Mechanistic insights into sequestration of U(VI) toward magnetic biochar: Batch, XPS and EXAFS techniques

The magnetic iron oxide(Fe_3O_4) nanoparticles stabilized on the biochar were synthesized by fast pyrolysis of Fe(II)-loaded hydrophyte biomass under N_2 conditions. The batch experiments showed that magnetic biochar presented a large removal capacity(54.35 mg/g)at pH 3.0 and 293 K. The reductive co-precipitation of U(VI) to U(IV) by magnetic biochar was demonstrated according to X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption near edge structure analysis. According to extended X-ray absorption fine structure analysis, the occurrence of U-Fe and U-U shells indicated that high effective removal of uranium was primarily inner-sphere coordination and then reductive co-precipitation at low pH. These observations provided the further understanding of uranium removal by magnetic materials in environmental remediation.     

Microbial reduction of uranium (VI) by Bacillus sp. dwc-2: A macroscopic and spectroscopic study

The microbial reduction of U(VI) by Bacillus sp. dwc-2, isolated from soil in Southwest China, was explored using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). Our studies indicated that approximately 16.0% of U(VI) at an initial concentration of 100 mg/L uranium nitrate could be reduced by Bacillus sp. dwc-2 at pH 8.2 under anaerobic conditions at room temperature. Additionally, natural organic matter (NOM) played an important role in enhancing the bioreduction of U(VI) by Bacillus sp. dwc-2. XPS results demonstrated that the uranium presented mixed valence states (U(VI) and U(IV)) after bioreduction, which was subsequently confirmed by XANES. Furthermore, the TEM and high resolution transmission electron microscopy (HRTEM) analysis suggested that the reduced uranium was bioaccumulated mainly within the cell and as a crystalline structure on the cell wall. These observations implied that the reduction of uranium may have a significant effect on its fate in the soil environment in which these bacterial strains occur.     

Distribution and mode of occurrence of uranium in bottom ash derived from high-germanium coals

The radioactivity of uranium in radioactive coal bottom ash(CBA) may be a potential danger to the ambient environment and human health. Concerning the limited research on the distribution and mode of occurrence of uranium in CBA, we herein report our investigations into this topic using a number of techniques including a five-step Tessier sequential extraction, hydrogen fluoride(HF) leaching, Siroquant(Rietveld) quantification, magnetic separation, and electron probe microanalysis(EPMA). The Tessier sequential extraction showed that the uranium in the residual and Fe–Mn oxide fractions was dominant(59.1%and 34.9%, respectively). The former was mainly incorporated into aluminosilicates,retained with glass and cristobalite, whereas the latter was especially enriched in the magnetic fraction, of which about 50% was present with magnetite(Fe_3O_4) and the rest in other iron oxides. In addition, the uranium in the magnetic fraction was 2.6 times that in the non-magnetic fraction. The experimental findings in this work may be important for establishing an effective strategy to reduce radioactivity from CBA for the protection of our local environment.     

Microbial reduction of uranium(Ⅵ) by Bacillus sp.dwc-2:A macroscopic and spectroscopic study

The microbial reduction of U(VI) by Bacillus sp. dwc-2, isolated from soil in Southwest China,was explored using transmission electron microscopy(TEM), X-ray photoelectron spectroscopy(XPS) and X-ray absorption near edge spectroscopy(XANES). Our studies indicated that approximately 16.0% of U(VI) at an initial concentration of 100 mg/L uranium nitrate could be reduced by Bacillus sp. dwc-2 at pH 8.2 under anaerobic conditions at room temperature.Additionally, natural organic matter(NOM) played an important role in enhancing the bioreduction of U(VI) by Bacillus sp. dwc-2. XPS results demonstrated that the uranium presented mixed valence states(U(VI) and U(IV)) after bioreduction, which was subsequently confirmed by XANES. Furthermore, the TEM and high resolution transmission electron microscopy(HRTEM) analysis suggested that the reduced uranium was bioaccumulated mainly within the cell and as a crystalline structure on the cell wall.These observations implied that the reduction of uranium may have a significant effect on its fate in the soil environment in which these bacterial strains occur.     

