Flocculation and dewatering behaviour of smectite dispersions: effect of polymer structure type

In this study, the influence of polymer structure type on the flocculation and dewatering behaviour of smectite clay dispersions has been investigated. Anionic polyacrylamide-acrylate copolymer (PAM) and non-ionic polyethylene oxide (PEO) polymer adsorption onto smectite particles, in the presence of 5 x 10(-2) M Ca(II) ions, led to polymer structure dependent modifications in surface chemistry, shear yield stress, settling rates and consolidation behaviour. The magnitude of the particle zeta potential decreased with increasing flocculant concentration for both polymers but was significantly greater for PEO than PAM. Polymer adsorption studies showed that PEO displayed a higher affinity and greater adsorbed density than PAM, consistent with the zeta potential data. An optimum flocculant dosage for an enhanced flocculation performance was observed at 500 g polymer/ton solid, where less than 50% the plateau adsorbed amount for both polymers occurred. The magnitude of the shear yield stress was strongly dependent upon the polymer structure and concentration. PEO produced greater particle interactions and more strongly networked floes, reflecting higher shear yield stress than PAM. Significant improvement in the dewatering rate was observed in the presence of PEO in comparison with PAM, at similar polymer concentration. Furthermore PEO flocculated dispersions showed dramatic improvement in consolidation upon shear whilst PAM produced no such effect. A strong correlation between the polymer structure type and flocculation performance, floc shear-sensitivity and the dewatering behaviour of smectite dispersions was established. (C) 2003 Elsevier Ltd. All rights reserved.