Redox behavior and chemical species of arsenic in acidic aqueous system

Arsenic(As)removal from smelting acidic wastewater is an urgent task.The most common method is oxidation of trivalent As(III)to pentavalent As(V)subsequently precipitated by ferric(Fe(III))salts.Foundations of redox behavior and chemical species are of great importance for understanding As removal.In this work,cyclic voltammetry(CV)and UV?Vis spectroscopy were used for laboratory observation;meanwhile HSC and MINTEQ software were employed for theoretical analyses.It is found that As(III)oxidation,a multiple electron transfer reaction,is diffusion-controlled.The oxidation over-potential is very high(about0.9V)in sulfuric acid solutions(pH1.0).In addition,Fe(III)?As(V)complexes are evidenced by UV?Vis spectra and chemical species analyses in series of Fe(III)?As(V)?H2SO4?H2O solutions.Therefore,the Fe(III)and As(V)species distribution against pH values are determined and a newφ?pH diagram with inclusion of Fe?As complexes is consequently compiled based on thermodynamic data predicted by other researchers.

Chemical Species of Aluminum Ions in Acid Soils *1

Soil samples collected from several acid soils in Guangdong, Fujian, Zhejiang and Anhui provinces of the southern China were employed to characterize the chemical species of aluminum ions in the soils. The proportion of monomeric inorganic Al to total Al in soil solution was in the range of 19% to 70%, that of monomeric organic Al (Al OM) to total Al ranged from 7.7% to 69%, and that of the acid soluble Al to total Al was generally smaller and was lower than 20% in most of the acid soils studied. The Al OM concentration in soil solution was positively correlated with the content of dissolved organic carbon (DOC) and also affected by the concentration of Al 3+ . The complexes of aluminum with fluoride (Al F) were the predominant forms of inorganic Al, and the proportion of Al F complexes to total inorganic Al increased with pH. Under strongly acid condition, Al 3+ was also a major form of inorganic Al, and the proportion of Al 3+ to total inorganic Al decreased with increasing pH. The proportions of Al OH and Al SO 4 complexes to total inorganic Al were small and were not larger than 10% in the most acid soils. The concentration of inorganic Al in solution depended largely on pH and the concentration of total F in soil solution. The concentrations of Al OM, Al 3+ ,Al F and Al OH complexes in topsoil were higher than those in subsoil and decreased with the increase in soil depth. The chemical species of aluminum ions were influenced by pH. The concentrations of Al OM, Al 3+ , Al F complexes and Al OH complexes decreased with the increase in pH.

The Algorithm of Chemical Species Analysis for Ab Intio Molecular Dynamics Simulations and Its Application

In ab initio molecular dynamics(AIMD)simulations of chemical reactions,it is important but difficult to identify the chemical species in the trajectory automatically and quickly.In this paper,based on the chemical graph theory,an algorithm for molecular species identification,according to the molecular coordinates and empirical bond length database,is presented.As an example,the chemical species in condensed glycine at room temperature are investigated with our algorithm in detail.The chemical species,including canonical and zwitterionic glycine,their protonated and de-protonated states,and the free protons,are all identified,counted and recorded correctly.Potential applications and further development of the algorithm are also discussed.

Using Self-referencing Interlaced Submatrices to Determine the Number of Chemical Species in a Mixture

Determining the number of chemical species is the first step in analyses of a chemical or biological system. A novel method is proposed to address this issue by taking advantage of frequency differences between chemical information and noise. Two interlaced submatrices were obtained by downsampling an original data spectra matrix in an interlacing manner. The two interlaced submatrices contained similar chemical information but different noise levels. The number of relevant chemical species was determined through pairwise comparisons of principal components obtained by principal component analysis of the two interlaced submatrices. The proposed method, referred to as SRISM, uses two self-referencing interlaced submatrices to make the determination. SRISM was able to selectively distinguish relevant chemical species from various types of interference factors such as signal overlapping, minor components and noise in simulated datasets. Its performance was further validated using experimental datasets that contained high-levels of instrument aberrations, signal overlapping and collinearity. SRISM was also applied to infrared spectral data obtained from atmospheric monitoring. It has great potential for overcoming various types of interference factor. This method is mathematically rigorous, computationally efficient, and readily automated.

