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Issue 41, 2011
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Sorption Speciation of Nickel(II) onto Ca-Montmorillonite: Batch, EXAFS Techniques and Modeling

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The sorption speciation of Ni(II) on Ca-montmorillonite was evaluated using a combination of batch experiments, extended X-ray absorption fine structure (EXAFS) spectroscopy and modeling. The pH and temperature at the aqueous-montmorillonite interface affects both the extent of Ni(II) sorption as well as the local atomic structure of the adsorbed Ni(II) ions. At 0.001 mol L−1 Ca(NO3)2 and low pH, the study reveals that the majority of Ni(II) is adsorbed in the interlayers of Ca-montmorillonite coordinated by six water molecules in an octahedron as an outer-sphere complex. At higher pH, inner-sphere surface complexes are formed. The Ni–Si/Al distances (RNiAl = 3.00 Å, RNi–Si1 = 3.10 Å and RNi–Si2 = 3.26 Å) determined by EXAFS confirm the formation of mononuclear complexes located at the edges of Ca-montmorillonite platelets at pH 7.5 and 8.5. At pH 10.0, the Ni–Ni/Si distances (RNiNi = 3.07 Å and RNiSi = 3.26 Å) indicates the formation of Ni-phyllosilicate precipitates. A rise in temperature promotes inner-sphere complexation, which in turn leads to an increase in Ni(II) sorption on Ca-montmorillonite. Sorption edges are fitted excellently by surface complexation model (SCM) with the aid of surface species determined from EXAFS spectroscopy.

Graphical abstract: Sorption Speciation of Nickel(ii) onto Ca-Montmorillonite: Batch, EXAFS Techniques and Modeling

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The article was received on 22 Apr 2011, accepted on 03 Aug 2011 and first published on 14 Sep 2011

Article type: Paper
DOI: 10.1039/C1DT10740B
Citation: Dalton Trans., 2011,40, 10953-10960
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    Sorption Speciation of Nickel(II) onto Ca-Montmorillonite: Batch, EXAFS Techniques and Modeling

    X. Tan, J. Hu, G. Montavon and X. Wang, Dalton Trans., 2011, 40, 10953
    DOI: 10.1039/C1DT10740B

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