Sedimentation tests of bentonite suspension were carried out by adding various concentrations of poly( N -isopropylacrylamide) (PNIPAM) with different molecular weights as flocculant below and above lower critical solution temperature (LCST). Also, the effect of PNIPAM on aggregation of bentonite was investigated by sedimentation rate, turbidity of supernatant. Additionally, XRD patterns and SEM photographs were measured in order to consider aggregation mechanism of PNIPAM. The sedimentation rate and turbidity for the PNIPAM with large molecular weight or PNIPAM solution of high concentration above LCST were faster and clearer than those with small molecular weight or low concentration. From XRD patterns, the peak of bentonite sediment with PNIPAM shifted to the low-angle side, suggesting that a part of PNIPAM chain entered between bentonite layers. Furthermore, it was confirmed by SEM photographs that PNIPAM covered bentonite surface after sedimentation test. It was indicated that PNIPAM adsorbs on the bentonite surface and aggregates each bentonite particle above LCST. From these results, PNIPAM works as a flocculant and the PNIPAM with large molecular weight has a good ability.
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