Reduction of Ag(I), Au(III), Cu(II), and Hg(II) by Fe(II)/Fe(III) hydroxysulfate green rust

Green rusts are mixed Fe(II)/Fe(III) hydroxides that are found in many suboxic environments where they are believed to play a central role in the biogeochemical cycling of iron. X-ray absorption fine structure analysis of hydroxysulfate green rust suspensions spiked with aqueous solutions of AgCH(3)COO, AuCl(n)(OH)(4-n), CuCl(2), or HgCl(2) showed that Ag(I), Au(III), Cu(II), and Hg(II) were readily reduced to Ag(0), Au(0), Cu(0), and Hg(0). Imaging of the resulting solids from the Ag(I)-, Au(III)-, and Cu(II)-amended green rust suspensions by transmission electron microscopy indicated the formation of submicron-sized particles of Ag(0), Au(0), and Cu(0). The facile reduction of Ag(I), Au(III), Cu(II), and Hg(II) to Ag(0), Au(0), Cu(0), and Hg(0), respectively, by green rust suggests that the presence of green rusts in suboxic soils and sediments can have a significant impact on the biogeochemistry of silver, gold, copper, and mercury, particularly with respect to their mobility.     

Atmospheric chemistry of HFE-7000 (CF(3)CF (2)CF (2)OCH (3)) and 2,2,3,3,4,4,4-heptafluoro-1-butanol (CF (3)CF (2)CF (2)CH (2)OH): kinetic rate coefficients and temperature dependence of reactions with chlorine atoms

Background, aim, and scope  The adverse environmental impacts of chlorinated hydrocarbons on the Earth’s ozone layer have focused attention on the effort to replace these compounds by nonchlorinated substitutes with environmental acceptability. Hydrofluoroethers (HFEs) and fluorinated alcohols are currently being introduced in many applications for this purpose. Nevertheless, the presence of a great number of C–F bonds drives to atmospheric long-lived compounds with infrared absorption features. Thus, it is necessary to improve our knowledge about lifetimes and global warming potentials (GWP) for these compounds in order to get a complete evaluation of their environmental impact. Tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase. Nevertheless, Cl atoms reaction may also be important since rate constants are generally larger than those of OH. In the present work, we report the results obtained in the study of the reactions of Cl radicals with HFE-7000 (CF₃CF₂CF₂OCH₃) (1) and its isomer CF₃CF₂CF₂CH₂OH (2). Materials and methods  Kinetic rate coefficients with Cl atoms have been measured using the discharge flow tube–mass spectrometric technique at 1 Torr of total pressure. The reactions of these chlorofluorocarbons (CFCs) substitutes have been studied under pseudo-first-order kinetic conditions in excess of the fluorinated compounds over Cl atoms. The temperature ranges were 266–333 and 298–353 K for reactions of HFE-7000 and CF₃CF₂CF₂CH₂OH, respectively. Results  The measured room temperature rate constants were k(Cl+CF₃CF₂CF₂OCH₃) = (1.24 ± 0.28) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹and k(Cl+CF₃CF₂CF₂CH₂OH) = (8.35 ± 1.63) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ (errors are 2σ + 10% to cover systematic errors). The Arrhenius expression for reaction 1 was k ₁(266–333 K) = (6.1 ± 3.8) × 10⁻¹³exp[−(445 ± 186)/T] cm³ molecule⁻¹ s⁻¹ and k ₂(298–353 K) = (1.9 ± 0.7) × 10⁻¹²exp[−(244 ± 125)/T] cm³ molecule⁻¹ s⁻¹ (errors are 2σ). The reactions are reported to proceed through the abstraction of an H atom to form HCl and the corresponding halo-alkyl radical. At 298 K and 1 Torr, yields on HCl of 0.95 ± 0.38 and 0.97 ± 0.16 (errors are 2σ) were obtained for CF₃CF₂CF₂OCH₃ and CF₃CF₂CF₂CH₂OH, respectively. Discussion  The obtained kinetic rate constants are related to the previous data in the literature, showing a good agreement taking into account the error limits. Comparing the obtained results at room temperature, k ₁ and k ₂, HFE-7000 is significantly less reactive than its isomer C₃F₇CH₂OH. A similar behavior has been reported for the reactions of other fluorinated alcohols and their isomeric fluorinated ethers with Cl atoms. Literature data, together with the results reported in this work, show that, for both fluorinated ethers and alcohols, the kinetic rate constant may be considered as not dependent on the number of –CF₂– in the perfluorinated chain. This result may be useful since it is possible to obtain the required physicochemical properties for a given application by changing the number of –CF₂– without changes in the atmospheric reactivity. Furthermore, lifetimes estimations for these CFCs substitutes are calculated and discussed. The average estimated Cl lifetimes are 256 and 38 years for HFE-7000 and C₃H₇CH₂OH, respectively. Conclusions  The studied CFCs’ substitutes are relatively short-lived and OH reaction constitutes their main reactive sink. The average contribution of Cl reactions to global lifetime is about 2% in both cases. Nevertheless, under local conditions as in the marine boundary layer, τ _Cl values as low as 2.5 and 0.4 years for HFE-7000 and C₃H₇CH₂OH, respectively, are expected, showing that the contribution of Cl to the atmospheric degradation of these CFCs substitutes under such conditions may constitute a relevant sink. In the case of CF₃CF₂CF₂OCH₃, significant activation energy has been measured, thus the use of kinetic rate coefficient only at room temperature would result in underestimations of lifetimes and GWPs. Recommendations and perspectives  The results obtained in this work may be helpful within the database used in the modeling studies of coastal areas. The knowledge of the atmospheric behavior and the structure–reactivity relationship discussed in this work may also contribute to the development of new environmentally acceptable chemicals. New volatile materials susceptible of emission to the troposphere should be subject to the study of their reactions with OH and Cl in the range of temperature of the troposphere. The knowledge of the temperature dependence of the kinetic rate constants, as it is now reported for the case of reactions 1 and 2, will allow more accurate lifetimes and related magnitudes like GWPs. Nevertheless, a better knowledge of the vertical Cl tropospheric distribution is still required.     

