Low grade nickel ores containing large amounts of serpentine minerals have historically been difficult to process efficiently. The Mt Keith ore was no exception with recoveries in the first five years of operation averaging just 60%. In this research, the factors limiting performance have been identified and a new process has been devised that raises recovery significantly. The process exploits the particle size dependence of nickel sulphide flotation and the different ways that pH change and pulp density influence the response of coarse and fine particles. Implementation of the new process at Mt Keith has raised nickel recovery by 10%. In turn, nickel production has increased by over 6000 t.p.a. and the net present value (NPV) of the operation has increased by over A$300 m. These outcomes illustrate the large commercial benefits that can be gained by understanding particle size effects in flotation. (c) 2005 Elsevier B.V. All rights reserved.