Chitosan was exploited as a selective depressant in the differential Pb-Zn sulfide flotation at pH 4 on artificial galena and sphalerite mixtures. The mixtures were prepared in two different approaches. In the first approach, the high purity galena and sphalerite were blended directly whereas in the second approach, the sphalerite was coated with copper before blending with galena. Using the first approach, it was found that lead ions contaminated the sphalerite surface making the separation non-selective. After adding EDTA, sphalerite was depressed by chitosan while galena was floated at pH 4. Using the second approach, i.e., that the sphalerite was pre-coated with copper before mixing with galena, it was found that the sphalerite was selectively depressed by chitosan without the need to add EDTA. ToF-SIMS and XPS were used to study the interactions of chitosan with uncoated sphalerite and copper-coated sphalerite. The results indicated that the amine groups and the hydroxyl groups in chitosan were involved in the strong interaction between chitosan and sphalerite whether the latter was coated by copper or not. Chitosan did not interact strongly with galena as reported previously. (C) 2013 Elsevier B.V. All rights reserved.