Simultaneous conversion of CHClF(2) and CH(3)Br to CH(2)CF(2)

Gas phase reaction of CHClF(2) with CH(3)Br in an alumina tube reactor at 773-1123 K as a function of various input ratios of CH(3)Br to CHClF(2) is presented. The major products detected include C(2)F(4), CH(2)CF(2), and CH(4). Minor products include CH(3)Cl, CHF(3), C(2)H(4), C(2)H(2), CH(2)CF-CF(3), and C(2)H(3)F. The reaction produces a high yield of CH(2)CF(2) (53% based on CHClF(2) feed) at 1123 K and an input molar ratio of CH(3)Br to CHClF(2) of 1.8, suggesting that the reaction potentially can be developed as a process to convert two ozone depleting substances (CHClF(2) and CH(3)Br) to a highly valuable chemical, CH(2)CF(2). The reaction of CHClF(2) with CH(3)Cl and CH(3)I was also investigated under similar reaction conditions, to assist in understanding the reaction chemistry involved in the reaction of CHClF(2) with CH(3)Br.     

Effects of Mn(II) and Fe(II) on microbial removal of arsenic (III)

Goal, scope, and background  Arsenic contamination in groundwater creates severe health problems in the world. There are many physiochemical and biological methods available for remediation of arsenic from groundwater. Among them, microbial remediation could be taken as one of the least expensive methods, though it takes longer treatment time. The main objective of this research was to study the improvement on remediation by addition of some essential ion salts such as Mn and Fe. Materials and methods   Staphylococcus aureus, Bacillus subtilis, Klebsiella oxytoca, and Escherichia coli were taken as model microbes from Dhulikhel, 30 km east from Kathmandu, Nepal. Results and discussion  Microbes used in this study showed different abilities in their removal of As(III) with and without addition of Mn and Fe salts. The trend of remediation increased with time. S. aureus was found to be the best among the microbes used. It showed almost 100% removal after 48-h culture, both with and without Fe and Mn salts. Rate of removal of As increased with addition of Fe and Mn for all microbes. Removal efficiency was found to increase by about 32% on average after addition of salts in 24-h cultures of S. aureus.     

