The variation in surface properties of pyrite in the presence of potassium amyl xanthate (PAX) and a lignosulfonate-based biopolymer depressant (DP-1775) was investigated by electrochemical techniques to explain the depression behavior of DP-1775 on pyrite flotation. Electrical impedance spectroscopy and cyclic voltammetry of pyrite electrode were conducted in the absence and presence of PAX and DP-1775, individually or in combination. It was found that in the absence of PAX, DP-1775 was discontinuously distributed on pyrite surface and progressively passivating the pyrite surface. In the presence of PAX, the pre-adsorbed DP-1775 reduced the extent of electrochemical oxidation of PAX. The indication of a lower degree of FAX oxidation can explain why DP-1775 acts as a depressant in pyrite flotation. (C) 2015 Elsevier Ltd. All rights reserved.