Extraction of nanosize copper pollutants with an ionic liquid

Speciation and possible reaction paths of nanosize copper pollutants extracted with a RTIL (room-temperature ionic liquid ([C4mim][PF6], 1-butyl-3-methylimidazolium hexafluorophosphate)) have been studied in the present work. Experimentally, in a very short contact time (2 min), 80-95% of nanosize CuO as well as other forms of copper (such as nanosize Cu, Cu2+, or Cu(II)(ads) (in the channels of MCM-41)) in the samples could be extracted into the RTIL. The main copper species extracted in the RTIL as observed by XANES (X-ray absorption near edge structure) were Cu(II). Existence of Cu-N bondings with coordination numbers (CNs) of 3-4 for copper extracted in the RTIL was found by EXAFS (extended X-ray absorption fine structural) spectroscopy. Interestingly, chelation of Cu(II) with 1-methylimidazole (MIm) in the RTIL during extraction was also observed by 1H NMR (nuclear magnetic resonance). At least two possible reaction paths for the rapid extraction of nanosize copper pollutants with the RTIL might occur: (1) an enhanced dissolution of nanosize CuO (to form Cu2+) and (2) formation of [Cu(MIm)4(H2O)2]2+ that acted as a carrier of copper into the RTIL matrix.     

Study of thermally immobilized Cu in analogue minerals of contaminated soils

Thermal immobilization of copper contaminants in soil analogue minerals, quartz and kaolin, at low temperatures such as 300 degrees C is studied to corroborate its technical feasibility as a method for soil remediation. We use a synchrotron-based, X-ray absorption spectroscopy (XAS) technique to study the speciation of and the local structure around copper in the soil analogues that are thermally treated at 300-900 degrees C for 1 h. The toxicity characteristic leaching procedure (TCLP) method is employed to investigate the leaching behavior of copper compounds. CuO, being predominately transformed from Cu(OH)2 with a lesser amount from Cu(NO3)2 by 1-h heat application at 300-900 degrees C, is identified by the spectroscopy of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) as the key species that is leaching-resistant due to its low solubility and its chemisorption onto the soil analogue minerals. Fourier transform of EXAFS spectrum of the Cu-doped kaolin heated at 900 degrees C for 1 h indicates that the intensity of Cu-Cu peaks (2.50 and 5.48 A, both without phase shift correction) is either relatively smaller or disappearing as compared with that of kaolin samples heated at 300 and 500 degrees C. The EXAFS analysis suggests that the Cu solid phase in the 900 degrees C kaolin sample is different from the lower temperature samples, the 900 degrees C SiO2 sample, and the Cu standards. The leaching studies also support the formation of a less soluble phase in the 900 degrees C kaolin sample. An increase of heating temperature, in the range of 105-900 degrees C, reduces the Cu leaching percentage; this reduction trend is more marked for Cu-doped kaolin than for Cu-doped SiO2.     

Identification of the non-pertechnetate species in Hanford waste tanks, Tc(I)--carbonyl complexes

Immobilization of the high-level nuclear waste stored at the Hanford Reservation has been complicated by the presence of soluble, lower-valent technetium species. Previous work by Schroeder and Blanchard has shown that these species cannot be removed by ion-exchange and are difficult to oxidize. The Tc K-edge XANES spectra of the species in Tanks SY-101 and SY-103 were reported by Blanchard, but they could not be assigned to any known technetium complex. We report that the XANES spectra are most likely those of Tc(I)-carbonyl species, especially fac-Tc(CO)3(gluconate)(2-). This is further supported by EXAFS and 99Tc-NMR studies in nonradioactive simulants of these tank wastes.     

Dynamic change of copper in fly ash during de novo synthesis of dioxins

Although many researchers have reported that copper chloride is an important catalyst that generates relatively large amounts of dioxins in heat experiments involving model fly ash, details on the behavior of copper during the process are still unavailable. In this study, we used in situ XANES experiments involving one type of real fly ash, which originated from a municipal solid-waste incinerator (MSWI), and two fly ash models to investigate the behavior of copper in fly ash at temperatures that are suitable for de novo synthesis, which is the major formation route for dioxins during waste incineration and thermal processes. Cupric compounds in real fly ash and model fly ash A(CuCl2.2H2O + activated carbon (AC) + boron nitride (BN)) were reduced to cuprous compounds or elemental copper at low temperatures. The changes in the Cu XANES spectra of real fly ash were similar to those of model fly ash A and those of an oxychlorination catalyst. In model fly ash B (CuO + AC + KCl + BN), CuO did not vary dramatically in the temperature range studied. In this study, we found strong evidence that oxychlorination, the key mechanistic step in the formation of dioxins, occurred in both real MSWI and model fly ash.     

