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The influence of interparticle surface forces on the coagulation of weakly magnetic mineral ultrafines in a magnetic field
YKI – Ytkemiska institutet.
1994 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 90, 117-133 p.Article in journal (Refereed)
Abstract [en]

In this paper, it is shown that the coagulation of dispersions of weakly magnetic mineral ultrfines (such as hematite and chromite) in an external magnetic field can be described theoretically by invoking interparticle forces. Essentially, coagulation occurs when the short-range London-van der Waals interactions and the long-range magnetic forces outweight the stabilizing electric double layer repulsion. From classical colloid chemistry theory, we have calculated the the various components of the potential energy for different-sized particles at a series of ionic strenghts and magnetic field intensities. Principles governing the stability of the suspensions of weakly magnetic oxide mineral ultrafines in a "wet magnetic separation process". Experimentally, the magnetic-field induced coagulation of ultrafines of natural hematite and chromite in aqueous suspensions at moderate ionic strenght was investigated using a laboratory -scale electromagnetic solenoid. The experimental results relate the coagulation process (as determined by magnetosdimentation analysis) to particle size, slurry pH and the external magnetic field. In the magnetic fields, maximum coagulation occured near the pH of the point of zero charge (pH PZC)of the minerals (where the electrostatic double layer repulsionwas reduced to a minimum) enabling the particles to enter the"primary minimum" energy sink. In contrast, in cases where the electrostatic repulsion was not supressed, the long-range magnetic forces enabled coagulation to occur in the "secondary minimum". This caused the formation of chains which appeared to be relatively stable at enhanced rates of setting. The experimental results could be interpreted from a theoretical analysis of the interparticle forces controlling the process.

Place, publisher, year, edition, pages
1994. Vol. 90, 117-133 p.
Keyword [en]
Chromite, colloidal stability, haematite, magnetic coagulation, magnetic properties, ultrafine
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-26468OAI: oai:DiVA.org:ri-26468DiVA: diva2:1053470
Note
A823Available from: 2016-12-08 Created: 2016-12-08Bibliographically approved

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