Relevant bibliographies by topics / Hexavalent metal compounds

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Academic literature on the topic 'Hexavalent metal compounds'

Author: Grafiati
Published: 4 June 2021
Last updated: 17 February 2022

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Journal articles on the topic "Hexavalent metal compounds"

1

Kasmiyati, Sri, Santosa S, Irfan Dwidja Priyambada, Kumala Dewi, and Rintawati Sandradewi. "Perkecambahan Biji Dan Pertumbuhan Kecambah Varietas Sorgum (Sorghum bicolor L.) Pada Cekaman Krom Heksavalen." Bioma : Berkala Ilmiah Biologi 17, no. 1 (June 17, 2015): 41. http://dx.doi.org/10.14710/bioma.17.1.41-54.

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In contrast to other toxic trace metals, Cr has received little attention. Since valence level of chromium determines its toxicity, chromium is categorized as unique heavy metal. Chromium hexavalent (Cr6+) has the biggest toxicity among other valence levels. Seed germination and seedling growth are sensitive to heavy metal stresses. This research aimed to find out the responses of seed germination and seedling growth of 12 sorghum varieties toward Cr6+. Seed germination and seedling growth experiment was done on 12 sorghum varieties (Badik, UPCA-1, Keris, Keris M3, hegari Genjah, Gambela, Selayer, Sangkur, Mandau, Batari, Kawali, dan Numbu), planted in petridishes with Cr6+ treatment in form of chromate (K2CrO4) and dichromate (K2Cr2O7) compounds with 0, 50 and 500 mg of Cr/l concentration for a week. The parameters measured were the number of seeds germinate each day; the length of radicle and plumule, and fresh and dry weight at the end of experiment. The results showed that higher concentration of Cr6+ both in form of dichromate and chromate, significantly decreased the length of radicle and plumule, fresh and dry weight, and SVI (seedling vigor index) value. However, index germination (GI) value and percentage of germination of the 12 varieties sorgum significantly increased in the treatment of 50 mg Cr/l Cr6+ in form of dichromate and chromate. The treatment of dichromate compound showed bigger effect than chromate toward variables of seed germination and seedling growth of sorghum. It was noticed that 12 sorghum varieties possessed an integrated complex of adaptation to cope with the range of form of compound and concentration of Cr6+. Based on the responses of seed germination and seedling growth, Kawali, Hegari, Keris, Keris M3, Mandau, and Selayer varieties was more susceptible toward Cr6+ toxicity, and Sangkur, Selayer, Batari, and Numbu was more tolerant than other varieties. Keywords : chromate, dichromate, Sorghum bicolor, seedling, hexavalent chromium
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2

Averina, Yu M., G. E. Kalyakina, V. V. Menshikov, Yu I. Kapustin, and V. S. Boldyrev. "Neutralisation Process Design for Electroplating Industry Wastewater Containing Chromium and Cyanides." Herald of the Bauman Moscow State Technical University. Series Natural Sciences, no. 84 (June 2019): 70–80. http://dx.doi.org/10.18698/1812-3368-2019-3-70-80.

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Manufacturing processes in the electroplating industry employ hazardous chemicals and generate hazardous waste, including hexavalent chromium compounds and heavy metal cyanides. We designed a reagent-based treatment technology that can remove these contaminants and is relatively simple to implement and maintain. The technology features low reagent consumption but high treatment efficiency and simplifies separating precipitates from the treated effluent. The paper presents a detailed description of how to neutralise electroplating shop wastewater. We propose a system of organizational and technological measures to improve chemical safety.
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Marcus, Maria Iuliana, Mihaela Andreea Mitiu, Maria Vlad, Mariana Mincu, Gina Ghita, and Ana Maria Anghel. "Influence of Different Electroplating Sludge Types on the Iron Ions Recovery Yield." Revista de Chimie 69, no. 3 (April 15, 2018): 618–20. http://dx.doi.org/10.37358/rc.18.3.6161.