Visualizing different uranium oxidation states during the surface alteration of uraninite and uranium tetrachloride

Low-temperature alteration reactions on uranium phases may lead to the mobilization of uranium and thereby poses a potential threat to humans living close to uranium-contaminated sites. In this study, the surface alteration of uraninite (UO₂) and uranium tetrachloride (UCl₄) in air atmosphere was studied by confocal laser scanning microscopy (CLSM) and laser-induced fluorescence spectroscopy using an excitation wavelength of 408 nm. It was found that within minutes the oxidation state on the surface of the uraninite and the uranium tetrachloride changed. During the surface alteration process U(IV) atoms on the uraninite and uranium tetrachloride surface became stepwise oxidized by a one-electron step at first to U(V) and then further to U(VI). These observed changes in the oxidation states of the uraninite surface were microscopically visualized and spectroscopically identified on the basis of their fluorescence emission signal. A fluorescence signal in the wavelength range of 415–475 nm was indicative for metastable uranium(V), and a fluorescence signal in the range of 480–560 nm was identified as uranium(VI). In addition, the oxidation process of tetravalent uranium in aqueous solution at pH 0.3 was visualized by CLSM and U(V) was fluorescence spectroscopically identified. The combination of microscopy and fluorescence spectroscopy provided a very convincing visualization of the brief presence of U(V) as a metastable reaction intermediate and of the simultaneous coexistence of the three states U(IV), U(V), and U(VI). These results have a significant importance for fundamental uranium redox chemistry and should contribute to a better understanding of the geochemical behavior of uranium in nature. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Enhanced U(VI) bioreduction by alginate-immobilized uranium-reducing bacteria in the presence of carbon nanotubes and anthraquinone-2,6-disulfonate

Uranium-reducing bacteria were immobilized with sodium alginate, anthraquinone-2, 6-disulfonate (AQDS), and carbon nanotubes (CNTs). The effects of different AQDS-CNTs contents, U(IV) concentrations, and metal ions on U(IV) reduction by immobilized beads were examined. Over 97.5% U(VI) (20 mg/L) was removed in 8 hr when the beads were added to 0.7% AQDS-CNTs, which was higher than that without AQDS-CNTs. This result may be attributed to the enhanced electron transfer by AQDS and CNTs. The reduction of U(VI) occurred at initial U(VI) concentrations of 10 to 100 mg/L and increased with increasing AQDS-CNT content from 0.1% to 1%. The presence of Fe(III), Cu(II) and Mn(II) slightly increased U(VI) reduction, whereas Cr(VI), Ni(II), Pb(II), and Zn(II) significantly inhibited U(VI) reduction. After eight successive incubation-washing cycles or 8 hr of retention time (HRT) for 48 hr of continuous operation, the removal efficiency of uranium was above 90% and 92%, respectively. The results indicate that the AQDS-CNT/AL/cell beads are suitable for the treatment of uranium-containing wastewaters.     

细菌还原U(VI)分子生物学机理的研究进展

铀（U）污染对生态环境和人类健康的潜在危害受到越来越多的关注.U（VI）还原细菌可将U（VI）还原至U（IV）,从而降低铀在水中的溶解性和移动性,达到污染修复的目的.目前发现的U（VI）还原细菌主要包括但不限于铁还原菌和硫酸盐还原菌.本文综述了细菌还原U（VI）的分子生物学机理,重点阐述了U（VI）还原细菌的胞外电子转移方式,包括希瓦氏菌的金属还原方式、土杆菌的孔蛋白介导方式和微生物纳米线方式.竞争性电子受体和共存离子对细菌还原U（VI）有重要影响.目前细菌还原U（VI）过程中胞外电子转移的机理仍需更多实证,土杆菌利用微生物纳米线和细胞色素协作调控电子转移的机制尚不明确.今后可将研究聚焦于细菌还原U（VI）机理的验证和完善,并开发和优化基于微生物还原的铀污染修复技术,进而提高铀污染生物修复效率和稳定性.     

