Evaluation of the Role of Silt Content on the Flocculation Behavior of Clay‐Silt Mixtures

Abstract

AbstractThe interactions and impacts of silt content on clay‐silt mixture flocculation processes and settling and floc properties were investigated from a series of laboratory experiments. The results demonstrate that the silt content in clay‐silt mixtures has an impact on the time‐evolution average floc size, peak floc size, and equilibrium floc size. Increasing the silt content reduces the floc strength, recovery factor, and average floc size. The silt fraction can present both cohesive and noncohesive characteristics in silt‐clay suspensions. The bulk concentration of clay‐silt mixtures was found to reasonably correlate with the average floc sizes under equilibrium conditions and with maximal floc sizes under both equilibrium and nonequilibrium conditions. The results also show that the flux‐settling velocities increase with increasing silt content. Specifically, the flux‐settling velocities are 0.66, 0.87, and 1.39 mm/s for mixing ratios of clay‐silt of 1:0.5, 1:1, and 1:2.5, respectively, under equilibrium conditions. Under growth‐breakup‐reflocculation (G‐B‐R) conditions, the percentage changes in the flux‐settling velocities of flocs during the regrowth period are 22%, 41%, and 42% less than those under equilibrium conditions. Therefore, both the silt content and hydrodynamic conditions need to be taken into consideration when determining the flux‐settling velocities under variable shear conditions. The findings from this research provide better insight into the highly complex role of silt in the flocculation process of clay‐silt mixtures in natural water environments.