Artículos de revistas: "Cr (VI) reduction"

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Alexander, J., A. Mikalsen y D. Ryberg. "MICROSOMAL REDUCTION OF Cr VI". Acta Pharmacologica et Toxicologica 59 (13 de marzo de 2009): 267–69. http://dx.doi.org/10.1111/j.1600-0773.1986.tb02759.x.

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Standeven, Andrew M. y Karen E. Wetterhahn. "Chromium(VI) Toxicity: Uptake, Reduction, and DNA Damage". Journal of the American College of Toxicology 8, n.º 7 (diciembre de 1989): 1275–83. http://dx.doi.org/10.3109/10915818909009118.

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Much recent data supports the “uptake-reduction” model explaining the carcinogenicity of chromium(VI) compounds and the lack of carcinogenicity of chromium(III) com pounds. Cr(VI) readily enters cells by diffusion through a nonspecific anion channel, whereas cells are relatively impermeable to Cr(III). Glutathione appears to facilitate Cr(VI) uptake by reducing Cr(VI) to Cr(III) after it enters the cell, presumably keeping intracellular Cr(VI) concentration low and allowing for further Cr(VI) uptake. Some other nonenzymatic factors, for example, ascorbate and riboflavin, as well as enzymes, such as cytochrome P-450, DT-diaphorase, and the mitochondrial electron transport chain complexes, are capable of reducing Cr(VI) in vitro, but their contribution in vivo is not clear. Cr(VI), once reduced intracellularly, produces various forms of DNA damage including DNA interstrand crosslinks, DNA-protein crosslinks, DNA strand breaks, and Cr-DNA adducts. The pathway of Cr(VI) metabolism in different tissues appears to influence the type of “reactive intermediates” produced, for example, Cr(V) and radical species, and thus the nature and extent of DNA damage. This DNA damage presumably accounts for observed functional changes in DNA replication and transcription which may be crucial to the carcinogenicity of chromium(VI) compounds.

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Tsigaridas, Kostas, Thomas Sawidis y Afroditi Sivropoulou. "Cr(VI) reduction by bacteria species isolated from Cr(VI) polluted landfill". Current Opinion in Biotechnology 22 (septiembre de 2011): S57. http://dx.doi.org/10.1016/j.copbio.2011.05.156.

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4

Arias, Y. Meriah y Bradley M. Tebo. "Cr(VI) Reduction by Sulfidogenic and Nonsulfidogenic Microbial Consortia". Applied and Environmental Microbiology 69, n.º 3 (marzo de 2003): 1847–53. http://dx.doi.org/10.1128/aem.69.3.1847-1853.2003.

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ABSTRACT In time course experiments, bacterial community compositions were compared between a sulfidogenic and two nonsulfidogenic Cr(VI)-reducing consortia enriched from metal-contaminated sediments. The consortia were subjected to 0 and 0.85 mM or 1.35 mM Cr(VI), and Cr(VI) reduction, growth, and denaturing gradient gel electrophoresis profiles of PCR products of small-subunit (16S) ribosomal genes were compared. Results showed that although Cr(VI) was completely reduced by the three consortia, Cr(VI) inhibited cell growth, with sulfate-reducing bacteria being particularly sensitive to Cr(VI) toxicity relative to other bacteria in the consortia.

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Thesai, Annadurai Sakthi, Rajalingam Sangeetha, Lakshmanan Ashokkumar, Ramachandran Palanivelan, Sundaram Rajakumar y Pudukadu Munusamy Ayyasamy. "Evaluation of Cr(VI) Reducing Capability of Shewanella putrefaciens (MTTC8410) and Optimization of Operational Parameters". Journal of Pure and Applied Microbiology 14, n.º 4 (15 de diciembre de 2020): 2715–27. http://dx.doi.org/10.22207/jpam.14.4.49.

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Bioremediation is an important technology to remediate the chromium (Cr) contaminated soil and water. In this study, Shewanella putrefaciens (MTTC8410) was used to investigate the influence of carbon concentration, pH, and temperature on reduction of hexavalent chromium [Cr(VI)] into trivalent chromium [Cr(III)]. The increased bacterial growth rate was significantly reduced the Cr(VI) concentration. In batch mode experiments, 1% starch recorded the highest reduction of Cr(VI) (90%) followed by 1% glucose (88% reduction) and a reduction of 77% was by 1% cellulose. By using various pH conditions the maximum Cr(VI) reduction was achieved at pH 7.0. In this experiment the maximum Cr(VI) reduction (75%) was observed at 35°C, followed by 30°C with 62% of Cr(VI) reduction. Bioreactor analysis revealed the highest reduction of Cr(VI) (88%) in unsterile tannery effluent. The significant levels of physico- chemical parameters were reduced in unsterile tannery effluent, as compared to the sterile tannery effluent. The experimental results revealed that the S. putrefaciens (MTTC8410) could be used as a potential bacterial strain for reduction of Cr(VI) from contaminated groundwater.

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Zhang, Jun Hui. "Characterization of a Rhizobium larrymoorei FJ Exhibiting High Level Cr(VI) Reduction Potential". Advanced Materials Research 356-360 (octubre de 2011): 1009–14. http://dx.doi.org/10.4028/www.scientific.net/amr.356-360.1009.

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The investigation was conducted to evaluate mechanism of Cr(VI) resistance and reduction by a bacterial strain named FJ under different conditions. This strain, identified as a member of Rhizobium larrymoorei by analysis of its 16S rRNA gene sequence was previously isolated from a paddy soil contaminated by e-waste recycling. Good Cr(VI) reduction ability catalyzed by growing cells of R. larrymoorei FJ was observed in batch cultures conducted at different initial Cr(VI) concentrations. Up to 83.23% reduction was shown in LB medium supplemented with 2.50 mM Cr(VI). Cr(VI) was transformed to some soluble form of Cr(III) due to anaerobic respiration. Biosorption was also observed in the process of bioreduction. But only loosely cell-surface binding Cr(VI) was detected in cells grown in medium supplied with different concentrations of Cr(VI). Present of yeast or citrate could enhance Cr(VI) reduction of resting cells. However, Cr(VI) reduction by resting cells was only observed at Cr(VI) concentration lower than 0.25 mM. R. larrymoorei FJ exhibited a high efficiency of Cr(VI) reduction at temperatures from 28°C to 37°C and pH values from 6.0 to 7.0.

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Chen, Chiou-Pin, Kai-Wei Juang y Dar-Yuan Lee. "Effects of liming on Cr(VI) reduction and Cr phytotoxicity in Cr(VI)-contaminated soils". Soil Science and Plant Nutrition 58, n.º 1 (febrero de 2012): 135–43. http://dx.doi.org/10.1080/00380768.2011.653673.

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Kourtev, Peter S., Cindy H. Nakatsu y Allan Konopka. "Inhibition of Nitrate Reduction by Chromium(VI) in Anaerobic Soil Microcosms". Applied and Environmental Microbiology 75, n.º 19 (14 de agosto de 2009): 6249–57. http://dx.doi.org/10.1128/aem.00347-09.

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ABSTRACT Chromium is often found as a cocontaminant at sites polluted with organic compounds. For nitrate-respiring microbes, Cr(VI) may be not only directly toxic but may also specifically interfere with N reduction. In soil microcosms amended with organic electron donors, Cr(VI), and nitrate, bacteria oxidized added carbon, but relatively low doses of Cr(VI) caused a lag and then lower rates of CO2 accumulation. Cr(VI) strongly inhibited nitrate reduction; it occurred only after soluble Cr(VI) could not be detected. However, Cr(VI) additions did not eliminate Cr-sensitive populations; after a second dose of Cr(VI), bacterial activity was strongly inhibited. Differences in microbial community composition (assayed by PCR-denaturing gradient gel electrophoresis) driven by different organic substrates (glucose and protein) were smaller than when other electron acceptors had been used. However, the selection of bacterial phylotypes was modified by Cr(VI). Nine isolated clades of facultatively anaerobic Cr(VI)-resistant bacteria were closely related to cultivated members of the phylum Actinobacteria or Firmicutes. In Bacillus cereus GNCR-4, the nature of the electron donor (fermentable or nonfermentable) affected Cr(VI) resistance level and anaerobic nitrate metabolism. Our results indicate that carbon utilization and nitrate reduction in these soils were contingent upon the reduction of added Cr(VI). The amount of Cr(VI) required to inhibit nitrate reduction was 10-fold less than for aerobic catabolism of the same organic substrate. We speculate that the resistance level of a microbial process is directly related to the diversity of microbes capable of conducting it.

