Sulphide mineral collectors adsorbed on a ZnS internal reflection element : an infrared linear dichroism study

Sammanfattning: Separation and concentration of minerals by flotation is a well-known industrial process. In this process collector chemicals are used to modify the mineral surface to increase the hydrophobicity of the mineral particles. Still there is a lot to find out about adsorption mechanisms, orientation and organization of the adsorbed collectors on the surfaces to be able to improve the characteristics of the collectors or todesign new ones. In this work, the structure and orientation of sulphide mineral collectors adsorbed on a ZnS surface have been studied by the FTIR-ATR technique. The collectors that have been studied are heptylxanthate (R-CS2-, R = O-C7H15), O,O-dibutyldithiophosphate, 2-mercaptobenzothiazole and a mixture of 2-mercaptobenzothiazole and O,O-dibutyldithiophosphate. The adsorbed layer was prepared by self-assembly from solution or by spraying the solution onto the surfaces of the ATR-crystal for a short time. By using polarized light and the dichroic ratio a quantitative determination of the orientation of heptylxanthate could be performed. The tilt angle from the normal of the surface was found to be approximately 44 degrees. From the spectra it was concluded that the adsorbed species on the ZnS surface is a mixture between heptylxanthate and diheptyldixanthogen. A bridging coordination of the adsorbed heptylxanthate is proposed. The difference between the absorbance of the s-polarized light and p-polarized light was used to draw conclusions about the orientation of O,O-dibutyldithiophosphate and 2-mercaptobenzothiazole adsorbed on ZnS. The collectors are mixed in the flotation process and the influence on the orientation of O,O-dibutyldithiophosphate and 2-mercaptobenzothiazole when adsorbing from a mixture of the two collectors is also reported. In ATR-experiments very small amounts of substances are detected and problem due to contamination of the surfaces and the adsorbed thin film can be severe. Such problems encountered in the present work are described and discussed.