Competitive and Cooperative Effects during Nickel Adsorption to Iron Oxides in the Presence of Oxalate
- Washington Univ., St. Louis, MO (United States)
Iron oxides are ubiquitous in soils and sediments and play a critical role in the geochemical distribution of trace elements and heavy metals via adsorption and coprecipitation. The presence of organic acids may potentially alter how metals associate with iron oxide minerals through a series of cooperative or competitive processes: solution complexation, ternary surface complexation, and surface site competition. The macroscopic and molecular-scale effects of these processes were investigated for Ni adsorption to hematite and goethite at pH 7 in the presence of oxalate. The addition of this organic acid suppresses Ni uptake on both minerals. Aqueous speciation suggests that this is dominantly the result of oxalate complexing and solubilizing Ni. Comparison of the Ni surface coverage to the concentration of free (uncomplexed) Ni2+ in solution suggests that the oxalate also alters Ni adsorption affinity. EXAFS and ATR-FTIR spectroscopies indicate that these changes in binding affinity are due to the formation of Ni–oxalate ternary surface complexes. Here, these observations demonstrate that competition between dissolved oxalate and the mineral surface for Ni overwhelms the enhancement in adsorption associated with ternary complexation. Oxalate thus largely enhances Ni mobility, thereby increasing micronutrient bioavailability and inhibiting contaminant sequestration.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); National Science Foundation (NSF)
- Grant/Contract Number:
- DGE-1745038; AC02-06CH11357; ECS-0335765
- OSTI ID:
- 1379430
- Journal Information:
- Environmental Science and Technology, Vol. 51, Issue 17; ISSN 0013-936X
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- ENGLISH
Web of Science
Influence of low molecular weight anionic ligands on the sorption of heavy metals by soil constituents: a review
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journal | April 2019 |
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