Coordination structure of adsorbed Zn(II) at water-TiO2 interfaces

The local structure of aqueous metal ions on solid surfaces is central to understanding many chemical and biological processes in soil and aquatic environments. Here, the local coordination structure of hydrated Zn(II) at water-TiO(2) interfaces was identified by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopy combined with density functional theory (DFT) calculations. A nonintegral coordination number of average ～4.5 O atoms around a central Zn atom was obtained by EXAFS analysis. DFT calculations indicated that this coordination structure was consistent with the mixture of 4-coordinated bidentate binuclear (BB) and 5-coordinated bidentate mononuclear (BM) metastable equilibrium adsorption (MEA) states. The BB complex has 4-coordinated Zn, while the monodentate mononuclear (MM) complex has 6-coordinated Zn, and a 5-coordinated adsorbed Zn was found in the BM adsorption mode. DFT calculated energies showed that the lower-coordinated BB and BM modes were thermodynamically more favorable than the higher-coordinated MM MEA state. The experimentally observed XANES fingerprinting provided additional direct spectral evidence of 4- and 5-coordinated Zn-O modes. The overall spectral and computational evidence indicated that Zn(II) can occur in 4-, 5-, and 6-oxygen coordinated sites in different MEA states due to steric hindrance effects, and the coexistence of different MEA states formed the multiple coordination environments.     

Mechanisms and products of surface-mediated reductive dehalogenation of carbon tetrachloride by Fe(II) on goethite

Natural attenuation processes of chlorinated solvents in soils and groundwaters are increasingly considered as options to manage contaminated sites. Under anoxic conditions, reactions with ferrous iron sorbed at iron(hyro)xides may dominate the overall transformation of carbon tetrachloride (CCl4) and other chlorinated aliphatic hydrocarbons. We investigated mechanisms and product formation of CCl4 reduction by Fe(II) sorbed to goethite, which may lead to completely dehalogenated products or to chloroform (CHCl3), a toxic product which is fairly persistent under anoxic conditions. A simultaneous transfer of two electrons and cleavage of two C-Cl bonds of CCl4 would completely circumvent chloroform production. To distinguish between initial one- or two-bond cleavage, 13C-isotope fractionation of CCl4 was studied for reactions with Fe(II)/ goethite (isotopic enrichment factor epsilon = -26.5% percent per thousand) and with model systems for one C-Cl bond cleavage and either single-electron transfer (Fe(II) porphyrin, epsilon = -26.1 percent per thousand) or partial two-electron transfer (polysulfide, epsilon = -22.2 percent per thousand). These epsilon values differ significantlyfrom calculations for simultaneous cleavage of two C-Cl bonds (epsilon approximately equal to -50 percent per thousand), indicating that only one C-Cl bond is broken in the critical first step of the reaction. At pH 7, reduction of CCl4 by Fe(II)/ goethite produced approximately 33% CHCl3, 20% carbon monoxide (CO), and up to 40% formate (HCOO-). Addition of 2-propanol-d8 resulted in 33% CDCl3 and only 4% CO, indicating that both products were generated from trichloromethyl radicals (*CCl3), chloroform by reaction with hydrogen radical donors and CO by an alternative pathway likely to involve surface-bound intermediates. Hydrolysis of CO to HCOO-was surface-catalyzed by goethite butwastoo slow to account for the measured formate concentrations. Chloroform yields slightly increased with pH at constant Fe(II) sorption density, suggesting that pH-dependent surface processes direct product branching ratios. Surface-stabilized intermediates may thus facilitate abiotic mineralization of CCl4, whereas the presence of H radical donors, such as natural organic matter, enhances formation of toxic CHCl3.     

