Enhanced Hg(II) removal by polyethylenimine-modified fly ash-based tobermorite

The polyethylenimine (PEI)-modified fly ash based tobermorite (PTFA) was prepared from fly ash (FA) by hydrothermal synthesis of fly ash-based tobermorite (TFA) and PEI grafting. The TFA and PTFA were systematically characterized, and their Hg(II) removal properties from aqueous solutions were investigated. The influences of pH, adsorbent dosage, contact time, initial concentration, and coexisting ions on removing Hg(II) by PTFA were systematically investigated. The results showed that PTFA had good adsorption capacity and adsorption selectivity towards Hg(II). The optimum dosage of PTFA was 1 g/L, and the preferred pH range was 3 similar to 5. The adsorption of Hg(II) on PTFA was found to follow the pseudo-second-order and Langmuir model, indicating chemical adsorption and monolayer adsorption between Hg(II) ions and PTFA. The thermodynamic results suggested that the adsorption of Hg(II) on PTFA was spontaneous, heat-absorbing, and entropy-increasing. The maximum adsorption capacity of PTFA for Hg(II) was 43.89 mg/g, which was higher than that of TFA and other reported FA-based adsorbents. The main removal mechanisms involved chemical chelation with oxygen and nitrogen atoms and ion exchange with Ca(II). This study shows that PTFA has good application prospects in treating wastewater containing Hg(II).