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S.h Ribeiro - One of the best experts on this subject based on the ideXlab platform.

Maria Chrysochoou - One of the best experts on this subject based on the ideXlab platform.

  • origin and concentration profile of Chromium in a greek aquifer
    Journal of Hazardous Materials, 2015
    Co-Authors: Dimitris Dermatas, Thanasis Mpouras, Iraklis Panagiotakis, Christos Vatseris, Nikos Linardos, Eleni Theologou, Nefeli Boboti, Anthimos Xenidis, Maria Chrysochoou, Nymphodora Papassiopi
    Abstract:

    Abstract In this paper the origin and concentration of Chromium (Cr) in an ophiolitic aquifer in Vergina, northern Greece were investigated. The study area has only agricultural activity so that industrial Cr contamination was precluded. Soil sampling included topsoil and drillcore samples collected down to 98 m depth. Groundwater samples were collected from three existing wells and a spring at the area and from different depths of the soil boring using the disCrete sampling method. Mineralogical analysis of soils confirmed the presence of ultramafic minerals, including chrysotile and chromite. Soil elemental analysis showed significant concentration of total Chromium (Crtot; max 12,000 mg/kg) and hexavalent Chromium (Cr(VI); max 7.5 mg/kg). Significant Crtot (91 μg/L) and Cr(VI) (64 μg/L) concentrations exceeding the drinking water limit of 50 μg/L were also detected in groundwater. In both the disCrete soil and groundwater samples a deCreasing trend of Cr(VI) concentration was observed with inCreasing depth, while Crtot inCreased. The inCreasing trend in Crtot is attributed to the inCreasing contribution of unweathered ultramafic minerals with depth, while the deCreasing Cr(VI) may be related to the inCreasing soil pH that does not favor Cr(III) oxidation by Mn-oxides.

  • a comparative evaluation of hexavalent Chromium treatment in contaminated soil by calcium polysulfide and green tea nanoscale zero valent iron
    Journal of Hazardous Materials, 2012
    Co-Authors: Maria Chrysochoou, Chad P Johnsto, Geeta Dahal
    Abstract:

    Abstract A column study for hexavalent Chromium (Cr(VI)) removal from contaminated soil was performed using calcium polysulfide (CPS) and nanoscale zero-valent iron stabilized with green tea extract (GT-nZVI). Injection of CPS at 12 times the stoichiometric requirement (12×) resulted in quantitative Cr(VI) removal for up to 195 days of equivalent groundwater flow. Solid-bound Cr(VI) was reduced up to >99% (

  • Remediation of chromite ore processing residue using ferrous sulfate and calcium polysulfide
    Geosciences Journal, 2007
    Co-Authors: Mahmoud Wazne, Dimitris Dermatas, Deok Hyun Moon, Santhi Chandra Jagupilla, Christos Christodoulatos, Maria Chrysochoou
    Abstract:

    Batch tests were conducted to assess the potential use of ferrous sulfate and calcium polysulfide for the remediation of chromite ore processing residue (COPR). The remediation process entails addition of ferrous sulfate or calcium polysulfide to chemically reduce hexavalent Chromium [Cr(VI)] to trivalent Chromium [Cr(III)] in slurry form and pH adjustment to precipitate Cr(III) as Chromium hydroxide. The present study investigates the effects of COPR particle size, treatment pH, and chemical dosage on the performance of the treatment. Smaller particle size resulted in inCreases in alkaline digestion and Toxicity Characteristic Leaching Procedure (TCLP) Cr(VI) concentrations for the untreated samples. The chemical reduction of Cr(VI) with ferrous iron and sulfides was non-stoichiometric. Four times the stoichiometric amount of ferrous iron of two times the stoichiometric amount of polysulfide were needed to meet both the New Jersey Department of Environmental Protection (NJDEP) regulatory limit of 240 mg/kg for Cr(VI) and EPA TCLP regulatory limit of 5 mg/L for Chromium [C,r]. pH adjustment was necessary to prevent the formation of ettringite, a swell causing mineral, upon the introduction of sulfate to the COPR material via ferrous sulfate or calcium polysulfide. The slow hydration of some COPR minerals caused the pH of the treated COPR to Creep upward during the curing period. However, when sufficient acid was added, the pH value was controlled at less than 9.27 for a curing period of 1.5 years, which prevented the formation of ettringite.

Peng Yuan - One of the best experts on this subject based on the ideXlab platform.

