Mine Clay Washing Residues as a Source for Alkali-Activated Binders

Area of Science:

• Materials Science
• Geochemistry
• Sustainable Construction Materials

Background:

• Mine clay washing residues are often industrial by-products with potential as precursors for alkali-activated materials (AAMs).
• The environmental impact of traditional materials like kaolinite necessitates exploring sustainable alternatives.
• The geopolymerization process is sensitive to the precursor's properties, particularly after thermal treatment.

Purpose of the Study:

• To evaluate the feasibility of using calcined mine clay washing residues for preparing alkali-activated binders.
• To investigate the influence of calcination temperature on the chemical stability and durability of the resulting AAMs.
• To promote the utilization of industrial by-products for sustainable binder production.

Main Methods:

• Halloysitic clay by-product was subjected to calcination at 450°C, 500°C, and 600°C.
• Calcined clays were mixed with alkaline activators (NaOH and sodium silicate) and cured at room temperature for 28 days.
• Chemical stability was assessed by measuring pH and ionic conductivity of eluates after water immersion; microstructure was analyzed using SEM and XRD.

Main Results:

• Calcination significantly improved the chemical stability and microstructure of alkali-activated materials (AAMs).
• Samples prepared with clay calcined at 600°C exhibited the best performance, with ionic conductivity (292 mS/m) significantly lower than untreated or low-temperature calcined clays (≥756 mS/m).
• The optimal sample showed dense microstructure, comparable integrity, pH, and ionic conductivity to metakaolin-based geopolymers.

Conclusions:

• Proper calcination, especially at 600°C, is essential for producing chemically stable and durable AAMs from halloysitic clay by-products.
• Untreated or low-temperature calcined clays yield AAMs with poor chemical stability and microstructure.
• This halloysitic clay shows significant potential as a sustainable aluminosilicate precursor for high-performance alkali-activated binders.