Sulfur polymer solidification/stabilization of elemental mercury waste

Area of Science:

• Environmental Science
• Materials Science
• Chemical Engineering

Background:

• Elemental mercury waste, often contaminated with radionuclides, poses significant disposal challenges within the Department of Energy complex.
• Existing disposal methods struggle to meet stringent environmental regulations for mercury containment.

Purpose of the Study:

• To develop and evaluate a novel process for the stabilization and solidification of elemental mercury waste.
• To ensure the treated waste is non-dispersible, meets EPA leaching criteria, and exhibits low mercury vapor pressure.

Main Methods:

• Elemental mercury was combined with sulfur polymer cement (SPC) and sulfide additives, heated to ~40°C to form mercuric sulfide (HgS).
• The mixture was further heated to 135°C with additional SPC, then cooled and solidified.
• Characterization included powder X-ray diffraction and assessment of mercury releases using the Toxicity Characteristic Leaching Procedure (TCLP).

Main Results:

• The final treated waste consisted of hexagonal and orthorhombic mercuric sulfide.
• Optimized process TCLP results averaged 25.8 µg/l, with some samples below the EPA Universal Treatment Standard of 25 µg/l.
• Effective diffusion coefficient averaged 7.6x10⁻¹⁸ cm²/s, indicating diffusion-controlled leaching; mercury vapor concentration averaged 0.6 mg/m³.

Conclusions:

• The described stabilization and solidification process effectively immobilizes elemental mercury waste, including radionuclide-contaminated forms.
• The treated waste meets critical environmental standards for leachability and mercury vapor emission.
• This method offers a viable solution for managing hazardous mercury waste.