UV and infrared spectroscopies have been used to follow the adsorption of ethyl xanthate on pyrrhotite as a function of time, pH, and ethyl xanthate concentration. Only ethyl xanthate and its derivative, diethyl dixanthogen, were observed in solution, while diethyl, dixanthogen was the only xanthate species detected on the pyrrhotite surface. A model involving the adsorption of an ethyl xanthate ion onto a surface site followed by the subsequent adsorption of a second xanthate ion to form dixanthogen on the pyrrhotite surface has been proposed. Dixanthogen remains at the pyrrhotite surface, but is also found in solution, with its concentration reaching a maximum value corresponding to its solubility limit, independent of pH and initial xanthate concentration, For a law initial xanthate concentration, the amount of adsorbed xanthate species goes through a maximum, shifting to longer times with increasing pH values. The kinetics of xanthate adsorption have been analyzed by the Runge-Kutta method and the rate constants for the various reactions have been calculated. Both the rate of xanthate adsorption and the rate of formation of diethyl dixanthogen increase with decreasing pH values, while the rate of dixanthogen desorption is pH independent.