Abstract
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.
Highlights
Bentonite is a layered clay mineral, whose main component is montmorillonite composed of 2:1-layer structure of two tetrahedral silica sheets sandwiching one octahedral alumina sheet [1] [2]
From X-ray diffraction (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
The boundary between sediment and supernatant solution observed in this study indicates the terminal sedimentation rate of minimum bentonite particles
Summary
Bentonite is a layered clay mineral, whose main component is montmorillonite composed of 2:1-layer structure of two tetrahedral silica sheets sandwiching one octahedral alumina sheet [1] [2]. It takes enormous cost to carry and treat these suspensions To solve this problem, coagulating sedimentation method is generally used to separate bentonite and treated water by adding flocculant [17]. Above its LCST, PNIPAM turns hydrophobic due to strong intermolecular hydrogen bonding This reversible solubility of PNIPAM is attributed to a coil-globule conformational transition of polymer chains [25] [26] [27]. The reports of bentonite aggregation with PNIPAM as flocculant cannot be found except for our studies. In this study, aggregating performance of PNIPAM for bentonite was observed by sedimentation test. The effect of molecular weight of PNIPAM on aggregation behavior in the temperature change was investigated by observation of the change in sedimentation rate and volume and by measur-. A role of PNIPAM on bentonite aggregation was discussed by evaluating shift of diffraction angle of bentonite sediment, from X-ray diffraction (XRD) patterns, and the change in morphology of bentonite surface, from scanning electron microscopy (SEM), with change in molecular weight and concentration of PNIPAM
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
