Release kinetics of vanadium from vanadium (III, IV and V) oxides: Effect of pH, temperature and oxide dose

Batch experiments were performed to derive the rate laws for the proton-promoted dissolution of the main vanadium (III, IV and V) oxides at pH 3.1–10.0. The release rates of vanadium are closely related to the aqueous pH, and several obvious differences were observed in the release behavior of vanadium from the dissolution of V₂O₅ and vanadium(III, IV) oxides. In the first 2 hr, the release rates of vanadium from V₂O₃ were r = 1.14·([H⁺])^0.269 at pH 3.0–6.0 and r = 0.016·([H⁺])^? 0.048 at pH 6.0–10.0; the release rates from VO₂ were r = 0.362·([H⁺])^0.129 at pH 3.0–6.0 and r = 0.017·([H⁺])^? 0.097 at pH 6.0–10.0; and the release rates from V₂O₅ were r = 0.131·([H⁺])^? 0.104 at pH 3.1–10.0. The release rates of vanadium from the three oxides increased with increasing temperature, and the effect of temperature was different at pH 3.8, pH 6.0 and pH 7.7. The activation energies of vanadium (III, IV and V) oxides (33.4–87.5 kJ/mol) were determined at pH 3.8, pH 6.0 and pH 7.7, showing that the release of vanadium from dissolution of vanadium oxides follows a surface-controlled reaction mechanism. The release rates of vanadium increased with increasing vanadium oxides dose, albeit not proportionally. This study, as part of a broader study of the release behavior of vanadium, can help to elucidate the pollution problem of vanadium and to clarify the fate of vanadium in the environment.     

Catalytic decomposition performance for O3 and NO2 in humid indoor air on a MnOx/Al2O3 catalyst modified by a cost-effective chemical grafting method

Processes based on non-thermal plasma (NTP) for indoor air treatment inevitably lead to the formation of toxic by-products such as ozone (O₃) and nitrogen oxides (NO_x). Adding a step of heterogeneous catalysis in series with NTP could allow for the decomposition of the by-products. Therefore, different catalysts were developed based on transition metal oxides, such as NiO_x, CoO_x and MnO_x with different weight percentage 1, 5 and 10 wt.%, deposited on a γ-Al₂O₃ support. The O₃ removal efficiency (ORE) and the NO_x removal efficiency (NRE) were very encouraging in dry air: about 65% and 80%, respectively, by using 2 g 5 wt.% MnO_x/Al₂O₃ catalyst under the experimental conditions. However, strongly negative effects of relative humidity (RH) on the catalytic decomposition performance were observed. To overcome this limitation, the catalyst surface was modified to make it hydrophobic using a cost-effective chemical grafting method. This treatment consisted in impregnating the 5 wt.% MnO_x/Al₂O₃ catalyst with different trichloro(alkyl)silanes (TCAS). The effects of different linker lengths and amounts of TCAS for the hydrophobicity and the decomposition performance of surface-modified catalysts under humid conditions were investigated. Our results show that the surface-modified catalyst with the shortest linker and 0.25 mmol/g_cat of modifying agent represents the best catalytic decomposition performance for O₃. Its ORE is 41% at 60% RH, which is twice that of the non-modified catalyst.     

Study on the simultaneous reduction of methylmercury by SnCl2 when analyzing inorganic Hg in aqueous samples

Mercury (Hg) is among the most concerned contaminants in the world. It has three major chemical forms in the environment, including Hg⁰, Hg^2 +, and methylmercury (MeHg). Due to their differences in toxicity, mobility, and bioavailability, speciation analysis is critical for understanding Hg cycling and fate in the environment. SnCl₂ reduction-atomic fluorescence spectrometry detection is the most commonly used method for analyzing inorganic Hg. However, it should be noted that MeHg may also be reduced by SnCl₂, which would result in the overestimation of inorganic Hg. In this study, the reduction of MeHg by SnCl₂ in both de-ionized (DI) water and four natural waters was investigated. The results showed that MeHg could be reduced by SnCl₂ in DI water whereas this reaction was hard to occur in tested natural waters. By investigating the effects of water chemical characteristics (dissolved organic matter, pH and common anions and cations) on this reaction, SO₄^2 ? was identified to be the dominant factor prohibiting SnCl₂ induced MeHg reduction in natural waters. SO₄^2 ? in natural waters was evidenced to be reduced to S^2 ? by SnCl₂ and the generated S^2 ? can complex with MeHg to form MeHgS^? which is hard to be reduced by SnCl₂. Findings of this study indicate that the effect of MeHg reduction by SnCl₂ on inorganic Hg analysis is negligible in natural waters; however, at simulated experimental systems without SO₄^2 ?, SO₄^2 ? should be added as protecting agents to prevent MeHg reduction when analyzing inorganic Hg if it would not cause any other unwanted effects.     

