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Flotation of oxidized copper minerals: an infrared spectroscopic study Coelho, Elcio Marques

Abstract

Chemical and physical properties of the copper oxide surface as modified by flotation collectors have been investigated. The flotation behaviour of copper oxide minerals in the presence of anionic and cationic collectors has been studied using the Hallimond tube method. An eleven reflection, 70° incidence angle, specular reflection infrared spectroscopic technique has been employed to investigate the adsorption of carboxylic acid onto copper oxide substrates. An ATR "in situ" technique has been developed to record the spectra of the adsorbates which were present at the copper oxide/aqueous surfactant solution interface. Micro-flotation tests indicated that mineral surface charge played the most important role in flotation of copper oxide minerals with ionic collectors. Tenorite was easily floated with an anionic collector such as lauric acid when the pH of the solution was lower than the IEP of the mineral (pH 9.4). On the other hand, lauryl amine, a cationic collector, yielded better flotation recoveries at pH values greater than the IEP. Adsorption experiments conducted using the highly sensitive specular reflection spectroscopic technique suggested that mineral surface charge was the major variable affecting adsorption of aqueous lauric acid onto copper oxide substrates. Therefore, a relationship between floatability, surface charge and adsorption was established. The infrared spectroscopic studies showed that adsorption of collector species did not occur at pH values above the IEP. Qualitative and quantitat analyses of the spectra indicated that, at pH values below the IEP, chemisorption of laurate ions as counter ions in the internal part of the electrical double layer was the predominant adsorption mechanism responsible for collection. In addition, the adsorption of monomeric lauric acid molecules, probably by hydrogen bonding to the substrate, was also observed. In the presence of excess copper ions, cupric laurate and monomeric lauric acid-copper complexes were physically adsorbed on the chemisorbed film. Effects of molecular orientation on specular reflection spectra were analyzed on the basis of existing optical theories. The qualitative interpretation of the infrared reflection spectra of carboxylic surface species required the recording of a series of reference spectra. These included specular reflection spectra of films formed by condensing lauric and stearic acid from the vapour phase onto copper oxide and gold substrates. Standard quantitative references were obtained by transferring solidified monolayers of stearic acid from the air/water interface to the substrates according to the Langmuir-Blodgett method. Remarkable effects of molecular orientation were observed in the reflection spectra of the films mentioned above. These effects were In agreement with the predictions of the Francis and Ellison theory. In addition, these studies contributed to the understanding of the behaviour of organic monolayers on solid and liquid surfaces. A thin film of cuprous oxide on an infrared transparent ATR prism was used as adsorbent and infrared spectra of the compounds present at the cuprous oxide/aqueous lauric acid interface were recorded "in situ". Results of these tests indicated that the composition of the adsorbed carboxylic films was not altered to any significant extent by the removal of the substrate from the aqueous phase.

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