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Showing papers on "Chromium published in 2004"


Journal ArticleDOI
TL;DR: An inexpensive and effective adsorbent was developed from bagasse fly ash, obtained from a sugar industry, for the dynamic uptake of lead and chromium, and found to be exothermic in nature.

675 citations


Journal ArticleDOI
TL;DR: In this article, a suite of chromium oxides and other compounds were studied under high spectral resolution conditions chosen to reduce the possibility of differential charging, and the fine structure observed for compounds such as chromium (III) chloride had a distinctly different pattern.
Abstract: Photoelectron spectra of a number of chromium oxides and other compounds were studied under high spectral resolution conditions chosen to reduce the possibility of differential charging. Some of the suite of Cr(III) compounds chosen for study produced Cr 2p spectra containing fine structure that could be identified with multiplet splitting. The splitting patterns produced were similar for all trivalent binary and ternary oxides and sulphides whose patterns closely reproduced the splitting predicted for the Cr(III) free ion by Gupta and Sen. The fine structure observed for compounds such as chromium (III) chloride had a distinctly different pattern. A number of other chromium (III) compounds were studied that did not exhibit the fine structure described above; nonetheless, well-defined line shapes and reproducible peak centroids were obtained by fitting protocols. The use of such information to determine surface chemistry on chromated steels is described, based on the spectral knowledge of chromium (III) oxides and hydroxides and the chromium (VI) oxide systems.

404 citations


Journal ArticleDOI
TL;DR: SrTiO 3 photocatalysts doped with chromium ions showed photocatalysis for H 2 evolution from an aqueous methanol solution under visible light irradiation as mentioned in this paper.
Abstract: SrTiO 3 photocatalysts doped with chromium ions showed photocatalytic activities for H 2 evolution from an aqueous methanol solution under visible light irradiation However, it had a long induction period Codoping of niobium or tantalum ions with chromium ions shortened the induction period, and increased the photocatalytic activities in respect of the H 2 evolution The photocatalytic activities of chromium- and chromium/tantalum-doped SrTiO 3 were improved when they were pretreated at 773 K in the hydrogen reduction atmosphere Codoping of tantalum ions suppressed the formation of Cr 6+ ions and oxygen defects which would work as nonradiative recombination centers between photogenerated electrons and holes, resulting in the shortening of induction periods and the improvement of photocatalytic activities

323 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of pH and coagulant dosages on the coagulation process was studied and conditions were optimised corresponding to the best removal of organic matters, suspended solids as well as chromium.

323 citations


Journal ArticleDOI
TL;DR: It is concluded that plant could grow under chromium stress and protect themselves from phytotoxicity of Cr by altering various metabolic processes.

317 citations


Journal ArticleDOI
TL;DR: In this paper, the photonic efficiencies for Cr(VI) reduction are nearly the same under aerobic and anaerobic conditions, but show a significant increase at the lowest pH.
Abstract: Cr(VI) photocatalytic reduction experiments over TiO2 particles under near UV irradiation in the presence of excess oxalate were performed at acid pH (2 and 3) and under air and N2 bubbling. Initial photonic efficiencies for Cr(VI) reduction are nearly the same under aerobic and anaerobic conditions, but show a significant increase at the lowest pH. At pH 2, the addition of oxalate facilitates Cr(VI) reduction, hindering the electron-shuttle mechanism taking place in pure water. The oxalate synergistic effect at pH 2 is lower than that previously found for EDTA and negligible at pH 3. Chromium(V) oxalate concentration profiles were obtained by EPR spectroscopy in the presence of excess oxalate at pH 1.5. Coordinated Cr(V) complexes [CrV(O)(Ox)2]-, [CrV(OH2)(Ox)2]-, and [CrV(O)(OH)2(Ox)]- were identified, on the basis of the comparison of their corresponding g values with recent literature data. The kinetic analysis of the temporal evolution of the paramagnetic Cr(V) species indicates also an effective pho...

313 citations


Journal ArticleDOI
TL;DR: It is shown that chromium can be electrodeposited efficiently to yield a crack-free deposit and this approach could circumvent the use of chromic acid for chromium electroplating, which would be a major environmental benefit.
Abstract: A dark green, viscous liquid can be formed by mixing choline chloride with chromium(III) chloride hexahydrate and the physical properties are characteristic of an ionic liquid. The eutectic composition is found to be 1:2 choline chloride/chromium chloride. The viscosity and conductivity are measured as a function of temperature and composition and explained in terms of the ion size and liquid void volume. The electrochemical response of the ionic liquid is also characterised and it is shown that chromium can be electrodeposited efficiently to yield a crack-free deposit. This approach could circumvent the use of chromic acid for chromium electroplating, which would be a major environmental benefit. This method of using hydrated metal salts to form ionic liquids is shown to be valid for a variety of other salt mixtures with choline chloride.

