Speciation Of Vanadium Research Articles

Vanadium speciation using magnetic multi-walled carbon nanotubes coated with ion-imprinted polymer and electrothermal atomic absorption spectrometry

ABSTRACT For selective extraction of vanadium (V) from water and food samples, ion-imprinted polymer was synthesised on magnetic multi-walled carbon nanotubes. For this purpose, the complex of V(V)-8-hydroxyquinoline, 4-vinylpyridine, ethylene glycol dimethacrylate, and magnetic multi-walled carbon nanotubes were used as the template of V(V), functional monomer, cross-linker, and the core, respectively. The prepared sorbent was characterised by FTIR spectroscopy, scanning electron microscopy, X-ray diffraction, energy-dispersion X-ray, and vibrating sample magnetometer. The extracted vanadium (V) was assessed by electrothermal atomic absorption spectrometry. The total vanadium in the solution was extracted and determined after oxidation of V(IV) to V(V) by hydrogen peroxide. Under optimised conditions, limits of detection and quantification of 2.9, and 10.0 ng L−1 were obtained, respectively. The maximum capacity of sorbent was 44.1 mg g−1. The method was successfully employed for the extraction and quantification of vanadium species in different water samples and total vanadium in food samples.

Speciation of vanadium and the interacted solid surface of δ-alumina adsorbent in aqueous media in presence of humic acid

Speciation of vanadium elements in the presence of δ-alumina in aqueous media was studied to simulate the environmental impact of soil/sediment–water interacted system. Factors affecting this process are pH, presence of humic acid, and δ-alumina concentrations as an abundant sediment/soil components. Different species of both vanadium and surface of δ-alumina were deduced theoretically using MintaqA2 programme. Due to the effect of pH, the anionic species of vanadium at pH 1–3 is prevailed and changed to cationic species at pH range 6–10 at different levels of alumina. Additionally, based on the effect of alumina concertation, high percent uptake, almost 100% was found at 10.0 g/1 concentration of alumina while at level of 0.2 g/1 alumina, the maximum adsorption of vanadium was become 91%. The effect of humic acid on the speciation behavior of vanadium (V) was also studied and compared with that of vanadium (IV) based on XANES (X-ray absorption near edge structure). Adsorption behaviors were studied at concentration 4.71E-4M for vanadium at 0.1M ionic strength. The mechanism of vanadium adsorption in the presence of alumina under the same working conditions was studied and explained based on TLM (Triple layer model) where the results proved good validation and verification of the practically produced data.

Separation of V(Ⅴ) and Cr(Ⅵ) from vanadium-containing solutions based on E-pH diagrams of V-Cr-S-H2O system

The extremely similar physicochemical properties of vanadium and chromium lead to the difficulty in separating from each other. In this study, a novel hydrometallurgical process was devised to selectively precipitate chromium from vanadium-containing solutions, facilitating the efficient separation of V(V) and Cr(VI) while enabling the recovery of both vanadium and chromium species. The speciation of vanadium and chromium in solutions was investigated through the construction of E-pH diagrams for V-Cr-S-H2O system at 298 K, 363 K, and 453 K. The results revealed that under conditions of pH approximately 12 and temperature 363 K, the reduction potential of SO42-/S2- was found to lie between that of CrO42-/Cr(OH)3 and VO43-/V2O3. This suggests that selective reduction of Cr(VI) could be achieved using S2- as reducing agent. In order to validate the theoretical findings, single-factor experiments were conducted on a laboratory scale. The effects of various parameters including initial pH, sodium sulfide dosage, reaction time, temperature, and initial concentration of vanadium-containing solutions on the chromium precipitation ratio and vanadium loss ratio were investigated. The experimental outcomes showed that the chromium precipitation ratio reached 99.8 % while the vanadium loss rate was only 3.5 % when the experiment was conducted at the optimal conditions: the initial pH was set to 12, sodium sulfide dosage was 2.0 times of the theoretical dosage, reaction time was 60 min and the temperature was 363 K. Then, the chromium concentration in the solution decreased from 2407 mg/L to 3.3 mg/L. Ultimately, V2O5 with a purity of 99.0 % and Cr2O3 with a purity of 97.2 % were successfully obtained.

