Aluminum Hydroxide - Polyacrylamide Hybrid Materials Preparation And Dilute Solution Behavior And Flocculation Performance Study

Four kinds of organic-inorganic hybrid flocculants, i.e., ionic hybrid of Al(OH)3-polyacrylamide (I-hPAM), ionic hybrid of modified palygorskite - polyacrylamide (I-hMPAM), covalent hybrid of Al(OH)3-poiyacrylamide (C-hPAM) and covalent hybrid of Al(OH)3-cationic polyacrylamide (C-hCPAM) , have been synthesized respectively. The hybrids were characterized with 1H-NMR, IR spectrum, viscosity, conductivity, size exclusion chromatography (SEC), TEM and TGA. It was found that the hybrids above could be star-like hybrids.Two kinds of ionic hybrids have been prepared in different ways. The I-hPAM flocculants have been synthesized using a redox initiation system ((NH4)2S2O8/NaHSO3) by in-situ polymerization of acrylamide in aqueous medium of colloidal Al(OH)3. The I-hMPAM flocculants have been synthesized by in-situ polymerization of acrylamide using heterogeneous redox initiator system, composed of ethanolamine modifying palygorskite together with oxidant Ce4+. It was found that ionic bond formed between inorganic particles and polyacrylamide, i.e., PAM with negative chain end(-SO42-) bonding to the positive particle of Al(OH)3 colloid in I-hPAM and PAM with positive chain end(NH3+) bonding to palygorskite with O in I-hMPAM . Dilute solution viscosity behaviors of ionic hybrids have been studied. The reduced viscosity (sp/C) ~ concentration (C) curve of the I-hPAM has been found having a discontinuity or downturn at low concentration region. This discontinuity phenomenon is accounted for assuming ionization of the ionic hybrid PAM. Studies on conductivity behavior and incipient concentration dependence of SEC graph for I-hPAM and I-hMPAM support the ionization of the ionic hybrids in the dilute solution.C-hPAM hybrid has been synthesized by polymerization of acrylamide using a redox initiation system of Al(OH)3-diglycol hybrid / Ce4+. Characterizations showed the covalent bond between Al(OH)3 and PAM in the hybrid. Dilute solution viscosity behavior of C-hPAM has been studied. The reduced viscosity (sp/C) ~ concentration (C) curve of the C-hPAM has been found having a discontinuity or upturn at low concentration region same as the star-like polymer.Five kinds of flocculants with different chain end groups (PAM, star-PAM, I-hPAM, I-hMPAM and C-hPAM hybrids) have been used. The flocculation behavior for 0.25wt% kaolin suspension was evaluated by spectrophotometer and phase contrast microscope (PCM). It was found that their flocculation efficiencies decease in the following order: C-hPAM>I-hMPAM>I-h-PAM>star-PAM>PAM. Also, the hybrid flocculants showed less shear sensitivity and give more dense flocs than pure PAM. Much better flocculation of hybrid flocculants was attributed to the synergism of the inorganic particle and polymer, which act as the charge neutralization or adsorption and bridging respectively. In addition, the hybrid flocculants were used to treat mixture of domestic and industrial wastewater. The result shows that hybrid flocculants are promising flocculants in wastewater treatment.The cluster theory of polymer solution was first applied to explain the mechanism of flocculation. It was found that the optimal dose (Cod) of polymer flocculants is proportional to the dynamic contact concentration (Cs) of polymer flocculants and to the suspension solid content (Css) in kaolin suspensions, i.e., Cod = 5.74×104(Cs·Css) 0.5—3.1. The result shows that it is important to form the polymer clusters in dilute solutions for reaching the best flocculation.