Showing papers on "Chromium published in 2007"
574 citations
TL;DR: Experimental results indicated that expanded SRTs (stationary phase) can be recommended while using the fungal and bacterial Cr-resistant isolates for removing chromium and nickel from industrial wastewater.
541 citations
TL;DR: The results showed that studied adsorbents can be an attractive low cost alternative for the treatment of wastewaters in batched or stirred mode reactors containing lower concentrations of chromium.
505 citations
TL;DR: It is demonstrated that Cr(III) within ultramafic- and serpentinite-derived soils/sediments can be oxidized and dissolved through natural processes, leading to hazardous levels of aqueous Cr(VI) in surface and groundwater.
Abstract: Naturally occurring Cr(VI) has recently been reported in ground and surface waters. Rock strata rich in Cr(III)-bearing minerals, in particular chromite, are universally found in these areas that occur near convergent plate margins. Here we report experiments demonstrating accelerated dissolution of chromite and subsequent oxidation of Cr(III) to aqueous Cr(VI) in the presence of birnessite, a common manganese mineral, explaining the generation of Cr(VI) by a Cr(III)-bearing mineral considered geochemically inert. Our results demonstrate that Cr(III) within ultramafic- and serpentinite-derived soils/sediments can be oxidized and dissolved through natural processes, leading to hazardous levels of aqueous Cr(VI) in surface and groundwater.
445 citations
TL;DR: This study verifies the possibility of using inactivated marine green alga U. lactuca and its activated carbon as valuable material for the removal of chromium from aqueous solutions, saline water or wastewater.
350 citations
TL;DR: The presented method was applied for the speciation of chromium in natural water sample with satisfactory results (recoveries>95%, R.S.D.'s<9%).
317 citations
TL;DR: Evaluating the performance of commercial ion exchange resins for removing chromium trivalent from industrial effluents found two resins were tested: a chelating exchange resin (Diaion CR11) and a weak cationic resin (Amberlite IRC86).
285 citations
TL;DR: The results suggest that the reaction product of Cr(VI)-treated nano Fe0 is either a poorly ordered Cr( OH)3 precipitate or possibly a mixed phase CrxFe(1 - x)(OH)3 product, both of which are highly insoluble under environmental conditions.
Abstract: The reaction of hexavalent chromium (Cr(VI)) with zerovalent iron (Fe0) during soil and groundwater remediation is an important environmental process. This study used several techniques including X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy to investigate nanometer scale Fe0 particles (nano Fe0) treated with Cr(III) and Cr(VI). X-ray diffraction and XPS analyses of oxidized nano Fe0 showed the crystalline Fe(III) phase is composed of lepidocrocite (γ-FeOOH). Results of XPS Cr 2p data and Cr K-edge X-ray absorption near edge spectroscopy (XANES) provided evidence that Cr(VI) was entirely reduced to Cr(III) by nano Fe0 with no residual Cr(VI) after reaction. In addition, XPS and XANES results of Cr(III) precipitated as Cr(OH)3 in the presence of corroding nano Fe0 were nearly identical to the Cr(VI)-nano Fe0 reaction product. Detailed analysis of XPS O 1s line spectra revealed that both Cr(III)- and Cr(VI)-treated nano Fe0 yielded a predominantly hydroxylated Cr(OH)3 and/or a mix...
275 citations
TL;DR: It was found that adsorbents chemically modified with an oxidizing agent demonstrated better chromium removal capabilities as compared to pure adsorbent in terms of their adsorption rate.
270 citations
TL;DR: Metal removal reached about 74% under optimum conditions at low pH and at basic pH it became as high as 90%, probably due to the contribution from the flotation of metal precipitates.
265 citations
TL;DR: The proposed electrode was used as an indicator electrode in potentiometric titration of chromium ion with EDTA and in direct determination in different water and food samples, revealing a considerable improvement as compared to the best previously PVC-membrane electrode for chromium(III) ion.
TL;DR: Competitive sorption and desorption of Cd, Cr, Cu, Ni, Pb and Zn by humified organic matter, Fe and Mn oxides, kaolinite, vermiculite and mica were investigated and suggest that cations were least reversibly bound by Mn oxide, and most reversibly by verMiculite.
