Vacuum method for carbonation of cementitious wasteforms.

Area of Science:

• Materials Science
• Environmental Engineering
• Chemical Engineering

Background:

• Carbonation treatment reduces the leachability of contaminants in cement-based wasteforms.
• Conventional methods use high-pressure or supercritical CO2, limiting treatment efficiency.
• Understanding carbonation's impact on pore structure and permeability is crucial for waste immobilization.

Purpose of the Study:

• To introduce and evaluate a novel low-pressure carbonation technique for cement-based wasteforms.
• To investigate the mechanism of enhanced CO2 diffusion via water removal under near-vacuum conditions.
• To assess the effectiveness of this technique in reducing the leachability of various waste components.

Main Methods:

• Developed a low-pressure carbonation method utilizing near-vacuum conditions and a desiccant.
• Applied the technique to cement-based wasteform samples containing cationic and anionic contaminants.
• Conducted standardized leach tests to quantify contaminant release from treated and untreated samples.

Main Results:

• Achieved significant carbonation depths (up to 11 mm in 45 h for OPC, 15 mm in 6 d for blended cement).
• Observed reduced leachability for cationic waste constituents in carbonated samples.
• Noted increased leachability for anionic waste constituents with higher degrees of carbonation.

Conclusions:

• The low-pressure carbonation technique offers a more effective alternative to high-pressure methods for wasteform treatment.
• While beneficial for cationic contaminants, the technique requires further investigation for anionic contaminants due to increased leachability.
• This method shows promise for immobilizing specific waste components in cement-based matrices.