The synergistic effect of surfactants, i.e., Tween-80 (polyethylene glycol sorbitan monooleate), Span-80 (sorbitanoleate), and MES (fatty acid methyl ester sulfonates), on fatty acid collectors were investigated using single mineral flotation experiments, surface tension measurement, Fourier transform infrared spectrum, and contact angle measurements. The single mineral flotation experiments showed that it was possible to efficiently separate apatite from magnetite, quartz, and biotite by mixing fatty acids with surfactants. The surface tension measurement showed that the surfactants could significantly reduce the surface tension and Critical Micelle Concentration (CMC) of fatty acids. Fourier transform infrared spectroscopy analysis indicated that all of the surfactants did not react with the fatty acids, but only physically adsorbed on the surface of apatite, thus promoting the chemical adsorption of fatty acids on apatite. However, the surfactant chemisorbed on magnetite and competing with a fatty acid, which led to a decrease in the flotation recovery. The results for contact angle measurement showed that the contact angle difference between apatite and magnetite increased with the addition of surfactant, and resulted in an efficient separation.
Low-grade magnesite is not effectively used mainly due to high silicon content, especially the separation of magnesite and hornblende. In this research, a novel mixture of sodium oleate and dodecyl phosphate collector was used to increase the flotation difference between magnesite and hornblende. Artificially mixed mineral concentrates grade 47.10% (MgO content) concentrate recovery of 84.45% was obtained by micro flotation test, the results showed that the mixed collector of sodium oleate and dodecyl phosphate played a better selective promotion role in the flotation of magnesite. The interaction mechanism of this mixed collector with hornblende and magnesite surfaces was investigated using Fourier transform infrared spectroscopy (FTIR), zeta potential, and X-ray photoelectron spectroscopy (XPS), which showed that the mixed collector in terms of magnesium selection was mainly adsorbed on these magnesium sites of magnesite, and the surface of magnesite thus became hydrophobic, allowing magnesite to float and separate from hornblende.
The microflotation experiments were systematically carried out to investigate the inhibitory effect of citric acid (CA) on the flotation behavior of hornblende and magnesite. When the mixture consisted of sodium oleate and dodecyl phosphate was utilized as a mixed trapping reagent, CA could obviously inhibit the hornblende flotation but had little inhibitory effect on magnesite flotation. The desilication of magnesite flotation was accomplished when CA was employed as the hornblende inhibitor. Moreover, to reveal the adsorption mechanism of CA on the surfaces of hornblende and magnesite, a series of surface analysis techniques, such as X-ray photoelectron spectroscopy (XPS), zeta potential and Fourier transform infrared spectroscopy (FTIR), were conducted. Based on the zeta-potential and FTIR analyses, it is revealed that CA or CA together with collector (sodium oleate and dodecyl phosphate mixture) was applicable for the magnesite flotation tests. In the meanwhile, the introduced CA had obviously hindered the adsorption of sodium oleate and dodecyl phosphate mixtures on the hornblende surface, resulting in a significant difference in the flotation performance of hornblende and magnesite minerals. Moreover, XPS measurements revealed that the strong adsorption of CA on the hornblende surface can be ascribed to its affinity for the negative electron groups of CA and Ca ions.
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