Synthesis of Zeolite A from Coal Fly Ash by Alkali Fusion and Hydrothermal

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 ℃, 200 ℃, 300 ℃), 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 ℃, 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.

Possibility of removing cadmium pollution from the environment using a newly synthesized material coal fly ash

Coal fly ash (FA) is a solid waste produced in coal combustion. This study focused on the removal of Cd²⁺ from wastewater by a newly synthesized adsorbent material, the low-temperature and sodium hydroxide-modified fly ash (SHM-FA). The SEM and BET analyses of SHM-FA demonstrated that the adsorbent was porous and had a huge specific surface area. The XRF, XRD, FTIR and TGA characterization showed that SHM-FA has an amorphous structure and the Si-O and Al-O in the fly ash dissolved into the solution, which improved the adsorption capacity of Cd. The results indicated that SHM-FA has desired adsorption performance. The adsorption performance was significantly affected by the dosage, starting pH, Cd²⁺ initial concentrations, and temperature, as well as adsorption time. In the optimal conditions, the removal efficiency and adsorption capacity of Cd²⁺ by SHM-FA were 95.76% and 31.79 mg g^-1, respectively. The experiment provided clearly explained adsorption kinetics and isotherms. And the results confirmed that the adsorption behavior was well described by the pseudo-second-order kinetic and Langmuir isotherm model, which means that the adsorption of Cd²⁺ was controlled by SHM-FA through surface reaction and external diffusion process. In addition, the recycling of SHM-FA for reuse after Cd²⁺ adsorption showed high removal efficiency up to six times of use. Therefore, it can be concluded that SHM-FA is a low-cost adsorbent for Cd²⁺ removal from wastewater.