叠氮活化烟草多酚氧化酶II的机理

至今人们一直报道叠氮作为金属蛋白(特别是铜蛋白)的一种抑制剂,本研究表明叠氮也可以作为烟草多酚氧化酶Ⅱ (简称PPOⅡ)的激活剂。在天然PPOⅡ、叠氮-PPOⅡ络合物和过氧化物-PPOⅡ络合物的方波电位学研究中,从硝基蓝四唑(nitro bluetetrazolium)能被酶还原和PPOⅡ能被过氧化物激活的试验结果可以看出,叠氮与PPOⅡ的结合诱导了天然PPOⅡ活性中心的CuO₂2-Cu生成了CuO₂2-Cu活性中心结构。叠氮作为激活剂的原因应归因于叠氮分子与PPOⅡ的络合反应导致了CuO₂2-Cu的生成,它恰是过氧化物-PPOⅡ络合物的活性中心,其实质是过氧负离子起到激活剂的作用。      

Deposition of uranium precipitates in dolomitic gravel fill

Uranium-containing precipitates have been observed in a dolomitic gravel fill near the Department of Energy (DOE) S-3 Ponds former waste disposal site as a result of exposure to acidic (pH 3.4) groundwater contaminated with U (33 mg L(-1)), Al3+ (900 mg L(-1)), and NO3- (14 000 mg L(-1)). The U containing precipitates fluoresce a bright green under ultraviolet (UV) short-wave light which identify U-rich coatings on the gravel. Scanning electron microscopy (SEM) microprobe analysis show U concentration ranges from 1.6-19.8% (average of 7%) within the coatings with higher concentrations at the interface of the dolomite fragments. X-ray absorption near edge structure spectroscopy (XANES) indicate that the U is hexavalent and extended X-ray absorption fine structure spectroscopy (EXAFS) shows that the uranyl is coordinated by carbonate. The exact nature of the uranyl carbonates are difficult to determine, but some are best described by a split K(+)-like shell similar to grimselite [K4Na(UO2)(CO3)3 x H2O] and other regions are better described by a single Ca(2+)-like shell similar to liebigite [Ca2(UO2)(CO3)3 x 11(H2O)] or andersonite [Na2CaUO2(CO3)3 x 6H2O]. The U precipitates are found in the form of white to light yellow cracked-formations as coatings on the dolomite gravel and as detached individual precipitates, and are associated with amorphous basalumnite [Al4(SO4)(OH)10 x 4H2O].     

Spectroscopic study of copper(II)--wheat straw cell wall residue surface complexes

The sorption of copper(II) by wheat straw cell wall residue (CWR) was studied and revealed a relatively stable surface complexation on the acid sites of the substrate (carboxylic and phenolic moieties). The copper binding capacity at pH = 5.75 and ionic strength of 0.1 M was evaluated at 63 micromol x g(-1) CWR. The Langmuir and Freundlich isotherm equations were then used to describe the partitioning behavior for the system at different pH values. Batch experiments have been achieved in the presence of calcium in order to mimic the calcareous soil of the Champagne region. A competitive effect on copper complexation has been shown, which is presumably due to the calcium ability to form outer-sphere complexes far less stable than copper(II) ones. Electron spin resonance and X-ray absorption spectroscopy were combined to obtain information on the geometry and structure of Cu bound to CWR. At least two different binding sites for Cu2+ were found to take place in CWR. From ESR parameters, we deduced that copper(II) ions, when complexed with CWR, are coordinated in a square-planar arrangement with four oxygen-containing groups. EXAFS and XANES experiments revealed that Cu(II) is surrounded by four oxygen atoms, with an average Cu-O equatorial distance equal to 1.94 A.     

Surface complexation of copper(II) on soil particles: EPR and XAFS studies

The interactions of transition metals with natural systems play an important role in the mobility and the bioavailability of these metals in soils. In this study, the adsorption of copper(II) onto natural soil particles was studied as a function of pH and metal concentration. The retention capacity of soil particles was determined at pH 6.2 to be equal to 6.7 mg of copper/g of solid. The Langmuir and Freundlich isotherm equations were then used to describe the partitioning behavior of the system at different pH values. A combination of EPR, extended X-ray absorption fine structure (EXAFS), and X-ray absorption near-edge structure (XANES) spectroscopies was used to probe the Cu atomic environment at the soil particles/aqueous interface. The spectroscopic study revealed that copper(II) ions are held in inner-sphere surface complexes. It also revealed that Cu was in an octahedral coordination with first-shell oxygen atoms. A weak tetragonal distortion was pointed out due to the Jahn-Teller effect, with a mean Cu-Oequatorial bond distance of 1.96 A and a Cu-Oaxial bond distance of 2.06 A. A detailed analysis of the spectroscopic data suggested that Cu(II) was bonded to organic matter coated onto the mineral fraction of soil particles.     