Reconstructed Light Extinction Coefficients Using Chemical Compositions of PM_(2.5) in Winter in Urban Guangzhou, China

The objective of this study was to reconstruct light extinction coefficients （b ext ） according to chemical composition components of particulate matter up to 2.5 μm in size （PM 2.5 ）. PM 2.5 samples were collected at the monitoring station of the South China of Institute of Environmental Science （SCIES, Guangzhou, China） during January 2010, and the online absorbing and scattering coefficients were obtained using an aethalometer and a nephelometer. The measured values of light absorption coefficient by particle （b ap ） and light scattering coefficient by particle （b sp ） significantly correlated （R 2 0.95） with values of b ap and b sp that were reconstructed using the Interagency Monitoring of Protected Visual Environments （IMPROVE） formula when RH was 70%. The measured b ext had a good correlation （R 2 0.83） with the calculated b ext under ambient RH conditions. The result of source apportionment of b ext showed that ammonium sulfate [（NH 4 ） 2 SO 4 ] was the largest contributor （35.0%） to b ext , followed by ammonium nitrate （NH 4 NO 3 , 22.9%）, organic matter （16.1%）, elemental carbon （11.8%）, sea salt （4.7%）, and nitrogen dioxide （NO 2 , 9.6%）. To improve visibility in Guangzhou, the effective control of secondary particles like sulfates, nitrates, and ammonia should be given more attention in urban environmental management.

Physical, chemical, and surface charge properties of bauxite residue derived from a combined process

A detailed understanding of the composition,buffering capacity,surface charge property,and metals leaching behavior of bauxite residue is the key to improved management,both in reducing the environmental impact and using the material as an industrial by-product for other applications.In this study,physical,chemical,and surface charge properties of bauxite residue derived from a combined process were investigated.Results indicated that the main alkaline solids in bauxite residue were katoite,sodalite,and calcite.These minerals also lead to a higher acid neutralizing capacity of bauxite residue.Acid neutralizing capacity(ANC)to pH 7.0 of this residue is about 0.9 mol H^+/kg solid.Meanwhile,the Fe-,Al-,and Si-containing minerals in bauxite residue resulted in an active surface;The isoelectric point(IEP)and point of zero charge(PZC)were 7.88 and 7.65,respectively.This also leads to a fact that most of the metals in bauxite residue were adsorbed by these surface charged solids,which makes the metals not readily move under natural or even moderately acidic conditions.The leaching behavior of metals as a function of pH indicated that the metals in bauxite residue present low release concentrations(pH>3).

MHD flow and mass transfer of chemically reactive upper convected Maxwell fluid past porous surface

The magnetohydrodynamic （MHD） flow and mass transfer of an electrically conducting upper convected Maxwell （UCM） fluid at a porous surface are studied in the presence of a chemically reactive species. The governing nonlinear partial differential equations along with the appropriate boundary conditions are transformed into nonlinear ordinary differential equations and numerically solved by the Keller-box method. The effects of various physical parameters on the flow and mass transfer characteristics are graphically presented and discussed. It is observed that the order of the chemical reaction is to increase the thickness of the diffusion boundary layer. Also, the mass transfer rate strongly depends on the Schmidt number and the reaction rate parameter. Furthermore, available results in the literature are obtained as a special case.

