A comprehensive plant survey was conducted in the flotation circuits at Vale Inco's Thompson Mill. Results from the survey were validated by internal and external references. The Mill was operating with a feed of 1.8% Ni during the survey. A Ni concentrate assaying 13.8% Ni was produced at a Ni recovery of 84.9%. An additional 1.5% Ni recovery was achieved in the Cu concentrate, giving an overall Ni recovery of 86.4%. The Ni loss to the scavenger tails and scavenger cleaner tails was 6.5% and 7.1%, respectively. Chemical analysis and mass balance revealed the major diluent of the Ni concentrate and the main source of the diluent. A size-by-size mass balance identified the sources (streams and size fractions) of Ni losses. A mineralogical analysis using an MLA revealed the forms of lost Ni in terms of liberated versus locked particles, and in the case of locked particles, the mineral components that formed composite particles with pentlandite. The information gained from the above analyses has been used to develop a research strategy. Preliminary laboratory flotation tests on increasing Ni concentrate grade have produced promising results. More detailed and systematic experimental studies will follow. (C) 2008 Elsevier Ltd. All rights reserved.