Enhanced dechlorination of chlorinated methanes and ethenes by chloride green rust in the presence of copper(II)

The enhanced removal of carbon tetrachloride (CCl4), tetrachloroethene (C2Cl4), and trichloroethene (C2HCl3) by chloride green rust (GR(Cl)) in the presence of copper ions was investigated. X-ray powder diffraction (XRPD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the crystallization and chemical speciation, respectively, of the secondary mineral phases produced in the GR(Cl)-Cu(II) system. The addition of Cu(II) to GR(Cl) suspensions resulted in enhanced dechlorination of the chlorinated hydrocarbons examined in this study. The degradation reactions followed pseudo-first-order kinetics and the pseudo-first-order rate constant (k(obs)) for CCl4 (20 microM) removal by GR(CI) at pH 7.2 was 0.0808 h(-1). Addition of 0.5 mM Cu(II) completely dechlorinated CCl4 within 35 min, and the k(obs) was 84 times greater than that in the absence of Cu(II). Chloroform (CHCl3), the major chlorinated product in CCl4 dechlorination, accumulated at a concentration up to 13 microM in the GR(Cl) system alone, but was completely dechlorinated within 9 h in the GR(Cl)-Cu(II) suspension. Also, rapid removal of C2Cl4 and C2HCl3 by GR(Cl) was observed when Cu(II) was added. The k(obs) values for the removal of chlorinated ethenes were 4.7-7 times higher than that obtained in the absence of Cu(II). In addition, the k(obs) for PCE removal increased linearly with respect to Cu(II) concentrations in the range from 0.1 to 1.0 mM. Addition of Cu(II) at a concentration higher than 1.0 mM decreased the k(obs) for the removal of both C2Cl4 and C2HCl3 due to the decrease in structural Fe(II) concentration in GR(Cl) and the changes in redox potentials and pH values. Moreover, the highest removal efficiency and rate of C2Cl4 was obtained at near-neutral pH when Cu(II) was added into the GR(Cl) suspension. XPS and XRPD results showed that the Fe(II) in the GR(Cl) suspension could reduce Cu(II) to both Cu(I) and metallic Cu. These findings are relevant to the better understanding of the role of abiotic removal of chlorinated hydrocarbons during remediation and/or natural attenuation in iron-reducing environments.     

Speciation and characterization of arsenic in Ketza River mine tailings using X-ray absorption spectroscopy

Ketza River mine tailings deposited underwater and those exposed near the tailings impoundment contain approximately 4 wt % As. Column-leaching tests indicated the potential for high As releases from the tailings. The tailings are composed dominantly of iron oxyhydroxides, quartz, calcite, dolomite, muscovite, ferric arsenates, and calcium-iron arsenates. Arsenopyrite and pyrite are trace constituents. Chemical compositions of iron oxyhydroxide and arsenate minerals are highly variable. The XANES spectra indicate that arsenic occurs as As(V) in tailings, but air-drying prior to analysis may have oxidized lower-valent As. The EXAFS spectra indicate As-Fe distances of 3.35-3.36 A for the exposed tailings and 3.33-3.35 A for the saturated tailings with coordination numbers of 0.96-1.11 and 0.46-0.64, respectively. The As-Ca interatomic distances ranging from 4.15 to 4.18 A and the coordination numbers of 4.12-4.58 confirm the presence of calcium-iron arsenates in the tailings. These results suggest that ferric arsenates and inner-sphere corner sharing or bidentate-binuclear attachment of arsenate tetrahedra onto iron hydroxide octahedra are the dominant form of As in the tailings. EXAFS spectra indicate that the exposed tailings are richer in arsenate minerals whereas the saturated tailings are dominated by the iron oxyhydroxides, which could help explain the greater release of As from the exposed tailings during leaching tests. It is postulated that the dissolution of ferric arsenates during flow-through experiments caused the high As releases from both types of tailings. Arsenic tied to iron oxyhydroxides as adsorbed species are considered stable; however, iron oxyhydroxides having low Fe/As molar ratios may not be as stable. Continued As releases from the tailings are likely due to dissolution of both ferric and calcium-iron arsenates and desorption of As from high-As bearing iron oxyhydroxides during aging.     

