The electrochemical behaviour of natural galena (PbS) is studied in relation to mineral flotation, Following a previous paper mainly devoted to the study of the semiconducting properties of such electrodes, the present one is focused on two important problems related to mineral processing; the sample oxidation at high positive potentials and the reactivity with two collection reagents, ethylxanthate (EtX(-)), a collector, and Na2S, a depressant. By electrochemical impedance spectroscopy, it is found that the surface oxidation begins beyond +0.14 V (SCE) in the absence of these reactants. The kinetic law for the growth of the oxidised films is established, However, the competition between the adsorbabilities of OH-, collector and depressant, seems to play a determining role in the recovery or depression of galena.