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.

Construction of titanium-aluminum xerogel composite coagulant for removal of tetracycline in water: synergy effects and improvement mechanisms insight

Titanium xerogel coagulant (TXC) is a new type of coagulant that has attracted much attention in recent years. However, the tetracycline removal performance of TXC was not satisfactory because low isoelectric point (pH_iep) inhibited the electrical neutralization efficiency of TXC in an alkaline environment. To overcome this shortcoming, a composite xerogel coagulant (titanium-aluminum xerogel composite coagulant) was prepared. The removal of tetracycline and turbidity was used as evaluation indexes. It was proved that the combination of aluminum (III) and titanium (IV) enhanced the resistance of TXC to pH. The synthesized titanium-aluminum xerogel composite coagulant (TXAC) has an excellent removal ability of tetracycline in a wide pH range (pH = 5-10). At pH 8.8, the dosage required to remove 80% tetracycline from water decreased from 93 (TXC) to 35 mg/L (TXAC). The reason for this improvement could be attributed to (i) aluminum (III) enhanced the electric neutralization of TXC to negatively charged pollutants in an alkaline environment; (ii) the complexing ability of organic matter and aluminum (III) was enhanced. This work provides a feasible scheme for the pretreatment of tetracycline in water to meet the pretreatment requirements of special water.