Changes In Speciation Research Articles

Chemical speciation effects on the volumetric properties of aqueous sulfuric acid solutions

Densities of fifteen aqueous solutions of sulfuric acid (H2SO4) have been measured by vibrating-tube densimetry at solute molalities (m) from (0.01 to 3.0) mol·kg−1 over the temperature range 293.15 ≤ T/K ≤ 343.15. These data have been used to calculate the corresponding apparent molar volumes Vϕ(H2SO4,aq), which represent a significant expansion of the volumetric database for this industrially-important acid. At 298.15 K the present results agree well with literature data, notably with the century-old values given in the 1926 International Critical Tables. At other temperatures, where comparisons are possible agreement with the present Vϕ values is also very satisfactory. Consistent with earlier studies, Vϕ(H2SO4,aq) was found to exhibit an abnormally-large decrease at low concentrations (m ≤ 0.1 mol·kg−1). This effect is consistent with a change in the chemical speciation of H2SO4(aq), from an essentially 1:1 electrolyte (H+(aq) + HSO4− (aq)) at higher concentrations to a predominantly 1:2 electrolyte (2H+(aq) + SO42− (aq)) in dilute solutions. The Vϕ values were modelled using variants of Young’s rule and the Pitzer formalism. Combination of these results with literature values for the standard volume V°(SO42−,aq) enabled estimation of V°(HSO4−,aq) and the standard volume change, ΔrV°, for the first protonation of the sulfate ion (H+(aq) + SO42−(aq) → HSO4−(aq)) as functions of temperature. It is shown that V°(HSO4−,aq) is sensitive to the value of the first protonation constant and probably cannot be determined to better than ± 0.3 cm3·mol−1 at present.

Post depositional changes of sedimentary organic matter influence chromium speciation in continental slope sediments - A case study.

Influences of post depositional changes of sedimentary organic matter (SOM) on chromium (Cr) speciation in continental slope sediments from the east and west coast of India are presented in this study. Average concentrations of total sedimentary Cr (CrT) in the slope areas of both the coasts were not elevated and ranged from 56.8 to 163mg·kg-1 (avg. 97.3±28.3mg·kg-1). The geology of adjacent land masses influenced sedimentary Cr concentration in the slope areas. Geochemical fractionation study showed that a major fraction (51.6-159mg·kg-1; avg. 89.6±24.3mg·kg-1) of the total sedimentary Cr was present in residual part of the sediments. Prime hosting phase for non-residual sedimentary Cr was oxidizable binding phase (SOM) (1.4-23.9mg·kg-1; avg. 6.7±6.3mg·kg-1) followed by reducing binding phase (Fe/Mn-oxyhydroxide phase) (0.1-1.7mg·kg-1; avg. 0.7±0.3mg·kg-1). Concentration of Cr (VI) in the slope sediments, varied from 0.2 to 8.3mg·kg-1 (avg. 1.2±1.0mg·kg-1), was also predominantly associated with the SOM. The δ13Corg values of the SOM (ranged from -19.4 to -21.4‰; avg. -20.3±0.5‰) suggests that they were derived from marine sources. Based on molar C/N ratio (ranged from 6.3-12.9; avg. 9.0±2.0), the SOM were classified as labile organic matter. Increasing molar C/N ratio in the studied sediments was used as a proxy to reflect post depositional changes of the SOM. Association of normalized Cr (VI) (with respect to CrT) increased with increasing SOM concentration by 0.008mg·kg-1. One unit increase of sedimentary molar C/N ratio was found to increase normalized Cr (VI) (w.r.t. CrT) by 0.003mg·kg-1 in the sediments. This study suggests that post-depositional changes of SOM may increase Cr binding capacity and control its speciation and mobility in marine sediment system.

