『Abstract
The effects of elevated pH, ionic strength, and temperature on
sediments in the vadose zone are of primary importance in modeling
contaminant transport and understanding the environmental impact
of tank leakage at nuclear waste storage facilities like those
of the Hanford site. This study was designed to investigate biotite
dissolution under simulated high level waste (HLW) conditions
and its impact on Cr(VI) reduction and immobilization. Biotite
dissolution increased with NaOH concentrations in the range of
0.1 to 2 mol L-1. There was a corresponding release
of K, Fe, Si, and Al to solution, with Si and Al showing a complex
pattern due to the formation of secondary zeolite minerals. Dissolved
Fe concentrations were an order of magnitude lower than the other
elements, possibly due to the formation of green rust and Fe(OH)2. The reduction of Cr(VI) to Cr(III) also increased
with increased NaOH concentration. A homogeneous reduction of
chromate by Fe(II)aq released through biotite
dissolution was probably the primary pathway responsible for this
reaction. Greater ionic strengths increased biotite dissolution
and consequently increased Fe(II)aq release
and Cr(VI) removal. The results indicated that HLW would cause
phyllosilicate dissolution and the formation of secondary precipitates
that would have a major impact on radionuclide and contaminant
transport in the vadose zone at the Hanford site.』
1. Introduction
2. Materials and methods
3. Results and discussion
3.1. Biotite dissolution and secondary precipitate formation
under alkaline pH conditions
3.1.1. Biotite dissolution under alkaline pH conditions
3.1.2. Solid phase characterization and secondary precipitate
formation
3.2. Chromate reduction by biotite under alkaline pH conditions
3.2.1. Chromate reduction by biotite
3.2.2. Chromate reduction by preaged biotite in NaOH solutions
4. Conclusions and implications
Acknowledgments
References