Lead anthropogenic transfer and transformation in China

Information on lead redistribution and speciation changes in anthrosphere can help to analyze the whole lead cycle on the earth. Lead life cycle was traced based on the concepts of anthropogenic transfer and transformation. Lead transfer and the distribution of chemical species throughout the anthropogenic flow were identified in 2010 in China. The results show that 1.85 Mt lead ore was consumed(besides 1.287 Mt imported concentrated ore and 1.39 Mt lead scraps. After undergoing transformations, 3.53 Mt lead entered end services in chemical species of Pb, Pb O2 and PbSO4, altogether accounting for over 80% of the total lead products. Finally, 2.10 Mt ore was emitted into the environment in such species as PbSO4(26%), PbO(19%) and Pb(15%). Lead transfer begins in primary raw material sectors, and then transfers to manufacturing sectors. Lead provides services mainly in such industrial sectors as transportation, electrical power and buildings or construction.

Heavy metals distribution in fly ash from gangue power plant

To make assessment on its environmental security, fly ash samples were collected from the gangue power plant. Total content of heavy metals in sieved fly ash were analytically determined. We also carried out Tessier extractive experiments to check the chemical species of heavy metals. Experiment results show that the content of Cu, Zn, Pb and Cd ascend when particle size is smaller. Cu, Zn, Pb and Cd obviously enrich in particulate fly ash. The chemical species of heavy metal distribution ranking sequence generally is residual〉organic combinative〉Fe-Mn oxide combinative〉carbonate combinative〉ion-exchangeable. Lead＇s amiable-move species were high in proportion, amounted to 35%. Total content of Cadmium is at low level, but its ion-exchangeable species is relatively high in proportion. Nickel and zinc is mainly distributed in residue. Cu is mainly distributed in residue and organic combinative form. The content of manganese is relatively high in fly ash, and the carbonate combinative iron-manganese oxide combinative species are main chemical form. Cr is mainly distributed in residue, and its other chemical species are at low level. Compared with the soil background value of study area and Shandong Province, the content of Cu, Ni, Zn, Mn and Cr in fly ash of gangue power plant is lower. While contents of Pb and Cd were higher than background value, and amiable-move species is relatively high in proportion. They are more apt to cause heavy metal pollution.

Characteristics and geological significance of germanium in Taiyuan coal formation of Huainan Coalfield,Anhui,China

HN-1#is the first fully working coring well of the Taiyuan Formation(Ty)in the Huinan Coalfield and exploration studies are currently underway on the associated resources of the coal-bearing strata.The HN-1#well is located in the Fufeng thrust nappe structural belt in the south of the Huainan Coalfield.Three coal samples from the Ty were collected from HN-1#and inductively-coupled plasma mass spectrometry and inductively-coupled plasma atomic emission spectrometry were used to determine the Ge content of each sample.Based on proximate and ultimate analyses,microscopy data,and analyses of the ash products,some important findings were made.The Ty coal samples had a relatively high total sulfur(Sud)content(4.24%),thus the coal was considered to be a lower ranked coal(high volatility bituminous coal),which also had a low coal ash composition index(k,1.87).Collodetrinite was the main submaceral of the Ty coal.Small amounts of pyrite particles were found in the coal seams of the Ty,while the contents of pyrite and algae in the top and bottom sections of the coal seam were relatively high,which meant that the swampy peat conditions which existed during the formation of the coal seams were affected by seawater;also the degree of mineralization of the coal seam was relatively high,which is consistent with reducing conditions in a coastal environment setting.Atomic force microscopy(AFM)experiments showed that the modes of occurrence of Ge in the Ty coal were mainly those for organic-bound and adsorbed Ge species.The organic carbon isotope values for the Ty coal ranged from-24.1‰to-23.8‰,with an average value of-24.0‰,which is equivalent to the value for terrestrial plants(average value-24.0‰).The Ge content of the Ty coal was 13.57 mg/kg.The Ge content was negatively correlated with volatile matter and the ash yield.