煤及其燃烧产物中有害痕量元素的淋滤特性研究

通过对我国西北部上湾与石嘴山电厂原煤、底灰和飞灰中As、Pb、Cd、Mop、Mo、Co和U等有害痕量元素在不同条件下的淋滤实验,采用原子荧光光谱（AFS）和电感耦合等离子体质谱法（ICP-MS）测定了痕量元素在2套（6个）样品、3种淋滤介质、4个不同时间段获取的淋滤液中的浓度,对比不同元素间淋出率、60h的最大淋出率和淋滤强度的差异性,分析痕量元素在不同条件下的淋滤特性;通过对比元素在原煤和燃煤产物中的含量、60h的最大淋出率以及淋滤液中元素的浓度,参考相关地下水的环境质量标准对痕量元素的环境效应进行了综合评价：As与Se的淋滤性较差,淋滤液中的最大浓度较低,对环境造成危害的可能性很小;Pb与Cd在淋滤液中的最大浓度较高,可能对环境造成危害.Mo与Co的淋出性好,淋出率高,同时淋滤液中的最大浓度是三类地下水环境质量标准的5～10倍,对环境造成危害的可能性最大.     

灭活与非灭活条件下植物乳杆菌去除U(VI)的机理

在不同时间,pH值和生物量浓度条件下,进行了灭活与非灭活植物乳杆菌去除水中铀的对比试验,探讨了二者去除水中铀的机理,通过SEM-EDS、FTIR、XPS及XRD分析了铀与菌体表面的微观作用机理以及菌体表面沉积物的特征.结果表明：植物乳杆菌经灭活后,其吸附铀的能力得到显著的提高,当U（VI）初始浓度为10mg/L、pH值为6.0、37℃条件下,120min内灭活菌体对U（VI）的去除率为94.7%,而活菌体的去除率为88.9%.灭活菌体具有更高的铀吸附容量,在生物量浓度为0.06~0.24mg/L,pH值（3.0~7.0）条件下,灭活菌体与活菌体的U（VI）累积容量比W均大于1.SEM-EDS、FTIR分析结果表明,活细胞和灭活细胞都可通过细胞表面的羟基、酰基及羧基等官能团吸附、配位络合U（VI）.XRD分析表明,活菌体可生物磷酸矿化水中的U（VI）.活菌体的XRD谱图在2θ（18.023,25.492,27.343,40.813°处）有4个明显的磷酸铀酰晶体峰,而灭活菌体的XRD谱图显示为非晶态.XPS结果表明,活菌体可生物还原U（VI）.活菌体能谱图中U4f7/2和U4f5/2轨道出现了结合能为380.20eV和390.65eV的U（VI）分裂峰,而灭活菌体的能谱图中没有出现U（IV）的分裂峰.     

电场强化博落回修复铀镉复合污染土壤机理

采用盆栽试验,研究了在0.3V/cm的外加直流电场作用下,博落回的生物量、富集铀（U）的性能和抗氧化酶活性,以及其根际土壤中有机酸含量、U和镉（Cd）的结合形态、植物根部U的价态、微生物群落结构的变化等.结果表明,施加直流电场后,博落回总生物量升高了15.33%~29.88%,其中电场+铀污染（DC+U）和电场+镉污染（DC+Cd）处理组的博落回对U和Cd的富集系数提高了90.84%和93.33%;土壤中草酸、酒石酸、琥珀酸、苹果酸和乳酸含量分别增加了18.36%~45.31%、58.62%~503.22%、15.71%~118.99%、12.34%~123.27%和25.97%~36.05%;过氧化物酶（POD）和谷胱甘肽过氧化物酶（GSH-PX）的活性分别提高了13.63%~34.82%和9.70%~28.64%;根际土壤中植物可利用态U、Cd所占比例显著增大;博落回根部的大部分U由稳定的U（IV）变成了更容易从地下部分向地上部分转移的U（VI）;酸杆菌门（Acidobacteria）等细菌菌门和子囊菌门（Ascomycota）等真菌菌门比例升高,这些微生物通过提高酶活性增强了博落回对U、Cd的耐受性和富集作用.     