Speciation of antimony and vanadium in municipal solid waste incineration ashes analyzed by XANES spectroscopy

The use of ashes from municipal solid waste incineration as secondary building materials is an important pillar for the circular economy in Germany. However, leaching of potential toxic elements from these materials must be at environmentally acceptable levels. Normally, a three-month ageing period immobilizes most hazardous heavy metals, but antimony (Sb) and vanadium (V) showed previously unusual leaching. In order to clarify the mechanisms, we analyzed the Sb and V species in various bottom and fly ashes from municipal waste incineration by XANES spectroscopy. Antimony oxidizes from Sb(+ III) species used as flame retardants in plastics to Sb(+ V) compounds during waste incineration. However, owing to the similarity of different Sb(+ V) compound in the Sb K- and L-edge XANES spectra, it was not possible to accurately identify an exact Sb(+ V) species. Moreover, V is mainly present as oxidation state + V compound in the analyzed ashes. However, the coarse and magnetic fraction of the bottom ashes contain larger amounts of V(+ III) and V(+ IV) compounds which might enter the waste incineration from vanadium carbide containing steel tools. Thus, Sb and V could be critical potential toxic elements in secondary building materials and long-term monitoring of the release should be taken into account in the future.

Vanadium in a coastal Lagoon: distribution, sources, speciation, and ecological risks in sediments and water at Xiamen in China

ABSTRACT This study aimed to explore the spatial distribution, sources, contamination status, speciation, and risks of vanadium (V) in sediments and water from Yundang Lagoon (YL) at Xiamen in China. The concentration of V in YL water exhibited a similar distribution pattern, with an average concentration lower than the Chinese drinking water limit value. The V content in the sediments of various YL sampling sites varied significantly. The average V concentration in sediments was 108.28 mg/kg, ranging from 77.38 mg/kg to 151.20 mg/kg. Speciation investigations revealed that the largest amount of V was bound in the residual fraction, while the acid-soluble fraction had the lowest concentration in sediments. On average, the residual and acid-soluble fractions were 51.82% (ranging from 16.09% to 76.13%) and 1.22% (ranging from 0.16% to 2.60%), respectively. Enrichment factor values suggested minor anthropogenic enrichment of V in sediments. Correlation analysis indicated a weak correlation between silt and clay, while carbonate and Fe showed significant correlations with total V in sediments. This correlation suggests that concentrations of Fe and carbonate could favour V accumulation in YL sediments. Potential ecological risk values suggested no risk of V to aquatic biota in the study area.

Deciphering Vanadium Speciation in Smelting Ash and Adaptive Responses of Soil Microorganisms.

Abundant smelting ash is discharged during pyrometallurgical vanadium (V) production. However, its associated V speciation and resultant ecological impact have remained elusive. In this study, V speciation in smelting ash and its influence on the metabolism of soil microorganisms were investigated. Smelting ashes from V smelters contained abundant V (19.6-115.9 mg/g). V(V) was the dominant species for soluble V, while solid V primarily existed in bioavailable forms. Previously unrevealed V nanoparticles (V-NPs) were prevalently detected, with a peak concentration of 1.3 × 1013 particles/g, a minimal size of 136.0 ± 0.6 nm, and primary constituents comprising FeVO4, VO2, and V2O5. Incubation experiments implied that smelting ash reshaped the soil microbial community. Metagenomic binning, gene transcription, and component quantification revealed that Microbacterium sp. and Tabrizicola sp. secreted extracellular polymeric substances through epsB and yhxB gene regulation for V-NPs aggregation to alleviate toxicity under aerobic operations. The V K-edge X-ray absorption near-edge structure (XANES) spectra suggested that VO2 NPs were oxidized to V2O5 NPs. In the anaerobic case, Comamonas sp. and Achromobacter sp. reduced V(V) to V(IV) for detoxification regulated by the napA gene. This study provides a deep understanding of the V speciation in smelting ash and microbial responses, inspiring promising bioremediation strategies to reduce its negative environmental impacts.

