Synthesis of hexagonal mesoporous silica from coal fly ash and their evaluation as adsorbent for gallium recovery

Adsorption of gallium (Ga) utilizing solid waste synthetic materials can achieve both high-value solid waste use and solve the supply–demand paradox of Ga. To efficiently recover Ga in solution, this article describes a hydrothermal synthesis technique of mesoporous materials from the acid leaching residue of coal fly ash (CFA). According to the findings, the mesoporous silica synthesized by hydrothermal reaction with CTAB: nSiO 3 2- =1:0.085 around 120℃ during 24 h exhibits a maximum specific surface area (771.25 m 2 /g) along with hexagonal mesoporous structure. Pseudo-second-order kinetic model that has an excellent correlation coefficient (R 2  > 0.99) can explain this adsorption system. Since Freundlich model fits this adsorption action better, the process is multi-molecular layer adsorption. The thermodynamic fitting results show that the adsorption of Ga by mesoporous silica is an endothermic and spontaneous chaotic reaction. The adsorption mechanism could be depicted using ion exchange and coupling. The adsorption efficiency of Ga is still higher than 80 % after the material has been regenerated by multiple resolution. In conclusion, mesoporous silica prepared by CFA acid leaching residue has the potential to adsorb Ga.