Effect and mechanisms of synthesis conditions on the cadmium adsorption capacity of modified fly ash

In this study, modified coal fly ash (NMFA) was prepared by sodium hydroxide (NaOH) with low-temperature hydrothermal method. The differences of the ash to alkali mass ratio (5:3, 5:4, 5:5, 5:6), calcination temperature (100 degrees C, 200 degrees C, 300 degrees C), and calcination time (1 h, 3 h, 5 h) were investigated. The adsorption experiments obtained the optimal result with the ash to base ratio of 5:5, calcination temperature of 200 degrees C, and calcination time of 3 h, adsorbing 90.27 mg/g of Cd2+. The characterization results (SEM-EDS, FTIR, XRD, and XPS) also confirmed the effective adsorption of Cd2+ by NMFA. The functional groups of Si-O, Al-O, and Fe-O played an important role in Cd2+ removal. Meanwhile, the influences of dosage, different pH, and co-existing cations were also investigated. Quasi-secondary adsorption kinetics and Langmuir isotherm model were also referred to the Cd2+ adsorption by NMFA. Therefore, the good adsorption of NMFA-3 on Cd2+ provided new ideas for the safe utilization of fly ash and heavy metal purification in wastewater.

Automated summary

The study prepared modified coal fly ash (NMFA) through sodium hydroxide treatment using a low-temperature hydrothermal method. The optimal conditions for Cd2+ adsorption by NMFA were found to be ash to base ratio of 5:5, calcination temperature of 200 degrees C, and calcination time of 3 h. Characterization results confirmed the crucial role of functional groups such as Si-O, Al-O, and Fe-O in Cd2+ removal.