Perpustakaan Digital ITB

Coal-fired Power Plants (PLTUs) generate large amounts of fly ash (FA), while its utilization remains relatively limited. One approach to increasing the added value of FA is to transform it into geopolymer fly ash (GFA) as an adsorbent material for Rare Earth Elements (REE), such as Ce³? and Y³?. GFA has the potential to be applied for the recovery of REE contained in Acid Mine Drainage (AMD). This study aims to analyze the comparative characteristics of FA and GFA, evaluate the adsorption effectiveness of FA and GFA under acidic conditions (pH 4), and investigate the adsorption mechanisms and capacities through kinetic and isotherm tests. The characterization results showed that geopolymerization altered Si, Al, Ca, and Mg in FA, forming new reaction products in GFA. The BET surface area increased from 3.88 m²/g to 23.02 m²/g, while the zeta potential became more negative, with an isoelectric point below pH 3, indicating a surface with a higher abundance of reactive sites. The screening test demonstrated that GFA exhibited substantially higher adsorption performance, achieving up to 100% removal of Ce³? and Y³? (0 ppm) within only 2 hours. In contrast, within the same contact time, FA removed only 13% of Ce³? and 7% of Y³?. FA required a longer contact time to achieve 100% removal, reaching this level after 24 hours for both Ce³? and Y³?. The dosage variation test showed that the optimum adsorbent dosage was 2 g/L. The kinetic modeling results indicated that GFA adsorption was better fitted by the Pseudo-Second-Order model (R² = 0.99–1.00), suggesting stronger adsorbate– adsorbent interactions and a tendency toward chemisorption characteristics within the observation period of up to 72 hours. Meanwhile, FA was better fitted by the Pseudo-First-Order model (R² = 0.71–0.87), indicating relatively weaker adsorbate–adsorbent interactions and a tendency toward physisorption characteristics. For equilibrium isotherms, GFA adsorption was empirically better described by the Freundlich model, with R² values of 1.00 for Y³? and 0.626 for Ce³?, indicating a heterogeneous surface with the possibility of multilayer adsorption. Meanwhile, FA adsorption also followed the Freundlich model, with n values of 1.52 for Ce³? and 1.45 for Y³?. Overall, geopolymerization altered the nature of adsorbate–adsorbent interactions and enhanced the effectiveness of GFA in adsorbing trivalent rare earth ions.