Deserpentinization in Subduction Zones as a Source of Oxidation in Arcs: a Reality Check

AbstractPrevious studies have concluded that dehydration of serpentinites in subduction zones produces oxidizing fluids that are the cause of oxidized arc magmas. Here, observations of natural samples and settings are combined with thermodynamic models to explore some of the factors that complicate interpretation of the observations that form the basis of this conclusion. These factors include the variability of serpentinite protoliths, the roles of carbon and sulfur in serpentinite evolution, variability in serpentinization in different tectonic settings, changes in the bulk compositions of ultramafic rocks during serpentinization, fundamental differences between serpentinization and deserpentinization, and the absence of precise geothermobarometers for ultramafic rocks. The capacity of serpentinite-derived fluids to oxidize sub-arc magma is also examined. These fluids can transport redox budget as carbon-, sulfur-, and iron-bearing species. Iron- and carbon-bearing species might be present in sufficient concentrations to transport redox budget deep within subduction zones, but are not viable transporters of redox budget at the temperatures of antigorite breakdown, which produces the largest proportion of fluid released by serpentinite dehydration. Sulfur-bearing species can carry significant redox budget, and calculations using the Deep Earth Water (DEW) model show that these species might be stable during antigorite breakdown. However, oxygen fugacities of ∼ΔFMQ + 3 (where FMQ refers to the fayalite–magnetite–quartz buffer, and ΔFMQ is log fO2 – log fO2, FMQ), which is close to, or above, the hematite–magnetite buffer at the conditions of interest, are required to stabilize oxidized sulfur-bearing species. Pseudosection calculations indicate that these conditions might be attained at the conditions of antigorite breakdown if the starting serpentinites are sufficiently oxidized, but further work is required to assess the variability of serpentinite protoliths, metamorphic pressures and temperatures, and to confirm the relative positions of the mineral buffers with relation to changes in fluid speciation.

Sulfur speciation and network structural changes in silicate-phosphate glasses

Sulfur speciation and the network structure of glasses from the SiO2-P2O5-K2O-MgO-SO3 system were studied by Raman and MAS NMR techniques. Glasses were synthesized by melting powders containing reducing agents. Bulk composition and homogeneity of the glasses were confirmed by X-Ray Fluorescence Spectroscopy and Scanning Electron Microscopy, combined with analysis of microregions via Energy Dispersive X-Ray Spectroscopy.Raman spectra demonstrate that S-bearing glasses can contain more reduced forms of sulfur than SO42−, such as S2O42−, S2O32−, S2O52−, and polysulfides Sx2−, depending on the reducing conditions. The 31P and 29Si MAS NMR spectra did not reveal peaks corresponding to P-S and Si-S linkages and indicate slight polymerization of the silico-oxygen and phospho-oxygen subnetworks.

From hazardous agriculture waste to hazardous metal scavenger: Tobacco stalk biochar-mediated sequestration of Cd leads to enhanced tobacco productivity

Tobacco is a super-enriched plant for heavy metals, and its productivity is sensitively affected by Cd. In this study, tobacco stalk was converted to biochar (TS-biochar) for the sequestration of Cd in soils to enhance the productivity of tobacco. FTIR, SEM-EDX, and XPS characterizations of TS-biochar together with Cd2+ adsorption kinetics revealed that oxy-containing functional groups (‒OH, C˭O, and ‒COOH) in TS-biochar played a crucial role on Cd2+ adsorption. The changes of soil property and Cd speciation by adding TS-biochar in red (acidic) and cinnamon (alkaline) soils was evaluated. Effects of TS-biochar on tobacco growth and development under Cd stress was also investigated. Results indicated that a 2 wt% addition of TS-biochar in red soil could significantly increase the soil pH value (from 5.21 to 7.39) and reduce exchangeable Cd fractions (from 40% to 23%), but those were not obvious in cinnamon soil. Under the stress of Cd, TS-biochar could obviously improve the tobacco dry biomass, and decrease the accumulation of Cd in the middle and upper leaves, thus reducing economic loss. Overall, the application of TS-biochar on Cd contaminated soil can transform bioavailable Cd into low hazardous forms, so as to repair soils and improve the productivity of tobacco.