TL;DR: In this article, the effects of the transport properties of the cathode and electrolyte materials of solid oxide fuel cells (SOFCs) were reviewed, with a focus on the effect of the chromium poisoning of SOFC cathodes.
TL;DR: The objective of this study was to show reliable evidences that the removal mechanism of Cr(VI) by natural biomaterials is 'adsorption-coupled reduction'.
TL;DR: In binary mixtures with Cd(II) ions as the dominant species, there is a profound selectivity for cadmium biosorption, reaching 96% and 89% for Pseudomonas sp.
TL;DR: In this article, a small amount of chromium is added to the WO 3 matrix in order to enhance sensor response, which results in a shorter response time and improved sensor response to the lowest NO 2 concentrations tested.
Abstract: SBA-15 (2D hexagonal structure) and KIT-6 (3D cubic structure) silica materials are used as templates for the synthesis of two different crystalline mesoporous WO 3 replicas usable as NO 2 gas sensors. High-resolution transmission electron microscopy (HRTEM) studies reveal that single-crystal hexagonal rings set up the atomic morphology of the WO 3 KIT-6 replica, whereas the SBA-15 replica is composed of randomly oriented nanoparticles. A model capable of explaining the KIT-6 replica mesostructure is described. A small amount of chromium is added to the WO 3 matrix in order to enhance sensor response. It is demonstrated that chromium does not form clusters, but well-distributed centers. Pure WO 3 KIT-6 replica displays a higher response rate as well as a lower response time to NO 2 gas than the SBA-15 replica. This behavior is explained by taking into account that the KIT-6 replica has a higher surface area as demonstrated by Brunauer-Emmett-Teller analyses and its mesostructure is fully maintained after the screen-printing step involved in sensors preparation. The presence of chromium in the material results in a shorter response time and improved sensor response to the lowest NO 2 concentrations tested. Electrical differences related to mesostructure are reduced as a result of additive introduction.
TL;DR: In this article, the effects of chromium species from chromia scales on planar solid oxide fuel cells (SOFCs) were investigated and it was shown that the vaporization of chromia-forming steels can be reduced by more than 90% by alloying.
Abstract: The vaporization of chromium species from chromia scales limits the applicability of chromia-forming steels at high temperatures and is one of the major reasons for degradation in the development of planar solid oxide fuel cells (SOFCs). Cr(VI) vaporized from the interconnector is reduced at the cathode and deposits in the form of solid Cr(III)-oxide, thereby inhibiting the electrochemical processes. This work presents the first systematic study on the Cr vaporization of Cr-, Fe-, Ni-, and Co-based alloys in air and in H 2 atmospheres at high temperatures. The influence of outer oxide layers of (Cr,Mn) 3 O 4 , (Fe, Cr) 3 O 4 , Co 3 O 4 , TiO 2 , and Al 2 O 3 on the Cr vaporization is investigated. It is shown that the Cr vaporization of chromia-forming steels can be reduced by more than 90% by alloying. An estimate of the expected degradation effects on planar SOFC designs for the use of uncoated interconnector materials is used to show that in order to achieve the desired lifetimes for SOFC systems, additional Cr-retention coatings are necessary. Additionally, equilibrium vaporization measurements are carried out for pure Cr 2 O 3 (s) in humid air in order to elucidate controversies in the literature concerning the thermodynamic data of CrO 2 (OH) 2 (g).
TL;DR: In this paper, the authors investigated the enhancement of chromium biosorption capacity of dead Aspergillus niger fungal biomass by pretreatment and its use in a column mode.
TL;DR: The pre-operative ion levels, component size, female gender and the inclination of the acetabular component were inversely proportional to the values of chromium and/or cobalt ions at one year postoperatively, and other factors did not correlate with the levels of metal ions.
Abstract: We evaluated the concentrations of chromium and cobalt ions in blood after metal-on-metal surface replacement arthroplasty using a wrought-forged, high carbon content chromium-cobalt alloy implant in 64 patients. At one year, mean whole blood ion levels were 1.61 microg/L (0.4 to 5.5) for chromium and 0.67 microg/L (0.23 to 2.09) for cobalt. The pre-operative ion levels, component size, female gender and the inclination of the acetabular component were inversely proportional to the values of chromium and/or cobalt ions at one year postoperatively. Other factors, such as age and level of activity, did not correlate with the levels of metal ions. We found that the levels of the ions in the serum were 1.39 and 1.37 times higher for chromium and cobalt respectively than those in the whole blood. The levels of metal ions obtained may be specific to the hip resurfacing implant and reflect its manufacturing process.
