In the clarification process of coal slurry water in coal preparation plants, most of them use anionic polyacrylamide as a flocculant. For different types of coal slurry water, which type of polyacrylamide is the best and how the molecular weight affects the flocculation effect, different researchers have different conclusions. This study used UV polymerization method to synthesize nonionic, anionic and cationic types of polyacrylamide in the laboratory, and explored the flocculation effect and mechanism of different types of polyacrylamide on coal slurry water.
Through the research, it can be concluded that the flocculation effect (transmittance) of nonionic polyacrylamide is related to its molecular weight. As the molecular weight increases, the flocculation effect on coal slurry water gradually improves. This is because the amide group (-CONH2) of polyacrylamide ( — CONH2) is in close contact with the coal slurry particles and adsorbs to form hydrogen bonds, and the high molecular chain forms bridges between the adsorbed particles. Therefore, the flocculation effect of nonionic polyacrylamide mainly depends on the molecular weight of polyacrylamide. However, due to the decrease in the solubility of polyacrylamide with the increase in molecular weight, when the molecular weight is greater than 6 million, the increase in flocculation effect slows down, and when it is greater than 8 million, the increase is not obvious. Generally, it is considered that the polyacrylamide flocculant used for coal slurry water treatment has a molecular weight of about 8 million as being relatively appropriate.
Anionic polyacrylamide for coal slurry sedimentation not only has the high molecular flocculation effect, but also undergoes ion adsorption, bridging and electrical neutralization. When the anion degree is 30%, these effects superimpose to achieve the best flocculation effect. Therefore, the anion degree of polyacrylamide used for coal slurry water treatment should be controlled at around 30%.
Cationic polyacrylamide is suitable for treating fine-grained and high-sulfur flotation tailings. The flocculation effect is best when the cation degree is 10% - 20%. Further increase in the cation degree reduces the bridging and flocculation effects due to the interference of high-density charges, and the synthesis of polyacrylamide with high cation degree is difficult. Generally, the cation degree of polyacrylamide is 5% - 10% is sufficient.