286 citations


Journal ArticleDOI
TL;DR: The potential reuse of chromium-containing seaweed for the preparation of basic chromium sulfate (tanning agent) has been demonstrated and Fourier transform infrared spectroscopy, energy-dispersive X-ray analysis, and flame photometry studies have been carried out to understand the mechanistic pathway for the removal of Chromium.
Abstract: The presence of chromium in the effluent is a major concern for the tanning industry. Currently, chemical precipitation methods are practiced for the removal of chromium from the effluent, but that leads to the formation of chrome-bearing solid wastes. The other membrane separation and ion exchange methods available are unfeasible due to their cost. In this study, the removal of chromium from tannery effluent has been carried out using abundantly available brown seaweed Sargassum wightii. Simulated chrome tanning solution was used for the standardization of experimental trials. Various factors influencing the uptake of chromium, viz., quantity of seaweed, concentrations of chromium, pH of the chrome-bearing wastewater, and duration of treatment, have been studied. Chemical modification of the seaweed through pretreatment with sulfuric acid, magnesium chloride, and calcium chloride showed improved uptake of chromium. Langmuir and Freundlich isotherms have been fitted for various quantities of seaweed. The dynamic method of treatment of protonated seaweed with simulated chrome tanning solution at a pH of 3.5-3.8 for a duration of 6 h gave the maximum uptake of about 83%. A similar uptake has been established for commercial chrome tanning wastewater containing the same concentration of chromium. The Sargassum species exhibited a maximum uptake of 35 mg of chromium per gram of seaweed. Fourier transform infrared spectroscopy, energy-dispersive X-ray analysis, and flame photometry studies have been carried out to understand the mechanistic pathway for the removal of chromium. The potential reuse of chromium-containing seaweed for the preparation of basic chromium sulfate (tanning agent) has been demonstrated.

280 citations


Journal ArticleDOI
TL;DR: In this article, the effect of iron and manganese concentration on the morphology of complex intermetallics has been studied in an Al-12.7.% Si alloy with three levels of iron (0.4, 0.8, 1.2), and five different levels of manganous ranging from 0.0 to 0.5
Abstract: The effect of iron and manganese concentration on the morphology of complex intermetallics has been studied in an Al–12.7 wt.% Si alloy containing 0.1 wt.% Cr with three levels of iron (0.4, 0.8, 1.2 wt.%), and five different levels of manganese ranging from 0.0 to 0.5 wt.%. The intermetallic compounds form at high iron contents or at high concentrations of manganese and chromium with low iron. Star-like intermetallics form when the segregation factor is greater than 1.30. Chromium (0.1 wt.%) with more than 0.2 wt.% manganese are needed to convert all platelet phases to small star-like intermetallics. A power equation describes the relation between sludge formation temperature and iron content. The volume percentage of intermetallic compounds increases as the iron or manganese content increases. The amount of intermetallic can be estimated from a linear segregation factor.

276 citations


Journal ArticleDOI
TL;DR: This adsorbent is Beech (Fagus orientalis L.) sawdust studied by using batch techniques indicated that the percent adsorption decreased with increasing initial concentration of chromium(VI), and a contact time of 80 min was found to be optimum.

264 citations


Journal ArticleDOI
TL;DR: In this paper, high temperature corrosion tests were performed on low-alloyferritic steel and austenitic stainless steel, five high velocityoxy -fuel (HVOF) coatings, a laser cladding, and a diffusion chromized steel.

Journal ArticleDOI
TL;DR: In this paper, the kinetics and thermodynamics of the chromium(III) adsorption on novel activated carbons prepared from co-mingled natural organic wastes have been studied by the sets of equilibrium and time-based experiments at various conditions (temperature, initial chromium concentration and carbon loading).

Journal ArticleDOI
TL;DR: In this article, the authors studied the phytotoxicity of Brassica juncea in Cr(III)- and Cr(VI)-contaminated soils using chemical, light microscopy, scanning electron microscopy (SEM) and transmission electron microscope (TEM) analyses.
Abstract: Summary • Brassica juncea is a potential candidate plant for phytoremediation of a number of heavy metals, but little is known about the phytotoxicity of chromium (Cr) for this plant in Cr(III)- and Cr(VI)-contaminated soils. • Chromium distribution and phytotoxicity at the whole plant and cellular levels were studied using chemical, light microscopy, scanning electron microscopy and transmission electron microscopy analyses. • Bioavailability of Cr in soils was low, but the uptake significantly increased at phytotoxic levels. Chromium from Cr(VI)-contaminated soils was more phytotoxic than from Cr(III)-contaminated soils. Chromium causes growth retardation, reduces the number of palisade and spongy parenchyma cells in leaves, results in clotted depositions in the vascular bundles of stems and roots, and increases the number of vacuoles and electron dense materials along the walls of xylem and phloem vessels. • Our results suggest that B. juncea is not a good candidate for phytoremediation of soils with lower Cr. However, it is able to accumulate significant amounts of Cr in both shoots and roots at higher soil-Cr concentrations despite severe phytotoxic symptoms.