Transformation of pig manure by passage through the gut of black soldier fly larvae (Hermetia illucens): Metal speciation, potential pathogens and metal-related functional profiling

Black soldier fly larvae (BSFL) have great potential in livestock manure disposal. However, the changes in metal speciation, microbial communities, potential pathogens during the manure transformation process by BSFL is still largely uncharacterized, as well as the underlying metal tolerance mechanism of larval gut microbiome. Here we used BSFL to convert pig manure (PM) into larval feces (BF), and investigated the metal and microbial changes in the conversion process. Physicochemical parameters (e.g. pH, electrical conductivity, total nitrogen, total phosphorus and total potassium) in PM were significantly altered compared to BF. After conversion, less than 10% of Cu and Zn were accumulated in larval bodies. The bioavailable fraction of Cu (88.3%–86.2%) and Zn (80.6%–82.3%) occupied as the primary form in PM and BF. Genera Enterococcus, Clostridium_sensu_stricto_1, Terrisporobacter and Romboutsia were substantially enriched in the final BSFL gut (GF) compared with initial gut (GI). BSFL transformation substantially reduced pathogen abundances (decreased by 89%) derived from pig manure. Functional genes involved in metal homeostasis and resistance (e.g. CutC, pcoC, cusR, zurR and zntB) were obviously strengthened (by 2.3–7.7 folds) in GF than in GI, which might partly explain the metal tolerance ability of BSFL during the livestock manure transformation process.

Immobilization and assessment of heavy metals in chicken manure compost amended with rice straw-derived biochar

ABSTRACT In this study, a 30-days laboratory experiment was implemented to investigate the impact of additive biochar on the stabilization of heavy metals in chicken manure compost. Results showed that after the addition of rice straw-derived biochar, heavy metals were more stabilized except Cu, of which the residual fractions distinctly decreased due to the interaction with organic functional groups from biochar. Given the bioavailability of heavy metals, the biochar addition at a 10% proportion decreased the concentration of CaCl2-extractable Cr, Zn, Ni, and Cd. Besides, CaCl2-extractable As did not differ significantly between treatments with and without biochar addition. Furthermore, the CaCl2-extractable Cu was higher than the control, in agreement with the observed changes in speciation. Environment pollution assessment by integrating potential ecological risk assessment explicated the chicken manure compost reached avery high-risk pollution level, and decreased with biochar addition. Therein, Cd was the dominant pollutant with very high potential risk.

Alleviation of Cadmium Toxicity to Medicago Truncatula by AMF Involves the Changes of Cd Speciation in Rhizosphere Soil and Subcellular Distribution

Arbuscular mycorrhizal fungi (AMF) can improve plant tolerance to several abiotic stresses, including heavy metals, drought or salinity exposure. However, the role of AMF in alleviation of soil cadmium (Cd)-induced toxicity to plants is still largely unknown. In this study, Cd speciation in soil and subcellular distribution of Cd were used to characterize the roles of application AM fungi in the alleviation of Cd toxicity in alfalfa plants. Our results showed that the addition of <i>Glomus mosseae</i> in Cd contaminated soil (10 mg/Kg) significantly increased soil pH, cation exchange capacity (CEC) and organic matter in rhizosphere soil with <i>Medicago truncatula</i> L., and then account for significantly decreased contents of exchangeable and carbonate-bounded Cd speciation in rhizosphere soil, indicating alleviation of plant toxicity by reduction of bioavailable fractions of Cd. Although there is no significant difference found in Cd accumulation by roots and shoots respectively between Cd and AM-Cd treatments, more portion of Cd was recorded compartmentalization in cell wall fraction of both root and shoot in treatment of Cd with AM application, indicating alleviation of Cd toxicity to plant cell. Herein, application of AM fungi in Cd treatments performed to inhibit the appearance of Cd toxicity symptoms, including the improvement of leaf electrolyte leakage, root elongation, seedling growth and biomass. This information provides a clearer understanding of detoxification strategy of AM fungi on Cd behavior with development and stabilization of soil structure and subcellular distribution of plant.