Quick vaporization of sprayed sodium hypochlorite (NaClO(aq)) for simultaneous removal of nitrogen oxides (NOx), sulfur dioxide (SO2), and mercury (Hg0)

Sodium hypochlorite (NaClO) has been widely used as a chemical additive for enhancing nitrogen oxide (NO_x; NO + NO₂), sulfur dioxide (SO₂), and mercury (Hg⁰) removals in a wet scrubber. However, they are each uniquely dependent on NaClO_(aq) pH, hence making the simultaneous control difficult. In order to overcome this weakness, we sprayed low liquid-to-gas (L/G) ratio (0.1 L/Nm³) of NaClO_(aq) to vaporize quickly at 165 °C. Results have shown that the maximized NO_x, SO₂, and Hg⁰ removals can be achieved at the pH range between 4.0 and 6.0. When NO_x and Hg⁰ coexist with SO₂, in addition, their removals are significantly enhanced by reactions with solid and gaseous by-products such as NaClO_(s), NaClO_2(s), OClO, ClO, and Cl species, originated from the reaction between SO₂ and NaClO_(aq). We have also demonstrated the feasibility of this approach in the real flue gases of a combustion plant and observed 50%, 80%, and 60% of NO_x, SO₂, and Hg⁰ removals, respectively. These findings led us to conclude that the spray of NaClO_(aq) at a relatively high temperature at which the sprayed solution can vaporize quickly makes the simultaneous control of NO_x, SO₂, and Hg⁰ possible.

Implications: The simple spray of NaClO_(aq) at temperatures above 165 °C can cause the simultaneous removal of gaseous NO_x, SO₂, and Hg⁰ by its quick vaporization. Their maximized removals are achieved at the pH range between 4.0 and 6.0. NO_x and Hg⁰ removals are also enhanced by gaseous and solid intermediate products generated from the reaction of SO₂ with NaClO_(aq). The feasibility of this approach has been demonstrated in the real flue gases of a combustion plant.     

Effect of N-hydroxyethyl-ethylenediamine-triacetic acid (HEDTA) on Cr(VI) reduction by Fe(II)

The complexation of Fe(II) with organic ligand results in the decrease of redox potential, and enhances the reduction ability of Fe(II). An important example is the use of Fe(II)-organic complexes to accelerate Cr(VI) reduction. Dissolved O(2) and light can potentially affect Cr(VI) reduction; however, these two factors have not been adequately evaluated. A batch technique was used to investigate the Cr(VI) reduction as influenced by the light and dissolved O(2) using N-hydroxyethyl-ethylenediamine-triacetic acid (HEDTA) and Fe(II) solutions. The oxidation of Fe(II) by dissolved O(2) was rapid in the presence of HEDTA at low pH; nonetheless, the oxidation proceeded slowly when HEDTA was absent. Although Cr(VI) could be reduced by free Fe(II) at low pH, the reaction was considerably slower than that of systems involving HEDTA. The enhancement of Cr(VI) reduction by Fe(II) in the presence of high concentrations of HEDTA was achieved as a result of two processes. First, HEDTA acted as a ligand for expediting electron transfer between Fe(II) and Cr(VI). Secondly, HEDTA served as a reductant for Cr(VI) under illumination.     

Abiotic reduction of antimony(V) by green rust (Fe(4)(II)Fe(2)(III)(OH)(12)SO(4).3H(2)O)

Green rust (Fe(4)(II)Fe(2)(III)(OH)(12)SO(4).3H(2)O) is an intermediate phase in the formation of iron (oxyhydr)oxides such as goethite, lepidocrocite, and magnetite. It is widely considered that green rust occurs in many soil and sediment systems. Green rust has been shown to reduce sorbed Se(VI), Cr(VI), and U(VI). In addition, it is also reported that green rust does not reduce As(V) to As(III). In this study, we have investigated for the first time the interaction between Sb(V) and green rust using XAFS and HPLC-ICP-MS. Most of the added Sb(V) was adsorbed on green rust, and Sb(III), a reduced form, was observed in both solid and liquid phases. Thus, it was shown that green rust has high affinity for Sb(V), and that Sb(V) was reduced to more toxic Sb(III) by green rust despite the high stability of the Sb(V) species even under reducing condition as reported in previous studies. Therefore, green rust can be one of the most important reducing agents for Sb(V), which can influence the Sb mobility in suboxic environments where green rust is formed.     

