Ethanol-assisted mechanical activation of zero-valent aluminum for fast and highly efficient removal of Cr(VI)

Abstract

Mechanical ball milling is a promising approach to activate zero-valent aluminum (ZVAl), in which the grinding aids are essential. Yet, more previous researches focused on solid grinding aids while the benefits of liquid grinding aids are seldom revealed. Here, we demonstrated a novel mediating mechanism of ethanol (EtOH), a liquid grinding aid, and corresponding mechanical activated ZVAl (termed as MA-ZVAl) was employed to remove Cr(VI) from water. Firstly, SEM, BET, XRD and XPS characterizations indicated that EtOH can quickly diffuse to ZVAl surface and serve as a surface coating to inhibit the cold welding of ZVAl, and the kinetic energy produced in ball milling process can effectively promote the fracture of ZVAl. Then, Cr(VI) removal experiment results showed that complete removal of Cr(VI) was observed in MA-ZVAl system, while there was no removal of Cr(VI) by pristine ZVAl. Moreover, the longer ball milling time of ZVAl, the faster the Cr(VI) removal rate. Finally, surface corrosion mechanisms were unveiled. Electrons were released after the corrosion of MA-ZVAl, then Cr(VI) captured the electrons and reduced to Cr(III), which precipitated to Cr(OH)3 on MA-ZVAl surface. In conclusion, EtOH-assisted mechanical ball milling can successfully activate ZVAl that could efficiently removal of Cr(VI) from water.