Abstract/Details

Formation and occurrence of metal-arsenate precipitates in the environment


2004 2004

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Abstract (summary)

The reactivity of metals and arsenic (As) was investigated to determine how differently behaving contaminants react in co-contaminated environments and in model systems. In order to minimize the bioavailability of several co-occurring contaminants, their interactions must be well understood. Micro-focused synchrotron x-ray fluorescence mapping and x-ray absorption spectroscopy (μSXRF, μXAS, respectively) were used to investigate a copper chromated arsenate contaminated soil. Micro-SXRF mapping showed As to be well correlated to the co-contaminants Cu, Cr, and Zn (>80%). Principal component, target transformation, and linear combination fit analyses of μXAS spectra showed a continuum of partially mineralized species, precipitates and co-adsorbates of arsenate (As(V)) with Zn, Cu, and/or Cr sorbed on Al and Fe-oxides.

Co-sorbing As(V) and Zn solutions in goethite suspensions were investigated to determine solid phase partitioning and kinetic factors. A 100 ppm goethite suspension was titrated with As(V) and Zn stock solution at pH 4 and 7 and showed increased uptake of As(V) and Zn from solution at pH 7. EXAFS spectroscopy determined that the increased uptake at pH 7 occurred due to the formation of an adamite-like surface precipitate, while at pH 4, As(V) and Zn only formed co-adsorbed surface complexes. Precipitates did not form below site-saturation at pH 7 suggesting that the number of surface sites may influence precipitation reactions.

Subsequently, As(V) and Zn were reacted at pH 7 in either 10, 100, or 1000 ppm goethite suspensions and their sorption was monitored as a function time for six months. Arsenic and Zn K-edge EXAFS data suggested that a continuum of surface processes occurred (adsorption, precipitation, and structural refinement) leading to the formation of a koettigite-like and an adamite-like surface precipitate in 10 and 100 ppm goethite suspensions, respectively, after 6 months. We ascribed the precipitation reactions to a catalytic effect from goethite, which provided a good steric match for the surface-precipitates. In 1000 ppm goethite suspensions, co-adsorbed surface complexes dominated, because adsorption lowered As(V) and Zn concentrations in solution such that a precipitation reaction could not occur. Co-precipitated contaminants are less bio-available and hence more favorable for remediation and disposal purposes.

Indexing (details)


Subject
Soil sciences;
Environmental science
Classification
0481: Soil sciences
0768: Environmental science
Identifier / keyword
Health and environmental sciences; Biological sciences; Arsenic; Bioavailability; Contaminated soil; Metal arsenates; Precipitates; Sorption
Title
Formation and occurrence of metal-arsenate precipitates in the environment
Author
Grafe, Markus
Number of pages
212
Publication year
2004
Degree date
2004
School code
0060
Source
DAI-B 65/08, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
049602986X, 9780496029860
Advisor
Sparks, Donald L.
University/institution
University of Delaware
University location
United States -- Delaware
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3144793
ProQuest document ID
305206710
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/305206710
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