The depression of pyrite flotation is normally difficult especially when pyrite is activated by copper ions. In this study, different biopolymers, modified from lignosulfonate, were examined to depress the flotation of copper-activated pyrite. It was found that the biopolymers (DP-1775, DP-1777 and DP-1778), differing in composition, were able to depress the flotation of copper-activated pyrite. The depression was associated with the copper(I)-biopolymer complex formed on pyrite surface which enhanced the oxidation of copper(I) and inhibited xanthate adsorption. While the molecular weight corresponded to the adsorption capacity of biopolymers on pyrite, the content of functional groups of biopolymers interfered with xanthate adsorption. (C) 2016 Elsevier Ltd. All rights reserved.