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Marsh, Tamara L. y Michael J. McInerney. "Relationship of Hydrogen Bioavailability to Chromate Reduction in Aquifer Sediments". Applied and Environmental Microbiology 67, n.º 4 (1 de abril de 2001): 1517–21. http://dx.doi.org/10.1128/aem.67.4.1517-1521.2001.

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ABSTRACT Biological Cr(VI) reduction was studied in anaerobic sediments from an aquifer in Norman, Okla. Microcosms containing sediment and mineral medium were amended with various electron donors to determine those most important for biological Cr(VI) reduction. Cr(VI) (about 340 μM) was reduced with endogenous substrates (no donor), or acetate was added. The addition of formate, hydrogen, and glucose stimulated Cr(VI) reduction compared with reduction in unamended controls. From these sediments, an anaerobic Cr(VI)-utilizing enrichment was obtained that was dependent upon hydrogen for both growth and Cr(VI) reduction. No methane was produced by the enrichment, which reduced about 750 μM Cr(VI) in less than six days. The dissolved hydrogen concentration was used as an indicator of the terminal electron accepting process occurring in the sediments. Microcosms with sediments, groundwater, and chromate metabolized hydrogen to a concentration below the detection limits of the mercury vapor gas chromatograph. In microcosms without chromate, the hydrogen concentration was about 8 nM, a concentration comparable to that under methanogenic conditions. When these microcosms were amended with 500 μM Cr(VI), the dissolved hydrogen concentration quickly fell below the detection limits. These results showed that the hydrogen concentration under chromate-reducing conditions became very low, as low as that reported under nitrate- and manganese-reducing conditions, a result consistent with the free energy changes for these reactions. The utilization of formate, lactate, hydrogen, and glucose as electron donors for Cr(VI) reduction indicates that increasing the availability of hydrogen results in a greater capacity for Cr(VI) reduction. This conclusion is supported by the existence of an enrichment dependent upon hydrogen for growth and Cr(VI) reduction.

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Javaid, Mahwish y Sikander Sultan. "Plant growth promotion traits and Cr (VI) reduction potentials of Cr (VI) resistantStreptomycesstrains". Journal of Basic Microbiology 53, n.º 5 (26 de junio de 2012): 420–28. http://dx.doi.org/10.1002/jobm.201200032.

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Chen, ZiFang, YongSheng Zhao y Qin Li. "Characteristics and kinetics of hexavalent chromium reduction by gallic acid in aqueous solutions". Water Science and Technology 71, n.º 11 (31 de marzo de 2015): 1694–700. http://dx.doi.org/10.2166/wst.2015.157.

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Gallic acid (GA) is a naturally occurring plant polyphenol compound. Experiments were conducted to study the kinetics and effects of pH, temperature, irradiation, and initial hexavalent chromium (Cr(VI)) concentration on Cr(VI) reduction by GA. Results indicated that Cr(VI) could be reduced to chromium oxide (Cr(III)) with GA in a wide range of pH values from 2.0 to 8.5. The reaction followed a pseudo-first-order kinetic model with respect to Cr(VI) and GA in acid conditions (pH 2.0–5.0). However, the reaction did not follow the pseudo-first-order kinetic model at pH 6.5 and 8.5. Removal efficiencies and reaction rate constants of Cr(VI) significantly increased with decreasing pH value and increasing temperature. The effect of irradiation on Cr(VI) reduction increased with increasing pH, and irradiation improved the removal efficiency of Cr(VI) by 11.29% at pH 6.5. At pH 2.0, nearly all molar ratios of GA required for the reduction of Cr(VI) were 1:2 (±0.1) under different initial Cr(VI) concentrations; however, the molar ratios of GA required for the reduction of Cr(VI) were 1:1.29, 1:1.43, and 1:1.69, respectively, when the initial Cr(VI) concentrations were 10, 25, and 50 mg/L at pH 5.5.

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12

Molokwanne, P. E. y E. M. N. Chirwa. "Biological Cr(VI) reduction in indigenous sludge cultures from Gauteng, South Africa". Water Science and Technology 54, n.º 10 (1 de noviembre de 2006): 177–84. http://dx.doi.org/10.2166/wst.2006.880.

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The Cr(VI) reducing capability of an acclimated indigenous culture cultivated from primary sludge was evaluated in batch and packed-bed bioreactor systems. Performance evaluation was carried out in unmodified cultures, cultures modified by substituting terminal organisms in the consortium by a known Cr(VI)-reducing organism (Escherichia coli ATCC 33456), and pure cultures of Cr(VI)-reducing organisms. A high Cr(VI) reduction rate was observed in modified cultures and in the pure culture of the Cr(VI)-reducing bacteria (Bacillus sp.). Furthermore, the Bacillus sp. pure culture outperformed both the unmodified and modified consortium cultures in reducing Cr(VI). Abiotic Cr(VI) reduction activity was evaluated in heat-killed and azide (N3−) inactivated control cultures. No significant Cr(VI) reduction was observed in the controls. This study is part of the continuing research to identify synergistic culture systems for treating toxic compounds from polluted environments.

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13

Molokwane, Pulane E. y Evans M. N. Chirwa. "Modelling biological Cr(VI) reduction in aquifer microcosm column systems". Water Science and Technology 67, n.º 12 (1 de junio de 2013): 2733–38. http://dx.doi.org/10.2166/wst.2013.186.

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Several chrome processing facilities in South Africa release hexavalent chromium (Cr(VI)) into groundwater resources. Pump-and-treat remediation processes have been implemented at some of the sites but have not been successful in reducing contamination levels. The current study is aimed at developing an environmentally friendly, cost-effective and self-sustained biological method to curb the spread of chromium at the contaminated sites. An indigenous Cr(VI)-reducing mixed culture of bacteria was demonstrated to reduce high levels of Cr(VI) in laboratory samples. The effect of Cr(VI) on the removal rate was evaluated at concentrations up to 400 mg/L. Following the detailed evaluation of fundamental processes for biological Cr(VI) reduction, a predictive model for Cr(VI) breakthrough through aquifer microcosm reactors was developed. The reaction rate in batch followed non-competitive rate kinetics with a Cr(VI) inhibition threshold concentration of approximately 99 mg/L. This study evaluates the application of the kinetic parameters determined in the batch reactors to the continuous flow process. The model developed from advection–reaction rate kinetics in a porous media fitted best the effluent Cr(VI) concentration. The model was also used to elucidate the logistic nature of biomass growth in the reactor systems.

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Wang, Qian, Xinhua Xu, Fanglin Zhao, Zhihao Liu y Jinan Xu. "Reduction remediation of hexavalent chromium by bacterial flora in Cr(VI) aqueous solution". Water Science and Technology 61, n.º 11 (1 de junio de 2010): 2889–96. http://dx.doi.org/10.2166/wst.2010.186.

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Chromium(VI) is a priority pollutant in soils and wastewaters and reduction of Cr(VI) to Cr(III) is a solution to this problem. In this study a low-cost method was proposed to adapt indigenous bacteria and use them to reduce Cr(VI) in solutions. The experiment results show that Cr(VI) could be efficiently reduced by indigenous bacteria under anaerobic and pH-unadjusted conditions. After about 24 h the concentration of Cr(VI) could be reduced from 21.74 mg/L to below 0.5 mg/L. The observed Cr(VI) reduction rates were affected by temperature and pH. Cr(VI) in aqueous solutions could be reduced to Cr(III) completely and partly be incepted by the organisms. Cr(VI) reduction was enzyme-mediated. It was not an energy-conserving process but a detoxification reaction. This method could be used in an anaerobic reactor to treat low-concentration wastewater or industrial water as the last step.

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das Neves, R. Pires, T. Margarida Santos, M. De Lourdes Pereira y J. Pedrosa de Jesus. "Comparative histological studies on liver of mice exposed to Cr(VI) and Cr(V) compounds". Human & Experimental Toxicology 21, n.º 7 (julio de 2002): 365–69. http://dx.doi.org/10.1191/0960327102ht243oa.

