Relevant bibliographies by topics / Hexavalent metal complexes

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  2. Dissertations / Theses

Academic literature on the topic 'Hexavalent metal complexes'

Author: Grafiati
Published: 4 June 2021
Last updated: 11 February 2022

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Journal articles on the topic "Hexavalent metal complexes"

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Demetriou, Antri, and Ioannis Pashalidis. "Adsorption of hexavalent chromium on dunite." Water Science and Technology 63, no. 4 (February 1, 2011): 818–24. http://dx.doi.org/10.2166/wst.2011.118.

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The paper presents and discusses the effect of various physicochemical parameters (e.g. pH, ionic strength, Cr(VI) initial concentration, amount of the adsorbent, temperature and contact time between metal ion and adsorbent) on the adsorption efficiency of Cr(VI) on dunite in aqueous solutions under atmospheric conditions. Evaluation of the experimental data shows that dunite presents increased affinity for Cr(VI) over a wide pH range and Cr(VI) concentration, and the experimental data are well fitted by the Kd adsorption model. The relative adsorption is pH dependent and decreases slightly (about 10%) with increasing pH, because of changes in the surface charge of the solid. The effect of the ionic strength is significant (particularly at low pH), indicating the predominance of outer-sphere complexes. Moreover, adsorption experiments at various temperatures, two different pH values (pH 3 and pH 8) and three different ionic strengths (0.0, 0.1 and 1.0 M NaClO4), indicate an endothermic but spontaneous entropy-driven processes.
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Huang, Chin-Yuan, Pei-Cheng Cheng, Jih-Hsing Chang, Yu-Chih Wan, Xiang-Min Hong, and Shu-Fen Cheng. "Feasibility of Remediation Lead, Nickel, Zinc, Copper, and Cadmium-Contaminated Groundwater by Calcium Sulfide." Water 13, no. 16 (August 19, 2021): 2266. http://dx.doi.org/10.3390/w13162266.

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Metal contamination in groundwater often occurs in various industrial processes. Studies have confirmed that polysulfide could reduce hexavalent chromium to trivalent chromium, achieving the effect of in situ stabilization. For other metal contamination in groundwater, whether polysulfide also had a stabilizing ability to achieve in situ remediation. This research focused on metals in addition to chromium that often contaminated groundwater, including lead, nickel, zinc, copper, and cadmium, to explore the feasibility of using calcium polysulfide (CaSx) as an in situ stabilization technology for these metals’ contamination of groundwater. Results showed that CaSx had a great removal efficiency for metals lead, nickel, zinc, copper, and cadmium. However, for nickel, zinc, copper, and cadmium, when CaSx was added excessively, complexes would be formed, causing the result of re-dissolution, in turn reducing the removal efficiency. As it is difficult to accurately control the dosage of agents for in situ groundwater remediation, the concentration of re-dissolved nickel, zinc, copper, and cadmium may not be able to meet the groundwater control standards. CaSx had high lead removal efficiency and for a concentration of 100 mg/L, the dose of calcium polysulfide was more than the amount of 1/1200 (volume ratio of CaSx to groundwater). In addition, the removal rate was almost 100% and it would not cause re-dissolution due to excessive CaSx dosing. CaSx can be used as an in situ stabilization technique for lead-contaminated groundwater.
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Destanoğlu, Orhan, and Gülçin Gümüş Yılmaz. "Determination of cyanide, thiocyanate, cyanate, hexavalent chromium, and metal cyanide complexes in various mixtures by ion chromatography with conductivity detection." Journal of Liquid Chromatography & Related Technologies 39, no. 9 (May 27, 2016): 465–74. http://dx.doi.org/10.1080/10826076.2016.1192044.

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Hwang, J. David, and Wen-Jwu Wang. "Determination of Hexavalent Chromium in Environmental Fly Ash Samples by an Inductively Coupled Plasma-Atomic Emission Spectrometer with Ammonium Ion Complexation." Applied Spectroscopy 48, no. 9 (September 1994): 1111–17. http://dx.doi.org/10.1366/0003702944029523.

