Abstract
In order to enhance the sedimentation after precipitation processes, a high frequency ultrasound was irradiated to particle dispersion just after the reaction. The reaction system selected was calcium chloride and hydrogenphosphate which produces calcium phosphate. The reaction is used in sewage treatment plant to recover or to remove phosphate from the effluent. The formation of fine particles results in the lowering of the separation of phosphate. Enlarging the crystal or aggregation is highly effective for the separation due to the short settling time and easier dehydration of the solid-liquid mixture. In the present study, 2.0 MHz ultrasound was irradiated for 1 minute to the mixture of the solutions of calcium chloride and hydrogenphosphate just after the reaction. After settling for a while, the mixture separated into layers such as clear, cloudy and dense. With the progress of sedimentation, the clear layer develops and the boundaries move down. Change of the height of the boundaries was monitored with time and the separation was compared with and without ultrasonic irradiation. The seppration with ultrasonic irradiation was much faster than that without ultrasound. The result clearly shows that sedimentation of particles of calcium phosphate is successfully accelerated by ultrasonic irradiation. Furthermore, particles were observed with digital CCD microscope for both samples with and without irradiation. The picture shows that crystal formation in sonicated samples, while no crystals were found in the sample without sonication. The ultrasound triggered growth of the crystal.