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Chromium toxicity is strongly dependent on its oxidation state. Cr(VI) is carcinogenic and mutagenic, although its in vivo and in vitro toxic effects are related to its intracellular fate. Inside the cells, Cr(VI) is rapidly reduced to stable Cr(III). As Cr(V) and Cr(IV) species have been reported to be formed in the Cr(VI) reduction pathways, Cr(VI)induced damage is thought, at least in part, to arise from these hypervalent species. The study of Cr(VI) reduction mechanisms and the characterization of the effects of each reactive intermediate constitute important steps towards a better understanding of chromium toxicity. The purpose of this work is to enlarge the scope of Cr(VI)induced alterations in mouse to other chromium species. Our studies have led to the in situ preparation of a new Cr(V) complex, [CrV–BT]2–, a stable compound at neutral pH, which mimics Cr(VI) reduction intermediates. The effect of Cr(V) on the histology of mice liver is assessed and compared with similar Cr(VI) assays. Liver toxicity was examined after single administrations of Cr(VI) or [CrV–BT]2– to mice. Both compounds produced reversible hepatic damage in a time-dependent manner. However, Cr(V) toxic effects have proved to be more rapid than with Cr(VI), permitting the role of Cr(VI) intermediates formed during intracellular chromium reduction to be highlighted.

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Branco, Rita, M. Carmen Alpoim y Paula V. Morais. "Ochrobactrum tritici strain 5bvl1 — characterization of a Cr(VI)-resistant and Cr(VI)-reducing strain". Canadian Journal of Microbiology 50, n.º 9 (1 de septiembre de 2004): 697–703. http://dx.doi.org/10.1139/w04-048.

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Bacterial strain 5bvl1, isolated from a chromium-contaminated wastewater treatment plant and identified as Ochrobactrum tritici, was resistant to a broad range of antibiotics, to Cr(VI), Ni(II), Co(II), Cd(II), and Zn(II), and was able to grow in the presence of 5% NaCl and within the pH range 4–10. Characterization showed that strain 5bvl1 could be considered a halotolerant and alkalitolerant microorganism resistant to high concentrations of Cr(VI). This strain was able to grow aerobically in up to 10 mmol·L–1 Cr(VI). Cr(VI) resistance was independent of sulphate concentration. Under aerobic conditions strain 5bvl1 was also able to reduce high Cr(VI) concentrations (up to 1.7 mmol·L–1). Increasing concentrations of Cr(VI) in the medium lowered the growth rate of strain 5bv11 but the reduction in growth rate could not be directly correlated with the amount of Cr(VI) reduced. Unlike the type strain, which was only able to reduce Cr(VI), strain 5bvl1 was resistant to Cr(VI) and able to reduce it. Moreover, in strain 5bvl1, the rate and extent of Cr(VI)-reduction were higher than in the other strains of the genus Ochrobactrum. Ochrobactrum strain 5bvl1 resists high Cr(VI) concentrations and has a high Cr(VI)-reducing ability, making it a valuable tool in bioremediation.Key words: Ochrobactrum, Cr(VI) resistance, Cr(VI)-reduction, heavy metal, bioremediation.

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Liu, Liang, Yan Yang y Ding Long Li. "Accelerated Hexavalent Chromium [Cr (VI)] Reduction with Electrogenerated Hydrogen Peroxide in Microbial Fuel Cells". Advanced Materials Research 512-515 (mayo de 2012): 1525–28. http://dx.doi.org/10.4028/www.scientific.net/amr.512-515.1525.

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Cr(VI) was reduced at a carbon felt cathode in an air-cathode dual-chamber microbial fuel cell (MFC). The reduction of Cr(VI) was proven to be strongly associated with the electrogenerated H2O2 at the cathode. At pH 3.0, only 27.3% of Cr(VI) was reduced after 12h in the nitrogen-bubbling-cathode MFC, while complete reduction of Cr(VI) was achieved after 6h in the air-bubbling-cathode MFC in which the reduction of oxygen to H2O2was confirmed. The results showed that the efficient reduction of Cr(VI) could be achieved with an air-bubbling-cathode MFC.

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Watts, Mathew P., Tatiana V. Khijniak, Christopher Boothman y Jonathan R. Lloyd. "Treatment of Alkaline Cr(VI)-Contaminated Leachate with an Alkaliphilic Metal-Reducing Bacterium". Applied and Environmental Microbiology 81, n.º 16 (5 de junio de 2015): 5511–18. http://dx.doi.org/10.1128/aem.00853-15.

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ABSTRACTChromium in its toxic Cr(VI) valence state is a common contaminant particularly associated with alkaline environments. A well-publicized case of this occurred in Glasgow, United Kingdom, where poorly controlled disposal of a cementitious industrial by-product, chromite ore processing residue (COPR), has resulted in extensive contamination by Cr(VI)-contaminated alkaline leachates. In the search for viable bioremediation treatments for Cr(VI), a variety of bacteria that are capable of reduction of the toxic and highly soluble Cr(VI) to the relatively nontoxic and less mobile Cr(III) oxidation state, predominantly under circumneutral pH conditions, have been isolated. Recently, however, alkaliphilic bacteria that have the potential to reduce Cr(VI) under alkaline conditions have been identified. This study focuses on the application of a metal-reducing bacterium to the remediation of alkaline Cr(VI)-contaminated leachates from COPR. This bacterium, belonging to theHalomonasgenus, was found to exhibit growth concomitant to Cr(VI) reduction under alkaline conditions (pH 10). Bacterial cells were able to rapidly remove high concentrations of aqueous Cr(VI) (2.5 mM) under anaerobic conditions, up to a starting pH of 11. Cr(VI) reduction rates were controlled by pH, with slower removal observed at pH 11, compared to pH 10, while no removal was observed at pH 12. The reduction of aqueous Cr(VI) resulted in the precipitation of Cr(III) biominerals, which were characterized using transmission electron microscopy and energy-dispersive X-ray analysis (TEM-EDX) and X-ray photoelectron spectroscopy (XPS). The effectiveness of this haloalkaliphilic bacterium for Cr(VI) reduction at high pH suggests potential for its use as anin situtreatment of COPR and other alkaline Cr(VI)-contaminated environments.

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Molokwane, P. E., C. K. Meli y E. M. N. Chirwa. "Chromium (VI) reduction in activated sludge bacteria exposed to high chromium loading". Water Science and Technology 58, n.º 2 (1 de agosto de 2008): 399–405. http://dx.doi.org/10.2166/wst.2008.669.

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A mixed-culture of bacteria collected from a wastewater treatment plant in Brits, North-West Province (South Africa) biocatalytically reduced Cr(VI) at much higher concentrations than previously observed in cultures isolated in North America. Complete Cr(VI) reduction in aerobic cultures was achieved at a high concentration of 200 mg/L after incubation for only 65 hours. Under anaerobic conditions up to 150 mg, Cr(VI)/L was completely removed after incubating for 130 to 155 hours, still higher than the Cr(VI) reduction achieved with previous cultures where complete removal was only observed in cultures with the added Cr(VI) concentration not greater than 30 mg/L. Cr(VI) reduction capability of the cultures was verified in purified cultures. Consortium cultures were characterised using 16S rRNA partial sequence analysis. Results showed that the gram-positive Bacillus genera predominated under aerobic conditions with a small composition of the gram-negative Microbacterium sp. There was more biodiversity observed in the anaerobic cultures with the marked appearance of Enterococcus, Arthrobacter, Paenibacillus and Oceanobacillus species. The results showed that Cr(VI) reduction rate in the new culture was up to eight times higher than that previously observed in other Cr(VI) reducing cultures isolated from Cr(VI) contaminated soil environments in Newark (New Jersey) and other sites in North America.

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Innation, Theodorus Olwyn, Vincentia Irene Meitiniarti y Desti Christian Cahyaningrum. "THE REDUCTION OF Cr(VI) IN SOIL BY Microbacterium sp. STRAIN SpR3 IN VERMICOMPOST CARRIER". Jurnal Bioteknologi & Biosains Indonesia (JBBI) 8, n.º 1 (19 de mayo de 2021): 33–41. http://dx.doi.org/10.29122/jbbi.v8i1.4160.

