3.4. Infrared spectra analysis
In order to determine the functional groups responsible
for metal uptake, infrared spectroscopy was used. A
raw, unreacted biosolids sample (Fig. 4) and biosolids
pretreated with a 100 mgyl zinc solution (Fig. 5) were
analysed. The spectra indicate the presence of carboxyl
groups. Carboxylic acids display a broad, intense –OH
stretching absorption from 3300 to 2500 cmy1, although
the bands are dominated by the –OH stretch due to
bonded water. Weaker –CH stretch bands are superimposed
onto the side of the broad –OH band at 3000–
2800 cmy1. The strong peak at 1647 cmy1 is caused