TL;DR: A resinous polymer, aniline formaldehyde condensate (AFC) coated onsilica gel was used as an adsorbent in batch system for removal of hexavalent chromium from aqueous solution by considering the effects of various parameters like reaction pH, dose of AFC coated silica gel, initial Cr(VI) concentration and anilines to formaldehyde ratio in AFC synthesis.
TL;DR: Mesorhizobium strain RC3, isolated from chickpea nodules, tolerated chromium up to 500 μg/ml and reduced it by 90% at pH 7 after 120 h and produced plant growth-promoting substances, both in the presence and absence of chromium.
Abstract: Mesorhizobium strain RC3, isolated from chickpea nodules, tolerated chromium up to 500 μg/ml and reduced it by 90% at pH 7 after 120 h. It produced plant growth-promoting substances, both in the presence and absence of chromium. Strain RC3 produced 35 μg indole acetic acid/ml in Luria Bertani broth with 100 mg tryptophan/ml, which decreased with an increase in chromium concentration. Chromium application to soil at 136 mg/kg was toxic to chickpea plants but when RC3 at 136 mg/kg was also added, it increased the dry matter accumulation, number of nodules, seed yield and grain protein by 71, 86, 36 and 16%, respectively, compared to non-inoculated plants. Nitrogen in roots and shoots were increased by 46 and 40%, respectively, at 136 mg Cr/kg. The bio-inoculant decreased the uptake of chromium by 14, 34 and 29% in roots, shoots and grains, respectively.
TL;DR: It is shown that cobalt and chromium are able to cross the placenta in the study patients with metal-on-metal hip resurfacings and in control subjects without any metal implants, suggesting that the Placenta exerts a modulatory effect on the rate of metal ion transfer.
Abstract: Metal-on-metal bearings are being increasingly used in young patients. The potential adverse effects of systemic metal ion elevation are the subject of ongoing investigation. The purpose of this study was to investigate whether cobalt and chromium ions cross the placenta of pregnant women with a metal-on-metal hip resurfacing and reach the developing fetus. Whole blood levels were estimated using high-resolution inductively-coupled plasma mass spectrometry. Our findings showed that cobalt and chromium are able to cross the placenta in the study patients with metal-on-metal hip resurfacings and in control subjects without any metal implants. In the study group the mean concentrations of cobalt and chromium in the maternal blood were 1.39 microg/l (0.55 to 2.55) and 1.28 microg/l (0.52 to 2.39), respectively. The mean umbilical cord blood concentrations of cobalt and chromium were comparatively lower, at 0.839 microg/l (0.42 to 1.75) and 0.378 microg/l (0.14 to 1.03), respectively, and this difference was significant with respect to chromium (p 0.05). The mean cord blood level of cobalt in the study patients was significantly greater than that in the control group (p 0.05) The transplacental transfer rate was in excess of 95% in the controls for both metals, but only 29% for chromium and 60% for cobalt in study patients, suggesting that the placenta exerts a modulatory effect on the rate of metal ion transfer.
TL;DR: The chromium stress decreased CO2 assimilation rates mainly due to stomatal closure, which reduced water loss by transpiration without decreasing the cellular available CO2, and non-radiative energy dissipation mechanisms were triggered during stress.
TL;DR: In this paper, the passivity of AISI 304L and 316L stainless steels in a borate buffer solution, with and without the addition of chloride ions, was studied using cyclic voltammetry and potentiodynamic measurements.
TL;DR: In this article, the removal of trivalent chromium (Cr 3+ ) from aqueous solutions in a batch stirred electrocoagulator with mild steel electrode pair was investigated.
TL;DR: In this article, the corrosion resistance of the Al 0.5 CoCrCuFeNiB x alloys with various amounts of added boron was investigated and the anodic polarization curves and electrochemical impedance spectra were obtained in 1 N H 2 SO 4 aqueous solution.
