Reaction sequence of nickel(II) with kaolinite: Mineral dissolution and surface complexation and precipitation
- Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Crop and Soil Environmental Sciences
- Univ. of Idaho, Moscow, ID (United States). Soil Science Div.
The dissolution kinetics of Ni(II) sorbed to kaolinite at pH 7 were examined as a function of initial aqueous Ni(II) concentrations; the local molecular structure of the Ni surface complexes were determined using extended x-ray absorption fine structure (EXAFS) spectroscopy. The dissolution of kaolinite was nonstoichiometric with a preferential release of Si over Al. The dissolution rate, R{sub Si}, increased with an increase in the aqueous concentration of Ni. A rate law was developed representing a fractional-order dissolution reaction with respect to the surface concentration of Ni. Absorption spectra were obtained from kaolinite samples washed with 0.10 M NaNO{sub 3} adjusted to pH 3.4 to remove amorphous Al-hydroxide surface deposits or adsorbed Al and from kaolinite that was untreated. For all samples, EXAFS results revealed the presence of multinuclear Ni surface complexes wit h a similar, but not identical, local structural environment to pure crystalline Ni(OH){sub 2}. The Ni-Ni bond distances were shorter (3.06--3.11 {angstrom}) than in Ni(OH){sub 2}(s) (3.13 {angstrom}) and increased with an increase in surface coverage. Additionally, Al was present in all but the highest surface coverage as a second neighbor backscatterer. At the lower surface coverages, Al is present at 2.69 {angstrom}, indicating the formation of a bidentate Ni surface complex. With increased surface coverage, the d(Ni-Al) increases to 2.96 {angstrom}, which is believed to result from a Ni,Al-hydroxide precipitate. No significant structural differences were found between kaolinite pretreatments. Based on these results, a hypothesized mechanism for Ni sorption on kaolinite is proposed.
- Sponsoring Organization:
- National Science Foundation, Washington, DC (United States); Petroleum Research Fund (United States); USDOE, Washington, DC (United States)
- OSTI ID:
- 290177
- Journal Information:
- Soil Science Society of America Journal, Vol. 62, Issue 5; Other Information: PBD: Sep-Oct 1998
- Country of Publication:
- United States
- Language:
- English
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