  • removal of hexavalent Chromium Cr vi from aqueous solutions by the diatomite supported unsupported magnetite nanoparticles
    Journal of Hazardous Materials, 2010
    Co-Authors: Peng Yuan, Fei Ge, Mingde Fan, Jianxi Zhu, Runliang Zhu, Dan Yang, Dong Liu, Hongping He
    Abstract:

    Abstract Diatomite-supported/unsupported magnetite nanoparticles were prepared by co-precipitation and hydrosol methods, and characterized by X-ray diffraction, nitrogen adsorption, elemental analysis, differential scanning calorimetry, transmission electron miCroscopy and X-ray photoelectron spectroscopy. The average sizes of the unsupported and supported magnetite nanoparticles are around 25 and 15 nm, respectively. The supported magnetite nanoparticles exist on the surface or inside the pores of diatom shells, with better dispersing and less coaggregation than the unsupported ones. The uptake of hexavalent Chromium [Cr(VI)] on the synthesized magnetite nanoparticles was mainly governed by a physico-chemical process, which included an electrostatic attraction followed by a redox process in which Cr(VI) was reduced into trivalent Chromium [Cr(III)]. The adsorption of Cr(VI) was highly pH-dependent and the kinetics of the adsorption followed a pseudo-second-order model. The adsorption data of diatomite-supported/unsupported magnetite fit well with the Langmuir isotherm equation. The supported magnetite showed a better adsorption capacity per unit mass of magnetite than unsupported magnetite, and was more thermally stable than their unsupported counterparts. These results indicate that the diatomite-supported/unsupported magnetite nanoparticles are readily prepared, enabling promising applications for the removal of Cr(VI) from aqueous solution.

  • montmorillonite supported magnetite nanoparticles for the removal of hexavalent Chromium Cr vi from aqueous solutions
    Journal of Hazardous Materials, 2009
    Co-Authors: Peng Yuan, Mingde Fan, Jianxi Zhu, Dan Yang, Dong Liu, Aihua Yuan, Tianhu Chen
    Abstract:

    Montmorillonite-supported magnetite nanoparticles were prepared by co-precipitation and hydrosol method. The obtained materials were characterized by X-ray diffraction, nitrogen adsorption, elemental analysis, differential scanning calorimetry, transmission electron miCroscopy and X-ray photoelectron spectroscopy. The average sizes of the magnetite nanoparticles without and with montmorillonite support are around 25 and 15 nm, respectively. The montmorillonite-supported magnetite nanoparticles exist on the surface or inside the interparticle pores of clays, with better dispersing and less coaggregation than the ones without montmorillonite support. Batch tests were carried out to investigate the removal mechanism of hexavalent Chromium [Cr(VI)] by these synthesized magnetite nanoparticles. The Cr(VI) uptake was mainly governed by a physico-chemical process, which included an electrostatic attraction followed by a redox process in which Cr(VI) was reduced into trivalent Chromium. The adsorption of Cr(VI) was highly pH-dependent and the kinetics of the adsorption followed the Pseudo-second-order model. The adsorption data of unsupported and clay-supported magnetite nanoparticles fit well with the Langmuir and Freundlich isotherm equations. The montmorillonite-supported magnetite nanoparticles showed a much better adsorption capacity per unit mass of magnetite (15.3mg/g) than unsupported magnetite (10.6 mg/g), and were more thermally stable than their unsupported counterparts. These fundamental results demonstrate that the montmorillonite-supported magnetite nanoparticles are readily prepared, enabling promising applications for the removal of Cr(VI) from aqueous solution.

Marina Monteiro - One of the best experts on this subject based on the ideXlab platform.

Chunlei Jiao - One of the best experts on this subject based on the ideXlab platform.

  • preparation of activated carbon supported bead string structure nano zero valent iron in a polyethylene glycol aqueous solution and its efficient treatment of Cr vi wastewater
    Molecules, 2019
    Co-Authors: Chunlei Jiao, Xiao Tan, Aijun Lin, Wenjie Yang
    Abstract:

    Nanometer zero-valent iron (nZVI) has been widely used in the treatment of heavy metals such as hexavalent Chromium (Cr(VI)). A novel composite of bead string-structured nZVI on modified activated carbon (nZVI-MAC) is prepared here, using polyethylene glycol as the stable dispersant rather than traditional ethanol during the loading process. The miCrostructure characterization shows that nZVI particles are loaded on MAC with a bead string structure in large quantity and stably due to the addition of hydroxyl functional groups on the surface by polyethylene glycol. Experiments on the treatment of Cr(VI) in wastewater show that the reaction process requires only 20 min to achieve equilibrium. The removal rate of Cr(VI) with a low concentration (80-100 mg/L) is over 99% and the maximum saturation removal capacity is up to 66 mg/g. The system converts Cr(VI) to trivalent Chromium (Cr(III)) through an oxidation-reduction effect and forms an insoluble material with iron ions by coprecipitation, which is then adsorbed on the surface of the nZVI-MAC. The process conforms to the quasi-second order adsorption kinetics equation (mainly chemical adsorption process).