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Reduksi Cr(VI) pada Tanah Menggunakan Microbacterium sp. Strain SpR3 dengan Bahan Pembawa Vermikompos Kromium hexavalen [Cr(VI)] adalah polutan yang berasal dari kegiatan industri. Microbacterium sp. strain SpR3 dapat digunakan sebagai agen bioremediasi Cr(VI). Kemampuan agen biologi untuk mereduksi Cr(VI) umumnya meningkat bila diinokulasi dalam media pembawa. Tujuan penelitian ini adalah untuk menganalisis kemampuan Microbacterium sp. strain SpR3 dalam mengurangi Cr(VI) serta membandingkannya dengan kondisi ketika diinokulasi dalam media pembawa vermikompos. Pengamatan dilakukan selama tujuh hari pada tiga perlakuan yang berbeda, yakni Microbacterium sp. strain SpR3 dengan dan tanpa media pembawa vermikompos yang diinokulasi pada tanah steril yang mengandung 50 ppm Cr(VI), dan tanah steril tanpa inokulasi bakteri yang mengandung 50 ppm Cr(VI). Variabel yang diamati adalah jumlah bakteri, konsentrasi, dan kecepatan reduksi Cr(VI) oleh bakteri tersebut di dalam tanah pada T0 (hari ke-0) dan T7 (hari ke-7). Hasil penelitian ini menyimpulkan bahwa vermikompos bisa digunakan sebagai media pembawa Microbacterium sp. strain SpR3 karena dapat meningkatkan jumlah bakteri sampai 2 × 1010 CFU g-1 di dalam tanah dan dapat mengurangi Cr(VI) dengan kecepatan 0,095 mg L-1 jam-1. Hexavalent chromium [Cr(VI)] is a pollutant originated from industrial activities. Microbacterium sp. strain SpR3 can be used as Cr(VI) bioremediation agent. The ability of bioagent to reduce Cr(VI) usually improves when inoculated in a carrier. This research aimed to assess the ability of Microbacterium sp. strain SpR3 to reduce Cr(VI) in soil and compare its ability when inoculated in vermicompost carrier. Observations were carried out for seven days on three different treatments, namely Microbacterium sp. strain SpR3 with and without vermicompost inoculated in sterile soils containing 50 ppm Cr(VI), and sterile soils containing 50 ppm Cr(VI) without bacterial inoculation. The observed variables were the number of bacteria, the concentration of Cr(VI) and the rate of Cr(VI) reduction by these bacteria in the soil at T0 (day 0) and T7 (day 7). It was concluded that vermicompost could be used as a carrier of Microbacterium sp. strain SpR3 as it could increase the number of the bacteria to 2 × 1010 CFU g-1 in soil and could reduce Cr(VI) at the rate of 0.095 mg L-1 h-1.

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Shao, Dadong, Xiangxue Wang, Guangshun Hou, Fengliang Ma y Xiangke Wang. "Photocatalytic Elimination of Cr(VI) in Aqueous Solution by Using ZSM-5 Zeolite as Catalyst and Urea as Coexisting Organic Contaminants". Nano LIFE 05, n.º 02 (junio de 2015): 1542001. http://dx.doi.org/10.1142/s1793984415420015.

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The photocatalytic reduction of Cr ( VI ) to Cr ( III ) in aqueous solutions without or with urea (a model organic contaminant) using ZSM-5 zeolite as catalyst under UV illumination was studied. The used ZSM-5 zeolite has the characteristics of pure ZSM-5 zeolite crystalline structure, with the point of zero charge (pHPZC) value of pH = 3.7–3.9. The effects of illumination time, mass content of ZSM-5 zeolite, urea concentrations, Cr ( VI ) initial concentrations and ionic strength on the photocatalytic reduction of Cr ( VI ) to Cr ( III ) were investigated. The results indicated that both the increase of urea concentration and the mass content of ZSM-5 zeolite can improve the photocatalytic reduction of Cr ( VI ) to Cr ( III ) under UV illumination. The results are important to understand the photocatalytic reduction of Cr ( VI ) to Cr ( III ) in natural environment with organic contaminant.

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Lakshmipathiraj, P., G. Bhaskar Raju, M. Raviatul Basariya, S. Parvathy y S. Prabhakar. "Removal of Cr (VI) by electrochemical reduction". Separation and Purification Technology 60, n.º 1 (abril de 2008): 96–102. http://dx.doi.org/10.1016/j.seppur.2007.07.053.

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23

Deiana, Salvatore, Alessandra Premoli y Caterina Senette. "Reduction of Cr(VI) by caffeic acid". Chemosphere 67, n.º 10 (mayo de 2007): 1919–26. http://dx.doi.org/10.1016/j.chemosphere.2006.12.003.

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Antonopoulou, Maria, Aris Giannakas y Ioannis Konstantinou. "Simultaneous Photocatalytic Reduction of Cr(VI) and Oxidation of Benzoic Acid in Aqueous N-F-Codoped TiO2Suspensions: Optimization and Modeling Using the Response Surface Methodology". International Journal of Photoenergy 2012 (2012): 1–10. http://dx.doi.org/10.1155/2012/520123.

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The simultaneous photocatalytic reduction of Cr(VI) and oxidation of benzoic acid (BA) in aqueous suspensions using N-F-codoped TiO2and simulated solar irradiation were investigated in the present study. Chemometric optimization tools such as response surface methodology (RSM) and experimental design were used to model and optimize selected operational parameters of the simultaneous photocatalytic reduction of Cr(VI) and oxidation of BA. RSM was developed by considering a central composite design with three input variables, that are, N-F-codoped TiO2mass, ratio of Cr/BA, and pH. The removal of Cr(VI) and BA in binary systems, containing both Cr(VI) and BA, showed a synergistic photocatalytic decontamination as BA significantly facilitated Cr(VI) reduction, whereas Cr(VI) accelerated also BA degradation. Due to the anionic-type adsorption onto TiO2and its acid-catalyzed photocatalytic reduction, the removal of Cr(VI) decreased with increasing pH, while the degradation of BA followed also the same trend. Under the optimum conditions (N-F-TiO2) = 600 mg L−1, ratio of Cr(VI)/BA = 5, pH = 4, the removal for both Cr and BA followed a pseudo first-order kinetic model. It was found that the selected variables have significant effect both on Cr(VI) removal and BA degradation efficiency. The results revealed the feasibility and the effectiveness of using N-F-codoped TiO2as photocatalyst for simultaneous decontamination of Cr(VI) and organic pollutants such as BA due to the appropriate oxidation and reduction ability of the photogenerated h+VB-e−CBpairs.

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Sarkhosh, Maryam, Zahra atafar, Ehsan Ahmadi, Shahram Nazari, Yadolah Fakhri, Soheila Rezaei, Seyed Mohsen Mohseni, Mohammad Hossien Saghi y Majid Torkashvand. "Treatment of Electroplating Cr(VI) for Reduction Cr(VI) by Electrocoagulation in Continuous Operation". International Journal of Current Microbiology and Applied Sciences 5, n.º 4 (10 de abril de 2016): 615–25. http://dx.doi.org/10.20546/ijcmas.2016.504.070.

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26

Chen, Juan, Ri Chen y Mei Hong. "Influence of pH on hexavalent chromium reduction by Fe(II) and sulfide compounds". Water Science and Technology 72, n.º 1 (13 de abril de 2015): 22–28. http://dx.doi.org/10.2166/wst.2015.179.

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Abstract Batch experiments were conducted to investigate the influence of pH on Cr(VI) reduction with Fe(II), sulfide and mixtures of Fe(II) and sulfide at pH 3.0–12.0. The results showed that Fe(II) could reduce Cr(VI) with a high removal of nearly 100% in the pH range of 3.0–9.0, while the reduction of Cr(VI) decreased to approximately 60% considering the oxygenation of Fe(II) at pH 12.0. The reaction between Cr(VI) and sulfide, however, was largely pH dependent. H2S was the main sulfide species with the Cr(VI) removal of ∼80% at pH < 7.0, while sulfide mainly existed in the forms as HS− or S2− at pH ≥ 7.0, which had very limited removal of Cr(VI) (no more than 10%). The Cr(VI) removal by the mixtures of Fe(II) and sulfide was also compared with the sum of separate ones at different pH values. The sum of Cr(VI) removal by single Fe(II) and S(-II) was similar to that by the mixtures at pH 3.0–5.0 and pH 12.0, while the removal of Cr(VI) by the mixtures was observed to be more effective than the sum of the single-species removals at pH 7.0–9.0; the promoting effect was primarily attributed to the catalysis of ferric ion generated during the reduction process.

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Verma, Bharti y Chandrajit Balomajumder. "Hexavalent chromium reduction from real electroplating wastewater by chemical precipitation". Bulletin of the Chemical Society of Ethiopia 34, n.º 1 (24 de abril de 2020): 67–74. http://dx.doi.org/10.4314/bcse.v34i1.6.