Journal ArticleDOI
TL;DR: Chamberland et al. as mentioned in this paper found that chromium concentrations in serpentine soil profiles fluctuate between 1,725 to 4,760 mg kg−1 and do not correspond to variations in soil pH, organic carbon, or electrical conductivity.
Abstract: Weathering of ultramafic rocks and serpentinites in the Franciscan Complex of California produces serpentine soils containing high concentrations of Cr as well as other potentially toxic elements including Ni, Co, and Mn. Chromium concentrations in serpentine soils from Jasper Ridge Biological Preserve in the Central Coast Range are as high as 4,760 mg kg−1, nearly three times greater than the serpentinite protolith (∼1800 mg kg−1). Chromium-containing minerals within the bedrock include chlorite (∼0.3 Cr wt. %), enstatite (∼0.4 Cr wt. %), augite (∼0.7 Cr wt. %), chromite (∼10.8 Cr wt. %), magnetite (8.2-10.3 Cr wt. %), and an ultra fine-grained mixture of spinel and a silicate phase containing ∼13.3 Cr weight percent. Chromium concentrations in serpentine soil profiles fluctuate between 1,725 to 4,760 mg kg−1 and do not correspond to variations in soil pH, organic carbon, or electrical conductivity. The enrichment and variability of soil Cr is directly related to the modal abundance and weathering of chromite, Cr-magnetite, and the spinel-silicate mixture. By comparison, Cr silicates account for

Journal ArticleDOI
TL;DR: In this article, the adsorption and coadsorption of NH3, NO, and O2, in conjunction with in situ FT-IR spectroscopy, was used to elucidate the reaction mechanism as the samples were heated from 323 to 673 K.
Abstract: TiO2-supported transition metal oxides (Mn, Cr, and Cu) for the SCR of NO with NH3 have been synthesized by wet impregnation. The adsorption and coadsorption of NH3, NO, and O2, in conjunction with in situ FT-IR spectroscopy, was used to elucidate the reaction mechanism as the samples were heated from 323 to 673 K. While Cr was the only transition metal that generated significant amounts of Bronsted acidity, strong Lewis acid sites were present over all of the materials. The peak strength corresponding to the δs(NH3) coordinated to Lewis acid sites decreased in the following order: Ti > Mn > Cr ∼ Cu. Similarly, the peak strength corresponding to the δas(NH3) coordinated to Lewis acid sites decreased as follows: Mn > Cr ∼ Cu. Exposing the catalysts to oxygen before the introduction of NO did not impact the adsorption of NO as nitrates on the catalysts, suggesting that labile lattice oxygen plays an important role in the formation of nitrates. Three types of nitrates were observed after the adsorption of ...

Journal ArticleDOI
TL;DR: Increase in cell density and initial Cr(VI) concentration increased chromate reduction but was inhibited by metal ions like, Ni2+, Co2+, Cd2+ and Pb2+.

Journal ArticleDOI
TL;DR: The ability of mackinawite, an iron monosulphide, to reduce Cr(VI) was studied at pH values of 5 and 7, with solution concentrations ranging from 10 −4 to 6 × 10 −3 ǫM and fixed ionic strength.

Journal ArticleDOI
TL;DR: In this article, a gram-negative bacterium Pantoea sp. TEM18 exhibited the greatest copper tolerance and was able to survive in the medium containing copper at concentrations as high as 180 mg/l.

Journal ArticleDOI
TL;DR: Results indicate that vitamin C could be used in effective remediation of Cr(VI)-contaminated soils and groundwater in a wide range of pH, with or without sunlight.

Journal ArticleDOI
TL;DR: The model was further used to optimise the parameters to maximise the percentage Cr-removal to more than 98% and shows a close fit between the experimental results and the model predictions.

Journal ArticleDOI
TL;DR: In this paper, five chromium steels with different surface finishes (electropolished, polished, ground, sandblasted) were oxidised for 1, 10 or 100 h in three different atmospheres: H 2 −2.5%H 2 O, N 2 −20% H 2 -0.49% h 2 O and N 2 -20.5 % O 2 at 600 °C.

Journal ArticleDOI
01 Jul 2004-Talanta
TL;DR: It was found that Cr(VI) can undergo chemically irreversible reduction in acidic solutions at gold, glassy carbon and boron-doped diamond electrodes and was found to be diffusionally controlled at all three electrodes studied.

