Kinetics of collector in-situ adsorption on metal sulphide surfaces studied by ATR-FTIR spectroscopy

Abstract: In sulphide mineral flotation, a sufficient hydrophobicity of the mineral surfaces is obtained by the adsorption of collector chemicals at the metal sulphide/aqueous interface. This surface alteration is of fundamental and applied interest. In this thesis, attenuated total reflection infrared spectroscopy has been used to monitor the adsorption kinetics and the orientation of heptyl xanthate when adsorbed onto three solid surfaces - germanium, zinc sulphide and lead sulphide in-situ. The Chemical Bath Deposition method has been used to deposit metal sulphides onto germanium internal reflection elements, and verified as capable in synthesizing metal sulphide surfaces for adsorption studies recovering information about surface reactions at metal sulphide/solution interfaces. In the study of surface reactions the substrate is of great importance, implying that the chemistry of the surface has to be well characterised. This work has utilized X-ray photoelectron spectroscopy in the characterisation of the different surfaces. The adsorption kinetics has been followed to monitor the adsorption equilibria at different concentrations. In the case of heptyl xanthate adsorbed at the zinc sulphide/aqueous interface, an adsorption isotherm has been calculated from the equilibrium data. On the assumption that the adsorption step was rate controlling a pseudo-first order equation was derived and adsorption rate data, in all the three studied systems, tested according to this equation. In addition, an orientation study of the heptyl xanthate molecule at the different interfaces was performed, which requires polarised infrared light. Density Functional calculations of a free heptyl xanthate molecule, and a heptyl xanthate molecule adsorbed on a pure Ge(111) were utilized to get more information about the in-situ adsorption of heptyl xanthate on a germanium surface. The important vibration bands were assigned to different vibrations, and the theoretical infrared spectra were compared with the experimentally analyzed spectra. This study shows the strengths of using advanced first-principle Density Functional Theory in the interpretation of real surface adsorption systems.