Fig. 11 Diffuse reflectance infrared Fourier transform (DRIFT) spectra of goethite reacted at pH 5.0 with (a) 0.10 M Na₂SeO₄ + 1.0 M NaCl, and (b) 1.0 M NaCl alone, and the difference spectrum (a–b). The solid to KBr ratio was 5 to 95 mg. The BET N₂ surface area of goethite was 21.8 m² g^-1