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The immense use of chromium in the electroplating process leads to the discharge of hexavalent chromium in its effluent. Since Cr(VI) is highly toxic, its exposure poses an acute risk of health. On the contrary, Cr(III) which is naturally occurring, is much less toxic than Cr(VI). Therefore the easiest way to deal with Cr(VI) is to reduce it into its trivalent form. Exhaustive chemical analysis was done to reduce Cr(VI) to Cr(III) by using sodium metabisulfite (Na2S2O5) and ferrous sulfate (FeSO4). And after the reduction process, precipitating agents such as (Ca(OH)2), (NaOH) and a combination of the two were used to precipitate Cr(III) as hydroxides. Various parameters were varied and optimized. It was observed that the % Cr(VI) reduction increased from 88% to 99.97% when the dosage of sodium metabisulfite increased from 40 mg/L to 100 mg/L at a pH of 2. The maximum removal of 98.2% was achieved by using the combination of Ca(OH)2 + NaOH at a pH of 9. Bull. Chem. Soc. Ethiop. 2020, 34(1), 67-74. DOI: https://dx.doi.org/10.4314/bcse.v34i1.6

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Machado, Tiele Caprioli, Marla Azário Lansarin y Natália Matte. "Reduction of hexavalent chromium: photocatalysis and photochemistry and their application in wastewater remediation". Water Science and Technology 70, n.º 1 (22 de abril de 2014): 55–61. http://dx.doi.org/10.2166/wst.2014.193.

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Hexavalent chromium present in wastewater discharge of galvanic industries is toxic to most microorganisms and potentially harmful to human health. This work examines the photochemical reduction of Cr(VI) with ethanol under ultraviolet (UV) and visible radiation, and photocatalytic reduction of Cr(VI) with TiO2 in the presence of ethanol under UV radiation. By means of different experimental designs, this study investigates the influence of the initial pH, ethanol amount, catalyst concentration and initial Cr(VI) concentration on total Cr(VI) reduction. The results obtained showed that photochemistry with ethanol under UV radiation (96.10%) was more efficient than photochemistry with ethanol under visible light (48.07%). Furthermore, photocatalysis with TiO2 in the presence of ethanol under UV radiation showed high values of total Cr(VI) reduction: 94.15%, under the optimal conditions established by the experimental design. Finally, experiments were carried out with wastewater discharge from an electroplating plant in its original concentration, and higher values of total Cr(VI) reduction were observed.

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Tan, Xiaoli, Ming Fang y Xiangke Wang. "Preparation of TiO2/Multiwalled Carbon Nanotube Composites and Their Applications in Photocatalytic Reduction of Cr(VI) Study". Journal of Nanoscience and Nanotechnology 8, n.º 11 (1 de noviembre de 2008): 5624–31. http://dx.doi.org/10.1166/jnn.2008.242.

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The TiO2/multiwalled carbon nanotube (MWCNT) composites were prepared by hydrothermal deposition. Batch experiments were carried out to study the removal of Cr(VI) from aqueous solution to TiO2, MWCNTs and TiO2/MWCNTs. Scanning electron microscopy and X-ray diffraction were utilized to characterize the prepared TiO2/MWCNT composites. The introduction of MWCNTs onto TiO2 catalyst led to a remarkable increase of Cr(VI) removal through adsorption and photocatalytic reduction under ultraviolet irradiation. Results of X-ray photoelectron spectroscopy analysis of chromium species adsorbed on TiO2/MWCNTs phase revealed that the removal mechanism of Cr(VI) by TiO2/MWCNTs under UV-irradiation was the reduction of Cr(VI) into Cr(III). The adsorption and photocatalytic activity of Cr(VI) decreased with increasing in pH, and was not affected by the concentration of sulphate obviously. In the ternary systems humic acid (HA)/fulvic acid (FA)-Cr(VI)-TiO2/MWCNTs, the increasing of FA/HA concentration did not cause any drastic changes in the adsorption capacity in terms of Cr(VI) concentration in the dark, but a minor increasing trend for the photocatalytic reduction of Cr(VI). The presence of humic substances enhanced the photocatalytic reduction and adsorption of Cr(III) to TiO2/MWCNTs.

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30

Wang, Tian Gui, Ji Sheng Li y Li Ling Qin. "Remediation of Chromite Ore Processing Residues with Bacteria, Biomass and Ferrous Sulfate". Applied Mechanics and Materials 295-298 (febrero de 2013): 1776–79. http://dx.doi.org/10.4028/www.scientific.net/amm.295-298.1776.

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Large amounts of chromite ore processing residues (COPR) containing hexavalent chromium (Cr(VI)) discharged from the production processes of sodium chromate and dichromate need to be treated since Cr(VI) has been recognized as a carcinogen internationally and has posed a great threat to the environment and human health. Remediation of COPR containing Cr(VI) with bacteria, biomass and ferrous sulfate was studied in this work. A strain of Cr(VI)-reducing bacteria (CRB), a strain of sulfate-reducing bacteria (SRB), orange peels and ferrous sulfate were used as antidotes to reduce Cr(VI) to Cr(III). The experimental design methodologies — Uniform Design and Orthogonal Experimental Design were adopted to investigate the effects of the reductants on the reduction of the Cr(VI) in COPR. The results show that orange peels and CRB can reduce Cr(VI) in COPR over 95% in 30 days. Together using the four stuff can reduce Cr(VI) over 97% in 12 days. However, it seems that presence of the SRB is not beneficial to Cr(VI) reduction because it might refrains the action of CRB. Therefore, it is not surely beneficial to apply multiple microorganisms simultaneously to the reduction of Cr(VI) in COPR.

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31

Feng, Xiang Hua, Xiao Rong Zheng y Shi Min Ding. "Photoreduction of Cr(VI) in Fe(III)-lactate System". Advanced Materials Research 512-515 (mayo de 2012): 2317–20. http://dx.doi.org/10.4028/www.scientific.net/amr.512-515.2317.

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The photochemical reduction of Cr(VI) in aqueous solutions containing Fe(III)-lactate complex was preliminarily investigated. The effects of initial pH, initial concentrations of Fe (III), lactate and Cr(VI) were studied in detail and the photoreduction mechanism of Cr(VI) was discussed preliminarily. The results indicate that Cr(VI) can be effectively photochemically reduced by Fe(III)-lactate complex, and the optimum pH for photoreduction of Cr(VI) is 3.0. The reduction efficiency of Cr(VI) decreases with increase of the initial concentrations of Cr(VI) over the range of 12.0~48.0 μM. The initial rate of Cr (VI) photoreduction increases with increase of the initial concentrations of Fe (III) or lactate. The photoreduction reaction is accordance with the law of apparent first-order dynamics reaction.

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32

Wang, Chunyong y Yanshan Cui. "Recognition of a New Cr(VI)-Reducing Strain and Study of the Potential Capacity for Reduction of Cr(VI) of the Strain". BioMed Research International 2019 (10 de febrero de 2019): 1–9. http://dx.doi.org/10.1155/2019/5135017.

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The biotransformation of hexavalent chromium [Cr(VI)] via Cr(VI)-reducing microorganisms is considered an ecofriendly approach to detoxify Cr(VI). A new Cr(VI)-reducing bacterium named Microbacterium sp. QH-2 was isolated in this study. Scanning electron microscopy (SEM) images showed protrusions on the bacterial surface of strain QH-2 after an 18 h incubation in media under 10 mM Cr(VI) treatment. Results of the experiments on the capacity of reducing Cr(VI) indicated that strain QH-2 could reduce 100% Cr(VI) less than 48-96 h. When media with 4 mM Cr(VI) were incubated, the fastest reduction rate of strain QH-2 could come up to 2.17 mg/L Cr(VI) h−1. Furthermore, strain QH-2 could reduce Cr(VI) over the pH between 7 and 10. The optimum pH to reduce Cr(VI) by strain QH-2 was 9. Strain QH-2 also exhibited a relatively high tolerance even to 20 mM Cr(VI). These results declared that strain QH-2 had the potential to detoxify Cr(VI) in the Cr(VI)-contaminated soil or effluent.

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Gangadharan, Praveena y Indumathi M. Nambi. "Hexavalent chromium reduction and energy recovery by using dual-chambered microbial fuel cell". Water Science and Technology 71, n.º 3 (24 de diciembre de 2014): 353–58. http://dx.doi.org/10.2166/wst.2014.524.

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Microbial fuel cell (MFC) technology is utilized to treat hexavalent chromium (Cr(VI)) from wastewater and to generate electricity simultaneously. The Cr(VI) is bioelectrochemically reduced to non-toxic Cr(III) form in the presence of an organic electron donor in a dual-chambered MFC. The Cr(VI) as catholyte and artificial wastewater inoculated with anaerobic sludge as anolyte, Cr(VI) at 100 mg/L was completely removed within 48 h (initial pH value 2.0). The total amount of Cr recovered was 99.87% by the precipitation of Cr(III) on the surface of the cathode. In addition to that 78.4% of total organic carbon reduction was achieved at the anode chamber within 13 days of operation. Furthermore, the maximum power density of 767.01 mW/m2 (2.08 mA/m2) was achieved by MFCs at ambient conditions. The present work has successfully demonstrated the feasibility of using MFCs for simultaneous energy production from wastewater and reduction of toxic Cr(VI) to non-toxic Cr(III).

