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Polyelectrolyte enhanced flocculation, particle interactions and dewaterability of fine gibbsite dispersions
Author(s) -
AddaiMensah Jonas,
Bal Heramb,
Yeap KaiYing
Publication year - 2008
Publication title -
asia‐pacific journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.348
H-Index - 35
eISSN - 1932-2143
pISSN - 1932-2135
DOI - 10.1002/apj.110
Subject(s) - flocculation , chemical engineering , settling , dewatering , polyacrylamide , rheology , polymer , gibbsite , chemistry , particle size , materials science , mineralogy , chromatography , composite material , environmental engineering , kaolinite , geotechnical engineering , geology , engineering
Enhanced dewaterability of colloidal hydrophilic mineral dispersions, via flocculation and gravity‐assisted thickening, remains an important and technically challenging issue. To develop the right customized approach for flocculant selection to improve dewaterability, the influence of eight polyacrylamide (PAM) copolymers on flocculation, particle interactions and dewatering behaviour of fine, 9.5 wt% gibbsite dispersions at pH 7.5, 9.5 and 11.5 at 22 °C is investigated. The results show that polymer charge type (anionic vs cationic) and charge density (5–45%) and molecular weight [(5–20) × 10 6 Da] had a striking, pH‐dependent impact on dewaterability and dispersion rheology. Depending upon polymer type and dosage (50–200 g t −1 solid) and pulp pH, good to extremely fast settling rates (14–200 m h −1 ) were obtained upon orthokinetic flocculation. Sediment solid loadings recorded also showed polymer structure‐ and pH‐dependency and were in the range 40–54 wt%. Upon shear of the pre‐sedimented pulps, a 6–10 wt% solid improvement in consolidation resulted. The polymer with lower charge density (5% anionic) and lower molecular weight [(5–10) × 10 6 Da] was more effective in producing enhanced dewaterability of charged and neutral gibbsite particles than the polymers with higher molecular weights and/or charges. The settling rate, sediment consolidation and particle interactions (rheology) correlated positively, where faster settling flocs displayed higher sediment yield stresses which were accompanied by greater compaction behaviour. The findings underscore the need for greater understanding of the interplay between pulp interfacial chemistry and flocculant characteristics for optimum dewaterability. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.