The crystal structure and Gibbs free energy of formation of chukanovite as an oxidation product of carbon steel in human liver

Chukanovite has been identified as an oxidation product of carbon steel in a human liver through powder X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Steel oxidation products include siderite, chukanovite, vivianite, magnetite, goethite, 2-line ferrihydrite. Hydroxylapatite and amorphous silica surrounding the oxidized steel are precipitated from body fluid. The Rietveld refinement of the chukanovite structure shows it is as expected monoclinic, space group of P21/a, with a = 12.402(2), b = 9.414(1), c = 3.216(1) Å, β = 97.73(3)°. The standard Gibbs free energy of formation of chukanovite is estimated at −1167.2 ± 1.2 kJ mol−1 from the equilibrium between siderite and chukanovite. By using linear free energy relationship, the Gibbs free energy of formation for other isostructural phases of pokrovskite, parádsasvárite, and nullaginite are predicted. The results of this study could improve the mineralogical and geochemical properties of chukanovite which is an oxidation product of carbon steel relevant also in radioactive waste containers and oil/gas pipes. Furthermore, the combined method of experimental measurements and geochemical modeling could be a useful tool to study the formation of inorganic solid precipitates and bio-materials in biofluids, and is especially important in medical mineralogy field.