Our recent studies revealed that the ground sulphide minerals in contact with water generate H2O2 but its effect on the oxidation of pulp components and hence in deteriorating the concentrate grade and recovery in flotation has not been explored yet. In this study, the effect of depressant and collector additions during grinding on the formation of H2O2 by metal sulphides and its influence on complex ore flotation was investigated. The results showed a decrease in the generation of H2O2 with the addition of depressants during grinding while the addition of depressant and collector together increased H2O2 formation in the flotation pulp liquid. The flotation results showed that pyrite is effectively depressed when the depressant and collector are added together during grinding, corresponding to a condition of higher amounts of H2O2 in the pulp liquid thereby causing the oxidation of pyrite surface and depression in flotation. The best results of metal sulphides grade and recovery achieved also correspond to the same flotation conditions. (C) 2016 Elsevier B.V. All rights reserved.