XAFS study of the coordination and local relaxation around Co (super 2+) , Zn (super 2+) , Pb (super 2+) , and Ba (super 2+) trace elements in calcite

Reeder, Richard J.; Lamble, G. M.; Northrup, Paul

doi:10.2138/am-1999-7-807

Cited by 158 publications

(118 citation statements)

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“…The fitting results for these shells are, therefore, less accurate than for the REE-O and REE-Ca shells. No evidence of a significant contribution from multiple scattering was found, although Reeder et al, (1999) noted a weak contribution in Co 2ϩ -and Zn 2ϩ -doped calcite.…”

Section: Resultsmentioning

confidence: 85%

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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Section: Resultsmentioning

confidence: 85%

EXAFS study of rare-earth element coordination in calcite

Elzinga

Reeder

Withers

et al. 2002

Geochimica et Cosmochimica Acta

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“…In this study the dominant mode of precipitation was nucleation in a system free of preexisting calcite. Reeder et al (1999) found that divalent trace metal ions both smaller and larger than calcium substitute into calcium sites within the calcite structure with varying degrees of local distortion. The smaller crystal sizes associated with nucleated calcite may more readily accommodate the distortion than larger crystals and permit more extensive substitution.…”

Section: Strontium Distribution Coefficientsmentioning

confidence: 99%

Strontium incorporation into calcite generated by bacterial ureolysis

Fujita

Redden

Ingram

et al. 2004

Geochimica et Cosmochimica Acta

214

141

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Abstract-Strontium incorporation into calcite generated by bacterial ureolysis was investigated as part of an assessment of a proposed remediation approach for 90 Sr contamination in groundwater. Urea hydrolysis produces ammonium and carbonate and elevates pH, resulting in the promotion of calcium carbonate precipitation. Urea hydrolysis by the bacterium Bacillus pasteurii in a medium designed to mimic the chemistry of the Snake River Plain Aquifer in Idaho resulted in a pH rise from 7.5 to 9.1. Measured average distribution coefficients (D EX ) for Sr in the calcite produced by ureolysis (0.5) were up to an order of magnitude higher than values reported in the literature for natural and synthetic calcites (0.02-0.4). They were also higher than values for calcite produced abiotically by ammonium carbonate addition (0.3). The precipitation of calcite in these experiments was verified by X-ray diffraction. Time-of-flight secondary ion mass spectrometry (ToF SIMS) depth profiling (up to 350 nm) suggested that the Sr was not merely sorbed on the surface, but was present at depth within the particles. X-ray absorption near edge spectra showed that Sr was present in the calcite samples as a solid solution. The extent of Sr incorporation appeared to be driven primarily by the overall rate of calcite precipitation, where faster precipitation was associated with greater Sr uptake into the solid. The presence of bacterial surfaces as potential nucleation sites in the ammonium carbonate precipitation treatment did not enhance overall precipitation or the Sr distribution coefficient. Because bacterial ureolysis can generate high rates of calcite precipitation, the application of this approach is promising for remediation of 90 Sr contamination in environments where calcite is stable over the long term.

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“…Tanaka et al (2004) and Tanaka and Kawabe (2006) estimated the abundance of REE in ancient seawater using REE analyses of marine limestone and partition coefficients experimentally determined be-XAFS has been used for the speciation of trace elements in various materials in terms of the oxidation state and local coordination structure of a given atom. Recently, the introduction of a multi-element Ge solid-state detector (SSD) into XAFS measurement improved sensitivities, which facilitated the application of XAFS to the speciation of trace elements in natural samples (e.g., Reeder et al, 1999;Takahashi et al, 2007). In a previous study (Tanaka et al, 2008), we found a peculiar white line of Y K-edge XANES spectrum for synthetic Y-doped calcite.…”

Section: Introductionmentioning

confidence: 99%

Determination of the host phase of rare earth elements in natural carbonate using X-ray absorption near-edge structure

2009

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The Y K-edge X-ray absorption near-edge structure (XANES) spectra of various materials were measured to investigate whether rare earth elements (REEs) are incorporated in carbonate phase or in other minor phases such as Fe-Mn oxides and phosphate within limestone. As reported in our previous work, a white line peak specific to synthetic Y-doped calcite is observed in the Y K-edge XANES spectrum. Natural limestone and dolomite samples show XANES spectra similar to that of the Y-doped calcite. The similarity of XANES spectra between natural and synthetic carbonates strongly indicates that Y is incorporated into the carbonate phase of natural samples, and that local coordination structures of Y in natural and synthetic carbonates are the same. Previous work reported a difference of local coordination structure between light and heavy REEs. Furthermore, we reported that local coordination structures of Y and Ho are similar. The results of this study therefore demonstrate that the Y K-edge XANES spectrum can be used as a fingerprint to trace heavy REEs including Y in natural carbonate. The information that REEs are not distributed to other minor phases is an important basis for the use of limestone to estimate REE pattern of ancient seawater coupled with the REE partition coefficient data between seawater and carbonate.

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XAFS study of the coordination and local relaxation around Co (super 2+) , Zn (super 2+) , Pb (super 2+) , and Ba (super 2+) trace elements in calcite

Cited by 158 publications

References 0 publications

EXAFS study of rare-earth element coordination in calcite

EXAFS study of rare-earth element coordination in calcite

Strontium incorporation into calcite generated by bacterial ureolysis

Determination of the host phase of rare earth elements in natural carbonate using X-ray absorption near-edge structure

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