Coagulation mechanisms of iron salt and salicylic acid

This study focused on the reaction mechanisms exhibited by two iron coagulants and salicylic acid molecules. Experiments were performed to investigate the influence of polymeric and monomeric iron coagulants on treating waters containing natural analog organic matter. As predicted by the formation function theory, polyferric sulfate (PFS) consumed less alkali than FeCl3 during the coagulation process. This means that the PFS forms amorphous Fe(OH)(3) colloid more easily than the FeCl3. On the other hand, when the pH value was less than 4, the Fe(HI) ion could complex with the salicylic acid through coordination reaction. However, the complex compounds that formed from either PFS or FeCl3 under such conditions were too small to remove with filtration. At higher pH levels, iron-salt coagulates immediately reacted with OH- ion, forming amorphous Fe(OH)3 colloids and resulting in the adsorption of salicylic acid on Fe(OH)(3) colloid surfaces. Because the -OH and -COOH functional groups of salicylic acid have complex-forming O-donors, they coordinated with Fe(OH)(3) colloids on the surface layer of the oxide. Therefore, salicylic acid adsorbed on the surfaces of hydrous oxides through specific adsorption.