Octyl hydroxamate

Normand, J., The Adsorption of Potassium Octyl Hydroxamate on Malachite, Thesis for Masters in Metallurgical Engineering, McGill University, Montreal, Canada, 1974. 

Free energy variations with temperature can also be used to estimate reaction enthalpies. However, few studies devoted to the temperature dependence of adsorption phenomena have been published. In one such study of potassium octyl hydroxamate adsorption on barite, calcite and bastnaesite, it was observed that adsorption increased markedly with temperature, which suggested the enthalpies were endothermic (26). The resulting large positive entropies were attributed to loosening of ordered water structure, both at the mineral surface and in the solvent surrounding octyl hydroxamate ions during the adsorption process, as well as hydrophobic chain association effects. 

Fig. 4.44. AG-pH diagrams and wolframite flotation for Mn +-Fe +-reagent systems (Hu, 1984 Wang, 1986) (a) nitro-)6-naphthol (b) sodium oleate (c) octyl hydroxamate. 1—MnL2, 2—FeL2.

Fig. 4.48. Species distribution diagram of Ca +, Mn -citric acid systems and flotation of calcite and wolframite using octyl hydroxamate (Wang and Hu, 1985).

Covalent-Ionic Interaction. Covalent-ionic interactions appear to be important in the adsorption of small molecules on various materials, for example, octyl hydroxamate on Fc203 (48), where the functional group of the adsorbate is known to form strong aqueous complexes with metal ions (in this case Fe ) present in surface sites of the respective substrate. 

For example, as shown in Figure 10.36 (15), no adsorption of myristate (an anionic surfactant) occurs below the isoelectric point (pH 7.0) of chromite (even though the surfaces are oppositely charged), while essentially complete flotation is achieved at about pH 9.0 (when the surfactant and surface are similarly charged). The lack of flotation below the lEP was attributed to the limited solubility of myristic acid under these conditions. A similar behaviour has been observed for the flotation of haematite with myristate. Chemisorption of another anionic collector, octyl hydroxamate, has also been observed on haematite at pH 9.0 (15). 

Figure 10.37. Flotation of chrysocolla as a function of pH with different concentrations of octyl hydroxamate (after ref. (15))...

IM octyl hydroxamate. Cupric octyl hydroxam-ate has major bands at 925, 1095, 1380, 1450, and 1535 cm while bands at 1380, 1450 and 1535 cm are observed on chrysocolla after it has been treated with the collector, hence indicating the formation of cupric octyl hydroxamate at the surface during the adsorption process. This surface reaction is evident from the fact that chrysocolla changes colour from its natural blue-green to a vivid green colour upon adsorption of the collector. 

Nickolov, Z. S., Wang, X., and Miller, J. D. 2004. Liquid/air interfacial structure of alcohol-octyl hydroxamic acid mixtmes A study by sum-frequency spectroscopy. Spectrochim. Acta, Part A. 60A 2711. 

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