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A method to determine hexavalent chromium in environmental solid waste has been developed by using an ammonium complexation technique in ICP-AES. This method consists of a two-step extraction and the complexation of ammonium ion. An ammonium hydroxide solution was used to extract the chromium(VI) out of the fly ash sample into the solution. Interfering metal ions, such as Pb, Fe, and Zn in the fly ash sample, were effectively removed by extracting them as diethyldithiocarbamate (DDTC) complexes at pH 9.5 into an MIBK (methyl isobutyl ketone) solution. The pH of the aqueous phase of the sample is then transferred and adjusted to 6.0, and the Cr(VI) is extracted as its complex with MIBK prior to the organic ICP analysis. A method detection limit of 50 ng/g or better, as well as spike recoveries of 90 to 110% (at a spike concentration level of 500 ng/g), is obtained when this method is applied to determine chromium(VI) in fly ash samples.
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Kumar, D., A. Syamal, and L. K. Sharma. "Synthesis and characterization of polystyrene-anchored monobasic bidentate Schiff base and its complexes with bi-, tri-, tetra- and hexavalent metal ions." Journal of Coordination Chemistry 61, no. 11 (June 4, 2008): 1788–96. http://dx.doi.org/10.1080/00958970701625598.

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Kumar, Dinesh, and Amit Kumar. "Syntheses, Characterization, and Biological Activities of Metal Complexes of N-(2-Carbamoylthienyl)-C-(3′-carboxy-2′-hydroxyphenyl) Azetidin-2-one with Some Di-, Tetra-, and Hexavalent Metal Ions." Journal of Chemistry 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/124790.

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The cyclization of the Schiff base, N-(2-carbamoylthienyl)-3′-carboxy-2′-hydroxybenzylideneimine with ClCH2COCl in dioxane, in the presence of triethylamine (Et3N) forms N-(2-carbamoylthienyl)-C-(3′-carboxy-2′-hydroxyphenyl) azetidin-2-one, LH3(I). A methanolic solution ofIreacts with Co(II), Cu(II), Zn(II), Zr(OH)2(IV), and MoO2(VI) ions and forms the coordination compounds, [Co(LH)(MeOH)]2(II), [Cu(LH)]2(III), [Zn(LH)(MeOH)2] (IV), [Zr(OH)2(LH)(MeOH)] (V), and [MoO2(LH)(MeOH)2] (VI). The compounds have been characterized on the basis of elemental analyses, molar conductance, molecular weight, spectral (IR, NMR, reflectance, and ESR) studies, and magnetic susceptibility measurements. All the coordination compounds are nonelectrolytes (ΛM=3.1-9.2 mho cm2mol−1) in DMF.Ibehaves as a dibasic tridentate OON donor ligand inV; a dibasic tetradentate OONO donor ligand inII,III, andVI; and a dibasic tetradentate OONS donor ligand inIV.IIandIIIare dimers, while others are monomers in diphenyl.IIIexhibits subnormal magnetic moment (1.55 B.M.) and is involved in antiferromagnetic exchange, while the other complexes are magnetically dilute. A square-pyramidal structure forIIIand an octahedral structure forII,IV, andVare suggested.VIexhibits an eight-coordinate structure. The ligand (I) and its compounds show antibacterial activities towardsE. coli(gram negative) andS. aureus(gram positive).
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Martins, G. P., Tawiwan Kangsadan, Grant Scott, Christopher Wagner, and Jeff Van Hoose. "A 21st. Century Perspective on Molybdenum Powder Production by Hydrogen Reduction." Materials Science Forum 561-565 (October 2007): 447–52. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.447.

