substrate supply and showed higher Fe(Ⅲ) reducing activity than the other two soil types. Bacteria in the Jiangxi paddy soil culture solution could not use propionate as a source of electrons for Fe(Ⅲ) reduction. Similarly, bacteria in the Jilin paddy soil culture could not use succinate effectively. Pyruvate was readily used by cultures from all three paddy soil solutions, thus indicating that there were some similarities in substrate utilization by bacteria for Fe(Ⅲ) reduction. The use of glucose and citrate as substrate for dissimilatory Fe(Ⅲ) reduction indicates important ecological implications for this type of anoxic respiration.     

Arsenic mobilization from soils in the presence of herbicides

Arsenic(As) mobilization in soils is a fundamental step controlling its transport and fate,especially in the presence of the co-existing components. In this study, the effect of two commonly used herbicides, glyphosate(PMG) and dicamba, and two competing ions including phosphate and humic acid, on As desorption and release was investigated using batch and column experiments. The batch kinetics results showed that As desorption in the presence of competing factors conformed to the pseudo-second order kinetics at pH range of 5–9. The impact of phosphate on desorption was greatest, followed by PMG. The competitive effect of dicamba and humic acid was at the same level with electrolyte solution. In situ flow cell ATR-FTIR analysis was performed to explore the mechanism of phosphate and PMG impact on As mobilization. The results showed that PMG promoted As(Ⅲ) desorption by competiting for available adsorption sites with no change in As(Ⅲ)complexing structure. On the other hand, phophate changed As(Ⅲ) surface complexes from bidentate to monodentate structures, exhibiting the most siginficant effect on As(Ⅲ)desorption. As(Ⅴ) surface complexes remained unchanged in the presence of PMG and phosphate, implying that the competitive effect for As(Ⅴ) desorption was primarily determined by the available adsorption sites. Long-term(10 days) soil column experiments suggested that the effect of humic acid on As mobilization became pronounced from 3 days(18 PVs). The insights of this study help us understand the transport and fate of As due to herbicides application.     

Electrochemical and spectroscopic characteristics of dissolved organic matter in a forest soil profile

Dissolved organic matter （DOM） represents one of the most mobile and reactive organic compounds in ecosystem and plays an important role in the fate and transport of soil organic pollutants, nutrient cycling and more importantly global climate change. Electrochemical methods were first employed to evaluate DOM redox properties, and spectroscopic approaches were utilized to obtain information concerning its composition and structure. DOM was extracted from a forest soil profile with five horizons. Differential pulse voltammetry indicated that there were more redox-active moieties in the DOM from upper horizons than in that from lower horizons. Cyclic voltammetry further showed that these moieties were reversible in electron transfer. Chronoamperometry was employed to quantify the electron transfer capacity of DOM, including electron acceptor capacity and electron donor capacity, both of which decreased sharply with increasing depth. FT-IR, UV-Vis and fluorescence spectra results suggested that DOM from the upper horizons was enriched with aromatic and humic structures while that from the lower horizons was rich in aliphatic carbon, which supported the findings obtained by electrochemical approaches. Electrochemical approaches combined with spectroscopic methods were applied to evaluate the characteristics of DOM extracted along a forest soil profile. The electrochemical properties of DOM, which can be rapidly and simply obtained, provide insight into the migration and transformation of DOM along a soil profile and will aid in better understanding of the biogeochemical role of DOM in natural environments.     

Redox potential E_H [Se(VI)/Se(IV)] of aqueous extractof soils from Yongshou Kaschin-Beck diseaseregion and the influence by humic acid

The relation between EH [Se(VI)/Se(IV)] and pH of soil aqueous extract in Kaschin-Beck disease region and the effects of natural redox agents, namely humic substances, MnO2 and Fe2+, on the redox property of the system were studied. The results indicated that both humic acid and Fe2+ could enhance the reducibility of Se(VI) and MnO2, a limited oxidizability for Se(IV). Fe2+ showed a weak reducibility only at low pH value. The reducibilities of three sulfur-containing compounds for Se(VI) were in following order:thioglycollic acid > L-cysteine > sulfide     

Effect of dissolved organic matter on sorption and desorption of phenanthrene onto black carbon

