Structural trends in the lanthanide trihydroxides

Beall, Gary W.; Milligan, W. O.; Wolcott, Herbert A.

doi:10.1016/0022-1902(77)80434-x

Cited by 119 publications

(60 citation statements)

References 20 publications

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“…6 which shows the XANES spectra of La LI edge of the untreated montmorillonites and those heated at 300 and 700~ (the spectrum of La203 has been included for comparison). Firstly, almost no changes are seen when the sample is heated at 300~ whereas significant changes are detected after heating at 700~ Secondly, compared with data in the literature (Larson etal., 1991), the spectra of the untreated and 300~ heated samples resemble more the spectra of La(OH)3, with a nine coordinated polyhedron of oxygen ions around La(III), forming a tricapped trigonal prism (Beall et al, 1977). The local structure of interlayer lanthanide ions ion-exchanged into vermiculite clay has been determined, the first coordination shell being very similar to that corresponding to aqueous nitrate solutions for the lighter lanthanide ions (Jones et al, 1991).…”

Section: X-ray Absorption Spectroscopies (Xanes Exafs)mentioning

confidence: 78%

Local environment of lanthanum ions in montmorillonite upon heating

et al. 1992

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Structural differences which occur on heating La-montmorillonite have been studied and compared with those for montmorillonite saturated with Na(I) and Li(I). Rehydration experiments show that La-montmorillonite swells after preheating up to 500~ However, FT-IR spectra suggest partial migration of the La(III) cations from the interlamellar region to the structural sheets and(or) deprotonation of hydrated La(III) cations, followed by migration of the resulting protons to vacant octahedral sites. Additional measurements of X-ray absorption spectra (EXAFS, XANES) and heating to 700~ suggest that interlamellar hydrated La(III) partially deprotonates producing polyoxocations.Smectites and their pillared derivatives made with trivalent lanthanide cations have recently attracted much attention as catalysts (Shabtai et al., 1984). In addition, La simulates Am in studies on the interaction of the latter with clay minerals. Determination of the interaction mechanism upon heating is important for the design of safe repositories for high-level nuclear wastes. Their storage in continental or marine repositories usually involves claybearing packing materials that act as a barrier.The aim of this paper is to study significant structural differences upon heating Na-, Liand La-montmorillonites. It has already been observed that lanthanide-montmorillonites show a decrease in cation exchange capacity (CEC) upon heating at temperatures above 160~ (Mozas et al., 1980). Miller et al. (1982 examined the effects of temperature on the sorption of Eu(III), Ho(III) and Yb(III) on an Upton, Wyoming montmorillonite and claimed that hydrolysis and migration into octahedral sites are likely mechanisms for 4lion fixation. Results already obtained in our laboratory contradict the migration mechanism on heating at 300~ (Trillo et al., 1990).The nature of the materials used demands a variety of experimental approaches and X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FT-IR), nitrogen adsorption isotherms and X-ray absorption spectroscopy techniques such as extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) have been used. EXPERIMENTAL MaterialsThe <2/~m fraction of a Trancos smectite mineral from Gador, Almeria, was saturated with Na using a 1 M solution of NaCI; chemical analysis, as described elsewhere (Trillo 9 1992 The Mineralogical Society

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Section: X-ray Absorption Spectroscopies (Xanes Exafs)mentioning

confidence: 78%

Local environment of lanthanum ions in montmorillonite upon heating

et al. 1992

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“…7 shows a plot of DE versus 1/d 2 for La (aq), La(OH) 3 , and La 2 O 3 and a line representing the results from a linear least-squares fit. Although the La-O bond lengths for La(OH) 3 and La 2 O 3 are well known (Table 5: Beall et al, 1977;Hirosaki et al, 2003), there has been much debate over the bond lengths in La(aq). The data for La(aq) in Table 5 and Fig.…”

Section: X-ray Absorption Fine-structure Spectroscopy Resultsmentioning

confidence: 99%

Cation field strength effects on high pressure aluminosilicate glass structure: Multinuclear NMR and La XAFS results

Kelsey

Stebbins

Singer

et al. 2009

Geochimica et Cosmochimica Acta

131

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“…In the Gd, Dy, Ho, and Yb compounds, a single eightfold-coordinated REE site occurs with exclusively monodentate CO 3 linkage. Beall et al, (1977) documented more subtle coordination differences with REE size in the lanthanide trihydroxide isostructural series REE(OH) 3 . The metal site is ninefold coordinated (a tricapped trigonal prism) with two distinct REE-O bond distances, apical and equatorial.…”

Section: Discussionmentioning

confidence: 99%

EXAFS study of rare-earth element coordination in calcite

Elzinga

Reeder

Withers

et al. 2002

Geochimica et Cosmochimica Acta

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Abstract-Extended X-ray absorption fine-structure (EXAFS) spectroscopy is used to characterize the local coordination of selected rare-earth elements (Nd 3ϩ , Sm 3ϩ , Dy 3ϩ , Yb 3ϩ ) coprecipitated with calcite in minor concentrations from room-temperature aqueous solutions. Fitting results confirm substitution in the Ca site, but first-shell Nd-O and Sm-O distances are longer than the Ca-O distance in calcite and longer than what is consistent with ionic radii sums for sixfold coordination in the octahedral Ca site. In contrast, first-shell Dy-O and Yb-O distances are shorter than the Ca-O distance and are consistent with ionic radii sums for sixfold coordination. Comparison of Nd-O and Sm-O bond lengths with those in lanthanide sesquioxides and with ionic radii trends across the lanthanide series suggests that Nd 3ϩ and Sm 3ϩ have sevenfold coordination in a modified Ca site in calcite. This would require some disruption of the local structure, with an expected decrease in stability, and possibly a different charge compensation mechanism between Nd and Sm vs. Yb and Dy. A possible explanation for the increased coordination for the larger rare-earth elements involves bidentate ligation from a CO 3 group. Because trivalent actinides such as Am 3ϩ and Cm 3ϩ have ionic radii similar to Nd 3ϩ , their incorporation in calcite may result in a similar defect structure.

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Structural trends in the lanthanide trihydroxides

Cited by 119 publications

References 20 publications

Local environment of lanthanum ions in montmorillonite upon heating

Local environment of lanthanum ions in montmorillonite upon heating

Cation field strength effects on high pressure aluminosilicate glass structure: Multinuclear NMR and La XAFS results

EXAFS study of rare-earth element coordination in calcite

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