Fig. 3. Scanning electron microscope (SEM) image of (a) granular Fe⁰ before use, bare surface (x60); (b) granular iron coated with magnetite after 20 h in the reactor with the initial conditions of Test 12 (x18k); and (c) black precipitate on a filter paper, obtained after 10 h from the reactor with the initial conditions of Test 13 (x20k).