Iron oxide hydrate sols

Changes in zeta potential and turbidity of iron(III) oxide hydrate sols flocculated by sodium dodecyl sulfate (SDS) are shown in Fig. 5.9. When SDS was... 

Figure 5.10 shows changes in zeta potential and turbidity of iron(III) oxide hydrate sols flocculated with NFIOO. The optimum flocculation concentration was about 3 X 10 mM NFIOO. The sols were redispersed by NF7 or NP7.5, a hydrocarbon-type nonionic surfactant (polyoxyethylene nonylphenyl ether with a polyoxyethylene chain of average 7.5 EO). The turbidity increased sharply. The zeta potential changed only a little, as expected for a nonionic surfactant. Sols flocculated by NFIOO were not redispersed by SDS. The inability of SDS, an anionic hydrocarbon surfactant, to redisperse the sols was attributed... 

Changes in zeta potential and turbidity of iron(III) oxide hydrate sols flocculated with lithium perfluorooctanesulfonate (LiFOS) are shown in Fig. 5.11. The nonionic surfactants NF7 and NP7.5 redispersed the sols. However, the anionic hydrocarbon surfactant LiDS (lithium dodecyl sulfate) had no significant effect. Accordingly, sols flocculated by LiDS were redispersed by a nonionic surfactant, NF7, but not by the anionic surfactant LiFOS (Fig. 5.12). 

Esumi et al. [65-67] explained the flocculation and redispersion mechanisms by adsorption processes. Low concentrations of anionic surfactants neutralize the positive charge of iron(III) oxide hydrate sols and cause flocculation. The adsorbed anionic surfactant is oriented with its hydrophilic groups toward the particle surface and the hydrophobic groups toward water. If the second addition of a surfactant results in adsorption on the flocculated sols, the sols redisperse. The adsorption is caused by hydrophobic interactions and the surfactant is oriented with its hydrophilic groups toward water. 

With Acyl Halides, Hydrogen Halides, and Metallic Halides. Ethylene oxide reacts with acetyl chloride at slightly elevated temperatures in the presence of hydrogen chloride to give the acetate of ethylene chlorohydrin (70). Hydrogen haUdes react to form the corresponding halohydrins (71). Aqueous solutions of ethylene oxide and a metallic haUde can result in the precipitation of the metal hydroxide (72,73). The haUdes of aluminum, chromium, iron, thorium, and zinc in dilute solution react with ethylene oxide to form sols or gels of the metal oxide hydrates and ethylene halohydrin (74). 

The interaction of hydrocarbon and fluorocarbon surfactants on the surface of dispersed particles has been studied through a flocculation and redispersion process [65-67]. Dispersions of positively charged particles can be flocculated with an anionic surfactant. An excess of the anionic surfactant forms a bilayer on the particle surface and causes redispersion of the flocculated sol. This flocculation reversal was used to study the interaction between mixed surfactants on a solid surface. A dispersion of iron(ITI) oxide hydrate particles was flocculated with an anionic hydrocarbon or fluorocarbon surfactant at pH 3.5, where the sols had a positive zeta potential. Subsequently, a second fluorocarbon or hydrocarbon surfactant was added to the flocculated sol. The extent of redispersion depended on the interaction between the two surfactants on the solid particle surface. 

If it is necessary to extract the rare metal from an acid or alkaline leach liquor, or similar solution, a resin should be selected which is known to be stable in the leaching reagent. For extraction of the rare metal ion itself, the resin would normally be of the cation-exchange type, unless the rare metal ion could be converted to an anionic complex. However, the possibility of designing a process in which the impurities are absorbed by the resin and the rare metal remains unextracted, should not be neglected. An example of this type has been developed by Ayres,i > in which iron, titanium, lanthanum and beryllium impurities are extracted from a zirconium nitrate solution by operation at a pH where the zirconium is converted to a non-ionic hydrated oxide sol. 

The starting materials were soluble salts, cobalt acetate (Co(C2H302)2 H2O) and iron nitrate (Fe(N03)2 9H2O). These salts produce hydroxides (M(OH)2), oxyhydroxides (MOOH) or hydrated oxides in water, where M is Co or Fe. These solutions were reacted with lithium hydroxide. Diluted ammonium hydroxide (3M) was added to form stable colloids (Barboux, 1991). Lithium hydroxide and cobalt acetate were dissolved separately in distilled water. These two solutions were then mixed together and stirred vigorously. The hydrolysis of the mixture was promoted by slow addition of 3M ammonium hydroxide. Similarly, sols with ferric nitrate, or ferric nitrate plus cobalt acetate, were prepared. The sols used for coating were diluted to give a 2 1 ratio of moles water to moles oxide. 

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