Highly efficient removal of Cd(II) in aqueous solution by attapulgite-loaded amorphous zero-valent Iron

Amorphous zero-valent iron (AZVI) is a promising material for heavy metal removal due to its special crystal structure. Its electron-donating ability is significantly improved compared to crystalline zero-valent iron (CZVI). However, the agglomeration of AZVI is needed to be resolved as such an issue impedes its treating performance obviously. Herein, AZVI was synthesized and the electron-donating ability was characterized in detail by radial distribution function, electrochemical test, ultraviolet photo-electron spectroscopy, and electronic density of states simulation. By loading AZVI onto attapulgite (ATP) to form ATP@AZVI, the agglomeration was alleviated. When ATP@AZVI (0.5 g/L) was mixed with Cd(II) (30 mg/L), the residual concentration (C_r) was 0.08 mg/L after 30 min. Removal efficiency of ATP@AZVI towards Cd(II) was improved by 275 % compared to AZVI. XPS, XRD, SEM, and TEM revealed the mechanism of Cd(II) removal primarily through the coprecipitation of Cd(II) with iron ions generated by the corrosion of ATP@AZVI. Even after 12 months of aging, ATP@AZVI removed 86.4 % of Cd(II) in 30 min. Once the reaction time was prolonged to 100 min, the C_r was as low as 0.07 mg/L. These results suggested that ATP@AZVI possessed excellent anti-oxidation ability. ATP@AZVI can be regarded as an efficient adsorbent for controlling Cd(II) pollution.