Weston J S, Chun J, Schenter G, Weigandt K, Zong M, Zhang X, Rosso K M, Anovitz L M
Russell School of Chemical Engineering, University of Tulsa, Tulsa, OK 74104, United States.
Pacific Northwest National Laboratory, Richland, WA 99354, United States; Benjamin Levich Institute, CUNY City College of New York, New York, NY 10031, United States.
J Colloid Interface Sci. 2020 Jul 15;572:328-339. doi: 10.1016/j.jcis.2020.03.109. Epub 2020 Mar 31.
The rheology of complex suspensions, such as nuclear waste slurries at the Hanford and Savannah River sites, imposes significant challenges on industrial-scale processing. Investigating the rheology and connecting it to the agglomerate morphology and underlying particle interactions in slurries will provide important fundamental knowledge, as well as prescriptive data for practical applications. Here, we use suspensions of nano-scale aluminum oxyhydroxide minerals in the form of boehmite as an analog of the radioactive waste slurry to investigate the correlation between particle interactions, agglomerate morphology, and slurry rheology.
A combination of Couette rheometry and small-angle scattering techniques (independently and simultaneously) were used to understand how agglomerate structure of slurry changes under flow and how these structural changes manifest themselves in the bulk rheology of the suspensions.
Our experiments show that the boehmite slurries are thixotropic, with the rheology and structure of the suspensions changing with increasing exposure to flow. In the slurries, particle agglomerates begin as loose, system-spanning clusters, but exposure to moderate shear rates causes the agglomerates to irreversibly consolidate into denser clusters of finite size. The structural changes directly influence the rheological properties of the slurries such as viscosity and viscoelasticity. Our study shows that solution pH affects the amount of structural rearrangement and the kinetics of the rearrangement process, with an increase in pH leading to faster and more dramatic changes in bulk rheology, which can be understood via correlations between particle interactions and the strength of particle network. Nearly identical structural changes were also observed in Poiseuille flow geometries, implying that the observed changes are relevant in pipe flow as well.
复杂悬浮液的流变学，如汉福德和萨凡纳河场地的核废料淤浆，给工业规模的处理带来了重大挑战。研究流变学并将其与淤浆中的团聚体形态及潜在的颗粒相互作用联系起来，将提供重要的基础知识以及实际应用的规范性数据。在此，我们使用勃姆石形式的纳米级氢氧化铝矿物悬浮液作为放射性废料淤浆的类似物，来研究颗粒相互作用、团聚体形态和淤浆流变学之间的相关性。
采用库埃特流变测量法和小角散射技术（单独和同时使用）相结合的方法，来了解淤浆的团聚体结构在流动状态下如何变化，以及这些结构变化如何在悬浮液的整体流变学中体现出来。
我们的实验表明，勃姆石淤浆是触变性的，悬浮液的流变学和结构随着流动时间的增加而变化。在淤浆中，颗粒团聚体最初是松散的、跨越整个体系的团簇，但在中等剪切速率作用下，团聚体会不可逆地固结为有限尺寸的更致密团簇。结构变化直接影响淤浆的流变学性质，如粘度和粘弹性。我们的研究表明，溶液的pH值会影响结构重排的程度和重排过程的动力学，pH值升高会导致整体流变学更快、更显著的变化，这可以通过颗粒相互作用与颗粒网络强度之间的相关性来理解。在泊肃叶流动几何形状中也观察到了几乎相同的结构变化，这意味着所观察到的变化在管道流动中也具有相关性。
