leaching kinetics of cr vi phases in the matrices of
Progress in Organic Coatings
the known toxicity of Cr(VI) many other alternatives are being studied 5–9 among others with the help of recently developed influence final leaching kinetics effect of moisture absorption process from top to bottom (y axis) is not incorporated. Phases in the response against corrosion in a
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Immobilization of Cr(VI) by sulphate green rust and
Aug 14 2020 · Chromate Cr(VI) contamination in soil and groundwater poses serious threat to living organisms and environmental health worldwide. Sulphate green rust (GRSO4) a naturally occurring mixed-valent iron layered double hydroxide has shown to be highly effective in the reduction of Cr(VI) to poorly soluble Cr(III) giving promise for its use as reactant for in situ remedial applications.
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(PDF) Leaching Mechanisms of Cr(VI) from Chromite Ore
Batch leaching tests qualitative and quantitative x-ray powder diffraction (XRPD) analyses and geochemical modeling were used to investigate the leaching mechanisms of Cr (VI) from chromite ore
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Kinetics and Mechanism of Metal Retention/Release in
Dec 29 2000 · The major objectives of the proposed study were to 1.) determine the leaching characteristics of hexavalent chromium Cr(VI) from contaminated sediments collected from 100 Area spill sites 2.) elucidate possible Cr(VI) mineral and/or chemical associations that may be responsible for Cr(VI) retention in the Hanford Site 100 Areas through the
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Oxidative Leaching Kinetics of Vanadium from the Vanadium
Oxidative-alkaline leaching of vanadium from vanadium-chromium-reducing residues with K 2 Cr 2 O 7 was investigated in this paper. The effects of processing parameters including dosage of NaOH dosage of K 2 Cr 2 O 7 reaction time and reaction temperature on the leaching efficiency of vanadium were studied.The results simulated by response surface methodology indicated that vanadium leaching
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Solid phase extraction of chromium (VI) from aqueous
Feb 01 2008 · The stability of the column was tested using 10 micro g Cr (VI) maintaining a sample volume of 100 mL. The adsorbed Cr (VI)-DPC complex was desorbed using 15 mL of 4.5 mol dm.sup.-3 sulphuric acid. The column was stable for five cycles and could be used with good precision and quantitative recovery (>95 ) for at least five cycles.
Chat OnlineThe Chemistry of Sludge Washing and Caustic Leaching
Chromium in the sludges has been shown to exist in both the 3 and 6 oxidation states. The relative concentrations of Cr(III) to Cr(VI) can vary greatly. X-ray spectroscopy revealed unsurprisingly that the Cr(V1) was readily removed. Conclusions based on thermodynamic modeling suggest that caustic
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The sulfuric acid leaching kinetics of South African chromite was investigated. The negative influence of a solid product layer constituted of a silicon-rich phase and chromium-rich sulfate was eliminated by crushing the chromite and by selecting proper leaching conditions. The dimensionless change in specific surface area and the conversion rate of the chromite were observed to exhibit a
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Progress in Organic Coatings
the known toxicity of Cr(VI) many other alternatives are being studied 5–9 among others with the help of recently developed influence final leaching kinetics effect of moisture absorption process from top to bottom (y axis) is not incorporated. Phases in the response against corrosion in a
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Continuous leaching-ICP-MS for the study of metal
phases. Ni Co and Zn are found to be associated with Fe/Mn phase and Cd Cr Cu is found to be less associated with Ca phase. Significant readsorption and redistribution happens for Ca Mg Mn Fe Ni Zn Co Cu and Al at different phases and it is quite clear at 1 HNO3. Key wards Leaching speciation association sorption phase pH ICP-MS
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Continuous leaching-ICP-MS for the study of metal
phases. Ni Co and Zn are found to be associated with Fe/Mn phase and Cd Cr Cu is found to be less associated with Ca phase. Significant readsorption and redistribution happens for Ca Mg Mn Fe Ni Zn Co Cu and Al at different phases and it is quite clear at 1 HNO3. Key wards Leaching speciation association sorption phase pH ICP-MS
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Continuous leaching-ICP-MS for the study of metal
phases. Ni Co and Zn are found to be associated with Fe/Mn phase and Cd Cr Cu is found to be less associated with Ca phase. Significant readsorption and redistribution happens for Ca Mg Mn Fe Ni Zn Co Cu and Al at different phases and it is quite clear at 1 HNO3. Key wards Leaching speciation association sorption phase pH ICP-MS
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Formation Mechanisms and Leachability of Hexavalent
Concentrations of Cr (VI) in the leachates (as in the TRGS 613 procedure) exceeded the European permissible limit. During the leaching tests in an acid condition Cr (VI) was reduced by Fe²⁺ which
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Oxidative Leaching Kinetics of Vanadium from the Vanadium
Oxidative-alkaline leaching of vanadium from vanadium-chromium-reducing residues with K 2 Cr 2 O 7 was investigated in this paper. The effects of processing parameters including dosage of NaOH dosage of K 2 Cr 2 O 7 reaction time and reaction temperature on the leaching efficiency of vanadium were studied.The results simulated by response surface methodology indicated that vanadium leaching
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Leaching kinetics of Cr(VI) phases in the matrices of
Dec 01 2020 · XRD SEM-EDS and leaching tests were done to study the influence of MS content on the formation inhibition and leaching kinetics of Cr (VI) phases. The formation of silicate phases is more favorable over Cr (VI) phases at higher temperatures and lower CaO/SiO 2 ratios.
