Figure shows different transmittances and absorptions of sludge collected over time . The transmittances of sludge observed after 5 min (blue line) were higher than other sludge densities. This indicates that this sludge is less dense while the sludge collected after 10 (pink line) and 25 min (black line) were denser than others. This highly correlates with their calculated concentrations provided in Table and The FT-IR spectra confirm the formation and presence of different minerals in the sludge produced during the experiment. The valuable peaks are 432.18 cm -1 could be attributed to the doubly degenerate ν2 SO4 2-bending mode . The peaks found at 554.82 cm -1 are attributable to the metal oxides such as Fe-O (iron oxide minerals), the peaks 1025.73 cm -1 corresponds to ν3 SO4 2-, and 1636.33 cm -1 might correspond to δH2O of the jarosite mineral . Five peaks are noted at 1104.21, 1163.90, 1314.32, 1432.05, 2894.66, and 3301.80 cm -1 are also due to water stretching bands of different minerals. The observation of these multiple water stretching bands gives credence to the non-equivalence of water units in the aluminum sulphate hydrate structure which may be present in the sludge . The infrared bands between 3167 and 3412 cm -1 are attributed to ν-OH due to water in the sludge . The peak observed between 1000 and 1170 cm -1 , with an intense band around 1015.10 cm -1 can be attributed to δ-OH vibration of mineral compounds such as akageneite [Fe 3+ O(OH, Cl)] and jarosite [Fe 3+ 3(OH)6(SO4)2] -, which are always present in the sludge .