Synchrotron-based X-ray microscopy for assessing elements distribution and speciation in mangrove tree-rings

Micro-X-ray fluorescence (μ-XRF) spectroscopy has been used for dendrochemistry as a high spatial resolution, multi-elemental and non-destructive technique. Furthermore, micro-X-ray absorption near edge structure (μ-XANES) spectroscopy has a potential application in environmental studies by adding speciation information under in-situ conditions. Both, μ-XRF and μ-XANES, techniques were used to assess the inter-ring and intra-ring chemical content variations of Avicennia schaueria mangrove tree from Southeastern Brazil. Ca, Cl, K, P, and S were the major chemical elements distributed in almost all tree-rings. Ca was the most abundant element and showed a decreasing trend from heartwood to sapwood tree-rings. Calcium also showed a characteristic distribution pattern along the growth layer, acting as a chemical marker of growth layers. Ca chemical species were distinct in sapwood (calcium oxalate and carbonate-rich) and heartwood tree-rings (calcium sulfate-rich), showing different physiological Ca roles on tree performance. The synchrotron radiation-based techniques at micrometer scale provided information on the distribution and speciation of chemical elements within and between tree-rings. We also present a µ-XANES procedure for data collection and processing for dendrochemical studies. Altogether, we opened opportunities for further studies aiming to understand which environmental or physiological variables are responsible for tree-ring chemical speciation and distribution changes in tree species.

Essential (Mg, Fe, Zn and Cu) and Non-Essential (Cd and Pb) Elements in Predatory Insects (Vespa crabro and Vespa velutina): A Molecular Perspective.

The recent introduction of the Asian yellow-legged hornet, Vespa velutina, into Europe has raised concern regarding the threat to honeybees and the competition with the European hornet, Vespa crabro. The aim of this study was to investigated essential (Mg, Fe, Zn, Cu) and non-essential (Cd and Pb) elements in these two species. Element concentrations were determined in the whole body and separately in the head, thorax and abdomen using atomic absorption spectrometry (AAS). The changes in essential element concentration and speciation during metamorphosis were also studied using size exclusion chromatography followed by AAS and proteomic analysis. In both species, the essential elements were more concentrated in the abdomen due to the presence of fat bodies. Magnesium, Fe and Zn concentrations were significantly higher in V. crabro than in V. velutina and could have been related to the higher aerobic energy demand of the former species required to sustain foraging flight. Low concentrations of Cd and Pb were indicative of low environmental exposure. The concentration and speciation of essential elements, particularly Fe, varied among the developmental stages, indicating a modification of ligand preferences during metamorphosis. Overall, the results in the present study provide a better understanding of the hornet metal metabolism and a foundation for additional studies.

Distinguishing the effects of Ce nanoparticles from their dissolution products: identification of transcriptomic biomarkers that are specific for ionic Ce inChlamydomonas reinhardtii

AbstractCerium (Ce) is a rare earth element that is incorporated in numerous consumer products, either in its cationic form or as engineered nanoparticles (ENPs). Given the propensity of small oxide particles to dissolve, it is unclear whether biological responses induced by ENPs will be due to the nanoparticles themselves or rather due to their dissolution. This study provides the foundation for the development of transcriptomic biomarkers that are specific for ionic Ce in the freshwater alga, Chlamydomonas reinhardtii, exposed either to ionic Ce or to two different types of small Ce ENPs (uncoated, ∼10 nm, or citrate-coated, ∼4 nm). Quantitative reverse transcription PCR was used to analyse mRNA levels of four ionic Ce-specific genes (Cre17g.737300, MMP6, GTR12, and HSP22E) that were previously identified by whole transcriptome analysis in addition to two oxidative stress biomarkers (APX1 and GPX5). Expression was characterized for exposures to 0.03–3 µM Ce, for 60–360 min and for pH 5.0–8.0. Near-linear concentration–response curves were obtained for the ionic Ce and as a function of exposure time. Some variability in the transcriptomic response was observed as a function of pH, which was attributed to the formation of metastable Ce species in solution. Oxidative stress biomarkers analysed at transcriptomic and cellular levels confirmed that different effects were induced for dissolved Ce in comparison to Ce ENPs. The measured expression levels confirmed that changes in Ce speciation and the dissolution of Ce ENPs greatly influence Ce bioavailability.

Influence of thermal hydrolysis treatment on chemical speciation and bioleaching behavior of heavy metals in the sewage sludge.

