Polyvalent metal ions, hydrolyzed

It is well known that hydrolyzed polyvalent metal ions are more efficient than unhydrolyzed ions in the destabilization of colloidal dispersions. Monomeric hydrolysis species undergo condensation reactions under certain conditions, which lead to the formation of multi- or polynuclear hydroxo complexes. These reactions take place especially in solutions that are oversaturated with respect to the solubility limit of the metal hydroxide. The observed multimeric hydroxo complexes or isopolycations are assumed to be soluble kinetic intermediates in the transition that oversaturated solutions undergo in the course of precipitation of hydrous metal oxides. Previous work by Matijevic, Janauer, and Kerker (7) Fuerstenau, Somasundaran, and Fuerstenau (I) and O Melia and Stumm (12) has shown that isopolycations adsorb at interfaces. Furthermore, it has been observed that species, adsorbed at the surface, destabilize colloidal suspensions at much lower concentrations than ions that are not specifically adsorbed. Ottewill and Watanabe (13) and Somasundaran, Healy, and Fuerstenau (16) have shown that the theory of the diffuse double layer explains the destabilization of dispersions by small concentrations of surfactant ions that have a charge opposite to... 

Precipitation of Hafnium Hydroxide. In order to interpret the adsorption data it was necessary to determine the conditions which lead to the precipitation of hafnium hydroxide. It is not usually advisable to depend on the solubility product because the information on this quantity is often unreliable for hydroxides of polyvalent metal ions. In addition, "radiocolloids may apparently form much below saturation conditions in radioactive isotope solutions. In the specific case of hafnium hydroxide only two measurements of the solubility seem to have been reported. According to Larson and Gammill (16) K8 = [Hf(OH)22+] [OH ]2 — 4 X 10"26 assuming the existence of only one hydrolyzed species Hf(OH)22+. The second reported value is Kso = [Hf4+] [OH-]4 = 3.7 X 10 55 (15). If one uses the solubility data by Larson and Gammill (Ref. 16, Tables I and III) and takes into consideration all monomeric hafnium species (23) a KBO value of 4 X 10 58 is calculated. 

Polyvalent metallic ions can adsorb specifically on oxides and silicates this phenomenon occurs when the cation involved hydrolyzes to its first hydroxy complex or its dioxide precipitates on the particle surface. Unintentional activation of silica by dissolved metallic species in anionic flotation circuits is a typical example (Hanna and Somasundaran, 1976). 

Numerous studies have been made of the interaction of polyvalent metal ions with the silica surface. The development of Zr-O-Si bridges has been examined by Nikolskii et al. (432), who concluded that as the basic Zr ions polymerized they were less reactive. Healy, cooper, and James (433) found that Fe and Cr are adsorbed on silica particles, giving them a positive charge. The chemistry of hydrolysis of cations Al, Zr, Th, Cr has been summarized by Baes and Mesmer (434). Matijevic, Janauer, and Kerker (435) have shown that it is the polymeric hydrolyzed species in aluminum nitrate solution and not the single AF ion that can cause charge reversal in silver halide sols. The same is true in charge reversal of silica sols. 

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