Ionic strength dependence of aggregate size and morphology on polymer-clay flocculation

Nikolas Wilkinson, Athena Metaxas, Eric Brichetto, Susith Wickramaratne, Theresa M. Reineke, Cari S. Dutcher

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

Polymer-driven flocculation of suspended particles is a critical process for many applications, including composite materials synthesis, paper manufacturing, and water treatment. However, the role of solution physicochemical properties on the polymer-particle assembly dynamics is nontrivial, particularly for non-spherical, polydisperse particulates such as natural clays. In this work, we study the effects of ionic strength and aggregate size and structure on the polymer behavior and flocculation performance with anisotropic bentonite clay particles. Using jar tests, laser diffraction, confocal microscopy, and X-ray diffraction, we demonstrate that for smectite clay particles, the final floc structure is largely informed by ionic-strength driven changes to the initial clay aggregate size and surface structure. With increasing bentonite aggregate size, a transition from a networked to a patched polymer − aggregate floc structure is observed, independent of ionic strength during flocculation. Solutions were studied over four orders of magnitude of NaCl ionic strength. Initial, pre-flocculated bentonite aggregate sizes ranging from 0.015 μm to 15 μm were used, produced by tuning the initial solution ionic strength. Bentonite aggregate size and structure were measured with laser and X-ray diffraction, internal floc structure was visualized using confocal microscopy, and macro floc structure (fractal dimension) was measured with optical imaging. These results shed new light on the fundamental complexity of ionic strength dependence and the importance of the aggregate size and structure of the initial dispersion, in determining optimal reagent dosing and structure control for flocculation of anisotropic clays.

Original languageEnglish (US)
Pages (from-to)1037-1046
Number of pages10
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Volume529
DOIs
StatePublished - Sep 20 2017

Bibliographical note

Funding Information:
This work was supported primarily by the National Science Foundation through the University of Minnesota MRSEC and REU programs under Award Number DMR-1420013. Parts of this work were carried out in the Minnesota Nano Center which receives partial support from NSF through the NNIN program. This research was conducted with Government support under and awarded by Department of Defense, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a. Parts of this work were carried out in the Characterization Facility, University of Minnesota, a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org) via the MRSEC program. We would like to thank Dr. Javier Garcia-Barriocanal for his assistance in operating the XRD instrument and data interpretation. We would also like to thank MRSEC summer REU student Patrick McCauley for assistance with zeta potential measurements.

Keywords

  • Anisotropic particles
  • Aqueous colloidal suspensions
  • Flocculation
  • Polyelectrolytes
  • Smectite clays

How much support was provided by MRSEC?

  • Primary

Reporting period for MRSEC

  • Period 4

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