DETACHMENT OF COLLOIDS FROM SEDIMENTS AND SAND GRAINS

The mechanisms of colloid transport and attachment have been studied in several fields and a reasonable understanding of the overall process has been developed over the past several decades. However, there is little fundamental understanding of the mechanisms of colloidal particle detachment from larger grains. The ongoing research explores particle detachment from both theoretical and experimental viewpoints. The theoretical studies have developed expressions that may be used to determine the magnitude of forces that would control particle detachment, including electrostatic and van der Waals forces. The results indicate differences when the computations are based on energies of interaction compared with forces of interaction. The initial experimental studies were performed on laboratory scale model systems with well-defined spherical particle suspensions. Latex particles (2 and 5 mum) were attached to a packed column containing glass beads as collector grains. Particle number concentrations were monitored using a laser, time of transition type, particle size analyzer (Brinkmann, Particle Size Analyzer). The detachment of particles during fluidized bed operations was studied in relation to the chemical characteristics of the water. Preliminary experimental results indicated that the detachment of latex particles was (a) independent of ionic strength of solution phase during attachment, but (b) was dependent on the ionic strength during detachment. Detachment efficiency was higher with lower ionic strength waters.