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Evaluating the impact of drying on leaching from a solidified/stabilized waste using a monolithic diffusion model.
Zhiliang Chen1, Peng Zhang2, Kevin G Brown1
1Department of Civil and Environmental Engineering, Vanderbilt University, Nashville, TN 37235, United States.
Waste Management (New York, N.Y.)
|April 20, 2023
Summary
Drying solidified waste forms reduces their ability to retain constituents, impacting future contaminant release. This study quanties the effects of drying on leaching, crucial for waste management safety.
Area of Science:
- Environmental Science
- Geochemistry
- Materials Science
Background:
- Solidified/stabilized cementitious waste forms are used for radioactive and hazardous waste disposal.
- The impact of drying on the long-term release rates of constituents from these waste forms is not well understood.
- Drying can alter the physical and chemical properties of cementitious waste forms, potentially affecting contaminant mobility.
Purpose of the Study:
- To investigate the effects of drying on the subsequent leaching behavior of Cast Stone, a representative cementitious waste form.
- To quantify the changes in release fluxes of major and redox-sensitive constituents after aging under various relative humidity conditions.
- To identify the primary mechanisms by which drying influences contaminant release.
Main Methods:
- Cementitious waste form (Cast Stone) monoliths were aged under controlled relative humidity (100%, 68%, 40%, 15%) for extended periods (16, 32, 48 weeks).
- Mass transfer tank leaching tests (EPA Method 1315) were conducted to determine the release fluxes of constituents.
- A monolithic diffusion model was calibrated using leaching data to simulate constituent release and identify key parameters.
Main Results:
- Drying significantly reduces the tortuosity factor, which is the primary impact on subsequent leaching.
- The model accurately described the release fluxes of major constituents (OH-, Na, K, Ca, Si, Al) and redox-sensitive elements (Tc, Cr, Fe, S).
- Drying-induced changes in porewater pH and redox conditions, along with reduced tortuosity, alter the release rates of pH- and redox-sensitive constituents.
Conclusions:
- Drying is a critical factor influencing the long-term performance of solidified/stabilized waste forms.
- Reduced tortuosity and altered porewater chemistry due to drying significantly impact the release of contaminants.
- Understanding these drying effects is essential for accurate performance assessments and safe disposal of cementitious waste forms.
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