Formation and occurrence of metal-arsenate precipitates in the environment

2004 2004

Other formats: Order a copy

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)

Soil sciences;
Environmental science
0481: Soil sciences
0768: Environmental science
Identifier / keyword
Health and environmental sciences; Biological sciences; Arsenic; Bioavailability; Contaminated soil; Metal arsenates; Precipitates; Sorption
Formation and occurrence of metal-arsenate precipitates in the environment
Grafe, Markus
Number of pages
Publication year
Degree date
School code
DAI-B 65/08, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
049602986X, 9780496029860
Sparks, Donald L.
University of Delaware
University location
United States -- Delaware
Source type
Dissertations & Theses
Document type
Dissertation/thesis number
ProQuest document ID
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
Access the complete full text

You can get the full text of this document if it is part of your institution's ProQuest subscription.

Try one of the following:

  • Connect to ProQuest through your library network and search for the document from there.
  • Request the document from your library.
  • Go to the ProQuest login page and enter a ProQuest or My Research username / password.