RESUMEN
The flocculation efficiency of polyelectrolytes in a high-ionic-strength environment is often affected and reduced due to shielding of the active ionizable functional groups, as well as changes in the surface chemistry of the solid slurry. To address this problem, a series of well-defined novel ABA triblock copolymers were employed for the flocculation of high-ionic-strength kaolin slurries at three different Ca2+ concentrations (0.05, 0.10, and 0.50 M). The primary focus was on the advancement in the polymer architecture, where the anionic functionalities were localized at the terminal ends. Typical commercial flocculants tend to have anionic functionalities randomly distributed throughout the polymer chain and hence a higher propensity toward condensed conformation and formation of insoluble species. In comparison to a control random copolymer, the ABA triblock copolymers were able to flocculate kaolin slurries to give faster settlement rates, particularly at the high Ca2+ concentrations of 0.10 and 0.50 M. In addition, these polymers had significantly better clarification ability at higher Ca2+ concentrations compared to the control random copolymer. The ABA triblock copolymer architecture may therefore have potential as a flocculant in high-ionic-strength applications.
RESUMEN
Temperature-responsive flocculants, such as poly(N-isopropylacrylamide) (PNIPAM), induce reversible particle aggregation upon heating above a lower critical solution temperature (LCST). The aim of this work is to investigate the aggregation of ground iron ore using PNIPAM and conventional polyacrylamide (PAM) flocculants in a continuously-sheared suspension, through in situ chord length measurements using Focused Beam Reflectance Measurement techniques and real-time imaging of the particle aggregates. In the presence of uncharged PNIPAM, particle aggregation occurs only upon heating to the LCST, and the aggregates continue to grow with further heating. Subsequent cooling re-disperses the aggregates, and repeated heating causes reformation. Unlike uncharged PNIPAM, anionic PNIPAM produces aggregates at temperatures below the LCST due to the polymer chains binding to two different particles via attractive interactions between the acrylic acid groups and the hematite surfaces, and can be added at temperatures above the LCST due to the formation of charge-stabilised micelles. Under continuous shear, the flocculant most able to resist aggregate size reduction was anionic PAM, followed by PAM, anionic PNIPAM, PNIPAM (6MDa), and PNIPAM (122kDa). Reversible aggregate breakage was found with all samples, except with PNIPAM (6MDa) after being subjected to shear rates above 550s-1. Furthermore, heating of the PNIPAM-dosed suspensions at shear rates below 200s-1 produced larger and more breakage-resistant aggregates.