Anaerobic oxidation of methane coupled to sulfate reduction: Consortium characteristics and application in co-removal of H2S and methane

Anaerobic sludge from a sewage treatment plant was used to acclimatize microbial colonies capable of anaerobic oxidation of methane (AOM) coupled to sulfate reduction. Clone libraries and fluorescence in situ hybridization were used to investigate the microbial population. Sulfate-reducing bacteria (SRB) (e.g., Desulfotomaculum arcticum and Desulfobulbus propionicus) and anaerobic methanotrophic archaea (ANME) (e.g., Methanosaeta sp. and Methanolinea sp.) coexisted in the enrichment. The archaeal and bacterial cells were randomly or evenly distributed throughout the consortia. Accompanied by sulfate reduction, methane was oxidized anaerobically by the consortia of methane-oxidizing archaea and SRB. Moreover, CH₄ and SO₄^2 ? were consumed by methanotrophs and sulfate reducers with CO₂ and H₂S as products. The H₃CSH produced by methanotrophy was an intermediate product during the process. The methanotrophic enrichment was inoculated in a down-flow biofilter for the treatment of methane and H₂S from a landfill site. On average, 93.33% of H₂S and 10.71% of methane was successfully reduced in the biofilter. This study tries to provide effective method for the synergistic treatment of waste gas containing sulfur compounds and CH₄.     

Oxidation of antimony (III) in soil by manganese (IV) oxide using X-ray absorption fine structure

The oxidation of antimony (III) in soils was studied using X-ray absorption fine structure (XAFS) spectra. An andosol soil sample and artificial soil samples (SiO₂ blended with iron (III) hydroxide and manganese (IV) oxide) were used herein. After adding antimony (III) oxide to all soil samples, the oxidation process was observed by recording the XAFS spectra of Sb K-edge, Fe K-edge, and Mn K-edge. The results indicated that manganese (IV) oxide played an important role in the oxidation of Sb(III); however iron (III) hydroxide was not directly related to the reaction. During a 2-hr continuous Sb K-edge X-ray absorption near edge structure (XANES) measurement with an interval of 1 min of one of the artificial soil samples (SiO₂ + MnO₂ + Sb₂O₃), a pseudo-first-order reaction was determined with an average estimated rate of 0.52 ± 0.04 hr^? 1. Compared to the lower oxidation rate of andosol, it is suggested that because of the low concentration of Mn(IV) in natural soils, the oxidation process of Sb(III) might be relatively slow and require more time to convert Sb(III) to Sb(V).     

Modified activated carbon with interconnected fibrils of iron-oxyhydroxides using Mn2 + as morphology regulator, for a superior arsenic removal from water

The arsenic removal efficiency of iron-modified activated carbons depends greatly on the number of available iron oxide surface sites, which are given by the surface area of the anchored particles. In this sense, aiming the generation of an adsorbent with superior arsenic adsorption capacity, we developed a protocol to anchor interconnected fibrils of iron oxyhydroxides, using Mn^2 + as a morphology regulator. The protocol was based on a microwave-assisted hydrothermal method, using bituminous based activated carbon and both Fe^2 + and Mn^2 + ions in the hydrolysis solution. The elemental analysis of modified carbons revealed that Mn does not anchor to the carbon. However, when Mn is included in the hydrolysis solution, the iron content in the activated carbon increased up to 3.5?wt%, without considerable decreasing the adsorbent surface area. Under specific hydrothermal conditions, the Mn^2 + promoted the formation of iron oxide nanoparticles shaped as interconnected fibrils. This material showed a superior arsenic adsorption capacity in comparison to similar iron modified activated carbons (5?mg As/g carbon, at 2?mg As/L), attributed to the increase in quantity and availability of active sites located on the novel interconnected fibrils of iron oxyhydroxides nanostructures.     