Influence of ozone and acid mist on the contents of gibberellic acid (GA(3)) in spruce needles (Picea abies) (L.) Karst

The phytohormone GA(3) in needles from 4-year-old Norway spruce trees was analyzed after treatment with ozone and acid mist in environmental chambers under controlled conditions. GA(3) was extracted with methanol from the lyophilized material. Subsequent purification steps included the use of polyvinylpyrollidone (PVP), cartridge reversed-phase purification, ethylacetate extraction and HPLC. The GA(3) was determined in the methylated form by means of a highly specific and sensitive enzyme immunoassay. Higher GA(3) contents were detected in young needles (year 1987) as compared to older ones (year 1986). However, no statistically significant differences were found in the GA(3) levels between the controls and the needles of trees which were treated with increased levels of ozone and acidic mist.     

Adsorption of arsenic(V) by iron-oxide-coated diatomite (IOCD)

Purposes and aims  

Economically efficient methods for removing arsenic from the drinking water supply are urgently needed in many parts of the world. Iron oxides are known to have a strong affinity for arsenic in water. However, they are commonly present in the forms of fine powder or floc, which limits their utility in water treatment. In this study, a novel granular adsorbent, iron-oxide-coated diatomite (IOCD), was developed and examined for its adsorption of arsenic from water.     

The ability of Azolla caroliniana to remove heavy metals (Hg(II), Cr(III), Cr(VI)) from municipal waste water

The aim of this paper was to investigate the capacity of a small water fern, Azolla caroliniana Willd. (Azollaceae), to purify waters polluted by Hg and Cr. Many plants are capable of accumulating heavy metals (called hyperaccumulators) and one of them is the water fern A. caroliniana. During 12 days of the experiment the fern was grown on the nutrient solution containing Hg2+, Cr3+ and CrO4(2-) ions, each in a concentration 0.1, 0.5 and 1.0 mg dm(-3). The presence of these ions caused a 20-31% inhibition of A. caroliniana growth, the highest in the presence of Hg(II) ions, in comparison to the control. After day 12 of the experiment, metal contents the solution decreased to 0-0.25 mg dm(-3), and this decrease comprised between 74 (Cr3+ 1.0 mg dm(-3) treatment) and 100% (CrO4(2-) 0.1 mg dm(-3) treatment). The fern took a lesser quantity of the metals from 0.1 mg dm(-3) treatments compared to 0.5 and 1.0 mg dm(-3) treatments. In the A. caroliniana tissues the concentration of heavy metals under investigation ranged from 71 to 964 mg kg(-1) dm; the highest level being found for Cr(III) containing nutrient solution.     

Photolysis of 2-(2-furyl)benzimidazole (Fuberidazole)

The photooxidatior. of 2-(4-thiazolyl)-1H-benzimidazole (Thia=bendazole (1) in methanol in presence and absence of a photo=sensitizer (methylene blue), is investigated. Dimethyl oxalate, thiazole-4-(N-carbomethoxy)-carboxamide (6), methyl benzimida=zole-2-carboxylate (7), benzimidazole-2-carboxamide (8), and benzimidazole (9), were the main products of the photolysis. Some reaction mechanisms are discussed.     

The effect of triethylene tetramine upon the selective removal of nickel (II), iron (II), manganese (II) and tin (II) in rats

The distribution of Nickel-63, Iron-59, Manganese-54 and Tin-113 in plasma was studied in rats which received single intravenous (i.v.) injection of aqueous solutions of their salts alone, and in rats which also received single intramuscular (im) injection of triethylene tetramine (TETA). TETA was extremely effective in reducing the plasma concentration of Nickel-63 followed by that of Iron-59, Manganese-54 and Tin-113.     

