Fourier transform infrared (FTIR) spectral components of three dominant groups of sulfate species in synthetic schwertmannite (Fe(8)O(8)(OH)(6-x)(SO(4))(x)*nH(2)O) are presented. These components were extracted by multivariate curve resolution analysis of spectra obtained from N(2)(g)-dry samples initially reacted in aqueous solutions (pH 3-9) at room temperature. Each component contains complex sets of bands that correspond to mixtures of similar species. We tentatively assign these components to sulfate ions that are hydrogen- (components I and III) and iron-bonded (component I) to schwertmannite. Another component (II) is assigned to protonated sulfate species. Heating experiments to 130 degrees C moreover confirmed this possibility for component II. The spectral components extracted from this study can be used to identify dominant sulfate species in FTIR spectra of naturally occurring schwertmannite samples.