Fig. 12 Attenuated total reflectance–Fourier transform infrared (ATR–FTIR) difference spectra of am-Fe(OH)₃ equilibrated at pH 5.0 with (a) 0.5 M Na₂SeO₃ + 1.0 M NaCl, and (b) 1.0 M NaCl alone. The subtracted reference spectra were the supernatant solutions. The initial solid concentration was 200 g L^-1 before centrifugation and the solid concentration in the ATR reservoir was 1000 g L^-1. The interfacial Se(IV) spectrum was presented as (a–b)