Task specific microextraction column based on monolith for magnetic field-assisted in-tube solid phase microextraction of vanadium species in complex samples prior to online chromatographic analysis

The dominant species of vanadium (V) are V(IV) and V(V) which exhibit different toxicity and biological effects. Thus, speciation of V(IV) and V(V) is highly essential. Efficient sample preparation is the core step in the quantification of V(IV) and V(V). In the present study, a new task specific microextraction column based on monolith mingled with Fe3O4 nanoparticles (MBMC) was in situ synthesized in capillary and utilized as the extraction phase of magnetic field-assisted in-tube solid phase microextraction (MA-IT-SPME) of V(IV) and V(V) species which were coordinated with ethylene diamine tetraacetic acid (EDTA). The prepared MBMC presented porous and superparamagnetic properties, and possessed abundant functional groups. Results revealed that the exertion of magnetic field during adsorption and eluting steps boosted the extraction efficiency of V(IV)-EDTA and V(V)-EDTA chelates from 65.1 % to 55.7 %–90.0 % and 80.1 %, respectively. Under the beneficial extraction parameters, the established MA-IT-SPME was online hyphenated with HPLC/DAD to perform speciation of trace vanadium in water and vegetable samples, the achieved limits of detection were 0.054–0.060 μg/L and 1.4–1.5 μg/kg in water and vegetable samples, respectively, and the spiked recoveries varied from 82.5 to 118 %. In addition, relevant extraction mechanism under magnetic field was explored. In comparison with existing methods, the developed MA-IT-SPME technique displays some attractive merits such as automation, good anti-interference ability, high extraction efficiency, low cost and less use of organic solvent, in the capture of V species. The established online MBMC@MA-IT-SPME-HPLC/DAD system can become a competitive approach for sensitive speciation of V(IV) and V(V) at trace levels in complex samples.

Green Alternatives to Zinc Dialkyldithiophosphates: Vanadium Oxide-Based Additives.

A functionalized vanadyl(IV) acetylacetonate (acac) complex has been found to be a superior and highly effective antiwear agent, affording remarkable wear protection, compared to the current industry standard, zinc dialkyldithiophosphates (ZDDPs). Analysis of vanadium speciation and the depth profile of the active tribofilms by a combination of X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) analyses indicated a mixed-valence oxide composite, comprising V(III), V(IV), and V(V) species. A marked difference in composition between the bulk and the surfaces of the tribofilms was found. The vanadyl(VI) acac precursor has the potential to reduce or even replace ZDDP, which would represent a paradigm shift in the antiwear agent design. A major benefit relative to ZDDPs is the absence of S and P moieties, eliminating the potential for forming noxious and environmentally harmful byproducts of these elements.

Biological Consequences of Vanadium Effects on Formation of Reactive Oxygen Species and Lipid Peroxidation

