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The aim of this work is to demonstrate the possibility of forecasting the efficiency and selectivity of chelating reagents in flotation of metallic minerals through a theoretical study of the reactivity of specific chelating reagents towards Zn and Pb cations. The theoretical method is based on calculation of conditional constants. The work reported here is concerned with the thermodynamic calculation of conditional constants of metal-ligand compounds of some mercaptobenzothiazole (MBT) reagents with lead and zinc cations, applied to evaluate the collecting action of MBT reagents on Pb and Zn minerals. From the comparison of the results of thermodynamic calculation with the flotation results previously obtained on oxidised and sulphidised minerals of Pb and Zn, it is evidenced that these reagents are optimum selective collectors of Pb with respect to Zn minerals and that the introduction of a methyl group increases efficacy. Therefore, the calculation results and the hypotheses on which they are based have been confirmed. Infrared and X-ray photoelectron spectroscopy studies have also shown that the formation of surface chelate complexes is responsible for the collecting action of these reagents.

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