Abstract: High entropy alloys are a newly developed family of multicomponent alloys that consist of various major alloying elements, including copper, nickel, aluminum, cobalt, chromium, iron, and others. Each element in the alloy system is present at between 5 and 35 atom %. A high entropy alloy has numerous beneficial mechanical, magnetic, and electrochemical characteristics. This investigation discusses the corrosion resistance of the Al 0.5 CoCrCuFeNiB x alloys with various amounts of added boron. Surface morphological and chemical analyses verified that the addition of boron produced Cr, Fe, and Co borides. Therefore, the fraction of Cr outside borides precipitates was scant. The anodic polarization curves and electrochemical impedance spectra of the Al 0.5 CoCrCUFeNiB x alloys, obtained in 1 N H 2 SO 4 aqueous solution, clearly reveal that the general corrosion resistance decreases as the concentration of boron increases.
TL;DR: In this article, the authors used X-ray diffraction, magnetic and Mossbauer spectral studies in chromium-substituted nickel ferrites prepared by aerosol route.
TL;DR: Leersia hexandra Swartz (Gramineae), which occurs in Southern China, has been found to be a new chromium hyperaccumulator by means of field survey and pot-culture experiment, and has potential for usage in the phytoremediation of Cr-contaminated soil and water.
TL;DR: In this article, conductive copper manganite and cobalt manganites spinel coatings with nominal composition MnCo 2 O 4 and Cu 1.4 Mn 1.6 O 4 were applied on the surface of UNS 430 stainless steel by electroplating and subsequent air annealing.
Abstract: At the usual temperature of solid oxide fuel cell (SOFC) operation, ferritic stainless steels form electrically insulating or poorly conducting oxide scales, which can cause high internal resistance losses and chromium poisoning. In an effort to avoid this problem, we applied conductive copper manganite and cobalt manganite spinel coatings, with nominal composition MnCo 2 O 4 and Cu 1.4 Mn 1.6 O 4 , which were deposited on the surface of UNS 430 stainless steel by electroplating and subsequent air annealing. Microstructural evaluation indicated that the spinel layers inhibited outward diffusion of chromium. Moreover, excellent structural and thermal stability were observed after several thermal cycles at 750 °C and for up to 28 days, and the coating layers showed good adhesion to the substrate.
TL;DR: A series of Cr-containing magnetites, Fe3−xCrxO4 (x = 0.00, 0.07,0.42 and 0.51) has been prepared using conventional co-precipitation method in this paper, which showed that the presence of Cr has a remarkable effect on the texturial properties of the material decreasing the pore diameter from meso-to micropore with a significant increase on the BET surface area.
Abstract: A series of Cr-containing magnetites, Fe3−xCrxO4 (x = 0.00, 0.07, 0.26, 0.42 and 0.51) has been prepared using conventional co-precipitation method. Mossbauer and powder X-ray diffraction measurements suggested the formation of the spinel crystalline phase with initial substitution of F e oct 3 + by Cr3+ and for higher Cr contents, chromium also replaces F e oct 2 + and F e tet 3 + in the crystalline structure. N2 adsorption/desorption revealed that the presence of Cr has a remarkable effect on the texturial properties of the material decreasing the pore diameter from meso- to micropore with a significant increase on the BET surface area. Thermal analyses (TG and DTA) coupled with XRD and Mossbauer showed that thermal treatment up to 270 °C with O2 leads to the oxidation of F e oct 2 + producing Cr-substituted maghemite but at 600 °C the cubic maghemite is converted to the hexagonal hematite and Cr is expelled from the iron oxide structure. The reactivity of Fe3−xCrxO4 was investigated using two H2O2 reactions, i.e. the decomposition to O2 and the oxidation of the dye methylene blue used as model contaminant. The obtained results showed that the presence of Cr directly promoted the H2O2 decomposition. On the other hand, the presence of small concentration of Cr, i.e. Cr0.07 and Cr0.21, caused a significant increase on the activity for the oxidation of the dyes with complete discoloration and high degree of mineralization. The higher activity of Fe2.93Cr0.07O4 was discussed in terms of a coupling of the redox pairs Fe3+/Fe2+ and Cr2+/Cr3+ producing a more efficient regeneration of the Fenton active specie Fe2+.