Degradation of 2,7-dichlorodibenzo-p-dioxin by Fe(3+)-H(2)O(2) mixed reagent

Fe(3+)-H(2)O(2) mixed reagent, but not Fe(2+)-H(2)O(2), was found to be capable of degrading 2,7-dichlorodibenzo-p-dioxin (DCDD). A reaction mixture of FeCl(3) (8 mM) and H(2)O(2) (1%) caused approximately 50% degradation within 6 h and >90% degradation within 24 h at 27 degrees C. Increasing the temperature remarkably stimulated degradation: at 70 degrees C, approximately 100% degradation was achieved within 15 min. When DCDD-treated model soil (5 micrograms/g) was conducted, approximately 100% of the DCDD was degraded within 30 min at 70 degrees C (both reagents were added every 10 min). These results suggest that Fe(3+)-H(2)O(2) mixed reagent may be a new tool for combating persistent environmental pollutants such as dioxins and polychlorinated biphenyls.     

Adsorption of As(III) on chitosan-Fe-crosslinked complex (Ch-Fe)

It was reported the adsorption of As(III) on the surface of the chitosan-Fe-crosslinked complex. Theoretical correlation of the experimental equilibrium adsorption data for As(III)/Ch-Fe system is best explained by the non-linearized form Langmuir-Freundlich isotherm model. At optimum conditions, pH 9.0, the maximum adsorption capacity, calculated using the Langmuir-Freundlich isotherm model was 13.4 mg g⁻¹. The adsorption kinetics of As(III) onto Ch-Fe are described by the pseudo-first-order kinetic equation. The results of the Mössbauer spectroscopy showed that there is no redox process on the surface of the adsorbent.     

Comparison of Fe(VI) (FeO4(2-)) and ozone in inactivating Bacillus subtilis spores

The protozoan parasites such as Cryptosporidiumparvum and Giardialamblia have been recognized as a frequent cause of recent waterborne disease outbreaks because of their strong resistance against chlorine disinfection. In this study, ozone and Fe(VI) (i.e., FeO(4)(2-)) were compared in terms of inactivation efficiency for Bacillus subtilis spores which are commonly utilized as an indicator of protozoan pathogens. Both oxidants highly depended on water pH and temperature in the spore inactivation. Since redox potential of Fe(VI) is almost the same as that of ozone, spore inactivation efficiency of Fe(VI) was expected to be similar with that of ozone. However, it was found that ozone was definitely superior over Fe(VI): at pH 7 and 20°C, ozone with the product of concentration×contact time (CˉT) of 10mgL(-1)min inactivate the spores more than 99.9% within 10min, while Fe(VI) with CˉT of 30mgL(-1) min could inactivate 90% spores. The large difference between ozone and Fe(VI) in spore inactivation was attributed mainly to Fe(III) produced from Fe(VI) decomposition at the spore coat layer which might coagulate spores and make it difficult for free Fe(VI) to attack live spores.     

Use of natural clinoptilolite to improve water quality: sorption and selectivity studies of lead(II), copper(II), zinc(II), and nickel(II).

Natural clinoptilolite can be used as an ion exchanger for removal of heavy metals and treatment of environmental pollution because of its desirable characteristics of high ion exchange selectivity and resistance to different media. In this work, the potential of natural clinoptilolite from G?rdes mines (West Anatolia, Turkey) for the uptake of lead(II), nickel(II), copper(II), and zinc(II), from their single and mixed ion solutions, was evaluated using the batch method. The mineralogical and chemical properties of the sorption material were carried out by X-ray diffraction, X-ray fluoremetry, scanning electron microscopy, and wet analysis. Contact time, initial solution pH, solid-to-liquid ratio, and initial metal cation concentration were determined as single ion sorption parameters. The silicon/aluminum ratio and the theoretical and equivalent exchange capacities, both in single and mixed solutions, were established. Corresponding adsorption constants and distribution coefficients have been found.     

Phytoextraction of cadmium by rice (Oryza sativa L.), soybean (Glycine max (L.) Merr.), and maize (Zea mays L.)