电场强化博落回修复铀镉复合污染土壤机理

采用盆栽试验,研究了在0.3V/cm的外加直流电场作用下,博落回的生物量、富集铀（U）的性能和抗氧化酶活性,以及其根际土壤中有机酸含量、U和镉（Cd）的结合形态、植物根部U的价态、微生物群落结构的变化等.结果表明,施加直流电场后,博落回总生物量升高了15.33%~29.88%,其中电场+铀污染（DC+U）和电场+镉污染（DC+Cd）处理组的博落回对U和Cd的富集系数提高了90.84%和93.33%;土壤中草酸、酒石酸、琥珀酸、苹果酸和乳酸含量分别增加了18.36%~45.31%、58.62%~503.22%、15.71%~118.99%、12.34%~123.27%和25.97%~36.05%;过氧化物酶（POD）和谷胱甘肽过氧化物酶（GSH-PX）的活性分别提高了13.63%~34.82%和9.70%~28.64%;根际土壤中植物可利用态U、Cd所占比例显著增大;博落回根部的大部分U由稳定的U（IV）变成了更容易从地下部分向地上部分转移的U（VI）;酸杆菌门（Acidobacteria）等细菌菌门和子囊菌门（Ascomycota）等真菌菌门比例升高,这些微生物通过提高酶活性增强了博落回对U、Cd的耐受性和富集作用.     

重庆电厂炉前煤及飞灰中As元素在有机酸作用下的淋滤行为

采用模拟酸雨手段，突出有机酸对Ａｓ元素的淋出作用。分别配置ｐＨ＝４．４７的硝酸、乙酸及硝酸与乙酸的混酸三种淋滤液，对重庆电厂炉前煤及飞灰中的Ａｓ元素进行４０ｈ的淋滤实验，以探讨有机酸淋滤条件下Ａｓ元素的淋出行为。结果表明：有机酸淋滤液对炉前煤及飞灰中的Ａｓ元素具有较强的淋出作用，有机酸中Ｈ＾＋的缓冲释放作用是导致Ａｓ元素较强淋出率的主要因素。     

电动修复过程中电解质浓度对U(Ⅵ)迁移和能耗的影响

采用了柠檬酸与氯化铁组合的一种复合电解质,研究不同的电解质浓度对U（Ⅵ）的迁移行为和能量利用率的影响.结果表明：柠檬酸和氯化铁的最佳浓度为0.1mol/L CA+0.03mol/L FeCl₃,该浓度时铀的去除效率约为（61.55±0.41）%,累积消耗能量为0.2559kW·h,能量有效利用率β为（0.24±0.02）×10³.采用Visual MNIETQ软件模拟铀在pH值为3.0的柠檬酸和氯化铁溶液中的存在形式,结果表明主要以大量铀-柠檬酸根络合物（UO₂-Citrate^-）和少量的铀酰离子（UO₂²⁺）存在,此时铀主要从阴极向阳极迁移.当氯化铁浓度增加至0.05mol/L时,铀的去除率相应减少,产生此现象与电渗流强度及方向、氢氧化铁胶体吸附等因素有关.相较于单一的柠檬酸和盐酸,以柠檬酸和氯化铁组合的电解液具备去除效率高、浸出毒性低、土壤修复后危害小等优势.     