Sorption and desorption of phenanthrene （PHE） onto black carbon （BC） extracted from sediments were studied in the presence of three types of dissolved organic matter （DOM）, including L-phenylalanine （L-PH）, peptone and citric acid. The nonlinearity of the sorption isotherms increased in the presence of DOM. The presence of L-PH reduced the sorption capacity and desorption hysteresis because of the solubilization of PHE in L-PH solution. Peptone at 50-500 mg/L also led to a decrease in sorption attributed to solubilization, although the sorbed peptone on the BC surface could slightly increase PHE sorption. Unlike L-PH and peptone, citric acid enhanced the sorption capacity and irreversibility of PHE on BC mainly due to the strong sorption of citric acid on the BC surface. Our results may help to understand the different impacts of DOM on the distribution and transport of PAH in the environment.     

Anaerobic oxidation of arsenite by bioreduced nontronite

The redox state of arsenic controls its toxicity and mobility in the subsurface environment. Understanding the redox reactions of arsenic is particularly important for addressing its environmental behavior. Clay minerals are commonly found in soils and sediments, which are an important host for arsenic. However, limited information is known about the redox reactions between arsenic and structural Fe in clay minerals. In this study, the redox reactions between As(III)/As(V) and structural Fe in nontronite NAu-2 were investigated in anaerobic batch experiments. No oxidation of As(III) was observed by the native Fe(III)-NAu-2. Interestingly, anaerobic oxidation of As(III) to As(V) occurred after Fe(III)-NAu-2 was bioreduced. Furthermore, anaerobic oxidization of As(III) by bioreduced NAu-2 was significantly promoted by increasing Fe(III)-NAu-2 reduction extent and initial As(III) concentrations. Bioreduction of Fe(III)-NAu-2 generated reactive Fe(III)-O-Fe(II) moieties at clay mineral edge sites. Anaerobic oxidation of As(III) was attributed to the strong oxidation activity of the structural Fe(III) within the Fe(III)-O-Fe(II) moieties. Our results provide a potential explanation for the presence of As(V) in the anaerobic subsurface environment. Our findings also highlight that clay minerals can play an important role in controlling the redox state of arsenic in the natural environment.     

Fe(Ⅲ)/苹果酸/H_2O_2体系对有机物的光降解特性研究

系统研究了可见光照射下染料橙黄Ⅱ在Fe(Ⅲ)/苹果酸/H2O2体系中的脱色情况,考查了光源、pH值、Fe(Ⅲ)、苹果酸、H2O2及染料初始浓度等因素对橙黄Ⅱ脱色效率的影响.结果表明,Fe(Ⅲ)/苹果酸/H2O2体系在可见光照射下能有效实现橙黄Ⅱ的脱色,在pH为5.0的条件下仍然具有较强的降解有机物的能力.该体系对橙黄Ⅱ的脱色率高于Fe(Ⅲ)/H2O2体系或Fe(Ⅲ)/苹果酸体系,光反应符合表观一级反应动力学规律.随着光强的增加,橙黄Ⅱ的脱色率增大.太阳光是该体系的有效光源,本体系具有利用太阳光的潜力.     

永寿大骨节病区硒的氧化还原电位及腐殖酸等的影响

以大骨节病病区土壤溶液环境为背景,研究了土壤溶液中E_H[Se(Ⅵ)/Se(Ⅳ)]—pH关系及天然环境中主要的氧化还原剂腐殖酸、MnO_2、Fe~(2+)等对硒氧化还原性质的影响。腐殖酸和Fe~(2+)可提高Se(Ⅵ)/Se(Ⅳ)体系的还原能力,MnO_2对Se(Ⅳ)有一定的氧化作用,而腐殖酸和Fe~(2+)只有在低pH条件下才对Se(Ⅵ)有弱的还原作用。几种含硫化合物还原Se(Ⅵ)的能力依次为:硫代乙醇酸>L-半胱氨酸>硫化物。     

Influence factors for the oxidation of pyrite by oxygen and birnessite in aqueous systems

