Other
Scientific paper
Aug 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993gecoa..57.3885l&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 57, Issue 16, pp.3885-3894
Other
Scientific paper
Chabazite, vermiculite, montmorillonite, hectorite, and kaolinite were used to remove Pb, through ion exchange, from 0.01 M aqueous Pb(NO 3 ) 2 solutions. These minerals contained 27 (Nachabazite), 16, 9, 9, and 0.4 wt% of Pb, respectively, after equilibration with the solutions. Ion exchange reached equilibrium within 24 h for Na-chabazite and vermiculite, but in less than 5 min for montmorillonite and hectorite. Na-chabazite took up more Pb than natural (Ca, Na)-chabazite (7 wt% Pb), whereas no such difference was observed in different cation forms of the clay minerals. Calcite impurities, associated with the clay minerals, effectively removed Pb from the aqueous solutions by the precipitation of cerussite (PbCO 3 ). 29 Si, 27 Al, and 23 Na magic angle spinning (MAS) nuclear magnetic resonance (NMR), 23 Na double rotation (DOR) NMR, and 23 Na variable-temperature MAS NMR were used to study the ion exchange mechanisms. In Na-chabazite, cations in all three possible sites take part in the fast chemical exchange. The chemical exchange passes from the fast exchange regime to the slow regime at -80 to -100°C. One site contains a relatively low population of exchangeable cations. The other two more shielded sites contain most of the exchangeable cation. The exchangeable cations in chabazite and vermiculite were found to be close to the SiO 4 and AlO 4 tetrahedra, while those in the other clay minerals were more distant. Two sites (or groups of sites) for exchangeable cations were observed in hectorite. Lead tended to occupy the one which corresponds to the -8 ppm peak on the 23 Na MAS NMR spectrum. The behaviour of the exchangeable cations in the interlayer sites was similar in all the clay minerals studied.
Liang Jian-Jie
Sherriff Barbara L.
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