(371p) Investigating Alkali-Activated Fly Ash Based Materials As Adsorbents for Heavy Metal Sorption

Due to the high CO₂ emissions associated with the production of conventional cements, research efforts have been directed towards developing alternative low-carbon cementitious materials. One widely researched alternative cementitious material, that has also found value as adsorbent for environmental remediation, is alkali-activated cement or geopolymers. Although geopolymer material have gained wide research attention in recent decades as promising adsorbent for the removal of aqueous heavy metals, the high variability of the material and several unanswered questions have limited the development and general adoption in the industry. This study evaluates the impacts of compositional and microstructural factors on the performance of geopolymers for aqueous lead (Pb²⁺) removal, with a view to reveal the composition-structure-property relationship thereof. The Pb sorption kinetics and efficiency of geopolymer adsorbents prepared using various fly ash precursors and activating alkaline solutions, were investigated. The investigated compositions featured high Pb removal efficiency of over 99.5%, with a slight decrease of efficiency with increasing Ca/(Si+Al) and Al/Si contents, while the sorption kinetics decreases exponentially with increasing Ca/(Si+Al) and Al/Si molar ratios. The performance of the geopolymers also shows strong correlation to the microstructure, wherein the sorption kinetic increases exponentially while the efficiency increases slightly, with increasing mass fraction of the amorphous phase in the geopolymer’s phase assemblage. The results of this research indicate that by using appropriate precursor formulation and curing conditions to evoke the best microstructures, geopolymer materials can be optimized for high performance in removing heavy metals, thereby improving the chances of the material’s general acceptability in the adsorbent industry.