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Lei, Xue Fei y Xiang Xin Xue. "Photocatalytic Reduction of Cr(VI) in the Presence of Citric Acid over Perovskite Type SO₄²^-/TBBFS under UV-Vis Light Irradiation". Advanced Materials Research 113-116 (junio de 2010): 1632–38. http://dx.doi.org/10.4028/www.scientific.net/amr.113-116.1632.

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The photocatalytic reduction experiments of Cr(VI) over the sulfate-modified titanium-bearing blast furnace slag photocatalyst under UV-vis light irradiation in the absence/presence of citric acid (0≤[citric acid]≤4 mM) were performed at different pH and different initial concentration. In the presence of citric acid, the photocatalytic reduction efficiency of Cr(VI) was significantly enhanced and kinetic constants of the compound system (in the presence of photaocatalyst, citric acid and Cr(VI))was nearly 9.2 times than that in the absence of citric acid. This enhanced efficiency may be attributed to the effective separation of electron-hole in the presence of citric acid. The maximum rate of Cr(VI) reduction was obtained for an initial citric acid/Cr(VI) molar ratio, R=3.75, a further increment in R being disadvantageous; however, the photocatalytic reduction efficiency of Cr(VI) in the presence of citric acid was always faster than in its absence. The synergistic effect factor is always greater than 6 in the compound system, indicating that a marked synergistic effect between the photocatalytic reduction of Cr(VI) and citric acid.

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35

Zhou, Ming, Hang Xu, Shu Fa Zhu y Ya Na Liu. "Reduction and Biosorption of Cr from Aqueous Solution Using Banana Skin". Advanced Materials Research 518-523 (mayo de 2012): 2708–11. http://dx.doi.org/10.4028/www.scientific.net/amr.518-523.2708.

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The possible use of biowaste-banana skin as an alternative, low-cost biosorbent and reductant for removal of Cr from aqueous solutions was investigated. Effects of pH, contact time, Cr(VI) initial concentration and temperature on the reduction and biosorption of Cr by banana skin were studied. Experimental results showed that 1 g of dried banana skin could reduce about 230 mg of Cr(VI) to Cr(III), at the condition of 30°C, pH 2 and 300 rpm. The maximum Qeq of Cr(III) by banana skin was 6.3mg g-1 at the Cr(VI) initial concentration of 200mg L-1, 30°C , pH 2 and 300 rpm.

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36

Chirwa, Evans M. N., Iwouda Venter y Hazel Wienand. "Biological Cr(VI) immobilisation in saturated aquifer zone using culture inoculated soil columns". Water Science and Technology 67, n.º 10 (1 de mayo de 2013): 2321–29. http://dx.doi.org/10.2166/wst.2013.091.

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Remediation of Cr(VI) requires the reduction of the mobile state [Cr(VI)], which exists in the natural environment as the oxyanionic species (CrxOyz−), to the less mobile trivalent state [Cr(III)], which readily forms the hydroxide precipitate [Cr(OH)3(s)] under natural pH conditions. In this study, Cr(VI) reduction is investigated using inoculated microcosm aquifer systems operated as fully submerged plug flow systems. The system was design to simulate the operation of a microbial contaminant barrier in the saturated zone of an open aquifer system. No organic carbon sources and no air was introduced to simulate Cr(VI) reduction under oxygen free conditions. The inoculated microcosm column operated at influent feed concentrations of 10, 20, and 40 mg/L, and a hydraulic retention time of 12 hours achieved complete removal of Cr(VI) over a 90 cm distance. Steady-state conditions were obtained in less than 48 hours under feed concentrations of 10 and 20 mg/L. Very little Cr(VI) reduction was observed in non-inoculated microcosm controls operated under identical conditions.

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Bencheikh-Latmani, Rizlan, Sarah Middleton Williams, Lisa Haucke, Craig S. Criddle, Liyou Wu, Jizhong Zhou y Bradley M. Tebo. "Global Transcriptional Profiling of Shewanella oneidensis MR-1 during Cr(VI) and U(VI) Reduction". Applied and Environmental Microbiology 71, n.º 11 (noviembre de 2005): 7453–60. http://dx.doi.org/10.1128/aem.71.11.7453-7460.2005.

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ABSTRACT Whole-genome DNA microarrays were used to examine the gene expression profile of Shewanella oneidensis MR-1 during U(VI) and Cr(VI) reduction. The same control, cells pregrown with nitrate and incubated with no electron acceptor, was used for the two time points considered and for both metals. U(VI)-reducing conditions resulted in the upregulation (≥3-fold) of 121 genes, while 83 genes were upregulated under Cr(VI)-reducing conditions. A large fraction of the genes upregulated [34% for U(VI) and 29% for Cr(VI)] encode hypothetical proteins of unknown function. Genes encoding proteins known to reduce alternative electron acceptors [fumarate, dimethyl sulfoxide, Mn(IV), or soluble Fe(III)] were upregulated under both U(VI)- and Cr(VI)-reducing conditions. The involvement of these upregulated genes in the reduction of U(VI) and Cr(VI) was tested using mutants lacking one or several of the gene products. Mutant testing confirmed the involvement of several genes in the reduction of both metals: mtrA, mtrB, mtrC, and menC, all of which are involved in Fe(III) citrate reduction by MR-1. Genes encoding efflux pumps were upregulated under Cr(VI)- but not under U(VI)-reducing conditions. Genes encoding proteins associated with general (e.g., groL and dnaJ) and membrane (e.g., pspBC) stress were also upregulated, particularly under U(VI)-reducing conditions, pointing to membrane damage by the solid-phase reduced U(IV) and Cr(III) and/or the direct effect of the oxidized forms of the metals. This study sheds light on the multifaceted response of MR-1 to U(VI) and Cr(VI) under anaerobic conditions and suggests that the same electron transport pathway can be used for more than one electron acceptor.

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Belchik, Sara M., David W. Kennedy, Alice C. Dohnalkova, Yuanmin Wang, Papatya C. Sevinc, Hong Wu, Yuehe Lin, H. Peter Lu, James K. Fredrickson y Liang Shi. "Extracellular Reduction of Hexavalent Chromium by Cytochromes MtrC and OmcA of Shewanella oneidensis MR-1". Applied and Environmental Microbiology 77, n.º 12 (15 de abril de 2011): 4035–41. http://dx.doi.org/10.1128/aem.02463-10.

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ABSTRACTTo characterize the roles of cytochromes MtrC and OmcA ofShewanella oneidensisMR-1 in Cr(VI) reduction, the effects of deleting themtrCand/oromcAgene on Cr(VI) reduction and the cellular locations of reduced Cr(III) precipitates were investigated. Compared to the rate of reduction of Cr(VI) by the wild type (wt), the deletion ofmtrCdecreased the initial rate of Cr(VI) reduction by 43.5%, while the deletion ofomcAor bothmtrCandomcAlowered the rate by 53.4% and 68.9%, respectively. In wt cells, Cr(III) precipitates were detected by transmission electron microscopy in the extracellular matrix between the cells, in association with the outer membrane, and inside the cytoplasm. No extracellular matrix-associated Cr(III) precipitates, however, were found in the cytochrome mutant cell suspension. In mutant cells without either MtrC or OmcA, most Cr(III) precipitates were found in association with the outer membrane, while in mutant cells lacking both MtrC and OmcA, most Cr(III) precipitates were found inside the cytoplasm. Cr(III) precipitates were also detected by scanning election microscopy on the surfaces of the wt and mutants without MtrC or OmcA but not on the mutant cells lacking both MtrC and OmcA, demonstrating that the deletion ofmtrCandomcAdiminishes the extracellular formation of Cr(III) precipitates. Furthermore, purified MtrC and OmcA reduced Cr(VI) with apparentkcatvalues of 1.2 ± 0.2 (mean ± standard deviation) and 10.2 ± 1 s−1andKmvalues of 34.1 ± 4.5 and 41.3 ± 7.9 μM, respectively. Together, these results consistently demonstrate that MtrC and OmcA are the terminal reductases used byS. oneidensisMR-1 for extracellular Cr(VI) reduction where OmcA is a predominant Cr(VI) reductase.

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Peng, Hao, Jing Guo, Hongzhi Qiu, Caiqiong Wang, Chenyu Zhang, Zhihui Hao, Yating Rao y Yanhong Gong. "Efficient Removal of Cr (VI) with Biochar and Optimized Parameters by Response Surface Methodology". Processes 9, n.º 5 (18 de mayo de 2021): 889. http://dx.doi.org/10.3390/pr9050889.