Effects of Na+ on Cu/SAPO-34 for ammonia selective catalytic reduction

Copper-exchanged chabazite (Cu/CHA) catalysts have been found to be affected by alkali metal and alkaline earth ions. However, the effects of Na⁺ ions on Cu/SAPO-34 for ammonia selective catalytic reduction (NH₃-SCR) are still unclear. In order to investigate the mechanism, five samples with various Na contents were synthesized and characterized. It was observed that the introduced Na⁺ ion-exchanges with H⁺ and Cu^2 + of Cu/SAPO-34. The exchange of H⁺ is easier than that of isolated Cu^2 +. The exchanged Cu^2 + ions aggregate and form “CuAl₂O₄-like” species. The NH₃-SCR activity of Cu/SAPO-34 decreases with increasing Na content, and the loss of isolated Cu^2 + and acid sites is responsible for the activity loss.     

Seasonal variation and chemical composition of particulate matter: A study by XPS, ICP-AES and sequential microanalysis using Raman with SEM/EDS

During the winter period (January–March 2016), the total suspended particles (TSP) and particulate matter smaller than 2.5 μm (PM_2.5) were characterized by the application of various analytical techniques in four zones of the Metropolitan Area of Monterrey in Mexico. To evaluate the seasonal variation of some elements in the particulate matter, the results of this study were compared with those obtained during the summer season (July–September 2015). The speciation of the C_1s signal by X-ray photoelectron spectroscopy revealed the contribution of aromatic and aliphatic hydrocarbons as the main components in both seasons. Conversely, carboxylic groups associated with biogenic emissions were detected only in winter. The percentages of SO₄^2 ? ions were lower in winter, possibly caused by the decrease in the solar radiation, and relative humidity recorded. The results of the ICP analysis revealed that Fe, Zn and Cu were the most abundant metals in both TSP and PM_2.5 in the two seasons. There were significant seasonal variations for concentrations of As, Ni and Zn in the urban area and for Fe, As, Cd, Ni and Zn in the industrial zone. This was attributed to the greater burning of fuels as well as to an increase in vehicular traffic, the effect of thermal inversion and changes in some meteorological parameters. The results of the sequential microanalysis by Raman spectroscopy and SEM/EDS allowed observation of deposits of carbonaceous material on the particles and to perform the speciation of particles rich in Fe and Pb, which helped infer their possible emission sources.     

Formation mechanism and control strategy for particulate nitrate in China

Over the past decade, fine particulate matter (PM) pollution in China has been abated significantly, benefiting from strict emission control measures, but particulate nitrate continues to rise. Here, we review the progress in particulate nitrate (pNO₃⁻) pollution characterization, nitrate formation mechanisms, and the proposed control strategies in China. The spatial and temporal distributions of pNO₃⁻ are summarized. The current status of knowledge on the chemical mechanism is updated, and the significance of its formation pathways is assessed by various approaches such as field observation and modelling of nitrate production rate, as well as isotopic analysis. The factors impacting pNO₃⁻ formation and the corresponding pollution regulation strategies are discussed, in which the importance of atmospheric oxidation capacity and ammonia are addressed. Finally, the challenges and open questions in pNO₃⁻ pollution control in China are outlined.     

Strong ozone production at a rural site in theNorth China Plain: Mixed effects of urban plumesand biogenic emissions

