Spent nanocryst. Fe catalyst for NH3 synthesis was nitrided and reduced with NH3+H-2 mixt. at 300 degrees C to a mixt. of nanocryst. alpha-Fe(N) + gamma'-Fe4N and gamma'-Fe4N + epsilon-Fe3-2N phases and a ternary alpha-Fe(N) + gamma'-Fe4N + epsilon-Fe3-2N system. The chem. and phase compn. was confirmed by X-ray diffractometry and at. emission spectroscopy. The nitriding degree increased with increasing nitriding potential of the NH3+H-2 Mixt.