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Electroplating sludge resulting from wastewater (washing wastewater and technological solutions) treatment is considered to be a hazardous waste, being a mixture of hydroxides of many heavy metals such us: iron, chromium, copper, nickel, cadmium or zinc. The metal compounds from electroplating sludge have a great economic value, thus, a number of techniques have been investigated in order to recover them. This paper presents the results of the research activity in the laboratory in order to recover Fe (II, III, VI) from two types of electroplating sludge: a fresh sludge from wastewaters treatment and an old sludge, stabilized by disposal for many years. Iron recovery was performed by the solubilization of the sludge in several stages, to yield hydroxides or metal salts of chromium, iron, or zinc. The iron recovery has been performed from the cake obtained after the chromium recovery. In this cake, the iron is present in the form of divalent, trivalent and hexavalent iron. The iron recovery yield was 98.50% from fresh sludge (recovery in one stage) and 96.80% from old sludge (recovery in two stages).
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Abrashov, Aleksey, Nelya Grigoryan, Tigran Vagramyan, and Naum Asnis. "On the Mechanism of Formation of Conversion Titanium-Containing Coatings." Coatings 10, no. 4 (March 29, 2020): 328. http://dx.doi.org/10.3390/coatings10040328.

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The present work is devoted to the study of the mechanism of the process of formation of adhesive oxide-titanium coatings on steel, zinc, and aluminum surfaces. For the first time, the following hypothesis has been confirmed experimentally, namely, that nickel, being the first metal to be deposited on a steel substrate, creates active centers on which titanium oxides are formed, because the hydrolysis of hexafluorotitanic acid is adsorbed, which then form a continuous film. The data obtained, regarding the dependence of the coating thickness on the linear rate of the solution flow along the treated surface, indirectly confirm that the formation of insoluble titanium oxides occurs because of the alkalization of the solution adjacent to the surface. It has been established that in the presence of hexavalent molybdenum compounds in the solution as oxidizers, molybdenum is included in the coating in the form of oxides. It has been revealed that in the lower layers of the coating, molybdenum is contained in the form of compounds of molybdenum (V) and (VI), while in the upper layers, it is contained only in the form of the compound of molybdenum (VI).
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Abdul Salam, Femina, and Anantharaman Narayanan. "Leached compounds from the extracts of pomegranate peel, green coconut shell, and karuvelam wood for the removal of hexavalent chromium." Green Processing and Synthesis 8, no. 1 (January 28, 2019): 281–87. http://dx.doi.org/10.1515/gps-2018-0085.

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Abstract During biosorption, the biosorbent releases many organic compounds to the medium. In the present study, extracts of pomegranate peel (PP), green coconut shell (GCS), and karuvelam wood (KW) were prepared at three different conditions, namely 12 h, 3 h, and 3 h at pH 2, for the removal of hexavalent chromium [Cr(VI)]. The amount of organic compounds, mainly the leached organic compounds in the extract before and after treatment with Cr(VI) solution, was determined by chemical oxygen demand analysis. The total phenolic content, antioxidant activity, and total flavonoid content were used to estimate the chromium reduction potential of the extracts. The PP extract is the richest in all the three factors, followed by GCS and KW. The disappearance rate of Cr(VI) in the presence of PP extract reached 99.63% for the 50 mg/l concentration within 3 min, while it was 12% and 10% for GCS and KW, respectively, for the same concentration and time. Reaction mechanisms were formulated with the help of Fourier transform infrared spectroscopy to confirm the role of leached compounds from natural materials for the removal of heavy metal.
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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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Daoud, Waseem, Taghi Ebadi, and Ahmad Fahimifar. "Removal of hexavalent chromium from aqueous solutions using micro zero-valent iron supported by bentonite layer." Water Science and Technology 71, no. 5 (December 17, 2014): 667–74. http://dx.doi.org/10.2166/wst.2014.493.

