Chemical and Biomolecular Engineering, University of Melbourne, Parkville, VIC 3010, Australia; CSIRO Mineral Resources, Clayton, VIC 3168, Australia.
Chemical and Biomolecular Engineering, University of Melbourne, Parkville, VIC 3010, Australia.
J Colloid Interface Sci. 2017 May 15;494:139-152. doi: 10.1016/j.jcis.2017.01.067. Epub 2017 Jan 21.
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. Furthermore, heating of the PNIPAM-dosed suspensions at shear rates below 200s produced larger and more breakage-resistant aggregates.
温度响应型絮凝剂，如聚（N-异丙基丙烯酰胺）（PNIPAM），在加热到低于临界溶液温度（LCST）以上时会引起可逆的颗粒聚集。本工作旨在通过使用聚焦光束反射测量技术原位测量弦长和实时观察颗粒聚集体，研究在连续剪切悬浮液中使用 PNIPAM 和常规聚丙烯酰胺（PAM）絮凝剂使磨碎铁矿石颗粒聚集。在不带电荷的 PNIPAM 存在下，仅在加热到 LCST 时才会发生颗粒聚集，并且随着进一步加热，聚集物会继续生长。随后的冷却会使聚集物重新分散，重复加热会导致重新形成。与不带电荷的 PNIPAM 不同，由于聚合物链通过丙烯酸钠基团与赤铁矿表面之间的吸引力与两个不同的颗粒结合，因此阴离子 PNIPAM 在低于 LCST 的温度下就会产生聚集物，并且可以在高于 LCST 的温度下添加，因为形成了荷稳胶束。在连续剪切下，最能抵抗聚集物粒径减小的絮凝剂是阴离子 PAM，其次是 PAM、阴离子 PNIPAM、PNIPAM（6MDa）和 PNIPAM（122kDa）。除了在剪切速率高于 550s 时的 PNIPAM（6MDa）外，所有样品都发现了可逆的聚集物破裂。此外，在剪切速率低于 200s 下加热 PNIPAM 加药悬浮液会产生更大和更不易破裂的聚集物。
