In this study, we report that liquid nitrogen treatment is a promising zero-valent iron activation method that does not remove the iron oxide shell; this can improve the apparent Cr(VI) removal rate constant of zero-valent iron by about 4-120 times, depending on the particle sizes and the suppliers of zero-valent iron. It was found that liquid nitrogen, with its low temperature of 77 K, could crack the iron oxide shell of zero-valent iron to produce abundant fractures because of the different thermal expansion coefficients of iron oxide and iro...
