Effect of ionic strength on the adsorption of cationic polyelectrolytes onto alumina studied using electroacoustic measurements

The adsorption of numerous cationic polyelectrolytes onto alumina in aqueou s suspensions was investigated using electroacoustic measurements. Initiall y, the isoelectric point (IEP) of the Sumitomo AA05 alumina was identified at several different electrolyte (KCl) strengths. The IEP was found to depe nd on the presence of the electrolyte. With no electrolyte present, the SEP was 9.4; but with electrolyte present, there was a slight shift to higher pH, possibly due to adsorption of potassium ions on the alumina surface. Th e natural pH of the aqueous suspensions was 4.9; at this pH value, the part icles were highly positively charged and none of the polyelectrolytes adsor bed. The pH of the suspensions was then increased to 11.4; at this value, t he particles were highly negatively charged and all the polyelectrolytes ad sorbed, causing charge reversal. The amounts of polyelectrolyte then requir ed to obtain both zero zeta potential and the maximum plateau zeta potentia l were found to depend on the electrolyte strength of the suspension. This was attributed to the different configurations taken up by the polyelectrol yte on adsorption. (C) 2000 Elsevier Science S.A. All rights reserved.