Characterization of Multiple Hindered Settling Regimes in Aggregated Mineral Suspensions

Michael Johnson, Jeffrey Peakall, Michael Fairweather, Simon Biggs, David Harbottle, Timothy N. Hunter

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

Aqueous suspensions of magnesium hydroxide are shown to exhibit low ζ-potential behavior and highly complex settling dynamics. Two distinct regimes of hindered settling behavior are observed on either side of a threshold concentration, η, of 2.38% v/v, which is considerably below the gel point, ηg, observed at 5.4 ± 1.6% v/v. The low-concentration regime was characterized by a very large Richardson and Zaki exponent of 146, a factor of 10 larger than that of the high-concentration regime. Michaels and Bolger analysis of the low-concentration regime implies settling governed by large, low-density macroaggregates of 138-147 μm diameter and low intraaggregate packing fractions on the order of 0.05, which is in good agreement with in situ particle characterization undertaken using particle vision and measurement (PVM) and focused-beam reflectance measurements (FBRM). The large macroaggregates must undergo some shear densification within the higher-concentration hindered settling regime in order for the suspension to gel at a concentration of 5.4% v/v. Consequently, fluid flow past small, shear-resistant primary agglomerates, observed within the aggregates using scanning electron microscopy and flow particle image analysis, during aggregate densification may represent the limiting step for dewatering within the high-concentration regime.

Original languageEnglish
Pages (from-to)9983-9993
Number of pages11
JournalIndustrial and Engineering Chemistry Research
Volume55
Issue number37
DOIs
Publication statusPublished - 21 Sep 2016
Externally publishedYes

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