Lipid peroxidation (LPO), a process that affects human health, can be induced by exposure to vanadium salts and compounds. LPO is often exacerbated by oxidation stress, with some forms of vanadium providing protective effects. The LPO reaction involves the oxidation of the alkene bonds, primarily in polyunsaturated fatty acids, in a chain reaction to form radical and reactive oxygen species (ROS). LPO reactions typically affect cellular membranes through direct effects on membrane structure and function as well as impacting other cellular functions due to increases in ROS. Although LPO effects on mitochondrial function have been studied in detail, other cellular components and organelles are affected. Because vanadium salts and complexes can induce ROS formation both directly and indirectly, the study of LPO arising from increased ROS should include investigations of both processes. This is made more challenging by the range of vanadium species that exist under physiological conditions and the diverse effects of these species. Thus, complex vanadium chemistry requires speciation studies of vanadium to evaluate the direct and indirect effects of the various species that are present during vanadium exposure. Undoubtedly, speciation is important in assessing how vanadium exerts effects in biological systems and is likely the underlying cause for some of the beneficial effects reported in cancerous, diabetic, neurodegenerative conditions and other diseased tissues impacted by LPO processes. Speciation of vanadium, together with investigations of ROS and LPO, should be considered in future biological studies evaluating vanadium effects on the formation of ROS and on LPO in cells, tissues, and organisms as discussed in this review.

Correction to Vanadium Speciation in Ancient Shales Revealed through Synchrotron-Based X-ray Spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to Vanadium Speciation in Ancient Shales Revealed through Synchrotron-Based X-ray SpectroscopyWilliam W. Bennett*William W. BennettMore by William W. Bennetthttps://orcid.org/0000-0002-8126-4555, Enzo LombiEnzo LombiMore by Enzo Lombihttps://orcid.org/0000-0003-3384-0375, Kirk G. ScheckelKirk G. ScheckelMore by Kirk G. Scheckel, Ryo SekineRyo SekineMore by Ryo Sekinehttps://orcid.org/0000-0001-9980-0603, Scott G. JohnstonScott G. JohnstonMore by Scott G. Johnstonhttps://orcid.org/0000-0002-5826-5613, Edward D. BurtonEdward D. BurtonMore by Edward D. Burtonhttps://orcid.org/0000-0002-9628-089X, Daryl L. HowardDaryl L. HowardMore by Daryl L. Howard, Peter KappenPeter KappenMore by Peter Kappen, and Donald E. CanfieldDonald E. CanfieldMore by Donald E. CanfieldCite this: ACS Earth Space Chem. 2023, 7, 3, 661Publication Date (Web):February 24, 2023Publication History Received20 February 2023Published online24 February 2023Published inissue 16 March 2023https://doi.org/10.1021/acsearthspacechem.3c00046Copyright © 2023 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views196Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (791 KB) Get e-Alerts Get e-Alerts

Vanadium Speciation in Ancient Shales Revealed through Synchrotron-Based X-ray Spectroscopy

Redox-sensitive trace elements, such as vanadium, are frequently used as paleoredox proxies to infer the redox status of ancient marine depositional environments. When applied to vanadium, this approach relies on an accurate understanding of vanadium geochemistry in marine sediments. This, in turn, requires the application of analytical techniques capable of providing reliable chemical information on vanadium host phases of vanadium and thus the ability to distinguish authigenic from detrital phases. The increasing availability of synchrotron-based X-ray spectroscopic techniques capable of providing chemical speciation information at both the bulk and micro-scale presents an opportunity to refine our understanding of vanadium geochemistry in ancient marine sediments. Here, we show the utility of synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy and scanning X-ray fluorescence microscopy (SXFM) for investigating vanadium host phases in ancient marine sediments. The studied samples from the 1400 Ma Xiamaling Formation came from strongly contrasting depositional settings (ranging from oxic to euxinic) with a wide range of vanadium enrichments (enrichment factors from 0.7 to 9.6), yet vanadium speciation determined by XANES was consistently found to be phyllosilicate-hosted vanadium (III). High-resolution elemental imaging by SXFM coupled with global statistical colocalization analyses revealed strong associations between vanadium and potassium, consistent with vanadium hosted by potassium-rich clay minerals. These findings, while demonstrating the power of synchrotron-based X-ray methods, imply that differentiating authigenic and detrital vanadium in ancient marine sediments is unlikely to be possible given that post-depositional processes result in similar chemical speciation for both fractions. This will also limit the reliability of vanadium isotope system studies that depend on differentiating authigenic and detrital fractions using selective extraction procedures.

