*3.4. SEM-EDX Analysis of Biochar*

The application of SEM-EDX proved that the metal ions can be bound on the biochar surface. Examination of the SEM-EDX element map, Figure 3, presents the relative increase in surface concentration of Co on biochar particle (<1 mm), shown by the image brightness after biochar incubation in contaminated soil. The location of Co "hot spots" on the biochar surface corresponded to sites with increased surface concentrations of Fe and Mn and oxygen functional groups.

**Figure 3.** Scanning electron microscope (SEM) images of wheat straw biochar surface and energy dispersive X-ray spectroscopy (EDX) mapping. (**a**) Fe; (**b**) Mn; and (**c**) Co ions, distribution on the biochar produced from wheat straw (WSBC) surface.
