The pivotal role of polymer adsorption and flocculation conditions on dewaterability of talcaceous dispersions

Abstract

In this study, the links between interfacial chemistry, polyethylene oxide (PEO) flocculant adsorption behaviour, orthokinetic flocculation and dewatering behaviour of talc mineral dispersion have been investigated. The effect of Mg(II) ions, suspension conditioning time, solid loading, PEO dosage and shear was probed. Unflocculated dispersion of weakly charged, polydispersed talc particles at pH 7.5 displayed very poor settling rate but good sediment consolidation (∼47 wt.% solid). PEO polymer adsorption rate and density were greater at higher than lower Mg(II) ion concentration. The adsorption propensity also decreased with increasing suspension conditioning time. An inverse correlation was observed between PEO adsorption rate/affinity and settling rate where slower adsorption kinetics led to larger and faster settling flocs. At equivalent PEO dosages (e.g., 200 g polymer t −1 solid), 8 wt.% solid dispersion solid produced both superior supernatant clarity and greater sediment consolidation than the markedly faster settling, dilute (2 and 4 wt.% solid) suspensions. The influence of Mg(II) ions and conditioning time on settling rate was PEO dosage dependent, however, these factors had no noticeable effect on sediment consolidation. Dramatic enhancement of flocculated sediment compaction (from 38 to 52 ± 2 wt.% solid) was achieved in secondary dewatering under moderate shear. The results provide useful fundamental knowledge of polymer adsorption rate, adsorption affinity and interparticle bridging behaviour which underpin the flocculation and dewatering of talcaceous clay suspensions for significant improvement.