Interactions between Sulfide Minerals and Alkylxanthate Ions .6. A Vibration Spectroscopic and Atomic-Absorption Spectrophotometric Study of the Interaction between Pyrite and Ethylxanthate Ions in Aqueous-Solution
The reaction between pyrite (natural iron (II) disulfide) powder and potassium alkylxanthate has been studied in aqueous solution. Qualitative analysis of the compounds present on pyrite surfaces before and after treatment with ethylxanthate ions under different oxidation conditions has been performed by means of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Atomic absorption spectrophotometry has been used to determine the total iron concentration in the aqueous phase of pyrite slurries. The only alkylxanthate species adsorbed on pyrite surfaces is dialkyl dixanthogen. The amount of dialkyl dixanthogen formed on pyrite surfaces is significantly smaller when wet-ground pyrite is used. The pyrite surfaces must be oxidized, most probably to an iron(III) oxosulfur compound, where the oxosulfur anion is a strong oxidizing agent. The formation of alkyl dixanthogen takes place on oxidized pyrite surfaces and in the absence of oxygen, which shows that oxygen is not the oxidizing agent. The proposed mechanism for the hydrophobizing of oxidized pyrite surfaces can be summarized as follows: (i) Disulfide ions in the pyrite surface are oxidized to oxosulfur anions with high oxidation potential(s): this oxidation product is most probably not dissolved from the surface before the reaction with alkylxanthate ions takes place; (ii) the alkylxanthate ions are oxidized to dialkyl dixanthogen by the oxidation agent on the pyrite surface; (iii) the highly hydrophobic dialkyl dixanthogen formed is physisorbed onto the pyrite surface. In the presence of barium ions, solid barium sulfate precipitates on oxidized pyrite surfaces. The pyrite surfaces become modified in the presence of calcium ions, but formation of gypsum has not been proved.