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- Wang, Y, et al.
(författare)
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Magnetic aggregation in dispersions of mineral ultrafines
- 1995
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Ingår i: Journal of Dispersion Science and Technology. - 0193-2691 .- 1532-2351. ; 16, s. 137-154
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Tidskriftsartikel (refereegranskat)abstract
- In the present paper, magnetic contribution on the aggregation of some magnetic mineral particle ultrafines were studied. There are two different magnetic properties that may enhance particle aggregation: a) field-induced magnetic moment; and b) magnetic moment due to the remanent magnetisation. The magnetic field-induced aggregation of the oxide mineral particle ultrafines (hematite and chromite) in aqueous suspension at moderate ionic strenght was investigated using a labortory scale electromagnetic solenoid. The experimental results relate the aggregation process (as determined by magneto-sedimentation analysis) to particle size and the external magnetic field in the antural pH value of the dispersions by using a modified form of the DLVO theory. In cases where the electrostratic repulsion was not suppressed, then the long range magnetic forces enabled aggregation to occur in the "secondary minimum" potential energy sink. This caused the formation of chains/rings, which appeared to be relatively stable at enhanced rates of settling. It is indicated in this paper that hematite ultrafines in a well-dispersed slurry are selectively aggregated with sized magnetite in the absence of aggregating reagents, high shear rates or an external magnetic field. The formation of aggregates is attributed to the presence of the remanent magnetisation in these oxide iron minerals, aminly in the magnetite.
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| 2. |
- Wang, Y, et al.
(författare)
-
The influence of interparticle surface forces on the coagulation of weakly magnetic mineral ultrafines in a magnetic field
- 1994
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 90, s. 117-133
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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