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A highly efficient reduction process of Cr (VI) with biochar was conducted in this paper. The results showed that nearly 100% Cr (VI) was reduced at selected reaction conditions: Dosage of biochar at m (C)/m(Cr) = 3.0, reaction temperature of 90 °C, reaction time of60 min, and concentration of H2SO4 of 20 g/L. The reduction kinetics analysis demonstrated that the reduction of Cr (VI) fitted well with the pseudo-first-order model and the apparent activation energy was calculated to be 40.24 kJ/mol. Response surface methodology confirmed that all of the experimental parameters had a positive effect on the reduction of Cr (VI). The influence of each parameter on the reduction process followed the order: Dosage of biochar>concentration of H2SO4>reaction temperature >reaction time. This paper provides a versatile strategy for the treatment of wastewater containing Cr (VI) and shows a bright tomorrow for wastewater treatment.

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Acharya, Rashmi, Brundabana Naik y Kulamani Parida. "Cr(VI) remediation from aqueous environment through modified-TiO2-mediated photocatalytic reduction". Beilstein Journal of Nanotechnology 9 (16 de mayo de 2018): 1448–70. http://dx.doi.org/10.3762/bjnano.9.137.

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Cr(VI) exhibits cytotoxic, mutagenic and carcinogenic properties; hence, effluents containing Cr(VI) from various industrial processes pose threat to aquatic life and downstream users. Various treatment techniques, such as chemical reduction, ion exchange, bacterial degradation, adsorption and photocatalysis, have been exploited for remediation of Cr(VI) from wastewater. Among these, photocatalysis has recently gained considerable attention. The applications of photocatalysis, such as water splitting, CO2 reduction, pollutant degradation, organic transformation reactions, N2 fixation, etc., towards solving the energy crisis and environmental issues are briefly discussed in the Introduction of this review. The advantages of TiO2 as a photocatalyst and the importance of its modification for photocatalytic reduction of Cr(VI) has also been addressed. In this review, the photocatalytic activity of TiO2 after modification with carbon-based advanced materials, metal oxides, metal sulfides and noble metals towards reduction of Cr(VI) was evaluated and compared with that of bare TiO2. The photoactivity of dye-sensitized TiO2 for reduction of Cr(VI) was also discussed. The mechanism for enhanced photocatalytic activity was highlighted and attributed to the resultant properties, namely, effective separation of photoinduced charge carriers, extension of the light absorption range and intensity, increase of the surface active sites, and higher photostability. Advantages and limitations for photoreduction of Cr(VI) over modified TiO2 are depicted in the Conclusion. The various challenges that restrict the technology from practical applications in remediation of Cr(VI) from wastewater were addressed in the Conclusion section as well. The future perspectives of the field presented in this review are focused on the development of whole-solar-spectrum responsive, TiO2-coupled photocatalysts which provide efficient photocatalytic reduction of Cr(VI) along with their good recoverability and recyclability.

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Nguema, Paul Fabrice, Zejiao Luo, Zachari Mohamadou Mounir y Ma Jun. "Treatment of Chromium Pollution by the Reductase Enzyme Generated by a Chromium-Resistant Bacterium Isolated in Dewatering Sludge". International Journal of Biology 9, n.º 3 (6 de mayo de 2017): 1. http://dx.doi.org/10.5539/ijb.v9n3p1.

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An efficient Cr (VI)-resistant and reducing bacterial strain was successfully isolated in dewatering sludge collected from a sewage treatment plant, and characterized in vitro Cr (VI) reduction through a reductase enzyme. Phylogenetic analysis using 16S rDNA gene sequencing revealed that the newly isolated strain namely Pf-1 was closely related to Bacillus cereus. The strain almost reduced 0.17 mM Cr (VI) within 24h incubation and the presence of different substrates such as glucose, sucrose, or acetate significantly enhanced the reduction rate of Cr (VI) to Cr (III). However, addition of the same substrate at the stationary phase of the microbial growth increased the reduction rate as well as bacterial growth. Additionally, raising the concentration of thiosulfate in the medium doubled the reduction rate under similar conditions. Assay with different fractions of the cells demonstrated that the reductase enzyme activity was mainly associated with the cytoplasmic fraction. The maximum activity was 23.3 µM h-1 mg-1 protein and was obtained at the Cr (VI) concentration of 2 mM. The promising strain can be efficiently employed for bioremediation of Cr (VI) polluted sites.

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Sulaiman, Syazwan Liyana, Sufizar Ahmad y Hariati Taib. "Effect of Silicon Oxide Size and Reducing Environment on the Photocatalytic Capability of Poly(Vinyl Alcohol)/Chitosan/Silicon Oxide Beads". Applied Mechanics and Materials 699 (noviembre de 2014): 1000–1005. http://dx.doi.org/10.4028/www.scientific.net/amm.699.1000.

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The present work assess the capability of silicon oxide (SiO2) nanoparticle and microparticle incorporated in poly (vinyl alcohol)/chitosan/silicon oxide (PVA/CS/SiO2) beads to reduce chromium (Cr) ions of Cr (VI) to Cr (III). PVA/CS/(nanoand micro)-SiO2beads were prepared through a simple drop wise method. The elemental analysis of prepared photocatalytic beads were confirmed by scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDX) and morphology of PVA/CS/SiO2beads before and after Cr ions reduction were observed with SEM. The reduction of chromium (Cr (VI)) ions by both of PVA/CS/(nanoand micro)-SiO2) beads, as evaluated by the reduction duration taken were studied by photocatalytic process in which factors of SiO2powders size and pH of reducing environment were varied. Photocatalytic studies revealed better performance of PVA/CS/nanoSiO2beads in compared to PVA/CS/micro-SiO2beads in Cr (VI) to Cr (III) ions reduction. Reduction Cr (VI) to Cr (III) ions by PVA/CS/nanoSiO2beads occurred in 30 minutes and 50 minutes by PVA/CS/micro-SiO2. Moreover, both PVA/CS/(nanoand micro)-SiO2showed excellent reduction of Cr (VI) ions at lower pH environment. It is thus concluded that both of PVA/CS/(nanoand micro)-SiO2beads are capable for chromium reduction in highly acidic environment in which PVA/CS/nanoSiO2beads showed better performance.

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Butler, Elizabeth C., Lixia Chen, Colleen M. Hansel, Lee R. Krumholz, Andrew S. Elwood Madden y Ying Lan. "Biological versus mineralogical chromium reduction: potential for reoxidation by manganese oxide". Environmental Science: Processes & Impacts 17, n.º 11 (2015): 1930–40. http://dx.doi.org/10.1039/c5em00286a.

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44

Yang, Chih-Chi, Khanh-Chau Dao, Yo-Sheng Lin, Teng-Yun Cheng, Ku-Fan Chen y Yung-Pin Tsai. "Impacts of Mixing Mode on Photocatalytic Reduction of Hexavalent Chromium over Titanium Dioxide Nanomaterial under Various Environmental Conditions". Water 13, n.º 16 (21 de agosto de 2021): 2291. http://dx.doi.org/10.3390/w13162291.

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This study explores the effects of initial Cr(VI) concentration, wavelength, hole-scavenger (absence and presence of salicylic acid), and oxygen conditions (aeration by air, nitrogen gas, and mechanical stir only) on photocatalytic reduction of hexavalent chromium over titanium dioxide photocatalyst and the chromic species distribution after photocatalysis. The experimental results show the existence of strong interactions between these factors. The factor of hole-scavenger was more important than the UV light wavelength condition for a reduction of 3 mg Cr(VI) L−1, whereas both factors became important when Cr(VI) concentration increased to 20 mgL−1. The higher the UV wavelength was, the less the amount of chromium retained on the TiO2 surface. The influence of oxygen-containing conditions in the solution on the reduction of 3 mgL−1 Cr(VI) was unobvious, whereas its influence became remarkable for the reduction of 20 mgL−1 Cr(VI) in the presence of SA. The interaction between oxygen-containing factor and other environmental factors, such as Cr(VI) concentration and scavenger presence (SA in this study), is a key factor about the degree of oxygen effect on Cr(VI) photo-reduction and the chromic species distribution. Simple stirring obtained better photocatalytic efficiency than aeration by air or nitrogen gas.

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Garza-González, María Teresa, Jonathan Eduardo Ramírez-Vázquez, María de los Ángeles García-Hernández, María Elena Cantú-Cárdenas, Adriana Liñan-Montes y Juan Francisco Villarreal-Chiu. "Reduction of chromium (VI) from aqueous solution by biomass of Cladosporium cladosporioides". Water Science and Technology 76, n.º 9 (17 de julio de 2017): 2494–502. http://dx.doi.org/10.2166/wst.2017.427.