Selecting a phytoextraction plant with high Cd-accumulating ability based on the plant's compatibility with mechanized cultivation techniques may yield more immediately practical results than selection based on high tolerance to Cd. Rice (Oryza sativa L., cv. Nipponbare and Milyang 23), soybean (Glycine max [L.] Merr., cv. Enrei and Suzuyutaka), and maize (Zea mays L., cv. Gold Dent) were grown on one Andosol and two Fluvisols with low concentration of Cd contamination ranging from 0.83 to 4.29 mg Cd kg(-1), during 60 days in pots (550 mL) placed in a greenhouse. Shoot Cd uptake was as follows: Gold Dent相似文献   

Comparative and competitive adsorption of Cr(VI), As(III), and Ni(II) onto coconut charcoal

This study evaluates the behavior of coconut charcoal (AC) to adsorb Cr(VI), As(III), and Ni(II) in mono- and multicomponent (binary and ternary) systems. Batch experiments were carried out for mono- and multicomponent systems with varying metal ion concentrations to investigate the competitive adsorption characteristics. The adsorption kinetics followed the mechanism of the pseudo-second-order equation in both single and binary systems, indicating chemical sorption as the rate-limiting step of adsorption mechanism. Equilibrium studies showed that the adsorption of Cr(VI), As(III), and Ni(II) followed the Langmuir model and maximum adsorption capacities were found to be 5.257, 0.042, and 1.748 mg/g, respectively. In multicomponent system, As(III) and Ni(II) adsorption competed intensely, while Cr(VI) adsorption was much less affected by competition than As(III) and Ni(II). With the presence of Cr(VI), the adsorption capacities of As(III) and Ni(II) on AC were higher than those in single system and the metal sorption followed the order of Ni(II)?>?As(III)?>?Cr(VI). The results from the sequential adsorption–desorption cycles showed that AC adsorbent held good desorption and reusability.     

As(V) and Sb(V) co-adsorption onto ferrihydrite: synergistic effect of Sb(V) on As(V) under competitive conditions

Competitive adsorption of As(V) and Sb(V) at environmentally relevant concentrations onto ferrihydrite was investigated. Batch experiments and XPS analyses confirmed that in a binary system, the presence of Sb(V) exhibited a slight synergistic effect on As(V) adsorption. XPS analyses showed that As(V) and Sb(V) adsorption led to obvious diminishment of Fe–O–Fe and Fe–O–H bonds respectively. At pH of 9, a more significant decrease of Fe–O–Fe was observed in the binary system than that in a single system, indicating that As(V) displayed an even stronger interaction with lattice oxygen atoms under competitive conditions. Basically, ionic strength demonstrated a negligible or positive influence on As(V) and Sb(V) adsorption in binary system. Study of adsorption sequence also indicated that the presence of Sb(V) showed a promotion effect on As(V) adsorption at neutral pHs. Considering that co-contamination of As and Sb in waters has been of great concern throughout the world, our findings contributed to a better understanding of their distribution, mobility, and fate in environment.

     

Biomagnification of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) studied in pike (Esox lucius), perch (Perca fluviatilis) and roach (Rutilus rutilus) from the Baltic Sea

Pike, perch and roach from rural waters of the Baltic Sea were investigated for possible biomagnification of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). For this we used data on delta15N, weight and sex of the fish. We were able to separate body size effects from trophic position effects on biomagnification. Both these parameters lead to biomagnification of PCBs and PBDEs. All investigated PCBs (tri- to deca-CBs) biomagnify and the biomagnification potential is positively correlated with hydrophobicity up to log Kow 8.18. Tri- to hepta-BDEs also biomagnify but showed a maximum biomagnification for the penta-BDEs (log Kow 6.46-6.97). The biomagnification of hexa- to hepta-PBDEs was negatively correlated with degree of bromination, likely due to large molecular size or high molecular weight (644-959 Da). Octa-, nona- and deca-BDEs did not biomagnify but were found in two (octa-BDE) and three (nona- and deca-BDEs) of the species, respectively. Increased size of pike is correlated with increased lipid weight based PCB and PBDE concentrations in males but not in females and mean PCB and PBDE concentrations in males are generally higher than in females. For the least hydrophobic PCBs, no sex difference is observed, probably as a consequence of faster clearance of these substances over the gills, making the spawning clearance of PCBs and PBDEs of lesser relative importance.