In this study, the transformation of chemical speciation of Cr, Mn, As and Cd in the sewage sludge before and after thermal hydrolysis treatment was investigated using modified BCR method. The effect of thermal hydrolysis treatment and chemical speciation change on the subsequent bioleaching behavior was also researched. The results showed that the concentrations of Cr, Mn, As and Cd in oxidizable fraction decreased in the sludge treated by thermal hydrolysis. Meanwhile, the proportions of Cr, Mn and As in the mobile fractions (acid-soluble/exchangeable and reducible fraction) all decreased, while Cd was concentrated in the sludge treated by thermal hydrolysis. The final pH value of bioleached sludge treated by thermal hydrolysis was lower than that in the bioleached raw sewage sludge. And faster increase of oxidation-reduction potential (ORP) was also found in the bioleaching process of the sludge treated by thermal hydrolysis. The removal percentage of Mn and Cd increased in the bioleached sludge treated by thermal hydrolysis. Thermal hydrolysis treatment can promote the bioleaching to some extent. Furthermore, the environmental risk of Cr, Mn, As and Cd in the bioleached sludge treated by thermal hydrolysis was all alleviated according to risk assessment analysis compared with the bioleached raw sewage sludge.

Supported nanoparticle synthesis with Au bis-Ethylenediamine: The mechanism of adsorption onto oxides and carbons

Gold bis-ethylenediamine ([Au(en)2]3+ or AuED) is an effective precursor for the preparation of small Au nanoparticles on common catalyst supports. By studying the adsorption of AuED over a wide variety of supports with surveys of uptake versus time and pH, including XAS studies of solution and adsorbed species, we have demonstrated that an electrostatic mechanism accounts for the data much better than the previously postulated cation exchange mechanism. In the electrostatic mechanism 1) uptake-pH curves are volcano-shaped and are higher in amplitude and broader in pH the lower the PZC of the support, 2) AuED complexes retain at least one hydration sheath with diameter 13.3 Å (0.72 complex/nm2) and adsorb as outer sphere complexes, 3) the monolayer limit in aqueous solutions basified with NaOH is not determined by cation exchange stoichiometry but is a steric limit of close-packed, hydrated complexes. They adsorb at a much lower surface density than that of the surface hydroxyl groups and never electrically saturate the surface. 4) The change in AuED speciation at high pH is consistent with a change in the coulombic attraction of a 3+ versus a 2+ complex.Over carbon supports, adsorption is predominantly electrostatic, but an additional parallel mechanism is apparent in proportion to the graphitic nature of the support.Synthesized Au nanoparticles over the oxide and carbon materials was characterized by high sensitivity powder XRD, STEM imaging, and TPR. The resultant nanoparticles were generally smaller than other synthesis methods reported in the literature for silica, titania, alumina, and carbon. The loading limit of electrostatic adsorption is a surface density of about 1 μmol/m2. At loadings less than or equal to this, electrostatic adsorption provides a simple method with which to synthesize well dispersed Au nanoparticles.

Geochemical Features of Element Speciation in Natural Waters of the Valdai Rise (March–November, 2019)

This paper considers the element distribution between species in the lysimetric waters and lakes of the Valdai National Park in different seasons. Seasonal studies of natural waters and element speciation in them in 2019 using membrane filtration and ion-exchange separation showed the differences in the seasonal distribution of species depending on geochemical factors. The seasonal temperature factor causes a change of metal speciation from suspended (after meltwaters) through soluble mainly organic (summer) to inorganic/organic low-molecular (autumn) forms. The humus content in the water objects affects the transformation of colloid systems.