Vanadium in biological systems and medicinal applications

The present review covers the environmental availability of vanadium and vanadium’s impact on the life sphere (geo-sphere, atmosphere, marine environments), as well as its potentiality in the treatment of diseases such as cancer, diabetes and bacterial infections. In particular, the following topics are addressed: (1) vanadium in marine environments (halide oxidation by haloperoxidases in the seaweed Ascophyllum nodosum and by marine bacteria associated with macroalgae; accumulation and redox transformation of vanadium by ascidians and fan worms); (2) the role of vanadium in nitrogen fixation by diazotrophs in the root nodules of legumes, and in liverworts and hornwarts; (3) amavadin in the fly agaric mushroom; (4) vanadium speciation by unicellular organisms (bacteria, protozoa) and adjunctive medicinal applications; (5) the potentiality of vanadium (coordination compounds) in the treatment of diseases such as cancer and diabetes, and bacterial infections.

The removal of toxic metals from liquid effluents by ion exchange resins. Part XVIII: Vanadium(V)/H+/Amberlite 958

The ion exchange resin Amberlite 958 was used to investigate its behaviour on the removal of hazardous vanadium(V) from aqueous media. This investigation was carried out under various hydrodynamic conditions and chemical conditions, such as variation of the stirring speed, variation of the pH of the aqueous solution, resin dosage, initial vanadium(V) in the aqueous solution, and temperature. Vanadium(V) uptake onto the resin was highly dependent on the pH of the solution, and thus, to the vanadium(V) speciation in this phase; the ion exchange process had an endothermic character. The experimental data, under different experimental conditions, were fitted to various models: kinetics (stirring speed), rate law (vanadium concentration) and model isotherms (resin dosage). Multiwalled carbon nanotubes were also investigated on vanadium(V) removal from the solution. Vanadium(V) loaded onto the resin can be eluted under acidic conditions.

Reduction mechanisms of V5+ by vanadium-reducing bacteria in aqueous environments: Role of different molecular weight fractionated extracellular polymeric substances

Extracellular polymeric substances (EPS) are high-molecular polymers secreted by microbes and play essential roles in metallic biogeochemical cycling. Previous studies demonstrated the reducing capacity of the functional groups on EPS for metal reduction. However, the roles of different EPS components in vanadium speciation and their responsible reducing substances for vanadium reduction are still unknown. In this study, the EPS of Bacillus sp. PFYN01 was fractionated via ultrafiltration into six components with different kDa (EPS>100, EPS100–50, EPS50–30, EPS30–10, EPS10–3, and EPS<3). Batch reduction experiments of the intact cells, EPS-free cells, the pristine and fractionated EPS with V5+ were conducted and characterized. The results demonstrated that the extracellular reduction of V5+ into V4+ by EPS was the major reduction process. Among the functional groups in EPS, C=O/C-N of amide in protein/polypeptide and CO of carboxyl in fulvic acid-like substances might act as the reductants for V5+, while CO in polysaccharide molecules and PO in phosphodiester played a key role in the adsorption process. The intracellular reduction was via translocating V5+ into the cells and releasing V4+ by the intracellular reductases. The reducing capacity of the fractionated EPS followed a sequence of EPS<3 > EPS10–3 > EPS50–30 > EPS100–50 > EPS30–10 > EPS>100. The small molecules of fulvic acid-like substances and amino acids were responsible for the high reducing capacity of EPS<3. EPS>100 had the lowest reducing capacity due to its macromolecular structure decreasing the exposure of the reactive sites. In addition to reduction, those intermediate EPS components may also have supporting functions, such as connecting protein skeletons and increasing the specific surface area of EPS. Therefore, the diverse effects of the EPS components cannot be neglected in vanadium biogeochemical cycling.

