Ultra flocculation of quartz suspensions: effects of shear rate, particle size distribution and solids content

Abstract

The process of ultra flocculation of fine quartz suspensions with a cationic flocculant has been studied. The influence of several variables such as quartz particle size distribution, solids content and shear rate has been investigated. It has been shown that the fine quartz suspensions (quartz particle diameter <5 μm) can be effectively flocculated in high non-uniform hydrodynamic fields (mean shear rate >2000 s–1) during a short treatment time (<6 s) whereas for the coarse quartz suspensions (particle size in the range from 5 to 10 μm) the optimum hydrodynamic regime is reached at mean shear rates in the range from 500 to 1000 s–1 and the treatment time longer than 10 s. The water content of the flocculated sediment, when plotted versus shear rate, shows minimum around the range 2000–3000 s–1. The water clarity after sedimentation of the flocculated material is quite good at shear rates higher than 2000 s–1. Increasing solids content in the suspension inhibits uniform distribution of flocculant in the suspension but this can be improved by increased shear rate.