Analytical methods used in the analysis of red iron pigments – opportunities and limitations

The purpose of this study was to investigate the chemical composition of red iron pigments based on waste iron sulfate. As a model waste, waste iron(II) sulfate from Grupa Azoty Zakłady Chemiczne POLICE S.A is used. Obtained pigments were also compared to commercially available materials from various manufacturers like BASF (Germany), Percheza (Czech Republic), Boruta-Zachem (Poland) or Edan (Poland).

Pigments were analyzed with several analytical methods like: X-Ray Diffraction, Dynamic Light Scattering, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, Helium Ion Microscopy and Scanning Electron Microscopy.

In determining the phase and chemical composition, we encounter some limitations of the methods. For example, during XRD analysis using Cu-Kα source, quartz-derived phases were visible in some commercial pigments. Comparing these results with FTIR analysis, the presence of quartz was confirmed, but in addition, vibrations from CaCO₃ were seen, which was not visible in XRD. Only by changing the radiation source in XRD to Co-Kα was it possible to detect phases originating from CaCO₃.

Precise knowledge of the contents of samples is frequently lacking prior to analysis. This is particularly true for external samples, which are frequently examined without prior information. Consequently, it is crucial to combine various analyses to obtain the most accurate results.