Stabilization of cadmium in polluted soil using palygorskite-coated nanoscale zero-valent iron

The palygorskite-coated nanoscale zero-valent iron (PAL-nZVI) was synthesized and used in the remediation of Cd-contaminated soils. The function of PAL-nZVI on fraction of Cd in soils, the growth, Cd translocation, and accumulation in corn (Zea mays L.) were investigated using a pot experiment. Cd-contaminated soils were amended with palygorskite, nanoscale zero-valent iron (nZVI), and PAL-nZVI (with varying mass ratios between PAL and nZVI) and with no amendment as control. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the changes in both the surface and the structure of stabilizers. CaCl2-extractable and toxicity characteristic leaching procedure (TCLP)-extractable Cd were measured in order to estimate the bioavailability and the stabilization efficiency. The Community Bureau of Reference (BCR) sequential extraction method was applied to evaluate the speciation change of Cd in soils stabilized by nZVI, PAL, and PAL-nZVI with different coating mass ratios of PAL to nZVI. The Cd accumulation in root and shoot fresh weight was measured to assess the stabilization efficiency. SEM and XRD indicated that nZVI particles were distributed uniformly and well fixed on the surface of palygorskite. After adding PAL-nZVI, the pH value of soil increased by 1 pH unit; CaCl2-extractable Cd decreased from 2.24 to 0.95 mg/kg; the residual Cd increased by 23.06% after 30-day incubation. The fresh weight of corn reached 43.02 g/plant, and the Cd contents in roots and shoots achieved minimum values of 1.50 and 0.73 mg/kg, respectively, when applying PAL-nZVI composite with a coating mass ratio of 2:1. The application of PAL-nZVI decreased the bioavailability and mobility of Cd in soils effectively. The stabilization showed a better effect when applying PAL-nZVI in Cd-contaminated soils than applying nZVI alone. Hence, it was a feasible and potential material that could be applied to amend the Cd-contaminated soil effectively, which would have a high and valuable utilization in field applications.

Corrosion Inhibition of Mild Steel by Cetrimonium trans-4-Hydroxy Cinnamate: Entrapment and Delivery of the Anion Inhibitor through Speciation and Micellar Formation.

Chemical inhibitors are widely used to protect metallic alloys from corrosion in aqueous environments. This Letter investigates the possible synergistic behavior of a quaternary ammonium carboxylate compound toward the development of a new system taking advantage of the surface activity of a known antimicrobial surfactant molecule, hexadecyl trimethylammonium cation, combined with a known organic corrosion inhibitor, the trans-4-hydroxy-cinnamate anion. Short-term potentiodynamic polarization (PP) studies combined with immersion in aqueous chloride solutions demonstrated the high inhibition efficiency of the combination of ions, and NMR pfg-diffusion measurements revealed micellar formation that was concentration- and pH-dependent. The NMR data suggest that speciation changes occur in the solution that correlate with enhanced corrosion inhibition efficiency at higher pH and at concentrations above the CMC of the compound. This new contribution may provide a rational molecular design toward delivering corrosion inhibitors to a metal surface through controlled speciation in solution.

Cadmium isotope fractionation during Cd-calcite coprecipitation: Insight from batch experiment

Cadmium (Cd) calcite coprecipitation experiments were conducted to constrain the possible Cd isotope fractionation mechanism under different conditions. The changes in Cd/Ca molar ratio, HCO3− concentration, addition of Mg2+, Na2EDTA, or ionic strength (INaNO3) did not affect the composition of the precipitation but resulted in substantial change in mineral morphology. Cd exhibited an apparent isotope fractionation in the process of coprecipitation with calcite, and the fractional coefficient αCaCO3-Cd(aq) was less than one, indicating that the solution is preferentially enriched in heavy isotopes. The Cd mainly existed in the form of Cd(H2O)62+ in the solution before the reaction and was dominated by Cd(NO3)2, CdNO3+, Cd(EDTA)2− at the end of the experiments. The different isotopic ratios of Cd between the liquid phase and the solid phase can be explained by changes in Cd speciation which have different bond lengths of CdO. Expect for the experiments with Na2EDTA and high ionic strength, the measured isotope ratios under different conditions plotted around the theoretical Rayleigh fractionation curve. This demonstrates that Cd isotopes almost reach equilibrium with Cd-calcite coprecipitation under the different experiment conditions and the Cd isotope fractionation mechanism is closely related to the thermodynamic isotope fractionation. In the experiment with Na2EDTA and high ionic strength, the formation of Cd(EDTA)2− and ion occlusion at surface sites inhibit Cd2+ entering the calcite and the isotopes of the solid and liquid phases do not reach equilibrium. As the result, obtained experiment data shift from the Rayleigh fractionation curve indicating the Cd isotope fractionation mechanism is closely related to the kinetic isotope effect. In general, the study results indicate that the Cd/Ca molar ratio, ionic strength, HCO3−, Na2EDTA, and Mg2+ concentrations of the solution can cause Cd isotope fractionation in different degrees during Cd-calcite coprecipitation. Cd isotope ratios might potentially provide important information on Cd mobilization and transportation in groundwater environment.