Journal ArticleDOI
TL;DR: In this paper, the sorptive removal of hexavalent chromium from aqueous solutions by Mg−Al−CO3 hydrotalcite was investigated in a batch mode.
Abstract: In this study, the sorptive removal of hexavalent chromium from aqueous solutions by Mg−Al−CO3 hydrotalcite was investigated in a batch mode. The influence of solution pH, conditioning duration, in...

Journal ArticleDOI
TL;DR: Transition metal salts were added to aerogels of TiO2-SiO2 mixtures as mentioned in this paper, and the resulting materials had very high surface areas (600-1000 m2/g) and pore volumes (1-4 cm3/g).
Abstract: Transition metal salts were added to aerogels of TiO2–SiO2 mixtures. The resulting M–TiO2–SiO2 (M = transition metal, in general present in the form of oxides) materials had very high surface areas (600–1000 m2/g) and pore volumes (1–4 cm3/g), and contained highly dispersed transition metal oxides. Several samples were active photocatalysts for acetaldehyde oxidation to carbon dioxide using visible light; in particular chromium, cobalt, and nickel. These intimate aerogel mixtures were only active when SiO2 was present (i.e. M–TiO2 aerogels were not). High oxidation states of the transition metal ions (e.g. Cr6+, Co3+) appear to be important in bringing about visible light photocatalyst activity.

Journal ArticleDOI
17 Jun 2004-Talanta
TL;DR: The developed procedure has been successfully utilized for the estimation of chromium(VI),chromium(total) (after oxidation with bromate) and chromium (III) (by subtracting chromia(VI) content from chromium-total) value contents of several tannery industries.

Journal ArticleDOI
TL;DR: In this article, an analytical model has been developed in order to predict the profiles of chromium depleted zones using a scanning transmission electron microscope (STEM) and an experimental criterion to sensitization-desensitization phenomenon was established.
Abstract: Chromium carbides and intermetallic phases which form in industrial AISI 316L stainless steel during ageing for up to 80 000 h between 550 and 650 °C were identified by combining transmission electron microscopy (TEM) thin foil imaging and electron diffraction and used to establish the time–temperature–precipitation (TTP) diagram. Following the precipitation phenomena, the chemical changes in the grain boundary region were determined by energy-dispersive X-ray microprobe analysis using a scanning transmission electron microscope (STEM). From the experimentally determined chromium profiles the chromium depleted zones were quantified. The interactions between carbide precipitation involving chromium depletion and intergranular corrosion (IGC) were clearly visible from superposition of TTP diagrams and time–temperature–sensitization (TTS) diagrams obtained from ASTM standardized tests. In addition, an experimental criterion to sensitization–desensitization phenomenon was established. Moreover, an analytical model has been developed in this study and successfully validated to predict the profiles of chromium depleted zones. This model coupled with the previously described criterion provides TTS diagrams in good agreement with experimental results.

Journal ArticleDOI
TL;DR: Mechanism of chromium adsorption by the persimmon tannin (PT) gel was examined and Hexavalent chromium was adsorbed on the PT gel through the esterification of chromate with catechol group to be recovered as a Cr(IV)-tannin complex at pH 3 or a Cr-III solution at pH 1 or lower pH region.

Journal ArticleDOI
01 Jul 2004-Talanta
TL;DR: The attractive behavior of the new "mercury-free" chromium sensor holds great promise for on-site environmental and industrial monitoring of chromium (VI).

Journal ArticleDOI
TL;DR: Chromium(VI) was more efficiently removed in continuous cultures than in batch culture, because the uptake of chromate could be favored by actively growing algae, and bivalent metals were not removed as efficiently as reported in batch cultures, probably due to the high pH values there recorded.

Journal ArticleDOI
TL;DR: In this article, a family of chromium complexes bearing tridentate pyridine-based ligands is disclosed as highly active precatalysts for the oligomerization of ethylene.
Abstract: A family of chromium complexes bearing tridentate pyridine-based ligands are disclosed as highly active precatalysts for the oligomerization of ethylene. The ligands are comprised of two distinct types: Type 1, in which both ketone groups of 2,6-diacetylpyridine are converted to imines to produce pyridine bisimine NNN ligands; and Type 2, in which only one ketone group of 2,6-diacetylpyridine is condensed with an aniline derivative to give monoimine NNO coordination sets. Ligands of either type are coordinated to chromium(II) or chromium(III) chlorides, and activation of the resultant complexes with methylaluminoxane (MAO) produces highly active ethylene oligomerization and polymerization catalysts. Catalysts of Type 1 (NNN set) generally produce 1-butene when only two ortho alkyl substituents are present but switch to making waxes or polyethylene when the size and/or number of ortho substituents are increased. Catalysts of Type 2 (NNO set) produce waxes and polyethylene under all of the substitution pat...