Complexation of carbonate species at the goethite surface: Implications for adsorption of metal ions in natural waters

Journal Article · Sun May 01 04:00:00 EDT 1994 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/0016-7037(94)90286-0· OSTI ID:145458

Van Geen, A; Robertson, A P; Leckie, J O ^[1]

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1. Stanford Univ., CA (United States)

Headspace P{sub CO{sub 2}} was measured with an infrared gas analyzer over an equilibrated goethite suspension to determine adsorption of carbonate species in the pH range 3 to 8. For a 2 g/L goethite suspension in 0.1 N NaClO{sub 4} ({approximately} 3 10{sup {minus}4} M surface sites), the fraction of carbonate species adsorbed increased from 0.15 at pH 3 to a maximum of 0.56 at pH 6. In 0.01 N NaClO{sub 4}, the fraction of carbonate species adsorbed at pH 6 increased to 0.67. The total concentration of CO{sub 2} in the suspension increased from about 0.4 to 0.6 10{sup {minus}4} M in the pH range of these experiments. The development of surface charge at the goethite surface was determined in the pH range 4 to 11 by potentiometric titration under controlled low CO{sub 2} conditions. No hysteresis was observed between the acid and base legs of titrations in 0.10, 0.03, and 0.01 N NaClO{sub 4} resulting in a pH{sub pzc} of 8.9. The carbonate species adsorption data were modelled using the least squares optimization program FITEQL for the diffuse double-layer model and the triple-layer model using stoichiometries of the type Fe-OCOOH and Fe-OCOO{sup {minus}} for surface bound carbonate species. The model results are consistent with separate experiments showing a significant reduction in chromate adsorption on goethite as the partial pressure of CO{sub 2} was increased from <5 to 450 and 40,000 {mu}atm. The data suggest that mineral oxide surface sites which control solid/solute partitioning of metal ions in natural systems may be largely bound to adsorbed carbonate species.

• OSTI ID: 145458
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 9 Vol. 58; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ADSORPTION
CARBONATES
ENVIRONMENTAL TRANSPORT
METALS
POLLUTION
SURFACE WATERS
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