Effect of electrolytes on interactions between a novel organic-inorganic hybrid polymer flocculant and kaolinite particles

Abstract

A novel copolymer, Al(OH)3-poly[N-isopropylacrylamide-co-N-[3-(Dimethylamino)propyl]methacrylamide] polyacrylamide (Al(OH)3-p[NIPAM-co-PMADMA]) was synthesized and characterized. The flocculation behavior of fine kaolinite by the temperature-responsive copolymer in different electrolyte solutions was studied by settling tests, measurements of lower critical solution temperature (LCST) and dissipative quartz crystal microbalance (QCM-D). The solution salinity and the type of electrolytes were shown to play a critical role in controlling the interactions between the synthesized flocculants and kaolinite particles. The initial settling rate (ISR) of kaolinite suspension increased initially and then decreased with further increasing the electrolyte concentration of NaCl, CaCl2, NaH2PO4 or Na2CO3. At low electrolyte concentrations, the electrolyte addition increased the adsorption of polymer on kaolinite particles. The effect of electrolyte addition on kaolinite flocculation followed the trend of Na2CO3＞CaCl2＞NaH2PO4＞NaCl, which can be described by the classical DLVO theory. However, the higher concentration of electrolytes led to a weaker adsorption and more compressed conformations of Al(OH)3-p[NIPAM-co-PMADMA] chains on both silica and alumina surfaces which mimic two types of kaolinite basal planes. The salting-out effect was found to be an important reason for polymer phase transfer, which inhibited the flocculation performance at higher electrolyte concentrations.