Competitive interactions of dextran sulfate with positively charged particles and polymers

Precipitated calcium carbonate (PCC) was flocculated with cationic polyacry lamide (CPAM) in the presence of dextran sulfate (DS). The charge density o f the CPAM had little effect on the extent of flocculation. The effect of c hanging the order of addition of DS and CPAM was studied, including premixi ng CPAM and DS before addition of DS. Results were discussed in terms of co mpetition of the particles and CPAM for the DS, and then compared with resu lts obtained using suspensions of TiO2 and cationic latex with added DS. Th ese systems contain a much smaller amount of bound DS as compared to free, and the charge density of the CPAM determined the extent of flocculation ab le to be achieved. (C) 2001 Elsevier Science B.V. All rights reserved.