The effects of oxidation on the flotation of chromite and olivine were studied in an effort to improve chromite recovery from domestic sources. The flotation behavior of pure chromite, pure olivine, and a chromite gravity concentrate were investigated. Minerals were heated in air at 50°C for 3 h, or at 150 or 250°C for 18 or 70 h to oxidize the mineral surfaces. The flotation response for the oxidized minerals was measured as a function of collector concentration and pH. Redox potential in the flotation slurries was measured. Freshly prepared chromite floated well between pH 2.2 and pH 4.5 but poorly at greater than pH 5. Oxidation at 150°C increased chromite floatability above pH 5 to about 30%. In contrast, oxidation did not measurably affect olivine flotation. This suggested that controlled oxidation may improve selectivity in the flotation of chromite from olivine. This concept was tested using a chromite gravity concentrate. Both flotation recovery and chromium oxide grade increased slightly following oxidation of the concentrate. Although the benefit from oxidation was small, this result shows promise for improving flotation selectivity using oxidation.

National Institute for Occupational Safety and Health