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Abstract The capacity of Cladosporium cladosporioides biomass for removal of Cr(VI) in aqueous solutions was evaluated. A 2 × 2 factorial experiment design was used to study the effects of pH and biomass doses. Lower pH values and larger biomass doses increased the capacity of C. cladosporioides biomass for removal of Cr(VI), reaching a reduction capacity of 492.85 mg g−1, a significantly higher value compared to other biomass reported. Cr(VI) removal kinetic rates followed a pseudo-second order model, like other fungal biomass reported previously. The apparent adsorption process was described well by the Freundlich isothermal model. However, determination of total chromium indicated that adsorption of Cr(VI) was followed by a redox reaction that released proportional quantities of Cr(III) into the experimental supernatant, suggesting a parallel adsorption-reduction process. Comparison of Fourier transform infrared spectroscopy spectra of C. cladosporioides biomass before and after the reduction process demonstrated the involvement of positively charged amino groups in the Cr(VI) adsorption-reduction process.

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Badrelzaman, Mohamed, Mustafa I. Khamis, Taleb H. Ibrahim y Fawwaz H. Jumean. "Scale-Up of Self-Regenerating Semi-Batch Adsorption Cycles through Concurrent Adsorption and Reduction of Cr(VI) on Sheep Wool". Processes 8, n.º 9 (2 de septiembre de 2020): 1092. http://dx.doi.org/10.3390/pr8091092.

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A previous publication by our group reported that adsorption of Cr(VI) on sheep wool reached 99% when allowed a long residence time, with concurrent reduction to Cr(III). In this study, the process was scaled up by optimizing a pilot plant based on semi-batch adsorption cycles. This yielded Cr(III), which is about 300 times less toxic than Cr(VI), and can be precipitated using lime at high pH. Since the reduction step is slower than the adsorption one, an adsorption column was designed to perform semi-batch operation cycles, whereby the extended “off cycle” allows reduction to take place. Since reduction of Cr(VI) frees active sites on wool, the plant acts in lieu of in situ regeneration, accompanied by additional adsorption of Cr(VI). The results show that 97% of the column efficiency can be recovered within 24 h of “off cycle”. Wastewater from a local electroplating industry was treated by this method with high removal of Cr(VI), reaching the limit permitted by environmental standards. This study also reveals that typical concentrations of heavy metals, present in wastewater produced from electroplating, had no substantial antagonistic interference with Cr(VI) adsorption.

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Hossan, Shanewaz, Saddam Hossain, Mohammad Rafiqul Islam, Mir Himayet Kabir, Sobur Ali, Md Shafiqul Islam, Khan Mohammad Imran et al. "Bioremediation of Hexavalent Chromium by Chromium Resistant Bacteria Reduces Phytotoxicity". International Journal of Environmental Research and Public Health 17, n.º 17 (19 de agosto de 2020): 6013. http://dx.doi.org/10.3390/ijerph17176013.

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Chromium (Cr) (VI) has long been known as an environmental hazard that can be reduced from aqueous solutions through bioremediation by living cells. In this study, we investigated the efficiency of reduction and biosorption of Cr(VI) by chromate resistant bacteria isolated from tannery effluent. From 28 screened Cr(VI) resistant isolates, selected bacterial strain SH-1 was identified as Klebsiella sp. via 16S rRNA sequencing. In Luria–Bertani broth, the relative reduction level of Cr(VI) was 95%, but in tannery effluent, it was 63.08% after 72 h of incubation. The cell-free extract of SH-1 showed a 72.2% reduction of Cr(VI), which indicated a higher activity of Cr(VI) reducing enzyme than the control. Live and dead biomass of SH-1 adsorbed 51.25 mg and 29.03 mg Cr(VI) per gram of dry weight, respectively. Two adsorption isotherm models—Langmuir and Freundlich—were used for the illustration of Cr(VI) biosorption using SH-1 live biomass. Scanning electron microscopy (SEM) analysis showed an increased cell size of the treated biomass when compared to the controlled biomass, which supports the adsorption of reduced Cr on the biomass cell surface. Fourier-transform infrared analysis indicated that Cr(VI) had an effect on bacterial biomass, including quantitative and structural modifications. Moreover, the chickpea seed germination study showed beneficial environmental effects that suggest possible application of the isolate for the bioremediation of toxic Cr(VI).

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Murugaiyan, Vanitha, S. Selvaraj y P. Kamatchi Selvaraj. "A Comparative Study on Conversion of Soluble Cr(VI) into Insoluble Cr(VI) and Reduction of Cr(VI) in Contaminated Groundwater at COPR Dump Site". Asian Journal of Chemistry 31, n.º 3 (2019): 533–37. http://dx.doi.org/10.14233/ajchem.2019.21688.

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The most common methodology for removal of Cr(VI) in literatures is the combination of reduction and precipitation process. The disadvantages of this method are presence of high total dissolved solids in the treated water and sludge generation. In order to find a new solution, efforts have been focussed to convert Cr(VI) present in the groundwater, into the useful products like zinc chromate and barium chromate under appropriate conditions. The efficiency of these conversions is compared with the efficiency of the reduction and precipitation process adopted in this study, using sodium metabisulphite. These experimental studies were carried out with stimulated water containing 2000 mg/L of Cr(VI) and then extended to Cr(VI) contaminated groundwater with same concentration. The results are compared and validated through batch experiments.

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Santoso, Uripto Trisno, Herdiansyah Herdiansyah, Wega Trisunaryanti y Sri Juari Santosa. "STUDY ON THE RATE OF REDUCTION OF Cr(VI) TO Cr(III) BY HUMIC ACID USING CONTINUM MULTICOMPONENT MODEL". Indonesian Journal of Chemistry 4, n.º 1 (9 de junio de 2010): 12–25. http://dx.doi.org/10.22146/ijc.21869.

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The objective of this study is to develop a rate equation for reduction of Cr(VI) by humic acid (HA) using a continuum multicomponent model. HA was extracted from peat soil samples in Gambut Subdistrict, South Kalimantan. Parameters influencing the rate of reduction, i.e., medium acidity ([H+]), as well as initial humic acid concentrations ([HA]o) and initial Cr(VI) concentrations ([Cr(VI)]o) were critically evaluated. Experiments were performed in triplicate tests. Aliquots of stock solution containing 100 mg/L HA were equilibrated for 24 h at pH 1.5, 2.05, 3.2, 5.6, and 6.5 before being spiked with 0.02 mM of Cr(VI). [Cr(VI)] was determined by 1,5-diphenylcarbazide spectrometric method. A similar set of rate experiments was conducted at a fixed pH of 1.5 and an [Cr(VI)]o of 0.02 mM and with [HA]o of 25, 50, 75, 100, 150, 200, and 250 mg/L. A third set of batch experiment was performed at pH 1.5, an [HA]o of 100 mg/L, and [Cr(VI)]o 0.01, 0.02, 0.05, 0.10, and 0.20 mM. The results showed that the rate of reduction cannot be adequately modeled by either a simple first- or second- order rate equation. A continum multicomponent model adequately describes the effect of solution parameters on the rates of Cr(VI) reduction.

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Li, Yongchao, Zhaohui Jin, Tielong Li y Shujing Li. "Removal of hexavalent chromium in soil and groundwater by supported nano zero-valent iron on silica fume". Water Science and Technology 63, n.º 12 (1 de junio de 2011): 2781–87. http://dx.doi.org/10.2166/wst.2011.454.

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Silica fume supported-Fe0 nanoparticles (SF-Fe0) were prepared using commercial silica fume as a support. The feasibility of using this SF-Fe0 for reductive immobilization of Cr(VI) was investigated through batch tests. Compared with unsupported Fe0, SF-Fe0 was significantly more active in Cr(VI) removal especially in 84 wt% silica fume loading. Silica fume had also been found to inhibit the formation of Fe(III)/Cr(III) precipitation on Fe nanoparticles' surface, which was increasing the deactivation resistance of iron. Cr(VI) was removed through physical adsorption of Cr(VI) onto the SF-Fe0 surface and subsequent reduction of Cr(VI) to Cr(III). The rate of reduction of Cr(VI) could be expressed by pseudo first-order reaction kinetics. The rate constant increased with the increase in iron loading but decreased with the increase in initial Cr(VI) concentration. Furthermore, column tests showed that the SF-Fe0 could be readily transported in model soil.

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