HAL will be down for maintenance from Friday, June 10 at 4pm through Monday, June 13 at 9am. More information
Skip to Main content Skip to Navigation
Journal articles

Sorption of metal ions on clay minerals. III. Nucleation and epitaxial growth of Zn phyllosilicate on the edges of hectorite

Abstract : The impact of dissolved Si ([Si]aq) on Zn uptake in dilute suspensions (0.65 g/L) of hectorite was investigated at pH 7.30, a total Zn concentration (TotZn) of 520 μM, and ionic strength of 0.3 M (NaNO3 salt) by kinetics experiments and polarized extended X-ray absorption fine structure (P-EXAFS) spectroscopy.

At low [Si]aq (∼30 to 60 μM), 5.8% of TotZn was adsorbed within the first 3 h of reaction. The sorption rate was lower afterwards, and Zn uptake amounted to 14.6% of TotZn after 168 h of reaction. These rates are consistent with Zn sorption on pH-dependent edge sites of hectorite platelets. At high [Si]aq (∼530 μM), a higher initial sorption rate was observed, the fraction of Zn removed amounting to 15.2% of TotZn at t = 3 h and 90.7% at t = 120 h. After 9 h of reaction time, Si uptake also occurred; the Si/Zn uptake ratio (1.09 ± 0.08) was between those of TO (∼0.67) and TOT (∼1.33) trioctahedral phyllosilicates, which suggests the neoformation of a Zn phyllosilicate. In the absence of hectorite, neither Zn nor Si were removed from solution, even at high [Si]aq, indicating that Zn uptake occurred by sorption on hectorite surface.

Comparison of spectra for sorption samples and Zn references indicated that sorbed Zn was located in a clay-like structural environment. The angular dependence observed for all P-EXAFS spectra demonstrated that Zn cations are structurally attached to the edges of hectorite platelets. The size and structure of these Zn surface complexes varied with [Si]aq and reaction time. At low [Si]aq and after a long reaction time (t = 96 h), Zn was surrounded by in-plane 1.7 ± 0.6 Zn and 1.4 ± 0.3 Mg at 3.08 Å, and by out-of-plane 0.6 ± 1.1 Si at 3.28 Å. These results point to predominant formation of small polymers containing on average two to three Zn cations and located in structural continuity with the hectorite octahedral sheet. At high [Si]aq, higher numbers of Zn and Si and lower numbers of Mg neighbors were detected at t = 9 h; at t = 120 h, Zn was surrounded by in-plane 6.0 ± 0.4 Zn at 3.10 Å and by out-of-plane 3.6 ± 0.4 Si at 3.27 Å as in a Zn phyllosilicate. These results document for the first time the nucleation and epitaxial growth at ambient temperature of Zn phyllosilicate at the edges of smectite minerals under controlled laboratory conditions.

Document type :
Journal articles
Complete list of metadata

https://hal-insu.archives-ouvertes.fr/insu-03606658
Contributor : Nathalie Pothier Connect in order to contact the contributor
Submitted on : Saturday, March 12, 2022 - 7:22:02 AM
Last modification on : Sunday, March 13, 2022 - 3:00:23 AM

Links full text

Identifiers

Collections

Citation

Michel L. Schlegel, Alain Manceau, Laurent Charlet, Daniel Chateigner, Jean-Louis Hazemann. Sorption of metal ions on clay minerals. III. Nucleation and epitaxial growth of Zn phyllosilicate on the edges of hectorite. GEOCHIMICA ET COSMOCHIMICA ACTA, 2001, 65, pp.4155-4170. ⟨10.1016/S0016-7037(01)00700-1⟩. ⟨insu-03606658⟩

Share

Metrics

Record views

7