Immobilization of metals using apatite minerals: Precipitation or sorption?
- NESTT, Richland, WA (United States)
- Washington State Univ., Richland, WA (United States)
- Bechtel Hanford, Richland, WA (United States); and others
Metals can be immobilized into stable phosphate phases (apatite minerals) in contaminated soils, sediments and groundwater. Most affected by this treatment are Pb, Zn, Cr, Cu, Cd, Ni, U, Ba, Cs, St, Pu, and all other lanthanides and actinides. The reaction can be nearly irreversible under subsurface conditions. Mine tailing soils from the Bunker Hill Mining District containing 0.4 wt% Pb, Zn and Cd, were treated using various apatites, and modelled using MINTEQA2. Under subsurface conditions, the metal-apatite phases were predicted to be the most stable for Pb, and only moderately stable for Zn and Cd. In column experiments on untreated and apatite-treated soils using vadose zone water, leachates from untreated Bunker Hill soils contained hundreds to thousands of mgkg{sup -1} (ppm) Pb, Zn and Cd, but leachates from apatite-treated Bunker Hill soils showed concentrations below the ICP/MS detection limits of 1 {mu}g kg{sup -1}. SEM and XRD indicated precipitation of Pb-hydropyromorphite that accounted for most of the Pb removal, but no Cd or Zn phosphate minerals appeared. A minor amount of otavite was precipitated, but most of the Cd and Zn were removed in such a way as to produce no XRD patterns. Either sorption dominated Cd and Zn removal or X-ray amorphous materials precipitated. pH had no effect on Pb removal, but significantly affected Cd and Zn.
- OSTI ID:
- 370486
- Report Number(s):
- CONF-960376--
- Country of Publication:
- United States
- Language:
- English
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