Lead Sorption at the Calcite-Water Interface: Synchrotron X-Ray Standing Wave and X-Ray Reflectivity Studies

Journal Article · Thu Jan 02 00:00:00 EST 1997 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(96)00326-2· OSTI ID:1578060

Sturchio, Neil C. ^[1]; Chiarello, Ronald P. ^[1]; Cheng, Likwan ^[1]; Lyman, Paul F. ^[2]; Bedzyk, Michael J. ^[1]; Qian, Yonglin ^[1]; You, Hoydoo ^[1]; Yee, Dennis ^[3]; Geissbuhler, Phillip ^[4]; Sorensen, Larry B. ^[3]; Liang, Yong ^[5]; Baer, Donald R.  ^[5]

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1. Argonne National Laboratory
2. Northwestern University
3. University of Washington
4. Washington University
5. BATTELLE (PACIFIC NW LAB)

By combining synchrotron X-ray standing wave (XSW) measurements with synchrotron X-ray reflectivity measurements, we have determined: (1) the precise three-dimensional location within the calcite unit cell of submonolayer Pb ions adsorbed at the calcite (104) surface from dilute aqueous solutions, and (2) the precise one-dimensional location of these unit cells relative to the calcite surface. Our XSW measurements, using three separate calcite Bragg reflections for triangulation, show that most adsorbed Pb ions occupy Ca sites in the calcite lattice with an ordered coverage of 0.05 equivalent monolayers, while the remaining Pb ions are disordered with a coverage of 0.03 equivalent monolayers. Our X-ray reflectivity measurements show that the ordered Pb ions occur primarily (>70%) in the surface atomic layer of calcite. Atomic force microscopy (AFM) was used to characterize the topography of the calcite (104) surface under conditions similar to the X-ray experiments. The quantitative morphological information obtained by AFM was used to develop realistic models of the calcite surface. The calculated X-ray reflectivities for these model surfaces were compared with the measured X-ray reflectivities. The new combined X-ray method that we have developed can be used to determine the atomic-scale structure of other metals adsorbed at mineral-water interfaces. Such high-resolution structural determinations are essential before detailed conceptual and theoretical models can be further developed to understand and predict the behavior of dissolved metals in mineral-water systems.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1578060
• Report Number(s): PNNL-SA-28609
• Journal Information: Geochimica et Cosmochimica Acta, Vol. 61, Issue 2
• Country of Publication: United States
• Language: English

Related Subjects

Lead Sorption
calcite
water
oxide
X-ray