Regional ozone (O₃) pollution has drawn increasing attention in China over the recent decade, but the contributions from urban pollution and biogenic emissions have not been clearly elucidated. To better understand the formation of the regional O₃ problem in the North China Plain (NCP), intensive field measurements of O₃ and related parameters were conducted at a rural site downwind of Ji'nan, the capital city of Shandong province, in the summer of 2013. Markedly severe O₃ pollution was recorded, with the O₃ mixing ratios exceeding the Chinese national ambient air quality standard on 28?days (a frequency of 78%) and with a maximum hourly value of 198 ppbv. Extensive regional transport of well-processed urban plumes to the site was identified. An observation-constrained chemical box model was deployed to evaluate in situ photochemical O₃ production on two episodes. The results show that the in situ formation accounted for approximately 46% of the observed O₃ accumulation, while the remainder (~ 54%) was contributed by regional transport of the O₃-laden urban plumes. The in situ ozone production was in a mixed controlled regime that reducing either NOx or VOCs would lead to a reduction of ozone formation. Biogenic VOCs played an important role in the local ozone formation. This study demonstrates the significant mixed effects of both anthropogenic pollution from urban zones and biogenic emission in rural areas on the regional O₃ pollution in the NCP region, and may have general applicability in facilitating the understanding of the formation of secondary pollution over China.     

Characteristics of size distributions and sources of water-soluble ions in Lhasa during monsoon and non-monsoon seasons

To understand the physical and chemical characteristics, particle size distribution and sources of size-separated aerosols in Lhasa, which is located on the Tibetan Plateau (TP), six sizes of aerosol samples were collected in Lhasa in 2014. Ca²⁺, NH₄⁺, NO₃^?, SO₄^2?and Cl^? were the dominant ions. The ratio of cation equivalents (CE) to anion equivalents (AE) for each particle size segment indicated that the atmospheric aerosols in Lhasa were alkaline. SO₄^2? and NO3^? could be neutralized by Ca²⁺, but could not be neutralized by NH₄⁺, according to the [NH₄⁺]/[NO₃^??+?SO₄^2?] and [Ca²⁺]/[NO₃^??+?SO₄^2?] ratios. Mobile sources were dominant in PM_0.95–1.5, PM_1.5–3 and PM_3–7.2, while stationary sources were dominant in the other three size fractions according to the [NO₃^?]/[SO₄^2?] ratios. The particle size distribution of all water-soluble ions during monsoon and non-monsoon periods was characterized by a bimodal distribution due to the different sources and formation mechanisms, and it was revealed that different ions had different sources in different seasons and different particle size segments by combining particle size distribution with correlation analysis. Source analysis of aerosols in Lhasa was performed using the Principal component analysis (PCA) for the first time, which revealed that combustion sources, motor vehicle exhaust, photochemical reaction sources and various types of dust were the main sources of Lhasa aerosols. Furthermore, Lhasa''s air quality was also affected by long-distance transmission, expressed as pollutants from South Asiaand West Asia, which were transmitted to Lhasa according to backward trajectory analysis.     

Determination of aerosol strong acidity losses due to interactions of collected particles: Results from laboratory and field studies

Existing methods of measuring atmospheric aerosol strong acidity adequately prevent neutralization of fine-particle acidity by removing course alkaline particles and gaseous ammonia from air samples. However, these techniques do not consider particle interactions on the collection medium; therefore, they may still underestimate the actual aerosol acidity. Assessment of acid neutralization due to such interactions is made possible using annular denuder technology in conjuction with a newly designed filter pack. The amount of sulfate-related acidity neutralized by the collected ammonium nitrate (and possibly ammonium chloride and organic acid ammonium salts) is determined. Laboratory data suggest that large fractions of sulfate-related aerosol acidity are neutralized by ammonium nitrate particles during collection on filter media. Field data from the Harvard Acid Aerosol Health Effects Study also suggest that ammonium nitrate and possibly other ammonium salts, such as ammonium chloride, neutralize collected acid aerosols. For low-acid aerosol concentrations, the correction factor is significant; whereas, for high-acid concentrations, correction is negligible.     

Preparation and utilization of wheat straw anionic sorbent for the removal of nitrate from aqueous solution

In order to reduce the impact of eutrophication caused by agricultural residues(i.e.,excess nitrate)in aqueous solution,economic and effective anionic sorbents are required.In this article,we prepared anionic sorbent using wheat straw.Its structural characteristics and adsorption properties for nitrate removal from aqueous solution were investigated.The results indicate that the yield of the prepared anionic sorbent,the total exchange capacity,and the maximum adsorption capacity were 350%,2.57 mEq/g,and 2.08 mmol/g, respectively.The Freundlich isotherm mode is more suitable than the Langmuir mode and the adsorption process accords with the first order reaction kinetic rate equation.When multiple anions(SO_4~(2-),H_2PO_4~-,NO_3~-,and NO_2~-)were present,the isotherm mode of prepared anionic sorbent for nitrate was consistent with Freundlich mode;however,the capacity of nitrate adsorption was reduced by 50%.In alkaline solutions,about 90% of adsorbed nitrate ions could be desorbed from prepared anionic sorbent.The results of this study confirmed that the wheat straw anionic sorbent can be used as an excellent nitrate sorbent that removes nitrate from aqueous solutions.     