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Hexavalent chromium Cr(VI) is of particular environmental concern due to its toxicity, mobility, and challenging removal from industrial wastewater. It is a strong oxidizing agent that is carcinogenic and mutagenic and diffuses quickly through soil and aquatic environments. Moreover, it does not form insoluble compounds in aqueous solutions; therefore, separation by precipitation is not feasible. While Cr(VI) oxyanions are very mobile and toxic in the environment, trivalent Cr(III) cations are the opposite and, like many metal cations, Cr(III) forms insoluble precipitates. Thus, reducing Cr(VI)–Cr(III) simplifies its removal from effluent and also reduces its toxicity and mobility. Permeable reactive barriers (PRBs) with zero-valent iron (ZVI) have been used to remediate contaminated groundwater with metals, but using ZVI in remediation of contaminated groundwater or wastewater is limited due to its lack of stability, easy aggregation, and difficulty in separation of iron from the treated solution. Thus, the technology used in the present study is developed to address these problems by placing a layer of bentonite after the PRB layer to remove iron from the treated water. The removal rates of Cr(VI) under different values of pH were investigated, and the results indicated the highest adsorption capacity at low pH.
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Daulton, Tyrone L., Brenda J. Little, Kristine Lowe, and Joanne Jones-Meehan. "Microbial Reduction of Chromium(VI): In-Situ Environmental Cell Transmission Electron Microscopy Study Using Electron Energy Loss Spectroscopy." Microscopy and Microanalysis 7, S2 (August 2001): 134–35. http://dx.doi.org/10.1017/s143192760002674x.

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The geochemistry and toxicity of chromium is controlled by its valence state. Chromium is a redox active 3d transition metal with a wide range (− to +6) of possible oxidation states; however only Cr(III) and Cr(VI) are stable. Hexavalent Cr(VI) can be readily reduced to the trivalent state by Fe2+, S2−, organic compounds, wetland plants, and several species of microorganisms. The associated mechanisms of Cr(VI) reduction are technologically and biologically important because they convert a toxic, mobile element into a less toxic, immobile form.Reduction of Cr(VI) by the bacterium, Shewanella oneidensis (previously classified Shewanella putrefaciens strain MR-1), was studied by absorption spectrophotometry and in-situ, environmental cell (EC) - transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS). Shewanella oneidensis (S. oneidensis), a gram-negative, facultative bacterium is capable of respiring aerobically and anaerobically using a variety of compounds, including O2, Fe(III), Mn(IV), NO2−, NO3−, SO2, SO32−, thiosulfate (S2O32−), trimethyamine oxide, fumarate, U(VI), and Cr(VI) as terminal electron acceptors.
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9

G. Saiz, Paula, Ainara Valverde, Bárbara Gonzalez-Navarrete, Maibelin Rosales, Yurieth Marcela Quintero, Arkaitz Fidalgo-Marijuan, Joseba Orive, et al. "Modulation of the Bifunctional CrVI to CrIII Photoreduction and Adsorption Capacity in ZrIV and TiIV Benchmark Metal-Organic Frameworks." Catalysts 11, no. 1 (January 1, 2021): 51. http://dx.doi.org/10.3390/catal11010051.