Speciation of inorganic vanadium by direct immersion dual-drop microextraction coupled with graphite furnace atomic absorption spectrometry detection

In this work, a new method based on direct immersion dual-drop microextraction (DIDDME) was proposed for simultaneous speciation and enrichment of V(IV) and V(V) by graphite furnace atomic absorption spectrometry. This strategy was initiated with the chelation of V(IV) and V(V) in sample solutions with 1-(2-Pyridylazo)-2-naphthol (PAN). In the following step, two organic solvent drops hold on needle tips of microsyringes were concurrently immersed in the stirred sample solution to selectively and simultaneously separate V(IV)-PAN and V(V)-PAN complexes under the same pH value. This procedure avoided the tedious and complicated pre-oxidation/pre-reduction and centrifugation/filtration operations, which may cause the risk of sample contamination and analysis errors. Main parameters affecting the separation, preconcentration of the target species were investigated. Under the optimized conditions, the detection limits of this method were 2.4 ng/L and 1.5 ng/L for V(IV) and V(V) with relative standard deviations of 6.1 and 5.3 %, respectively. An enrichment factor of 300-fold was achieved for V(IV) and V(V). This method was applied successfully for the determination of V(IV) and V(V) in water samples. In order to validate the proposed procedure, a certified reference material of water sample was analyzed, and the determined value was in good agreement with the certified value.

Enrichment and Chemical Speciation of Vanadium and Cobalt in Stone Coal Combustion Products in Ankang, Shanxi Province, China

Stone coal enriches more elements compared to other coals, especially Vanadium (V). The content of Co is relatively low, while its environmental risk is relatively high. This study collected the stone-coal samples to investigate the enrichment characteristics and the chemical speciation in the combustion products of V and Co in stone coal at an open-pit coal mine in Ankang City, Shanxi Province, China. A simulation combustion experiment and sequential chemical extraction were conducted. Mineral composition was analyzed for raw-stone coal and its combustion products. The results showed that most of V and Co are mainly enriched in combustion products during the combustion process, the enrichment capacity of Co is higher than V. With the increase in the combustion temperature, the bioavailable chemical speciation of V in stone coal combustion products increased, while Co decreased. If the combustion products are stored without effective treatment, the surrounding environment will be polluted, and then human health might be endangered.

Effect of ferrous sulfate modified sludge biochar on the mobility, speciation, fractionation and bioaccumulation of vanadium in contaminated soil from a mining area

In contaminated soil, pristine biochar has poor applicability for immobilizing vanadium (V), which mainly exists as oxyanions in soil. To elucidate the immobilization potential and biotic/abiotic stabilizing mechanisms of a ferrous sulfate (FS)-modified sludge biochar in a V-contaminated soil from a mining area, we investigated the effects of biochar addition on the soil characteristics, growth of alfalfa, leachability, bioavailability, speciation, and fractionation of V, and changes in the microbial community structure and metabolic response. The results showed that the water extractable, acid-soluble (F1), and pentavalent fractions of V in soil decreased by up to 99 %, 95 %, and 55 %, respectively, whereas the reducible and (F2) oxidizable (F3) fractions increased by up to 45 % and 76 %, respectively. After the soil was treated with the FS-modified biochar for 90 d, the V concentration in the roots and shoots of alfalfa (Medicago sativa L.) decreased by up to 81.5 % and 96 %, respectively. The changes in the speciation, fractionation, and efficient immobilization of V in the studied soil were due to the combined effects of the biochar-induced decrease in soil pH, adsorption and precipitation by elevated iron concentrations, reduction and complexation due to an increase in the organic matter content, and microbial reduction by Proteobacteria.

