In this paper, we have modeled a fractured surface of pyrite (1 0 0). From the viewpoint of bond lengths, we inferred that the chemical adsorption capacity of Fe(III) complexes follows the order [Fe(III)(OH)](2+) > [Fe(III)(OH)(3)] > [Fe(III)(OH)(5)](2-) > [Fe(III)(OH)(2)](+) > [Fe(III)(H2O)(6)](3+) > [Fe(III)(OH)(4)](-) > [Fe(III)(OH)(6)](3-). The Mulliken population analysis of the quantum chemical model reveals that bonding between the Fe(III) of complexes and the S of the pyrite surface occurs during the adsorption process. The interaction between the S of pyrite (1 0 0) and Fe of [Fe(III)(OH)](2+) most tends to be a covalent bonding, while the interactions between the S of pyrite (1 0 0) and Fe of [Fe(III)(OH)(4)](-)/[Fe(III)(OH)(5)](2-) most tend to be the ionic bonding and are confirmed by projected density of states (PDOS) analysis. The X-ray photoelectron spectroscopy (XPS) study of the S 2p core line reveals distinct contributions of the surface, which is determined to have contributions due to surface S2- monomers, S-2(2-) dimers, S-n(2-), S-0 and surface sulphate. The charge accumulation on the surface S2- monomers is conjectured to be achieved via a transfer of charge from the surface Fe2+ to the surface S2- monomers. The XPS spectra of the Fe 2p, C 1 s, and O 1s also prove that the addition of organic iron compounds (Fe(III)-EDTA and Fe(III)-citrate) and an inorganic iron compound (Fe-2(SO4)(3)) leads to oxidation of Fe2+ and sulfide species of the ruptured pyrite surface, resulting in a higher ratio of Fe3+ to Fe2+ and an increase of surface C=O and COOH groups and oxides.