Removal of arsenic from groundwater by zerovalent iron and the role of sulfide

Several recent investigations have shown encouraging potential for the removal of arsenic (As) from groundwater by granular zerovalent iron (Fe0). In contrast to previous studies conducted, we have investigated the applicability of this method and the nature of As bonding under conditions with dissolved sulfide. Three column tests were performed over the period of 1 year using solutions with either As(V) or As(II) (2-200 mg/L) in the input solution. Arsenic outflow concentrations decreased from initially 30-100 microg/L to concentrations of below 1 microg/L with time. XANES (X-ray absorptions near edge structure) and EXAFS (expanded X-ray absorption fine structure) spectra indicated that As in the solid phase is not only directly coordinated with oxygen, as is the case in adsorbed or coprecipitated arsenite and arsenate. Samples with high sulfur content showed additional bonding, for which Fourier transformations of EXAFS data exhibited a peak between 2.2 and 2.4 A. This bonding most likely originated from the direct coordination of sulfur or iron with As, which was incorporated in iron sulfides orfrom adsorbed thioarsenites. The formation of this sulfide bonding supports the removal of As by Fe0 because sulfide production by microbial sulfate reduction is ubiquitous in permeable reactive barriers composed of Fe0.     

Spectroscopic investigation of Cr(III)- and Cr(VI)-treated nanoscale zerovalent iron

The reaction of hexavalent chromium (Cr(VI)) with zerovalent iron (Fe0) during soil and groundwater remediation is an important environmental process. This study used several techniques including X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy to investigate nanometer scale Fe0 particles (nano Fe0) treated with Cr(III) and Cr(VI). X-ray diffraction and XPS analyses of oxidized nano Fe0 showed the crystalline Fe(III) phase is composed of lepidocrocite (gamma-FeOOH). Results of XPS Cr 2p data and Cr K-edge X-ray absorption near edge spectroscopy (XANES) provided evidence that Cr(VI) was entirely reduced to Cr(III) by nano Fe0 with no residual Cr(VI) after reaction. In addition, XPS and XANES results of Cr(III) precipitated as Cr(OH)3 in the presence of corroding nano Fe0 were nearly identical to the Cr(VI)-nano Fe0 reaction product. Detailed analysis of XPS O 1s line spectra revealed that both Cr(III)- and Cr(VI)-treated nano Fe0 yielded a predominantly hydroxylated Cr(OH)3 and/ or a mixed phase CrxFe(1 - x)(OH)3 product. The structure of the Cr(III)- and Cr(VI)-treated nano Fe0 determined using extended X-ray absorption fine structure spectroscopy (EXAFS) revealed octahedral Cr(III) with Cr-O interatomic distances between 1.97 and 1.98 A for both Cr(III) and Cr(VI) treatments and a pronounced Cr-Cr second interatomic shell at 3.01 A. Our results suggest that the reaction product of Cr(VI)-treated nano Fe0 is either a poorly ordered Cr(OH)3 precipitate or possibly a mixed phase CrxFe(1 - x)(OH)3 product, both of which are highly insoluble under environmental conditions.     

