Compositional effects of clay–fly ash geopolymers on the sorption process of lead and zinc

• Published in: Journal of environmental quality Vol. 50; no. 3; pp. 768 - 781
• Main Authors: Khaksar Najafi, Elmira, Jamshidi Chenari, Reza, Payan, Meghdad, Arabani, Mahyar
• Format: Journal Article
• Language: English
• Published: United States 01.05.2021
• ISSN: 0047-2425; 1537-2537
• DOI: 10.1002/jeq2.20207

Because long‐term leachate penetration through a hydraulic barrier is unavoidable, active–passive liners are widely used to mitigate the migration of potential contaminants. Geopolymerization represents a viable method for metals removal, which simultaneously improves the properties of local clay to compensate for the lack of suitable soil in the design of active–passive liners. This study investigated how clay–fly ash geopolymers enhance the sorption of divalent lead [Pb(II)] and divalent zinc [Zn(II)] from leachate compared with an untreated clay. Two clay–fly ash geopolymers were synthesized from the mixtures containing 50 and 60% fly ash to the total solid mass and then activated by 10 M NaOH solutions. The influence of Na/fly ash ratios and activator content was also examined. The results indicate that a fly ash–based geopolymer could be a simple solution to increase the sorption capacity of local clay. A lower ratio of Na/fly ash and activator content, resulting in a higher porosity, led to a better performance for metal removal. According to the results of sorption isotherms and batch experiments, Pb(II) and Zn(II) exhibit different sorption behaviors affected by the compositions of synthesized clay–fly ash geopolymers, which could be adjusted to reach a proper sorption capacity. The results of the kinetic study also show that the heterogeneous matrix of the clay–fly ash geopolymers with different porosities led to mutual cooperation between reaction and diffusion‐controlled steps for metal removal.