Salt concentration influence on the efficiency of two cationic polymeric flocculants

The influence of the increase of the solution ionic strength on the flocculation of charged latex particles in the presence of cationic polymers is reported. Empirical flocculation rate constants are experimentally determined using particle counting and for two cationic polymers, one linear and the second with two branches. Comparisons are made with a solution containing monovalent salt only at different ionic concentrations in the absence of polymers. In all cases, polymer-induced flocculation is significantly more efficient than charge screening effects using salt only. Analysis of zeta potential measurements indicates that the charge neutralization and surface charge variations dictate the stability of the latex suspensions. Moreover, the addition of a small amount of salt in the polymer–particle mixtures results in a dramatic decrease of the polymer efficiency which is more pronounced for the linear polymeric flocculant. By increasing further the ionic strength, the rates of polymer flocculation are found to increase again but remain smaller than in the absence of salt.