广州城区秋季大气PM_(2.5)中主要水溶性无机离子分析

分别在广州市中心城区高楼顶(距地50m)和交通干线路边(距地1.2m),于2006年秋季连续一周采集了大气PM2.5样品,对比分析了SO42-、NO3-、Cl-、F-、Na+、NH4+、Ca2+、K+、Mg2+等9种水溶性无机离子含量。结果表明,楼顶相对充分混合大气中PM2.5的质量浓度范围59.5～129.5μg/m3,均值为83.7μg/m3;交通干线路边大气PM2.5的质量浓度范围为108.4～132.2μg/m3,均值为121.1μg/m3。9种离子总浓度平均达到50.9(楼顶)和44.1(路边)μg/m3,占PM2.5质量浓度的60.8%(楼顶)和36.4%(路边)。SO42-和NO3-为水溶性无机离子主要组成,其占PM2.5质量浓度的比例均是楼顶高于路边,显示二次气溶胶对楼顶充分混合大气中PM2.5有较大贡献,而路边样品中一次来源贡献相对较大。计算表明采样期间海盐对广州大气PM2.5中的水溶性组分贡献较小。NH4+当量浓度远小于SO42-和NO3-的当量浓度,中和度远1,反映PM2.5酸性较强,且楼项PM2.5粒子酸性高于路边样品。     

广州市酸雨现状与发展趋势研究

叙述了广州小珠江三角洲范围历年来酸雨分布的特征及其发展趋势。分析表明,春季降水酸性最强,认为是局地源污染与外地源输送叠加的结果。酸性降水中起主要作用的阴离子是SO_4~(2-)和NO_3~-。尤以前者更为主要,NO_3~-的作用显著大于西南地区和上海地区;是美国的0.5倍。SO_4~(2-)/NO_3~-值低于西南地区2倍以上。广州市大气中H_2O_2及O_3浓度较高,光化学反应活跃。春季冷空气南下形成静止锋,有利于酸雨的形成。广州的酸雨已进入世界最强范围,与西欧、北美接近。     

2007年北京夏季降水分段采样酸度和化学成分分析

为掌握降水酸度和污染性化学成分随降水持续时间的变化规律,对北京2007年夏季5次典型降水过程分时段采样,分别测定了pH值、电导率,并分析了其中水溶性大气污染成分SO42-、NO3-、NH4+等随时间的变化特征.结果表明,pH加权平均值在降水初期为5.70±0.73,为非酸雨;平缓期为4.35±0.56,呈酸雨特征.pH、电导率和各离子浓度随降水时间的持续而迅速下降,10~45 min后进入平缓期,各污染离子随之下降率为50%~90%.来自北京西北方向云团的降水(8月1日)pH值较高、污染物浓度较低,SO42-、NO3-和NH4+分别为65.4、23.9和117.3μeq/L;而来自偏南云团降水(8月6日)pH值较低、污染物浓度较高,SO42-、NO3-和NH4+浓度分别为310.8、95.7和249.8μeq/L.北京夏季二次粒子浓度升高,将使降水酸化加剧.     