Selenium speciation in flue desulfurization residues

Flue gas from coal combustion contains significant amounts of volatile selenium (Se). The capture of Se in the flue gas desulfurization (FGD) scrubber unit has resulted in a generation of metal-laden residues. It is important to determine Se speciation to understand the environmental impact of its disposal. A simple method has been developed for selective inorganic Se(IV), Se(VI) and organic Se determination in the liquid-phase FGD residues by hydride generation atomic fluorescence spectrometry (AFS). It has been determined that Se(IV), Se(VI) and organic Se can be accurately determined with detection limits (DL) of 0.05, 0.06 and 0.06 g/L, respectively. The accuracy of the proposed method was evaluated by analyzing the certified reference material, NIST CRM 1632c, and also by analyzing spiked tap-water samples. Analysis indicates that the concentration of Se is high in FGD liquid residues and primarily exists in a reduced state as selenite (Se(IV)). The toxicity of Se(IV) is the strongest of all Se species. Flue gas desulfurization residues pose a serious environmental risk.     

微生物溶解载铀赤铁矿及再固定铀的试验研究

将载铀赤铁矿、核黄素(RF)和Sphingomonas sanxanigenens(S. sanxanigenens)同时投加到培养基中,监测培养过程中溶液的总铁、亚铁以及U(VI)浓度的变化,表征载铀赤铁矿还原性溶解前后固相产物中铁和铀的化学形态与价态,分析温度、共存离子对RF介导S. sanxanigenens还原性溶解载铀赤铁矿及再固定铀的影响.结果表明:S. sanxanigenens能够还原性溶解载铀赤铁矿,从而导致铀的释放;RF能够促进S. sanxanigenens还原性溶解载铀赤铁矿,且RF浓度越高越有利于这种还原性溶解;在30℃下RF能显著促进载铀赤铁矿的还原性溶解,且产物中稳定态铀的比例较高;添加2mmol/L Ca²⁺或CO₃^2-对RF介导S. sanxanigenens还原性溶解载铀赤铁矿具有促进作用;添加2mmol/L PO₄^3-能提高残渣态铀的比例,促进铀的固定;RF能够促进S. sanxanigenens对Fe(III)和U(VI)的还原,且反应过程伴随着次生铁矿物的生成.这些研究结果为提出RF介导S. sanxanigenens释放及再固定铀的新方法奠定了基础.     

Sorption of uranyl ions on TiO2: Effects of pH, contact time, ionic strength, temperature and HA

Sorption of U(VI) onto TiO₂ as functions of pH, ionic strength, contact time, soil humic acid (SHA), solid-to-liquid ratio and temperature was studied under ambient conditions using batch and spectroscopic approaches. The sorption of U(VI) on TiO₂ was significantly dependent on pH and ionic strength. The presence of SHA slightly enhanced the sorption of U(VI) on TiO₂ below pH 4.0, while it inhibited U(VI) sorption in the higher pH range. U(VI) sorption on TiO₂ was favored at high temperatures, and the sorption process was estimated to be endothermic and spontaneous. Reduction of U(VI) to lower valent species was confirmed by X-ray photo-electron spectroscopy analysis. It is very interesting to find that U(VI) sorption on TiO₂ was promoted in solutions with higher back-ground electrolyte concentrations. In the presence of U(VI), higher back-ground electrolyte made more TiO₂ particles aggregate through (001) facets, leading more (101) facets to be exposed. Therefore, the reduction of U(VI) was enhanced by the exposed (101) facets and more U(VI) removal was observed.     

表生环境中硒形态研究现状

硒是一种对环境具有灵敏指示意义的元素,在表生环境中存在诸多形态,如Se(IV)、Se(VI)、Se(0)、Se(-II)、Org-Se,每种形态都有独特的化学、生物化学性质(控制元素的可溶性、毒性、营养功能、环境行为)。在综合分析近年来国内外表生环境硒形态研究的基础上,作者分别对岩石(矿物)、土壤和沉积物、生物体、各种水体、大气中硒自然形态的分布进行了综述,并初步建立了不同体系之间硒在积累、迁移过程中形态迁移转化的地球化学模型;最后指出了硒形态研究方面有可能的前景。     