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The Chemistry of Sludge Washing and Caustic Leaching
Chromium in the sludges has been shown to exist in both the 3 and 6 oxidation states. The relative concentrations of Cr(III) to Cr(VI) can vary greatly. X-ray spectroscopy revealed unsurprisingly that the Cr(V1) was readily removed. Conclusions based on thermodynamic modeling suggest that caustic
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Metals Special Issue Leaching Kinetics of Valuable Metals
It has been shown that increasing the content of S in the concentrate from 8.22 to 22.44 leads to an average of 45 increase in the iron recovery across the entire range temperatures and concentrations of HNO 3 per one hour of leaching. The leaching kinetics of the studied types of concentrates correlates well with the new shrinking core model
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Modelling the leaching of Pb Cd As and Cr from
A leaching model was developed using the United States Geological Survey public domain PHREEQC geochemical package to simulate the leaching of Pb Cd As and Cr from cementitious wastes. The model utilises both kinetic terms and equilibrium thermodynamics of key
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Kinetics of steel slag leaching Batch tests and modeling
Feb 01 2011 · Cr retention can be linked to the formation of this secondary phase that tends to incorporate Cr(III) ions in a very stable form. In particular no oxidation of Cr(III) to Cr(VI) occurred in the solid matrix during leaching.
Chat OnlineLeaching of hexavalent chromium from young chromite ore
Mar 18 2020 · Flow interruptions for 10 100 and 1 000 h had little effect on Cr(VI) concentrations in the leachate suggesting that Cr(VI) leaching was not limited by slow release kinetics. Calcium aluminum chromium oxide hydrates (CAC) and highly soluble phases such as Na 2 CrO 4 may play a role in controlling Cr(VI) concentration in the leachates.
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The kinetic analysis of the photoreduction showed that the removal of Cr(VI) Photocatalyst Magnetic beads satisfactory obeyed the pseudo first-order kinetic according to the Langmuir–Hinshelwood (L–H) model Magnetic nanoparticles and the absorption of Cr(VI) on the magnetic beads surfaces was the controlling step in the entire reduc
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(PDF) Leaching kinetics of acid-soluble Cr(VI) from
Therefore the leaching process of Cr(VI) in the refractory castable matrices was controlled by the diffusion process other than the chemical reaction. and leaching kinetics of Cr(VI) phases
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Hydrogarnet A Host Phase for Cr(VI) in Chromite Ore
For understanding both the environmental behavior and developing remediation treatments for chromium ore processing residue (COPR) it is important to identify all the potentially soluble sources of Cr(VI). Hydrogarnet has been identified as a major phase in COPR and it has been previously speculated that it has a capacity to host Cr(VI). Here we provide direct evidence of this capacity by
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Leaching of Valuable Elements from the Waste Chromite Ore
Further study reveals that in the hydrothermal conditions SiO2-3 ions not only act as the anion exchange agent to delaminate layered phases in COPR like hydrotalcites to release the encapsulated Cr(VI) but also help to oxidize Cr(III) in COPR to sol. Cr(VI) both of which distinctively increased the leaching of chromium from COPR.
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Kinetics and pH Dependence of Chromium(VI) Reduction by
Iron(II) is one of the most important reductants of chromium(VI) a severe toxic contaminant of natural waters sediments and soils. We studied the reaction kinetics between pH 2 and pH 7.2 with UV−VIS and multicomponent fitting a method without the interference of added reagents. The reaction rate was minimal around pH 4. A rate increase with decreasing pH below 4 is documented in the
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Solid phase extraction of chromium (VI) from aqueous
Feb 01 2008 · The stability of the column was tested using 10 micro g Cr (VI) maintaining a sample volume of 100 mL. The adsorbed Cr (VI)-DPC complex was desorbed using 15 mL of 4.5 mol dm.sup.-3 sulphuric acid. The column was stable for five cycles and could be used with good precision and quantitative recovery (>95 ) for at least five cycles.
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Continuous leaching-ICP-MS for the study of metal
phases. Ni Co and Zn are found to be associated with Fe/Mn phase and Cd Cr Cu is found to be less associated with Ca phase. Significant readsorption and redistribution happens for Ca Mg Mn Fe Ni Zn Co Cu and Al at different phases and it is quite clear at 1 HNO3. Key wards Leaching speciation association sorption phase pH ICP-MS
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Kinetics of chromium(III) oxidation to chromium(VI) by
Cr(VI) Formation via Oxyhalide-Induced Oxidative Dissolution of Chromium Oxide/Hydroxide in Aqueous and Frozen Solution. Leaching Behaviors of Chromium(III) and Ammonium-Nitrogen from a Tannery Sludge in North China Comparison of Batch and Column Investigations. Kinetic Modeling of Cr(VI) Reduction by nZVI in Soil The Influence of
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Leaching of Valuable Elements from the Waste Chromite Ore
Further study reveals that in the hydrothermal conditions SiO2-3 ions not only act as the anion exchange agent to delaminate layered phases in COPR like hydrotalcites to release the encapsulated Cr(VI) but also help to oxidize Cr(III) in COPR to sol. Cr(VI) both of which distinctively increased the leaching of chromium from COPR.
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Comparative Sorption and Mobility of Cr(III) and Cr(VI
Nov 15 2013 · The sorption of chromium (Cr) species to soil has become the focus of research as it dictates the bioavailability and also the magnitude of toxicity of Cr. The sorption of two environmentally important Cr species Cr(III) and Cr(VI) was examined using batch sorption and the data were fitted to Langmuir and Freundlich adsorption isotherms. The effects of soil properties such as pH CEC
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