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.