Combined speciation analysis by X-ray absorption near-edge structure spectroscopy, ion chromatography, and solid-phase microextraction gas chromatography-mass spectrometry to evaluate biotreatment of concentrated selenium wastewaters

In this study we evaluate the potential of anaerobic granular sludge as an inoculum for the bioremediation of selenium-contaminated waters using species-specific analytical methods. Solid species formed by microbial reduction were investigated using X-ray absorption near-edge structure (XANES) spectroscopy at the selenium K-edge. Furthermore, dissolved selenium species were specifically determined by ion chromatography (IC) and solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS). Least-squares linear combination of the XANES spectra for samples incubated with the highest selenate/selenite concentrations (10(-3) M) show the predominance of elemental selenium and a Se(-I) selenide, such as ferroselite, the thermodynamically most stable iron selenide. In contrast, elemental selenium and Se(-II) selenides are the main species detected at the lower selenate/selenite concentrations. In each repeated fed batch incubation, most aqueous selenite anions were converted into solid selenium species, regardless of the type of electron donor used (acetate or H(2)/CO(2)) and the selenium concentration applied. On the other hand, at higher concentrations of selenate (10(-4) and 10(-3) M), significant amounts of the oxyanion remained unconverted after consecutive incubations. SPME-GC-MS demonstrated selenium alkylation with both electron donors investigated, as dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe). Selenite was even more alkylated in the presence of H(2)/CO(2) (maximum 2156 μg of Se/L of DMSe + DMDSe) as compared to acetate (maximum 50 μg of Se/L). In contrast, selenate was less alkylated using both electron donors (maximum 166 and 3 μg of Se/L, respectively). The high alkylation potential for selenite limits its bioremediation in selenium laden waters involving H(2)/CO(2) as the electron donor despite the fact that nontoxic elemental selenium and thermodynamically stable metal selenide species are formed.     

Mechanism of europium retention by calcium silicate hydrates: an EXAFS study

The uptake of Eu by calcium silicate hydrate (C-S-H) phases as a function of Eu/sorbate ratio (from 37 to 450 micromol g(-1) C-S-H), C-S-H Ca/Si mole ratio (1.3, 1.0, and 0.7), and initial supersaturating conditions was probed by solution kinetics experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy, to shed light on the retention mechanism of trivalent radionuclides under waste repository conditions. The rates of Eu (9.7 x 10(-10) M) uptake in C-S-H suspensions and in solutions at equilibrium with C-S-H were rapid. Uptake of more than 90% of dissolved Eu was generally observed within 15 min. Europium LIII-edge EXAFS spectra collected on samples of Eu sorbed on, or coprecipitated in, C-S-H differed from that of Eu(OH)3(s) expected to precipitate under the pH conditions of C-S-H waters, ruling out compelling precipitation of pure hydroxide phases. Fourier transforms for EXAFS spectra for Eu in sorption/coprecipitation samples displayed comparable features at distances typical of neighboring cationic shells, pointing to similar crystallochemical environments. Optimal spectral simulations were obtained by assuming the presence of Si, Si/Ca, and Ca cationic shells surrounding Eu at distances of 3.2, 3.7-3.8, and 3.8-3.9 A, respectively. The nearly continuous distribution of (Si, Ca) backscattering shells parallels the distribution in Ca-(Ca, Si) interatomic distances in structural models of C-S-H. Discernible effects of experimental parameters on the Eu local environment were observed by comparison of Fourier transforms, but could not be confirmed by EXAFS quantitative analysis. These results indicate that sorbed or coprecipitated Eu is located at Ca structural sites in a C-S-H-like environment. Kinetics and spectroscopic results are consistent with either Eu diffusion within C-S-H particles or precipitation of Eu with Ca and Si creating a C-S-H-like solid phase.     

EXAFS study on the reactions between iron and fulvic acid in acid aqueous solutions

Iron(III) competes with trace metals for binding sites on organic ligands. We used X-ray absorption fine structure (EXAFS) spectroscopy to determine the binding mode and oxidation state of iron in solutions initially containing only iron(III) and fulvic acid at pHs 2 and 4. EXAFS spectra were recorded at different times after sample preparation. Iron was octahedrally configured with inner-sphere Fe-O interactions at 1.98-2.10 A, depending on the oxidation state of iron. Iron(III) formed complexes with fulvic acid within 15 min. Iron(III) was reduced to iron(II) with time at pH 2, whereas no significant reduction occurred at pH 4. No signs of dimeric/trimeric hydrolysis products were found in any of the solution samples (<0.45 microm). However, the isolated precipitate of the pH 2 sample (>0.45 microm) showed Fe...Fe distances, indicating the presence of tightly packed iron(III) trimers and/or clusters of corner-sharing octahedra. It is suggested that the binding mode of iron(III) to fulvic acid at low pH may be phase-dependent: in solution mononuclear complexes predominate, whereas in the solid phase hydrolyzed polynuclear iron(III) complexes form, even at very low pH values. The observed pH dependence of iron(III) reduction was consistent with expected results based on thermodynamic calculations for model ligands.     

