A new efficient tannin-based flocculant made by a new modification idea: multiple rounds of Mannich reaction with aminated tannins as ammonia chloride.

This research provided a new modification idea and made a new high-efficiency plant-based flocculant through the three rounds of reactions using tannin, formaldehyde, and ammonia chloride. Tannins as a concerned natural flocculant are mainly through a round of Mannich reaction to cationic modification now. This research provided a new cationic modification idea with the three rounds of Mannich reactions to obtain a modified tannin with a larger molecular weight and more complex structure. The synthesis and flocculation tests were conducted to study the effects of rounds of reaction, reactants ratio, reaction time of each round, and pH on the flocculation ability of the synthetically modified tannins. The increased flocculation capacity of modified tannins occurred with the increased rounds of reactions by increasing the electric neutralization and bridging capacity. The results of this research showed the increased flocculation capacity of the modified tannins with the increased ratio ((formaldehyde or ammonium chloride)/tannin). The flocculation capacity of the modified tannins is the greatest in the appropriate reaction time of each round (4 + 4 h) and pH (pH = 2). According to model fitting, the optimal synthesis condition is 1:6.094:6.094, 7.092 h, and pH = 2.476, which has been tested experimentally. The new modification idea and new high-efficiency modified tannin are very meaningful to the application of environmentally friendly flocculants and to solve the disadvantages of traditional chemical flocculants.