Cd sup 2+ uptake by calcite, solid-state diffusion, and the formation of solid-solution: Interface processes observed with near-surface sensitive techniques (XPS, LEED, and AES)

Journal Article · Fri May 01 04:00:00 EDT 1992 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(92)90321-9· OSTI ID:7049682

Stipp, S L; Hochella, Jr, M F; Parks, G A; Leckie, J O ^[1]

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1. Stanford Univ., CA (United States)

X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES) allowed direct observations of structure and bonding environments at the calcite surface. Pure calcite crystals were cleaved from precleaned Iceland spar and were briefly exposed to aqueous solutions containing various concentrations of Cd{sup 2+}, CO{sub 3}{sup 2{minus}}, ClO{sub 4}{sup {minus}}, and/or Cl{sup {minus}}. LEED results demonstrate that the calcite surface is atomically ordered, even after hydration and cadmium uptake. {gamma}-scintillation data from crystals exposed briefly to solutions of {sup 109}Cd{sup 2+} indicate that surface uptake ranged from the equivalent of about 1 to 4 monolayers. XPS analyses in the first 2 hours after exposure detected Cd within the top 30 {angstrom}, but crystals stored in air or in ultra-high vacuum showed a decrease in Cd surface concentration with time such that after two days, C was barely detectable in the near-surface region. No Cd enrichment was observed at sites of surface defects using AES, indicating that solid-state diffusion into the mineral surface was not accomplished simply by migration along microfractures alone. This work suggests that solid-state diffusion may play a role in the rate and extent of uptake of certain trace metals from solution and probably leads to the formation of solid-solution in calcite and other carbonate minerals. It also suggests that the process of diffusion into the solid mineral host should be considered in hydrogeochemical models that intend to simulate and predict trace-metal mobility in carbonate terrains.

• OSTI ID: 7049682
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 56:5; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360602 -- Other Materials-- Structure & Phase Studies
54 ENVIRONMENTAL SCIENCES
540210 -- Environment
Terrestrial-- Basic Studies-- (1990-)
58 GEOSCIENCES
580000* -- Geosciences
ADSORPTION
AQUEOUS SOLUTIONS
AUGER ELECTRON SPECTROSCOPY
BETA DECAY RADIOISOTOPES
CADMIUM
CADMIUM 109
CADMIUM ISOTOPES
CALCITE
CARBONATE MINERALS
COHERENT SCATTERING
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DATA
DIFFRACTION
DIFFUSION
DISPERSIONS
ELECTRON CAPTURE RADIOISOTOPES
ELECTRON DIFFRACTION
ELECTRON SPECTROSCOPY
ELEMENTS
ENVIRONMENTAL TRANSPORT
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
GEOLOGIC MODELS
HYDROLOGY
INFORMATION
INTERMEDIATE MASS NUCLEI
ISOTOPES
LAYERS
MASS TRANSFER
METALS
MINERALS
MIXTURES
NUCLEI
NUMERICAL DATA
PHOTOELECTRON SPECTROSCOPY
RADIOISOTOPES
SCATTERING
SOLUTIONS
SORPTION
SPECTROSCOPY
SURFACE PROPERTIES
X-RAY SPECTROSCOPY
YEARS LIVING RADIOISOTOPES