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High purity molybdenum metal powder is produced commercially from hexavalent molybdenum precursors, viz.: ammonium dimolybdate (ADM) or molybdenum trioxide. One conventional process incorporates first-stage and second-stage flowsheet components, with hydrogen gas serving as reductant. This two-stage strategy is employed in order to minimize the formation of volatile molybdenum species that would otherwise be generated at the high temperature required to obtain molybdenum (Mo) in a single stage conversion of the molybdenum precursor. Although molybdenum powder has been produced commercially for over a century, a comprehensive understanding of the kinetic mechanisms and powder characteristics, e.g. oxygen content and particle morphology, is far from being definitive. In fact, it might be argued that the “art” and engineering, in a commercial context, has advanced ahead of the fine-detail science-derived metallurgical process-engineering. Theoretical contributions presented in this paper are focused primarily on the fundamentals of the conversion process associated with second-stage reduction process – MoO2 to Mo and the factors that contribute to the oxygen content of the molybdenum powder product (1000 to 100 ppm(w) O, range). Thus, equilibrium-configuration details concerning both solid and gas phases are addressed, including the volatile hexavalent molybdenum vapor complexes as well as solubility of oxygen in molybdenum. In regard to the role of a chemical vapor-transport mechanism on powder morphology in second-stage conversion of MoO2 to Mo, it is shown that the partial pressure of the prominent molybdenum hydroxide vapor-complex (MoO2(OH)2) is far too low to support such a mechanism. This contention has been corroborated by employing helium to control the partial pressures of hydrogen and water in the gas phase. Secondarily, a limited assessment of the intrinsic rate-controlling mechanisms that can contribute to the residual oxygen-content of the Mo powder product is also provided. Powder morphology, and its concomitant influence on specific surface-area of the Mo powder product, is found to correlate with the oxygen-content determination of the powder produced during second-stage reduction, and according to the processing strategy employed. Consequently, it has been found cogent to “partition” second-stage reduction into: i) a relatively high-rate Primary Reduction Sequence, and ii) a lower rate Deoxidation Sequence.
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Accornero, Marina, Luigi Marini, and Matteo Lelli. "Prediction of the thermodynamic properties of metal–chromate aqueous complexes to high temperatures and pressures and implications for the speciation of hexavalent chromium in some natural waters." Applied Geochemistry 25, no. 2 (February 2010): 242–60. http://dx.doi.org/10.1016/j.apgeochem.2009.11.010.

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9

Kumar, Dinesh, Arun Syamal, Jaipal, and Lalit Kumar Sharma. "Synthesis, magnetic and spectral studies on polystyrene-anchored coordination complexes of bi-, tri-, tetra- and hexavalent metal ions with unsymmetrical dibasic tetradentate ONNO donor Schiff base derived from 3-formylsalicylic acid, ethylenediamine and 2-benzoylacetanilide." Journal of Chemical Sciences 121, no. 1 (January 2009): 57–64. http://dx.doi.org/10.1007/s12039-009-0006-y.

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10

Sun, J., and J. C. Huang. "Co-removal of hexavalent chromium during copper precipitation." Water Science and Technology 46, no. 4-5 (August 1, 2002): 413–19. http://dx.doi.org/10.2166/wst.2002.0639.

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In our recent study using the nucleated precipitation technology to treat plating wastewater, it was found that about one half of hexavalent chromium was co-removed with copper, nickel and zinc. Since hexavalent chromium could not react with either hydroxide or carbonate to from precipitates, this study was undertaken to evaluate the mechanism(s) involved in the chromium co-removal. Batch tests were conducted with synthetic solutions containing either only copper or both copper and hexavalent chromium. Metal precipitation was induced by adding Na2CO3 to different pH, and the quantitative removal of copper and chromium was determined. Besides, the [Cr]/[Cu] molar ratio of produced precipitates were also assessed in conjunction with the EDAX analysis to determine their compositions. Experimental results indicate that for pure copper solution, precipitation begins at pH 6.0, and completes at pH 7.0. The chemical forms of the precipitates are copper carbonates [CuCO3.Cu(OH)2 and CuCO3.2Cu(OH)2]. On the other hand, in a bi-metal solution of copper plus chromium, precipitation of copper begins at about pH 5.0, and copper precipitation is always accompanied by some chromium removal. From the removal stoichiometry of the two metals, it is found that at low pH, the co-removal is a result of “co-precipitation” which results in the formation of CuCrO4 crystallites. Once such crystallites are formed, they provide a heterogeneous environment which enhances an early formation of copper carbonate at a lower pH (below 5.5). It is further found that once copper carbonate precipitates are produced, the remaining soluble will precipitate in such form, and at this stage further removal of copper is no longer accompanied by additional chromium removal. The test data also reflect that the produced copper carbonates are positively charged, as verified by zeta potential measurement, at pH below 7.5. Thus they are able to adsorb some anionic chromium (existing as chromate) through electrostatic attraction and/or inorganic ligand exchange. At pH of 6 to 10, the extent of adsorption decreases with increasing pH, and the adsorption capacity seems to coincide with the progressive reduction of positive zeta potentials of the precipitated particles.
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Dissertations / Theses on the topic "Hexavalent metal complexes"

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Cartié, Bernard. "Etude d'iso et d'heteropolyanions du molybdene pentavalent et hexavalent en milieu non aqueux : anions dodecamolybdosulfates et octodecamolybdodisulfates non reduits et partiellement reduits." Orléans, 1987. http://www.theses.fr/1987ORLE2029.

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