The oxidation of exposed pyrite causes acid mine drainage, soil acidification, and the release of toxic metal ions. As the important abiotic oxidants in supergene environments, oxygen and manganese oxides participate in the oxidation of pyrite. In this work, the oxidation processes of natural pyrite by oxygen and birnessite were studied in simulated systems, and the influence of pH, Fe(II) and Cr(III) on the intermediates and redox rate was investigated. SO₄^2 − and elemental S were formed as the major and minor products, respectively, during the oxidation processes. Ferric (hydr) oxides including Fe(OH)₃ and goethite were formed with low degree of crystallinity. Low pH and long-term reaction facilitated the formation of goethite and ferric hydroxide, respectively. The rate of pyrite oxidation by birnessite was enhanced in the presence of air (oxygen), and Fe(II) ions played a key role in the redox process. The addition of Fe(II) ions to the reaction system significantly enhanced the oxidation rate of pyrite; however, the presence of Cr(III) ions remarkably decreased the pyrite oxidation rate in aqueous systems. The introduction of Fe(II) ions to form a Fe(III)/Fe(II) redox couple facilitated the electron transfer and accelerated the oxidation rate of pyrite. The present work suggests that isolation from air and decreasing the concentration of Fe(II) ions in aqueous solutions might be effective strategies to reduce the oxidation rate of pyrite in mining soils.     

Determination of photochemically-generated reactive oxygen species (ROS) in natural water

Reactive oxygen species (ROS) can be produced by interactions between sunlight and light-absorbing substances in natural water environment. ROS may participate in the indirect photolysis of trace organic pollutants, therefore resulting in the changing of their environmental fates and ecological risks in natural water system. Bisphenol A (BPA), an endocrine-disrupting chemical, exits widely in natural water. The photodegradation of BPA promoted by ROS (·OH, 1O2, HO2·/O2·-) which were produced on the excitation of ubiquitous constituents (such as nitrate ion, humic substances and Fe(III)-oxalate complexes) in natural water under simulated solar radiation was investigated. Both molecular probe method and electron spin resonance (ESR) test were used for the determine the characterization of generated ROS. It was found that ·OH was photochemically produced with the presence of nitrate ion, humic substances and Fe(III)-oxalate complexes and 1O2 was produced with the presence of humic substances. The steady-state concentrations of ·OH was 1.27×10-14 mol/L in nitrate ion, and the second-order rate constant of BPA with ·OH was 1.01×1010L/( mol·s).     

聚合氯化铁对浊度和腐殖酸的絮凝特性研究

采用聚合氯化铁(PFC)絮凝剂在不同pH条件下处理高岭土悬浮液和腐殖酸溶液, 测试了絮凝过程中的Zeta电位、浊度和腐殖酸的去除率变化.结果表明:pH=4时, PFC投加量最小, 剩余浊度最大,投加范围最窄;pH=7时次之;pH=10时由于Fe(Ⅲ)离子的正电荷减弱, 电中和能力不强, 而且同时产生Fe(OH)₃(s)的吸附作用使得剩余浊度最低, 投加范围最宽, 但投加量很大;在酸性条件下腐殖酸与Fe(Ⅲ)离子最容易发生络合反应;腐殖酸的存在并没有影响PFC的絮凝效果.     

三种修复剂对铬污染土壤的修复效果

采用淋溶土柱的方式,探讨醋糟、醋糟+腐殖酸、醋糟+不锈钢尾渣三种修复剂对铬污染土壤的修复效果。结果表明:三种修复剂均能促进土壤Cr(Ⅵ)的还原,增强土壤对铬的固定能力,降低土壤的有效铬含量。其中,施加醋糟的效果要优于醋糟与不锈钢尾渣及腐殖酸的配施,且醋糟+不锈钢尾渣的修复效果要优于醋糟+腐殖酸。施加醋糟,Cr(Ⅵ)的还原率可达56.38%,总铬含量可增加95.08%;醋糟+不锈钢尾渣还原率可达47.94%,总铬含量可增加89.66%;醋糟+腐殖酸还原率可达到27.17%,总铬含量可增加39.78%。经过三种修复剂处理,土壤有机质含量及阳离子交换量显著增加,土壤氧化还原电位及有效铬含量显著下降。采用醋糟和醋糟+腐殖酸处理后可降低土壤pH值,而醋糟+不锈钢尾渣可提高土壤pH值。