氮素调控对冻融过程中土壤N2O排放的影响

应用室内冰柜模拟冻融过程,研究了不同氮素形态(铵态氮、硝态氮和酰胺态氮)和浓度(40、200和800 mg/L)对潮土N2O排放通量的影响.结果表明,随土壤冻结时间的延长N2O排放通量缓慢降低,土壤融化初期出现一个土壤N2O排放通量高峰,而后随土壤逐渐融化的进行N2O排放通量缓慢升高.3种氮素浓度条件下,铵态氮、硝态氮和酰胺态氮冻融过程中土壤平均N2O排放通量分别为119.01、205.28、693.95μg.(m2.h)-1,611.61、1 084.40、1 820.02μg.(m2.h)-1和148.22、106.13、49.74μg.(m2.h)-1,而对照处理仅为100.35μg.(m2.h)-1.随氮素浓度的增加,铵态氮、硝态氮源土壤N2O累积排放通量分别比对照增加17.49%、40.09%、425.67%和563.38%、915.28%、1458.6%,且施加的浓度越高累积排放量越大,但达到稳定N2O排放通量的时间向后推移.随浓度增加酰胺态氮处理土壤N2O排放通量随浓度增加而降低.建议潮土越冬水中铵态氮和硝态氮浓度应分别小于200 mg/L和40 mg/L,酰胺态氮的浓度不限,从而减少土壤N2O的排放.     

华北地区沙尘天气垂直气溶胶直接辐射强迫

利用CALIOP数据和SBDART（Santa Barbara DISORT Atmospheric Radiative Transfer）辐射传输模式研究了2013~2016年华北地区8d沙尘天气气溶胶及其直接辐射强迫垂直分布特征,分析了气溶胶垂直分布和光学特性对直接辐射强迫的影响.结果表明,气溶胶集中分布在地表及以上3km范围,其中纯净沙尘型和污染沙尘型气溶胶位于上层,污染大陆型气溶胶和烟雾位于下层.大气层顶、地表和大气层的日均气溶胶直接辐射强迫分别是-38.41~-88.44,-74.03~-225.86,9.06~137.42W/m².0~8km高度范围气溶胶直接辐射强迫是负值,且随着高度的增加绝对值逐渐减小.气溶胶垂直分布对大气层顶、地表和大气层的直接辐射强迫影响较小,但对直接辐射强迫垂直分布影响较大,由气溶胶廓线差异造成的同一高度层气溶胶直接辐射强迫最大差值能达到31.18W/m².气溶胶光学厚度和单次散射反照率对直接辐射强迫影响明显.消光能力相同时,吸收性气溶胶对短波太阳光的衰减作用大于散射性气溶胶,后向散射比例大的气溶胶大于后向散射比例小的气溶胶.     

华北地区沙尘天气垂直气溶胶直接辐射强迫

利用CALIOP数据和SBDART（Santa Barbara DISORT Atmospheric Radiative Transfer）辐射传输模式研究了2013~2016年华北地区8d沙尘天气气溶胶及其直接辐射强迫垂直分布特征,分析了气溶胶垂直分布和光学特性对直接辐射强迫的影响.结果表明,气溶胶集中分布在地表及以上3km范围,其中纯净沙尘型和污染沙尘型气溶胶位于上层,污染大陆型气溶胶和烟雾位于下层.大气层顶、地表和大气层的日均气溶胶直接辐射强迫分别是-38.41~-88.44,-74.03~-225.86,9.06~137.42W/m².0~8km高度范围气溶胶直接辐射强迫是负值,且随着高度的增加绝对值逐渐减小.气溶胶垂直分布对大气层顶、地表和大气层的直接辐射强迫影响较小,但对直接辐射强迫垂直分布影响较大,由气溶胶廓线差异造成的同一高度层气溶胶直接辐射强迫最大差值能达到31.18W/m².气溶胶光学厚度和单次散射反照率对直接辐射强迫影响明显.消光能力相同时,吸收性气溶胶对短波太阳光的衰减作用大于散射性气溶胶,后向散射比例大的气溶胶大于后向散射比例小的气溶胶.     

污水地表漫流处理系统中氮的迁移转化试验研究

采用试验室模拟的方法 ,对污水地表漫流处理系统中氮的迁移转化进行了试验研究 ,并对系统中氮的去除进行了分析。结果表明 ,地表漫流处理系统中氮的迁移转化包含 4个过程 :( 1 )土壤表层对NH4 + 的吸附作用 ,( 2 )NH4 + 的硝化作用 ,( 3)NO3- 向厌氧层的迁移作用 ,( 4 )作物吸收和反硝化作用。其中 ( 3)对整个系统氮的去除率起着决定性作用 ,可以通过投加CaCO3来强化系统的脱氮能力