Optimization of coal fly ash-based porous geopolymer synthesis and application for zinc removal from water

Coal fly ash-based porous geopolymer (CFAPG) is a potential adsorbent for heavy metal-contaminated water remediation and can also mitigate the accumulation of coal fly ash from thermal power plants. Production parameters influence the physicochemical properties (e.g., adsorption capacity) of CFAPG. Ten potential factors involved in the CFAPG production process were examined using a Plackett-Burman design (PBD) and then an orthogonal experimental design (OED). The results show the alkali activator modulus (MS), alkali-ash mass ratio (AA), foaming agent-ash mass ratio (FAR), and sodium dodecyl sulfate-ash mass ratio (SDSA) were the most important factors influencing the Zn adsorption capacity of CFAPG. Ternary plots confirm the interaction between these four factors, with the role of FAR being easily masked by other factors and MS being the least influenced by other factors. Furthermore, Zn adsorption on the CFAPG created with optimal parameters was best described by the Bi_Langmuir model, indicating two different sorption site classes on the surface of CFAPG with a total maximum Zn adsorption capacity of 13.42 mg g(-1). These results provide key parameters for the production of geopolymers as heavy metal adsorbents.