EFFECTS OF DOSING AND MIXING CONDITIONS ON POLYMER FLOCCULATION OF CONCENTRATED SUSPENSIONS

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Abstract
A simple monitoring technique has been used to derive information on Hoc growth and break-up in agitated clay suspensions of quite high solids content (1 and 3% w/v), under the influence of a high molecular weight cationic polymer. For fairly low polymer dosages and high mixing speeds floe growth in the 3% suspensions can be very fast initially, but the floes rapidly break up and do not re-form, even when the stirring speed is subsequently reduced. By reducing the mixing speed very soon after polymer dosing (typically after a few seconds), the break-up can be prevented and floes maintained at larger sizes. This effect is much less apparent for 1% solids suspensions, where longer periods of rapid mixing can be tolerated without significant floe break-up. For the higher solids case, great improvements in flocculation can be achieved by modifying the polymer dosing procedure—either by adding the solution over an extended period or by dosing a more dilute solution. These changes have much less effect at the lower solids concentration.