Mechanism of polyelectrolyte transfer during heteroflocculation

摘要

The flocculation kinetics of colloids (fines) on polymer-coated collectors (fibers) was quantified. The variables of interest include shear rate, salt concentration, and polymer chemistry. After an initial deposition on the collector surface, the colloids slowly detach to form a stable suspension. This is caused by polymer transfer. A theoretical model describing the simultaneous kinetics of colloid deposition on polymer-coated surfaces and polymer transfer was developed and validated. The flocculation is characterized by three rate constants: k(1) (deposition), k(2) (detachment), and beta (polymer transfer coefficient). Two limiting cases were identified in the colloids detachment/polymer transfer behavior, which correspond to flocculation mechanisms by bridging and by charge reversal. Low-M-W, highly charged polyelectrolytes provide weak bonds thigh detachment rates) and a low transfer coefficient. Contrarily, high-M-W, weakly charged PAMs provide stronger bonds (low detachment rates) but are more efficiently transferred. The different behavior was explained by the different layer conformations of both cases. References: 28