Partitioning CO2 effluxes from an Atlantic pine forest soil between endogenous soil organic matter and recently incorporated 13C-enriched plant material

Soil CO2 effluxes from recently added 13C-labeled phytomass versus endogenous soil organic matter (SOM) were studied in an acid soil from Atlantic pine forests (NW Spain). After several cultures to incorporate fresh 13C-enriched Lolium perenne to a Humic Cambisol with predominance of humus--Al over humus--Fe complexes, potential soil C mineralization was determined by laboratory aerobic incubation (84 days). Isotopic 13C analyses of SOM fractions were assessed to know in which organic compartments the 13C was preferentially incorporated. Although in the 13C-labeled soil the C mineralization coefficient totalized less than 3% of soil C, the 13C mineralization coefficient exceeded 14%, indicating a greater lability of the newly incorporated organic matter. Organic compounds coming from added phytomass showed a higher lability and contributed considerably to the total soil CO2 effluxes (52% of total soil CO2 evolved during the first decomposition stages and 27% at the end), even though added-C comprised less than 4% of total soil C. Good determination coefficients, when values of CO2--C released were fitted to a first-order double exponential kinetic model, support the existence of two C pools of different lability. Kinetic parameters obtained with this model indicated that phytomass addition augmented the biodegradability of the labile pool (instantaneous mineralization rate k increased from 0.07 d(-1) to 0.12 d(-1)) but diminished that of the recalcitrant pool (instantaneous mineralization rate h decreased from 2.7 x 10(-4) d(-1) to 1.6 x 10(-4) d(-1)). Consequently, the differentiation between both SOM pools increased, showing the importance of SOM quality on CO2 emissions from this kind of soil to the atmosphere.     

Speciation of arsenic, chromium, and vanadium in red mud samples from the Ajka spill site, Hungary

Results are presented from X-ray absorption spectroscopy based analysis of As, Cr, and V speciation within samples of bauxite ore processing residue (red mud) collected from the spill site at Ajka, Western Hungary. Cr K-edge XANES analysis found that Cr is present as Cr(3+) substituted into hematite, consistent with TEM analysis. V K-edge XANES spectra have E(1/2) position and pre-edge features consistent with the presence of V(5+) species, possibly associated with Ca-aluminosilicate phases. As K-edge XANES spectra identified As present as As(5+). EXAFS analysis reveals arsenate phases in red mud samples. When alkaline leachate from the spill site is neutralized with HCl, 94% As and 71% V are removed from solution during the formation of amorphous Al-oxyhydroxide. EXAFS analysis of As in this precipitate reveals the presence of arsenate Al-oxyhydroxide surface complexes. These results suggest that in the circumneutral pH, oxic conditions found in the Torna and Upper Marcal catchments, incorporation and sorption, respectively, will restrict the environmental mobility of Cr and As. V is inefficiently removed from solution by neutralization, therefore, the red mud may act as a source of mobile V(5+) where the red mud deposits are not removed from affected land.     

Optimizing municipal solid waste combustion through organic and elemental carbon as indicators

The temperature, redox conditions, and residence times of the solid waste on the grate and of the raw gas in the secondary combustion zone determine the mineralization processes of organics in municipal solid waste incinerators. An improved knowledge of the influence of these factors on the incineration process might help to optimize incinerators with regard to mineralization efficiency of organics. This paper presents a method for investigating the influence of process parameters on mineralization of organics to CO2 by using the elemental carbon (EC) and organic carbon (OC) concentrations in the solid residues as indicators. The results obtained by experiments in full-scale incinerators show that the EC concentration in these residues is a good indicator of oxygen supply, whereas the OC/EC ratio is a good indicator of temperature in and above the furnace bed. Very effective burnout of the bottom ash up to 0.95 g of TOC (EC + OC) per kilogram of dry matter (DM) and of the electrostatic precipitator (ESP) ash up to 0.24 g of TOC per kilogram of DM was achieved in a full-scale incinerator.