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The presence of hexavalent chromium water pollution is a growing global concern. Among the currently applied technologies to remove CrVI, its adsorption and photocatalytic reduction to CrIII less mobile and toxic forms are the most appealing because of their simplicity, reusability, and low energy consumption. However, little attention has been paid to bifunctional catalysts, that is, materials that can reduce CrVI to CrIII and retain both hexavalent and trivalent chromium species at the same time. In this work, the dual CrVI adsorption–reduction capacity of two iconic photoactive water-stable zirconium and titanium-based metal–organic frameworks (MOFs) has been investigated: UiO-66-NH2 and MIL-125. The bifunctionality of photoactive MOFs depends on different parameters, such as the particle size in MIL-125 or organic linker functionalization/defective positions in UiO-66 type sorbents. For instance, the presence of organic linker defects in UiO-66 has shown to be detrimental for the chromium photoreduction but beneficial for the retention of the CrIII phototransformed species. Both compounds are able to retain from 90 to 98% of the initial chromium present at acidic solutions as well as immobilize the reduced CrIII species, demonstrating the suitability of the materials for CrVI environmental remediation. In addition, it has been demonstrated that adsorption can be carried out also in a continuous flux mode through a diluted photoactive MOF/sand chromatographic column. The obtained results open the perspective to assess the bifunctional sorption and photoreduction ability of a plethora of MOF materials that have been applied for chromium capture and photoreduction purposes. In parallel, this work opens the perspective to develop specific chemical encoding strategies within MOFs to transfer this bifunctionality to other related water remediation applications.
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Tumolo, Marina, Valeria Ancona, Domenico De Paola, Daniela Losacco, Claudia Campanale, Carmine Massarelli, and Vito Felice Uricchio. "Chromium Pollution in European Water, Sources, Health Risk, and Remediation Strategies: An Overview." International Journal of Environmental Research and Public Health 17, no. 15 (July 28, 2020): 5438. http://dx.doi.org/10.3390/ijerph17155438.

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Chromium is a potentially toxic metal occurring in water and groundwater as a result of natural and anthropogenic sources. Microbial interaction with mafic and ultramafic rocks together with geogenic processes release Cr (VI) in natural environment by chromite oxidation. Moreover, Cr (VI) pollution is largely related to several Cr (VI) industrial applications in the field of energy production, manufacturing of metals and chemicals, and subsequent waste and wastewater management. Chromium discharge in European Union (EU) waters is subjected to nationwide recommendations, which vary depending on the type of industry and receiving water body. Once in water, chromium mainly occurs in two oxidation states Cr (III) and Cr (VI) and related ion forms depending on pH values, redox potential, and presence of natural reducing agents. Public concerns with chromium are primarily related to hexavalent compounds owing to their toxic effects on humans, animals, plants, and microorganisms. Risks for human health range from skin irritation to DNA damages and cancer development, depending on dose, exposure level, and duration. Remediation strategies commonly used for Cr (VI) removal include physico-chemical and biological methods. This work critically presents their advantages and disadvantages, suggesting a site-specific and accurate evaluation for choosing the best available recovering technology.
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Dissertations / Theses on the topic "Hexavalent metal compounds"

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Charbonnel, Marie-Christine. "Extraction de l'uranium (vi), du plutonium (iv) et des produits de fission par les n,n'-tetraalkyldiamides." Clermont-Ferrand 2, 1988. http://www.theses.fr/1988CLF21116.

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Etude des proprietes extractives de r::(2)nc(o)(ch::(2))::(3) c(o)nr::(2). Ces composes extraient u(vi) et pu(iv), les actinides et lanthanides trivalents restant en phase aqueuse. Mise en evidence des 3 complexes 2l. Hno::(3), l. Hno::(3) et l. 2hno::(3) (l-glutaramide). A faible acidite, on a pu observer les complexes l. Uo::(2)(no::(3))::(2) et l. Pu(no::(3))::(4) et a forte acidite l. Uo::(2)(no::(3))::(3)h et l. Pu(no::(3))::(6)h::(2)
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Rezrazi, El Mustafa. "Obtention par voie électrochimique et étude de quelques propriétés électrochromes de l'oxyde de tungstène WO3." Besançon, 1987. http://www.theses.fr/1987BESA2004.

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Preparation des couches electrochromes de wo::(3) par oxydation anodique sous courant pulse. Caracteristiques electrooptiques. Proprietes thermodynamiques des bronzes h::(x)wo::(3) et li::(x)wo::(3) responsables du phenomene coloration-decoloration
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Books on the topic "Hexavalent metal compounds"

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Emissions of metals, chromium and nickel species, and organics from municipal wastewater sludge incinerators.: Hexavalent chromium method evaluation. Cincinnati, Ohio: Risk Reduction Engineering Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, 1992.