TOTAL AND METHYL MERCURY LEVELS IN HUMAN SCALP HAIRS

The contents of total and methyl mercury in scalp hair samples of 1179 fishermenliving at a typical Hg-polluted region in Northeast China and 27 lying-in womenand their new born babies in Beijing have been determined by illstrumental neutronactivation analysis, gas chromatography (electron coupling) and other techniqlles.Only 18 of all fishermen have the Hg contents above 5 ig/g, which indicates that theHg pollution there has been substantially alleviated. The longitudinal Hg patternsof the lying-in women show a gradually lowering tendency during pregnant period.Further, the Hg contents of the new-born babies are generally above or close to those oftheir mothers, confirming the mechanism that the methyl Hg, an organic species of Hgwith high toxicity, is readily able to penetrate the placental barrier and accumulatedin fetus. Thus, the mercury poison hajs occurred at the early stage of pregnancy.

Preparation of Ti species coating hydrotalcite by chemical vapor deposition for photodegradation of azo dye

TiO2 in anatase crystal phase is a very effective catalyst in the photocatalytic oxidation of organic compounds in water. To improve its photocatalytic activity, the Ti-coating Mg Al hydrotalcite（Ti–Mg Al–LDH） was prepared by chemical vapor deposition（CVD） method.Response surface method（RSM） was employed to evaluate the effect of Ti species coating parameters on the photocatalytic activity, which was found to be affected by the furnace temperature, N2 flow rate and influx time of precursor gas. Application of RSM successfully increased the photocatalytic efficiency of the Ti–Mg Al–LDH in methylene blue photodegradation under UV irradiation, leading to improved economy of the process.According to the results from X-ray diffraction, scanning electron microscopy, Brunner–Emmet–Teller and Barrett–Joyner–Hallender, thermogravimetric and differential thermal analysis, UV–vis diffuse reflectance spectra analyses, the Ti species（TiO2or/and Ti^（4＋）） were successfully coated on the Mg Al–LDH matrix. The Ti species on the surface of the Ti–Mg Al–LDH lead to a higher photocatalytic performance than commercial TiO2-P25. The results suggested that CVD method provided a new approach for the industrial preparation of Ti-coating Mg Al–LDH material with good photocatalytic performances.

Hybrid Isothermal Model for the Ferrohydrodynamic Chemically Reactive Species

A hybrid isothermal model for the homogeneous-heterogeneous reactions in ferrohydrodynamic boundary layer ?ow is established. The characteristics of Newtonian heating and magnetic dipole in a ferro?uid due to a stretchable surface is analyzed for three chemical species. It is presumed that the isothermal cubic autocatalator kinetic gives the homogeneous reaction and the ?rst order kinetics gives the heterogeneous(surface) reaction. The analysis is carried out for equal diffusion coe?cients of all autocatalyst and reactions. Heat ?ux is examined by incorporating Fourier's law of heat conduction. Characteristics of materialized parameters on the magneto-thermomechanical coupling in the ?ow of a chemically reactive species are investigated. Further, the heat transfer rate and friction drag are depicted for the ferrohydrodynamic chemically reactive species. It is evident that the Schmidt number has increasing behavior on the rate of heat transfer in the boundary layer. Comparison with available results for speci?c cases is found an excellent agreement.

Fine particulate matter(PM_(2.5)/PM_(1.0)) in Beijing,China: Variations and chemical compositions as well as sources

Particulate matter(i.e.,PM_(1.0) and PM_(2.5)),considered as the key atmospheric pollutants,exerts negative effects on visibility,global climate,and human health by associated chemical compositions.However,our understanding of PM and its chemical compositions in Beijing under the current atmospheric environment is still not complete after witnessing marked alleviation during 2013–2017.Continuous measurements can be crucial for further air quality improvement by better characterizing PM pollution and chemical compositions in Beijing.Here,we conducted simultaneous measurements on PM in Beijing during 2018–2019.Results indicate that annualmean PM_(1.0) and PM_(2.5) concentrations were 35.49±18.61μg/m^(3) and 66.58±60.17μg/m^(3),showing a positive response to emission controls.The contribution of sulfate,nitrate,and ammonium(SNA)played an enhanced role with elevated PM loading and acted as the main contributors to pollution episodes.Discrepancies observed among chemical species between PM_(1.0) and PM_(2.5) in spring suggest that sand particles trend to accumulate in the range of 1–2.5μm.Pollution episodes occurred accompanied with southerly clusters and high formation of SNA by heterogeneous reactions in summer and winter,respectively.Results from positive matrix factorization(PMF)combined with potential source contribution function(PSCF)models showed that potential areas were seasonal dependent,secondary and vehicular sources became much more important compared with previous studies in Beijing.Our study presented a continuous investigation on PM and sources origins in Beijing,which provides a better understanding for further emission control as well as a reference for other cities in developing countries.