Thermally induced changes in solubility and speciation of lead and iron minerals in a contaminated soil

AbstractThis study investigated the effects of thermal treatment on the solubility and speciation of lead (Pb) adsorbed on synthesized hematite (Pb‐Hm) and in an anthropogenically contaminated soil. The temperature of thermal treatment ranged from 100 to 900 °C, and the speciations of Pb and iron were determined using X‐ray absorption fine structure spectroscopy. In Pb‐Hm samples, the concentration of water‐extractable Pb significantly decreased after being treated at 300 and 600 °C (∼0.50 mg Pb L–1) compared with the untreated sample (9.83 mg Pb L–1). Under this temperature range, about 50% of the Pb‐Hm was transformed into massicot (β‐PbO). At 700 °C and above, a slight increase of water‐extractable Pb was probably caused by the formation of minium (Pb3O4). In the contaminated soil, water‐extractable Pb increased gradually from 0.30 to 0.40 mg Pb L–1 with increasing temperature from 25 to 200 °C; then it decreased rapidly to 0.09 mg Pb L–1 at 300 °C and further decreased to 0.004 mg Pb L–1 at 900 °C. Cerussite (PbCO3) and Pb associated with hematite were the major Pb species in the contaminated soil. In the process of thermal treatment, the significant decrease of water‐extractable Pb in the contaminated soil was caused by the transformation of cerussite into hematite‐associated Pb, accompanied by the transformation from ferrihydrite to hematite.

Temporal and Spatial Patterns of Zinc and Iron Accumulation during Barley (Hordeum vulgare L.) Grain Development.

Breeding and engineering of biofortified crops will benefit from a better understanding of bottlenecks controlling micronutrient loading within the seeds. However, few studies have addressed the changes in micronutrient concentrations, localization, and speciation occurring over time. Therefore, we studied spatial patterns of zinc and iron accumulation during grain development in two barley lines with contrasting grain zinc concentrations. Microparticle-induced-X-ray emission and laser ablation-inductively coupled plasma mass spectrometry were used to determine tissue-specific accumulation of zinc, iron, phosphorus, and sulfur. Differences in zinc accumulation between the lines were most evident in the endosperm and aleurone. A gradual decrease in zinc concentrations from the aleurone to the underlying endosperm was observed, while iron and phosphorus concentrations decreased sharply. Iron co-localized with phosphorus in the aleurone, whereas zinc co-localized with sulfur in the sub-aleurone. We hypothesize that differences in grain zinc are largely explained by the endosperm storage capacity. Engineering attempts should be targeted accordingly.

Equation of state for CO and CO2 fluids and their application on decarbonation reactions at high pressure and temperature

Ab initio molecular dynamics simulations were performed at pressures and temperatures up to 160 GPa and 4000 K, in order to obtain equations of state (EOS) for CO and CO2 fluids. We found that polymerisation of CO and CO2 fluids starts at low pressures, and that including the effect of polymerisation is essential for accurate EOS. EOSs for CO and CO2 determined from methods using experimental data, or classical potentials that ignore the changes in speciation, should be treated with caution when extrapolated beyond the examined pressures and temperatures. The obtained data was fitted to a modified Lee and Kesler EOS for both CO and CO2 fluids. The thermodynamic calculations for the decarbonation reactions of both MgCO3 and CaCO3 using the derived CO2 EOS reproduced the experimental data and theoretical calculations at low pressures. Both MgCO3 and CaCO3 pure phases are found to be stable in the upper mantle compared to CO2. However, they both become destabilised when approaching lower mantle conditions.