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

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

Nov 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001gecoa..65.4155s&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 65, Issue 22, pp.4155-4170

Computer Science

11

Scientific paper

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 M, and ionic strength of 0.3 M (NaNO 3 salt) by kinetics experiments and polarized extended X-ray absorption fine structure (P-EXAFS) spectroscopy. At low [Si] aq (~30 to 60 M), 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 M), 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.

Affiliated with

Also associated with

No associations

Rating

Sorption of metal ions on clay minerals. III. Nucleation and epitaxial growth of Zn phyllosilicate on the edges of hectorite does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Sorption of metal ions on clay minerals. III. Nucleation and epitaxial growth of Zn phyllosilicate on the edges of hectorite, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sorption of metal ions on clay minerals. III. Nucleation and epitaxial growth of Zn phyllosilicate on the edges of hectorite will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1551879