A study of dual polymer flocculation

Flocculation of alumina fines with combinations of the anionic form of a polyacrylic acid (PAA) and a high molecular weight cationic copolymer of acrylamide and quaternary acrylate salt (Percol) was investigated. Effects of PAA and Percol molecular weights as well as Percol charge density on the rate of flocculation were also investigated. In order to determine the role of the polymer conformation and changes in it due to the presence of another polymer, the fluorescence label method was employed to monitor PAA conformation at the alumina ∣ water interface under different polymer addition modes, such as the sequential addition of the two polymers vs. co-addition. Importantly, polymer size distribution was found to have a marked effect depending on the polymer type: in the case of PAA, a broader distribution yielded better flocculation; no such effect was observed with Percol. Based on the results, an overall mechanistic picture of dual polymer flocculation is proposed.