Orientation of collectors adsorbed at the ZnS/solution interface

Sammanfattning: The separation and concentration of minerals by flotation is a well-known industrial process. In this process collectors are used to increase the hydrophobicity of the surfaces of the minerals. Still there is a lot to find out about adsorption mechanism, organisation, and orientation of the adsorbed collectors, to be able to improve the characteristics of the collectors or to design new ones. In this work the organisation and orientation of sulphide mineral collectors adsorbed on a ZnS surface have been studied by the FTIR-ATR (attenuated total reflection) technique. The collectors used in this study are heptyl xanthate, O,O-dibutyldithiophosphate, and 2-mercaptobenzothiazole. The adsorbed collectors were studied both in contact with air and exposed to water. The orientation could be determined by using polarized light and the dichroic ratio. The adsorption and orientation of heptyl xanthate on germanium has also been studied, mainly because Ge is a suitable ATR-crystal on which ZnS or other sulphide minerals may be precipitated and used for future studies of mineral surfaces. In flotation copper activation is used to increase the flotability of minerals. How this affect the orientation, as well as how minimizing the oxygen content of the solutions affect the adsorption have been investigated. The alkyl chains of adsorbed heptyl xanthate tilted approximately 44 degrees from the normal of the surface when the adsorbed layer was in contact with air. When the adsorbed layer was in contact with water the tilt angle increased to about 50 degrees, and the order of the adsorbed layer decreased according to the shift of the asymmetric methylene stretch to higher frequency. Dixanthogen formed during the adsorption process on ZnS but not on Ge. The Germanium surface resulted in an adsorbed heptyl xanthate monolayer with the highest order and a tilt angle of about 47 degrees from the surface normal when the adsorbed layer was in contact with water. Besides the information on orientation of collectors this study has given knowledge about the coordination of xanthate to ZnS surfaces and reactions that may occur in the interface between minerals and water.