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Book chapters on the topic "Hexavalent metal compounds"

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Anicai, L., and Teodor Visan. "Surface Modification of Aluminum and Its Alloys Using Conversion Coatings." In Encyclopedia of Aluminum and Its Alloys. Boca Raton: CRC Press, 2019. http://dx.doi.org/10.1201/9781351045636-140000302.

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This article presents some information related to the chemical conversion procedures applied onto Al and its alloys involving both classical hexavalent chromium-based solutions and the most recent ones involving transitional metals and/or rare earth compounds, as environmentally friendly alternatives. The main characteristics of the formed thin films, including appearance, composition, morphology, corrosion resistance, and performance, are also presented.
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Conference papers on the topic "Hexavalent metal compounds"

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Vesely, Andreas. "Processes for the Treatment of NORM and TENORM." In ASME 2003 9th International Conference on Radioactive Waste Management and Environmental Remediation. ASMEDC, 2003. http://dx.doi.org/10.1115/icem2003-4623.

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By contract with the Austrian government, the ARC is treating radioactive waste from research institutions and industries. In the last years, one focus was the development of processes for the treatment of NORM and TENORM. Our goal in developing such processes is to recycle valuable compounds for further industrial usage and to concentrate the radioactive elements as far as possible, to save space in the waste storage facilities. Austria is an important producer of tungsten-thoria- and tungsten-molybdenum-thoria-cermets. Scrap is generated during the production process in the form of turnings and grinding sludge and dust. Although big efforts have been undertaken to replace Thorium compounds, waste streams from past production processes are still waiting for treatment. The total amount of this waste stored in Austria may be estimated to be approx. 100 tons. In close co-operation with the tungsten industries, recycling processes were tested and further developed at ARC in laboratory, bench scale and pilot plants. Three different approaches to solve the problem were studied: Dissolution of tungsten in molten iron in an arc or induction furnace, thus producing an Fe-W or Fe-W-Mo alloy. Slag is produced upon the addition of lime and clay. This slag extracts nearly all of the Thorium contained in the metal melt. Selective dissolution of Tungsten in aqueous alkaline medium after oxidation of the metal to the hexavalent state by heating the scrap in air at temperatures of 500°C to 600°C. The resulting oxides are treated with sodium hydroxide solution. Tungsten and Molybdenum oxides are readily dissolved, while Thorium oxide together with silicon and aluminum compounds remain insoluble and are separated by filtration. Sodium tungstate solution is further processed by the usual hydrometallurgical tungsten mill process. Oxidation and dissolution of Tungsten can be achieved in one step by an electrochemical process. Thus, thoriated Tungsten scrap is used as an anode in an electrolysis cell, while sodium hydroxide or ammonia serve as electrolyte. After dissolution of Tungsten, the solids are separated from the liquid by filtration. With the electrochemical process, treatment of Tungsten-Thoria scrap can be achieved with high throughput in rather small reactors at moderate temperatures and ordinary pressure. The Tungsten solution exhibits high purity. Another process which we examined in detail is the separation of radium from rare earth compounds. Radium was separated by co-precipitation with barium sulfate from rare earth chloride solutions. The efficiency of the separation is strongly pH-dependent. Again, the valuable rare earth compound can be reused, and the radioactive elements are concentrated.
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Nagai, Yasuaki, Shinsuke Mochizuki, Kaoru Hanawa, Kenji Okubo, Shingo Watanabe, and Tsunehiko Abe. "Development of Compound Coating that Reduces Permeation of Chloride Ion in Salty Water for Hexavalent-Chromium-Free Metal Gasket for PWC Engines." In Small Engine Technology Conference & Exposition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2008. http://dx.doi.org/10.4271/2008-32-0047.

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