| dc.description.abstract | This research investigated the effect of converting the municipal solid waste incinerator (MSWI) fly ash to the non-hazardous material by geopolymer and the feasibility of fly ash-based geopolymer on the adsorption of copper and lead in the aqueous solution. The geopolymer preparation experiments used 8~12M of KOH as the alkaline activator and designed MSWI fly ash blending with 30% or 40% metakaolin to adjust the suitable Si/Al ratio. The curing conditions, including natural (25℃and 65% of humidity) and accelerated curing (60℃), were also discussed. On the other hand, the adsorption experiments were conducted by controlling the adsorbent dosage (1.5, 5, 10, and 20 g/L), the pH value of the heavy metal solution (2, 3, 4, 5, and 6), the contact time (15, 30, 60, 180, 360, 720, and 1,440 minutes), and the initial concentration of the heavy metal solution (100, 150, 200, and 250 mg/L). The adsorption kinetics and tested metal adsorption capacity were determined by controlling the contact time and the initial concentration of the heavy metal solution.
The experimental results showed that the fly ash-based geopolymer could provide enough compressive strength (4.59 ± 0.43 kgf/cm2) to ensure the geopolymerization in the case of 8M KOH and 30% metakaolin addition (Si/Al ratio=1.89) by the natural curing condition. The presence of Si-O-Si, Al-O-Si, quartz crystal, and aluminosilicate speciation of geopolymer were identified by FTIR, XRD, and SEM. It implied that the geopolymerization had occurred during the preparation process. On the other hand, toxicity characteristics leaching procedure (TCLP) concentrations of the tested metals in the geopolymer were all in compliance with current regulation thresholds. Especially for the lead (Pb) TCLP concentrations, it was decreased from 36.20 mg/L in the original MSWI fly ash to 0.05 mg/L in the geopolymer. The TCLP analysis results indicated that the non-hazardous treatment of MWSI fly ash had been successfully developed by geopolymer. To further understand the feasibility of adsorbent application in geopolymer, the BET analysis results of geopolymer indicated that the specific surface area was approximately 25.21 m2/g and belonged to the mesoporous adsorbent materials.
According to the adsorption test results, in the case of solid-liquid ratio was 5 g/L and the pH values ranging from 5 to 6, the Cu(II) and Pb(II) removal efficiencies were 99.91% and 99.93%, respectively, when the contact time was controlled at 720 minutes. However, when the initial concentration of heavy metals was 250 mg/L, the adsorption capacities of Cu(II) and Pb(II) were 20.90 mg/g and 25.96 mg/g, respectively. The adsorption kinetics results showed that the pseudo-second-order model could fit well in the adsorption test, and the Freundlich isotherm model also matched the tested metals adsorption phenomena. According to the results of metals speciation identified by XRD and simulated by the HSC model, the strong alkali geopolymer could increase the pH value of the heavy metal solution, resulting in the precipitation of tested heavy metals. It will enhance the tested Cu(II) and Pb(II) removal efficiency. In summary, this research confirmed that the MSWI fly ash-based geopolymer was both a non-hazardous material and a promosing adsorbent for effectively removing Cu(II) and Pb(II) from aqueous solutions. Therefore, MSWI fly ash-based geopolymer as the adsorbent materials will be valuable recovered materials and have good potential for practical application in the wastewater containing heavy metals treatment plant. | en_US |