The aggregation of Banko soil using temperature-responsive polymer and the consideration of aggregation mechanism

摘要

The soil particles are used in a wide range of field, such as a drilling fluid of construction site, drug and cosmetics. Solution including these soil particles, which are very fine particles and repel electrostatically by their negative charges in water, are easy to suspend. Hence, used-wastewater is generally discarded by coagulation sedimentation method with flocculant such as polyacrylamide. However, a further dehydration step is required because this flocculant aggregate with a large amount of water. To solve this problem, temperature-responsive polymer, which has a lower critical solution temperature (LCST), is being studied as a new flocculant. This polymer is soluble in water due to hydration below LCST and turns hydrophobic due to strong intermolecular hydrogen bond above LCST. In this study, two kinds of temperature-responsive polymer were used: One is a nonionic polymer of poly(N-isopropylacrylamide) (PNIPAM) which has LCST at 32°C. The other is a cationic polymer of poly((N,N-dimetylamino)ethyl methacrylate) (PDM) which has LCST at about 35°C. Using temperature-responsive polymer as a flocculant, these polymers adsorb surface on soil particles below LCST and they aggregate with soil particles while dewatering because they shrink with dehydrating. Furthermore, PDM is very easy to electrostatically adsorb on soil particles. In this study, aggregation performance of temperature-responsive polymer was observed by sedimentation test and filtration test using Banko soil. Also, polyacrylamide, which is a typical flocculant, was used as a comparative material and the aggregation mechanism of temperature-responsive polymer was investigated.