Abatement of SO2–NOx binary gas mixtures using a ferruginous active absorbent: Part I. Synergistic effects and mechanism

A novel ferruginous active absorbent, prepared by fly ash, industrial lime and the additive Fe(VI), was introduced for synchronous abatement of binary mixtures of SO₂–NOx from simulated coal-fired flue gas. The synergistic action of various factors on the absorption of SO₂ and NOx was investigated. The results show that a strong synergistic effect exists between Fe(VI) dose and reaction temperature for the desulfurization. It was observed that in the denitration process, the synergy of Fe(VI) dose and Ca/(S + N) had the most significant impact on the removal of NO, followed by the synergy of Fe(VI) and reaction temperature, and then the synergy of reaction temperature and flue gas humidity. A scanning electron microscope (SEM) and an accessory X-ray energy spectrometer (EDS) were used to observe the surface characteristics of the raw and spent absorbent as well as fly ash. A reaction mechanism was proposed based on chemical analysis of sulfur and nitrogen species concentrations in the spent absorbent. The Gibbs free energy, equilibrium constants and partial pressures of the SO₂–NOx binary system were determined by thermodynamics.     

A.ferrooxidans对高硫煤矸石去除酸性水体中Cr(VI)的强化作用

本研究考察了Acidithiobacillus ferrooxidans（A.ferrooxidans）联合高硫煤矸石（富含FeS₂）对模拟煤矿酸性水体中Cr（VI）的去除效果.结果表明,处理Cr（VI）初始浓度为50mg/L的模拟煤矿酸性废水（pH=2.5）时,投配率为6.67~33.33g/L高硫煤矸石可使Cr（VI）去除达到良好效果.50mg/LCr（VI）在24h内即可完全被高硫煤矸石中的FeS₂还原成Cr（III）,且在反应终点时（120h）,6.67,13.33,33.33g/L高硫煤矸石对还原产物Cr（III）的吸附去除率分别为7.1%、20.2%、29.1%.然而,在高硫煤矸石的还原和吸附作用下,大部分的Cr仍以Cr（III）形式残留在酸性水体中,且高硫煤矸石的大量投加也给水体带来了Fe²⁺、Fe³⁺、SO₄^2-等二次污染物.在高硫煤矸石-Cr（VI）体系中引入A.ferrooxidans和9K培养基后,A.ferrooxidans介导的Fe²⁺生物氧化及产物Fe³⁺水解矿化过程可促进部分Fe²⁺、Fe³⁺、SO₄^2-等向次生铁矿物（包括施氏矿物和黄钾铁矾）转变,从而使模拟酸性水体中残留的Cr（III）通过次生铁矿物的吸附或共沉淀作用被清除.在A.ferrooxidans强化作用下,模拟煤矿酸性废水中Cr（VI）在96h即可达到99.4%的去除率.     

Abatement of SO2-NOx binary gas mixtures using a ferruginous active absorbent: Part I. Synergistic effects and mechanism

A novel ferruginous active absorbent, prepared by fly ash, industrial lime and the additive Fe(VI), was introduced for synchronous abatement of binary mixtures of SO2–NOx from simulated coal-fired flue gas. The synergistic action of various factors on the absorption of SO2 and NOx was investigated. The results show that a strong synergistic effect exists between Fe(VI) dose and reaction temperature for the desulfurization. It was observed that in the denitration process, the synergy of Fe(VI) dose and Ca/(S + N) had the most significant impact on the removal of NO, followed by the synergy of Fe(VI) and reaction temperature, and then the synergy of reaction temperature and flue gas humidity. A scanning electron microscope(SEM) and an accessory X-ray energy spectrometer(EDS)were used to observe the surface characteristics of the raw and spent absorbent as well as fly ash. A reaction mechanism was proposed based on chemical analysis of sulfur and nitrogen species concentrations in the spent absorbent. The Gibbs free energy, equilibrium constants and partial pressures of the SO2–NOx binary system were determined by thermodynamics.