Chemical Components, Variation, and Source Identification of PM1 during the Heavy Air Pollution Episodes in Beijing in December 2016

Air pollution is a current global concern. The heavy air pollution episodes（HPEs） in Beijing in December 2016 severely influenced visibility and public health. This study aims to survey the chemical compositions, sources, and formation processes of the HPEs. An aerodyne quadruple aerosol mass spectrometer（Q-AMS） was utilized to measure the non-refractory PM1（NR-PM1） mass concentration and size distributions of the main chemical components including organics, sulfate, nitrate, ammonium, and chloride in situ during 15–23 December 2016. The NR-PM1 mass concentration was found to increase from 6 to 188 μg m–3 within 5 days. During the most serious polluted episode, the PM1 mass concentration was about 2.6 times that during the first pollution stage and even 40 times that of the clean days. The formation rates of PM2.5 in the five pollution stages were 26, 22, 22, 32, and 67 μg m^（–3） h–1, respectively. Organics and nitrate occupied the largest proportion in the polluted episodes, whereas organics and sulfate dominated the submicron aerosol during the clean days. The size distribution of organics is always broader than those of other species, especially in the clean episodes. The peak sizes of the interested species grew gradually during different HPEs. Aqueous reaction might be important in forming sulfate and chloride, and nitrate was formed via oxidization and condensation processes. PMF（positive matrix factorization） analysis on AMS mass spectra was employed to separate the organics into different subtypes. Two types of secondary organic aerosol with different degrees of oxidation consisted of 43% of total organics. By contrast, primary organics from cooking, coal combustion, and traffic emissions comprised 57% of the organic aerosols during the HPEs.

Chemical characteristics of PM_(2.5) during dust storms and air pollution events in Chengdu,China

Daily fine particulate （PM2.5） samples were collected in Chengdu from April 2009 to February 2010 to investigate their chemical profiles during dust storms （DSs） and several types of pollution events, including haze （HDs）, biomass burning （BBs）, and fireworks displays （FDs）. The highest PM2.5 mass concentrations were found during DSs （283.3 μg/m^3）, followed by FDs （212.7 μg/m^3）, HDs （187.3 μg/m^3 ）, and BBs （130.1 μ g/m^3）. The concentrations of most elements were elevated during DSs and pollution events, except for BBs. Secondary inorganic ions （NO3^- , SO4^2-, and NH4^＋） were enriched during HDs, while PM2.5 from BBs showed high K^＋ but low SO4^2- , FDs caused increases in K^＋ and enrichment in SO4^2-. Ca^2＋. was abundant in DS samples, Ion-balance calculations indicated that PM2.5 from HDs and FDs was more acidic than on normal days, but DS and BB particles were alkaline. The highest organic carbon （OC） concentration was 26.1 μg/m^3 during FDs, followed by BBs （23.6 μg/m^3 ）, HDs （19.6 μg/m^3 ）, and DSs （18.8 μg/m^3 ）. In contrast, elemental carbon （EC） concentration was more abundant during HDs （10.6μg/m^3） and FDs （9.5 μg/m^3） than during BBs （6.2μg/m^3） and DSs （6.0 μg/m^3）. The highest OC/EC ratios were obtained during BBs, with the lowest during HDs. SO4^2＋ /K^＋ and TCA/SO4^2- ratios proved to be effective indicators for differentiating pollution events. Mass balance showed that organic matter, SO4^2-, and NO3^- were the dominant chemical components during pollution events, while soil dust was dominant during DSs.