Abstract: A multi-stage froth flotation process is provided for concentrating sulphide minerals or middlings containing non-ferrous metal values such as nickel, cobalt and copper, which co-exist with significant amounts of pyrrhotite. The process is carried out without relying on any specific reagent as pyrrhotite depressant, but rather by exploiting the natural pulp environment with low REDOX potentials generated by mild steel grinding media in the grinding step preceding the froth flotation. The concentrate from the flotation stage(s) in which the REDOX potential rises above a predetermined value, is recycled back to the grinding step and/or to preceding flotation stage(s) from which concentrate is collected as the final product or is subjected to an up-grading in a further cleaning stage.