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Thermodynamic modeling of poorly complexing metals in concentrated electrolyte solutions: an X-ray absorption and UV-Vis spectroscopic study of Ni(II) in the NiCl2-MgCl2-H2O system.

Zhang N, Brugger J, Etschmann B, Ngothai Y, Zeng D - PLoS ONE (2015)

Bottom Line: Both methods confirm that the Ni(II) aqua ion (with six coordinated water molecules at RNi-O = 2.07(2) Å) is the dominant species over the whole NiCl2 concentration range.At high Cl:Ni ratio in the NiCl2-MgCl2-H2O solutions, small amounts of [NiCl2]0 are also present.We developed a speciation-based mixed-solvent electrolyte (MSE) model to describe activity-composition relationships in NiCl2-MgCl2-H2O solutions, and at the same time predict Ni(II) speciation that is consistent with our XAS and UV-Vis data and with existing literature data up to the solubility limit, resolving a long-standing uncertainty about the role of chloride complexing in this system.

View Article: PubMed Central - PubMed

Affiliation: College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, P. R. China; School of Chemical Engineering, The University of Adelaide, Adelaide 5000, South Australia, Australia; School of Geosciences, Monash University, Clayton 3800, Victoria, Australia.

ABSTRACT
Knowledge of the structure and speciation of aqueous Ni(II)-chloride complexes is important for understanding Ni behavior in hydrometallurgical extraction. The effect of concentration on the first-shell structure of Ni(II) in aqueous NiCl2 and NiCl2-MgCl2 solutions was investigated by Ni K edge X-ray absorption (XAS) and UV-Vis spectroscopy at ambient conditions. Both techniques show that no large structural change (e.g., transition from octahedral to tetrahedral-like configuration) occurs. Both methods confirm that the Ni(II) aqua ion (with six coordinated water molecules at RNi-O = 2.07(2) Å) is the dominant species over the whole NiCl2 concentration range. However, XANES, EXAFS and UV-Vis data show subtle changes at high salinity (> 2 mol∙kg(-1) NiCl2), which are consistent with the formation of small amounts of the NiCl+ complex (up to 0.44(23) Cl at a Ni-Cl distance of 2.35(2) Å in 5.05 mol∙kg(-1) NiCl2) in the pure NiCl2 solutions. At high Cl:Ni ratio in the NiCl2-MgCl2-H2O solutions, small amounts of [NiCl2]0 are also present. We developed a speciation-based mixed-solvent electrolyte (MSE) model to describe activity-composition relationships in NiCl2-MgCl2-H2O solutions, and at the same time predict Ni(II) speciation that is consistent with our XAS and UV-Vis data and with existing literature data up to the solubility limit, resolving a long-standing uncertainty about the role of chloride complexing in this system.

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Normalized Ni K-edge XANES spectra for the two solid compounds.
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pone.0119805.g001: Normalized Ni K-edge XANES spectra for the two solid compounds.

Mentions: Fig 1 shows the XANES spectra (Raw spectral data was collected in S1–S4 Tables) for the NiSO4∙6H2O(s) and NiCl2∙6H2O(s) reference compounds, which contain octahedral [Ni(H2O)6] [32] and [NiCl2(H2O)4] moieties [33], respectively. The main spectral differences between the two spectra are: (i) presence of a shoulder at ~8340 eV attributed to the 1s to 4p transition [31] in NiCl2∙6H2O(s) (feature A); (ii) a lowering of the intensity of the white line (feature B) and shift of its position by ~ -1.2 eV in NiCl2∙6H2O(s) relative to NiSO4∙6H2O(s); as well as (iii) reduced intensity of the oscillation in the 8360 to 8420 eV region in NiCl2∙6H2O(s) (features C and D in Fig 1).


Thermodynamic modeling of poorly complexing metals in concentrated electrolyte solutions: an X-ray absorption and UV-Vis spectroscopic study of Ni(II) in the NiCl2-MgCl2-H2O system.

Zhang N, Brugger J, Etschmann B, Ngothai Y, Zeng D - PLoS ONE (2015)

Normalized Ni K-edge XANES spectra for the two solid compounds.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4401718&req=5

pone.0119805.g001: Normalized Ni K-edge XANES spectra for the two solid compounds.
Mentions: Fig 1 shows the XANES spectra (Raw spectral data was collected in S1–S4 Tables) for the NiSO4∙6H2O(s) and NiCl2∙6H2O(s) reference compounds, which contain octahedral [Ni(H2O)6] [32] and [NiCl2(H2O)4] moieties [33], respectively. The main spectral differences between the two spectra are: (i) presence of a shoulder at ~8340 eV attributed to the 1s to 4p transition [31] in NiCl2∙6H2O(s) (feature A); (ii) a lowering of the intensity of the white line (feature B) and shift of its position by ~ -1.2 eV in NiCl2∙6H2O(s) relative to NiSO4∙6H2O(s); as well as (iii) reduced intensity of the oscillation in the 8360 to 8420 eV region in NiCl2∙6H2O(s) (features C and D in Fig 1).

Bottom Line: Both methods confirm that the Ni(II) aqua ion (with six coordinated water molecules at RNi-O = 2.07(2) Å) is the dominant species over the whole NiCl2 concentration range.At high Cl:Ni ratio in the NiCl2-MgCl2-H2O solutions, small amounts of [NiCl2]0 are also present.We developed a speciation-based mixed-solvent electrolyte (MSE) model to describe activity-composition relationships in NiCl2-MgCl2-H2O solutions, and at the same time predict Ni(II) speciation that is consistent with our XAS and UV-Vis data and with existing literature data up to the solubility limit, resolving a long-standing uncertainty about the role of chloride complexing in this system.

View Article: PubMed Central - PubMed

Affiliation: College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, P. R. China; School of Chemical Engineering, The University of Adelaide, Adelaide 5000, South Australia, Australia; School of Geosciences, Monash University, Clayton 3800, Victoria, Australia.

ABSTRACT
Knowledge of the structure and speciation of aqueous Ni(II)-chloride complexes is important for understanding Ni behavior in hydrometallurgical extraction. The effect of concentration on the first-shell structure of Ni(II) in aqueous NiCl2 and NiCl2-MgCl2 solutions was investigated by Ni K edge X-ray absorption (XAS) and UV-Vis spectroscopy at ambient conditions. Both techniques show that no large structural change (e.g., transition from octahedral to tetrahedral-like configuration) occurs. Both methods confirm that the Ni(II) aqua ion (with six coordinated water molecules at RNi-O = 2.07(2) Å) is the dominant species over the whole NiCl2 concentration range. However, XANES, EXAFS and UV-Vis data show subtle changes at high salinity (> 2 mol∙kg(-1) NiCl2), which are consistent with the formation of small amounts of the NiCl+ complex (up to 0.44(23) Cl at a Ni-Cl distance of 2.35(2) Å in 5.05 mol∙kg(-1) NiCl2) in the pure NiCl2 solutions. At high Cl:Ni ratio in the NiCl2-MgCl2-H2O solutions, small amounts of [NiCl2]0 are also present. We developed a speciation-based mixed-solvent electrolyte (MSE) model to describe activity-composition relationships in NiCl2-MgCl2-H2O solutions, and at the same time predict Ni(II) speciation that is consistent with our XAS and UV-Vis data and with existing literature data up to the solubility limit, resolving a long-standing uncertainty about the role of chloride complexing in this system.

Show MeSH
Related in: MedlinePlus