Molybdenum is the most important by-product of Chile's copper mining industry, and during the last decade gained international relevance because of its high price At mining deposits, copper and molybdenum are extracted together and then separated in a process consisting of several stages of flotation using sodium hydrosulfide (NaHS) as key reagent. However, environmental issues related to the potential emissions of toxic hydrosulfide gas (H2S), and bad odors make necessary the development of new environmentally friendly processes that incorporate non-toxic reagents. In this work, we hypothesize that a selective separation of chalcopyrite and molybdenite by flotation can be achieved by using lignosulfonates instead of NaHS. This approach was evaluated by testing the effect of lignosulfonates, produced by reacting kraft lignin with sodium sulfite and formaldehyde, and commercially available lignosulfonates, on molybdenite and chalcopyrite flotation. Chemical characterization of lignosulfonates was performed by determination of molecular mass, elemental analysis, fourier transform infrared, and mass spectroscopy with inductively coupled plasma. Also, interactions between molybdenite and lignosulfonates were studied through measurements of electrophoretic mobility. The main conclusions of the work are that molybdenite flotation can be depressed by the action of lignosulfonates, and such depressing effect increases with pH because of the interactions between lignosulfonates with the metallic calcium sites existing on the surface of the mineral particles. The experimental results also indicate that lignosulfonates can depress chalcopyrite flotation when sodium isopropyl xanthate is used as a collector, but this effect can be completely mitigated by using potassium amyl xanthate as a collector, thus, making it possible the potential separation of both minerals. (C) 2019 Elsevier B.V. All rights reserved.