KINETICS OF ADSORPTION OF ETHYL XANTHATE ON PYRRHOTITE - IN-SITU UV AND INFRARED SPECTROSCOPIC STUDIES

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, diethy l dixanthogen, were observed in solution, while diethyl, dixanthogen w as the only xanthate species detected on the pyrrhotite surface. A mod el involving the adsorption of an ethyl xanthate ion onto a surface si te followed by the subsequent adsorption of a second xanthate ion to f orm dixanthogen on the pyrrhotite surface has been proposed. Dixanthog en remains at the pyrrhotite surface, but is also found in solution, w ith its concentration reaching a maximum value corresponding to its so lubility limit, independent of pH and initial xanthate concentration, For a law initial xanthate concentration, the amount of adsorbed xanth ate species goes through a maximum, shifting to longer times with incr easing pH values. The kinetics of xanthate adsorption have been analyz ed by the Runge-Kutta method and the rate constants for the various re actions 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 . (C) 1995 Academic Press, Inc.