Stabilization of Chromium Waste by Solidification into Cement Composites

Area of Science:

• Materials Science
• Environmental Engineering
• Geochemistry

Background:

• Hazardous chromium waste poses environmental risks.
• Stabilization/solidification (S/S) is a method to immobilize contaminants.
• Cement CEM II is a common binder for S/S applications.

Purpose of the Study:

• To investigate chromium leaching from cement-stabilized mortars in an acidic environment.
• To evaluate the effect of chromium on cement hydration, mechanical properties, and mineralogy.
• To assess the efficiency of the S/S process for chromium immobilization.

Main Methods:

• Mortar preparation with varying Cr2O3 content (0.6-1.2%).
• X-ray diffraction (XRD) for mineralogical analysis.
• Toxicity Characteristic Leaching Procedure (TCLP) for chromium release assessment.
• Surface complexation modeling to determine the release mechanism.

Main Results:

• Chromium addition accelerated hydration and setting, increasing mechanical strength.
• XRD identified new phases: CaCrO4·2H2O and chromium-ettringite.
• Chromium release during TCLP depended on initial concentration and leaching time.
• The S/S process demonstrated high efficiency in immobilizing chromium.

Conclusions:

• Cement stabilization effectively immobilizes hazardous chromium waste.
• The formation of specific mineral phases confirms chromium fixation.
• Chromium release is primarily a surface phenomenon, indicating successful S/S.