On the Types of Bond Developing between the Aluminium and Iron (III) Hydroxides and Organic Substances

During the coagulation-flocculation processes involved in the treatment of surface waters, dissolved organics are also incorporated into the aluminium and iron (III) hydroxide flocs. A part of the dissolved organics can thus be removed by simple solid-liquid phase separation techniques, like sedimentation, flotation, sand filtration. According to laboratory evidence, durable bonds between the coagulant, or the metal hydroxides thereof, develop only over the extremely short (a few seconds) period which elapses from the formation of the metal hydroxides to the intense aggregation of the metal hydroxide sols. The bonds between these latter and the organic substances are mainly of the hydrogen bridge type, but other secondary chemical bonds and adsorption are also involved. Owing to the chemical structure and relatively low concentration levels of the organic substances, direct valence chemical bonds between the coagulants or the metal hydroxides thereof and the organic substances develop to a slight extent only.