The effective use of recycled supernatant that contains temperature-responsive flocculant is demonstrated for solid-liquid separations._x000D_
The recyclability of poly(N-isopropylacrylamide) (PNIPAM) of several different molecular weights and a 15 per cent negatively charged derivative are compared. Batch settling tests of -alumina suspensions are first conducted at 50C, with a subsequent 25C period, after which the supernatant is harvested and used to flocculate subsequent suspensions. Using this procedure consecutive separations are obtained with the repeated recycling of uncharged PNIPAM containing supernatant. Batch settling tests indicate that hindered settling rates increase with molecular weight of PNIPAM. Adsorption studies indicate that strong adsorption of PNIPAM onto alumina occurs with PNIPAM at 50C and that significant desorption occurs after cooling at 25C. However, the extent of desorption decreases with molecular weight resulting in low amounts of PNIPAM for recycling and poor settling behaviour when high molecular weight PNIPAM is recycled. Little recyclability was evident using the negatively charged PNIPAM. On the basis of these findings a recycling-thickener apparatus that uses low molecular weight uncharged PNIPAM is proposed._x000D_
CITATION:O'Shea, J-P, Qiao, G and Franks, G, 2010. Demonstration of solid-liquid separations using recycled supernatant that contains temperature-responsive polymer, in Proceedings XXV International Mineral Processing Congress (IMPC) 2010, pp 377-388 (The Australasian Institute of Mining and Metallurgy: Melbourne).