Soil indigenous microorganisms alleviate soluble vanadium release from industrial dusts

Vanadium-bearing dusts from industrial processes release abundant toxic vanadium, posing imminent ecological and human health concerns. Although the precipitation of these dusts has been recognized as the main source of soil vanadium pollution, little is known regarding the interrelationships between industrial dusts and soil inherent compositions. In this study, the interactions between dusts from vanadium smelting and soil indigenous microorganisms were investigated. Soluble vanadium (V) [V(V)] released from industrial dusts was reduced by 41.5 ± 0.39% with soil addition, compared to water leaching. Reducible fraction accounted for the highest proportion (55.1 ± 1.73%) of vanadium speciation in the resultant soils, while residual vanadium fraction increased to 83.7 ± 3.22% in the leached dusts. Functional genera (e.g., Aliihoeflea, Actinotalea) that transformed V(V) to insoluble vanadium (IV) alleviated dissolved vanadium release. Nitrate/nitrite reduction and glutathione metabolisms contributed to V(V) immobilization primarily. Structural equation model analysis indicated that V(V) reducers had significant negative impacts on soluble V(V) in the leachate. This first-attempt study highlights the importance of soil microorganisms in immobilizing vanadium from industrial dusts, which is helpful to develop novel strategies to reduce their environmental risks associated to vanadium smelting process.

Transformation behaviors of vanadium and nickel during petroleum coke and coal co-gasification

The transformation behaviors of vanadium and nickel during petroleum coke co-gasification with coal may cause ash-related fouling, slagging, and corrosion problems. In this work, we investigated the evolution of occurrence modes, volatilization behaviors, and speciation of vanadium and nickel in the process of steam co-gasification of petroleum coke and coal over the temperature range of 1100–1500 °C. The results showed that the main chemical states of vanadium and nickel in raw petroleum coke were organic matter and “stable forms”, of which vanadium and nickel associated with organic matter were thoroughly converted into other chemical states. The volatilities of vanadium and nickel in petroleum coke increased slightly from 1100 °C to 1500 °C, however the addition of coal inhibited their volatilization behaviors. Moreover, residence time had little effect on the release of vanadium and nickel. The crystalline phases of vanadium-bearing species, i.e., vanadium trioxide and coulsonite, as well as those of nickel-bearing species, i.e., nickel sulfide and elemental nickel, were formed in high-temperature ash. In addition, the diffraction peaks corresponding to another vanadium species, calcium orthovanadate, were found in the high-temperature ash of SX40%/HB60% with a coal content of 60 wt.%.

Cloud point extraction coupled with back-extraction for speciation of inorganic vanadium in water and determination of total vanadium in food samples by ICP-OES

A preconcentration procedure based on cloud point extraction and back-extraction (CPE-BE) was proposed for speciation of inorganic vanadium (V4+ and V5+) followed by determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). Two consecutive steps are used in this technique. The traditional CPE technique was applied as a first step, V5+ reacts with bis(3,4-dihydroxybenzylidene)isophthalohydrazide (DHBIP) forming a hydrophobic complex at pH 7.0. The formed complex is then entrapped in a surfactant-rich phase of Triton X-114, while V4+ kept in the aqueous phase. Following this stage, a back-extraction step was performed to minimize the deteriorating effect of the organic matrix on the plasma performance. For this purpose, the surfactant-rich phase containing the analyte was incubated at 45 °C with 1.0 mL of 1.0 mol L−1 of HNO3 solution for 15 min. Finally, the analyte in the aqueous phase was determined by ICP-OES. The total vanadium was determined as V5+ after oxidation of V4+ by using hydrogen peroxide. The calibration graph is linear from 0.4–750.0 μg L-1 for V5+ at the optimum conditions (pH 7.0, 10-4 mol L-1 DHBIP, 0.1 % (v/v) Triton X-114 and 45 °C). The detection and quantification limits of V5+ were 0.12 μg L-1and 0.40 μg L-1, respectively, with an enrichment factor of 49.5, and the relative standard deviation was less than 2.5 % (n = 7, c = 10 μg L-1). The method has been used for speciation of inorganic V in water samples and determination of total V in cabbage, carrots, mint, and tomato samples with satisfactory results.