Der Einfluß von pH, Elektrolytkonzentration und Mischverfahren auf die Flockung von gefällten und pyrogenen Silikahydrosolen durch Polyethylenglykol

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Abstract
With a laser photosedimentometer one obtaines parameters which enable characterization of the turbidity and of the sedimentation in the Silica suspension flocculated by the adsorption of Polyethyleneglycols. By continuous addition of the polymer solution to the silica suspension the influences of the time of addition, stirring time, stirring intensity, polymer coverage, concentration of silica, pH and ionic strength on the flocculation state can be quantified. In contrast to pyrogenic silica precipitated silica is only flocculable by decreasing the pH below pH 3.5 or by addition of salt above 10−2 mol/l. The flocculation of pyrogenic silica is markedly dependent on the mixing conditions at high pH and without salt. At high salt concentrations and pH <3.5 the flocculation of precipitated and pyrogenic silicas becomes independent of mixing conditions.