Coal fly ash-slag-based geopolymers: microstructure and metal leaching

Area of Science:

• Materials Science
• Environmental Science
• Geochemistry

Background:

• Fly ash utilization in geopolymer matrices is a sustainable approach.
• Geopolymerization involves highly alkaline conditions impacting element leaching.
• Understanding element mobility is key for safe fly ash-based material applications.

Purpose of the Study:

• To compare the leachability of elements from fly ash and geopolymer matrices.
• To assess the immobilization or mobilization of potentially harmful elements during geopolymerization.
• To evaluate the long-term stability and encapsulation efficiency of fly ash-based geopolymers.

Main Methods:

• Synthesis of geopolymer matrices using fly ash as a precursor.
• Leaching tests conducted on both raw fly ash and synthesized geopolymers.
• Analysis of leachable concentrations of various trace elements and oxyanionic species.

Main Results:

• Geopolymers effectively immobilized trace pollutants including Be, Cd, Co, Cr, Cu, Ni, Pb, U, and rare earth elements.
• Leachable concentrations of oxyanionic species such as As, B, Mo, Se, V, and W increased post-geopolymerization.
• The alkaline environment of geopolymers inhibits heavy metal leaching but enhances oxyanion mobilization.

Conclusions:

• Fly ash-based geopolymers demonstrate potential for immobilizing numerous heavy metals.
• Specific elements in oxyanionic forms may become more mobile, necessitating careful management.
• Optimizing geopolymer dosage, synthesis, and curing conditions is essential for long-term stability and effective encapsulation.