Electrophoretic Behavior of Imogolite under Alkaline Conditions

Karube, Jutaro

doi:10.1346/ccmn.1992.0400601

Cited by 30 publications

(18 citation statements)

References 8 publications

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“…The coagulation range, as judged from the viscosity, is pH 4-6.5 for deferrated samples and pH 5-7.2 for non-deferrated ones. This is related to the point of zero charge (PZC) of etectrophoretic behavior, that is, the viscosity of deferrated allophane shows a broad maximum centered at the PZC, pH 5.2 (Karube et al 1992). Deferrated allophane has a higher viscosity than non-deferrated allophane at approximately the PZC for the same clay concentration.…”

Section: Resultsmentioning

confidence: 99%

Size and Shape of Allophane Particles in Dispersed Aqueous Systems

Karube

1996

Clays and clay miner.

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Abstract--Aqueous suspensions of allophane show relatively high viscosity, presumably because of strong particle interaction between the unit particles. To test this hypothesis, we measured the particle weight and particle size of allophane during a dispersion using the light scattering method. The particle weight was more than several hundred times larger than that of the unit particle, and the size was 100-400 nm, whereas the Stokes' diameter of the particles in the sample was less than 50 nm. Particle weight and size varied with the pH of the sample. Particle sizes were cross-checked by ultrafiltration through membrane filters. The experimental findings show that the unit particles of allophane within dilute dispersions appear to be associated like strings of beads, forming domains (primary floccules) about 100 nm in diameter. When these domains coagulate under certain conditions, they do not grow analogously but form clusters, such as secondary floccules, then precipitate. Formation of secondary flocculation of loose structure accounts for the maximum relative viscosity at the transition pH between dispersion and coagulation.

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Section: Resultsmentioning

confidence: 99%

Size and Shape of Allophane Particles in Dispersed Aqueous Systems

Karube

1996

Clays and clay miner.

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“…No PZC was found for imogolite except with F. This contrasts with a PZC of 8.5-9.0 for a natural Japanese imogolite (Karube et al, 1992). They attributed their results to the use ofvery dilute sample (0.005 g liter 1); however, the impurities in the natural imogolite such as allophane, adsorbed citrate from extraction, and the structural defects could have resulted in the negative mobility.…”

Section: Monovalent Anionsmentioning

confidence: 87%

The Electrophoretic Mobility of Imogolite and Allophane in the Presence of Inorganic Anions and Citrate

1993

Clays and clay miner.

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Abstract--The purpose of this study was to investigate bonding mechanisms of representative inorganic anions and citrate with imogolite and allophane using electrophoresis. The electrophoretic mobility (EM) of synthetic imogolite and allophanes with A1/Si molar ratios of 2.02, 1.64, and 1.26 was determined in 0.001 and 0.01 M sodium solutions. The highest point of zero mobility (PZM) values for imogolite and the highest point of zero charge (PZC) values for allophane occurred in the presence of C104, NO3, Br, I, and C1. Below the PZM and PZC, C1 and t lowered the EM relative to the other anions but did not shift the PZM and PZC significantly. This indicates that Cl and I formed more outer-sphere complexes than the other ions. The EM of imogolite and allophane was negative at pH < 6 in 0.001 and 0.01 M NaF probably due to a phase change. We observed the formation of cryolite (Na3A1F6) with transmission electron microscopy (TEM) and X-ray diffraction (XRD) in the NaF systems at low pH. Conversely, phosphate at 0.001 and 0.01 M concentrations lowered both the PZM and the EM in imogolite and both the PZC and the EM in allophane compared with C104. Phosphate-treated allophane had the same PZC as a synthetic amorphous aluminum phosphate. The PZM values of imogolite and allophane with 2:1 A1/Si in 0.0001 M Na-citrate were 10.9 and 5.9, respectively. At pH 7.3, Na-citrate lowered allophane EM more than it lowered imogolite EM relative to C104.The EM in NaC104 and Na2SO4 was reversible by forward-and back-titration with NaOH and HC1Oa, indicated that C104 and SO4 were not specifically adsorbed. Chloride likely formed more outer-sphere complexes than C104. Imogolite EM and allophane EM in dilute NaF and NaHzPO4 solutions were not reversible, indicating either surface inner-sphere complexes or surface precipitates of aluminum fluoride and amorphous aluminum phosphate-like materials on these minerals. Sulfate gave a lower EM than the monovalent anions, implying a greater tendency to form outer-sphere complexes. Citrate appeared to form inner-sphere complexes on both imogolite and allophane, but formation was concentration-dependent. The tendency of anions to form surface complexes with imogolite and allophane is consistent with the tendency of anions to form soluble aluminum complexes.

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“…Concerning the mechanism of this unique behavior, Horikawa (1975) discussed the idea that the effects of negative charge that arise at the inner surface of imogolite might be weakened at the outer surface because of the distance between the surfaces. Karube et al (1992) reported that the mobility of imogolite toward the positive electrode was difficult to detect using a Briggs-cell due to the flocculation of the fibrous particles. Harsh et al (2002) and Tsuchida et al (2005) mentioned that cations may enter the tube and effectively neutralize the negative charge.…”

Section: Introductionmentioning

confidence: 99%

Imogolite flocculation under alkaline conditions

Karube

2013

Soil Science and Plant Nutrition

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Imogolite flocculates under alkaline conditions even though the net charge is considerably negative. To clarify the reason for this contradiction, we measured the charge characteristics of imogolite with an ion-exchange method using sodium ions (Na þ ) and chloride ions (Cl À ) as index ions, and estimated its electric field intensity at the outer surface using Gauss' law and the structural model of imogolite. The result showed that the electric field intensity of negative charge at the outer surface was about half of that at the inner surface. Further, we discussed that if cations could easily enter the imogolite tube, the electric field of negative charge would be drastically weakened due to the neighboring cations and, consequently, the outer surface would become electrically indifferent. If so, not only the reason for imogolite flocculation under alkaline conditions, but also the reason for imogolite dispersion at the point of zero net charge would be explained consistently. The reason for imogolite dispersion at the point of zero net charge was considered to be that the colloidal stability of imogolite would be affected only by the positive charges that appear on the outer surface of the tube. Finally, the hydrated sodium ions were considered to move in and out of the imogolite tube freely.

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Electrophoretic Behavior of Imogolite under Alkaline Conditions

Cited by 30 publications

References 8 publications

Size and Shape of Allophane Particles in Dispersed Aqueous Systems

Size and Shape of Allophane Particles in Dispersed Aqueous Systems

The Electrophoretic Mobility of Imogolite and Allophane in the Presence of Inorganic Anions and Citrate

Imogolite flocculation under alkaline conditions

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