Colloidal hydroxides

Tlie amphoteric behavior of aluminum hydroxide, wliich dissolves readily in strong acids and bases, is shown in Figure 4. In the pH range of 4 to 9, a small change in pH towards the neutral value causes rapid and voluminous precipitation of colloidal hydroxide wliich readily fomis a gel. Gels are also fomied by the hydrolysis of organoaluminum compounds such as aluminum alkoxides (see Alkoxides, metal). 

Farad. Boc. xiv. 10,1921) for the composition of the sols and gels of the inorganic colloidal hydroxides, e.g. zirconia produced by the hydrolysis of zirconium oxychloride. By electropotentiometric measurements of the hydrogen and chlorine ion concentrations of sols formed by hydrolysis as well as freezing point, conductivity and transport number determinations he has shown that a series of salts are formed of the types ... 

From solutions of pure arsenic acid the pentasulphide separates in a highly disperse form which adsorbs arsenic acid so strongly that the last traces of the latter react with great difficultv at the ordinarv temperature,6 although this is not the case at AO" C. In the presence of salts of multivalent cations which by hydrolysis yield colloidal hydroxides, the arsenic pentasulphide is flocculated, but the completion of the reaction is greatly delayed owing to adsorption of the arsenic acid, especially at low temperatures. 

At least some of these difficulties have been overcome in the work to be reported in this study, which deals with the adsorption of hafnium hydrolyzed species on powdered glass as a function of the acidity of the medium. The adsorption of hafnium species from aqueous solution has apparently never been investigated, yet this ion lends itself conveniently to studies of the problems discussed above. The chemistry of the hafnium ion in water is fairly well understood (23) and a suitable isotope, 181Hf, is available for adsorption studies. What makes hafnium a particularly interesting system is the fact that it forms the entire series of hydrolyzed species Hf(OH)n(4 r )+ where n 4. At intermediate acidities (pH > 4) the solutions of low concentrations contain only the neutral, soluble species Hf(OH)4. It should be emphasized that there is a pH and a concentration range over which this species is present without simultaneous formation of hafnium hydroxide. Thus, it is possible to elucidate the effect of the ionic charge upon the adsorption of hydrolyzed species in systems void of colloidal hydroxides. The glass powder was used in... 

Leaching studies indicate that these radionuclides associated with sediment are not in the form of adsorbed ions, but in the form of discrete minerals, or are partly trapped inside the colloidal hydroxides of Fe and Mn coated on the sediment. Further studies by other leaching agents, such as hydroxylamine hydrochloride, and ammonium oxalate, and by X-ray diffraction and scanning-electron microscopy on sediment minerals will reveal the geochemical status of these radionuclides in the sediment. 

It should be noted that the sol-gel process is particularly attractive for the synthesis of multicomponent particles with binary or ternary compositions using double alkoxides (two metals in one molecule) or mixed alkoxides (with mixed metaloxane bonds between two metals). Atomic homogeneity is not easily achieved by coprecipitating colloidal hydroxides from a mixture of salt solutions, since it is difficult to constmct double metaloxane bonds from metal salt. Hybrid... 

On addition of a dilute solution of potassium permanganate to one of ferrous chloride, and subjecting to dialysis, the pure colloidal hydroxide is readily obtained.5 The sol is also obtained by oxidising a solution of ferrous chloride containing one gram equivalent of FeCl2 per litre with a 3 per cent, solution of hydrogen peroxide.6... 

Iron of inorganic dissolved compounds (bicarbonates, sulfates, chlorides, fluosilicates, etc.) may enter into the dissolved form of iron of inorganic origin (Fcj"" ), but their existence is governed by an acid environment with a pH not higher than 3. As a rule the pH in sea water is close to 8 ( 0.5). Under these conditions iron compounds are easily hydrolyzed and converted into hydroxides, which form colloidal solutions in sea water. In appropriate conditions colloidal hydroxide condenses to clots of gel and converts to the suspended state. Therefore there are practically no ionic forms of iron (Fe "" proper). As early as 1937 Cooper (1937) concluded, on the basis of the solubility product and activity of ferrous and ferric iron ions and FeOH ions, that until equilibrium is reached sea water may contain about 10 jiig/1 of iron ions in true solution at pH = 8.5 the amount of ionic Fe in ferric form is still less—10 which corresponds to the extremely... 

The second problem is that the greater portion of iron occurs in the sea-water as colloidal hydroxide. The synthesis of iron smectite should work with iron hydroxide and not only with dissolved iron ions if enough of iron was removed from the sea-water. 

Manganese and iron hydroxides are extremely insoluble in sea-water. Maximum concentrations of free ions in sea-water are 0.887 x 10 pg Fe/1 and 1.09 x 10 pg Mn/1, the excess manganese and iron building colloidal hydroxides which sooner or later precipitate. 

The author studied the temporal evolution of a /iN solution of zirconoxychloride. The electrical conductivity increased during 7 days continuously to up to 30%. After cooking the solution, the conductivity increased further, to a final value about double the initial one. After heating, the reactivity of solutions of zirconoxychloride changed. Precipitation after Na2S04 addition was observed only in heated solutions. The changes were explained based on the formation of a colloidal hydroxide, the presence of which was identified by dialysis techniques. Potential polymer formation as a precursor of colloid formation has not been discussed in this paper. 

The yellow sulfate is produced on solution of moist hydrated rhodium (III) oxide (rhodium hydroxide) in dilute (1 10) sulfuric acid at temperatures not exceeding 50 °C. Then the hydrated Rh (in) oxide is precipitated from the cold solution with KOH (avoiding an excess of the latter) and washed on a membrane filter until the colloidal hydroxide passes through. Suction is then applied and as much water as possible is removed the residue is dissolved without heating in dilute sulfuric acid. 

It is due to dissolved organic matter, to ferritic iron precipitated out in a colloidal hydroxide form, to ferrous iron bonded to organic complexes and to a number of colloids,... 

Surface oxidation of sulfide minerals has been reviewed recently by Smart et al. [78]. Studies of the physical and chemical forms of oxidation products by SAM, XPS, STM. AFM, SEM and ToF-SIMS have revealed several different proces.ses of oxidation. The seminal work of Buckley et al. (e.g., [79,80)) was the first to identify the process of formation of oxyhydroxide products on underlying metal-deficient, sulfur-rich layers of similar forms to those described in Section 4.3. Other oxidation products have been observed directly, such as polysulfides, elemental sulfur, oxidized fine sulfide particles, colloidal hydroxide particles and flocculated aggregates, as well as continuous surface layers of... 

---