Oxidation of magnetite pellet concentrates (from LKAB, Sweden) during drying and storage was studied using thermogravimetric analysis (TGA). The Fe2+ content of a standard LKAB pellet feed decreased by 0.2% during heat treatment at 105 C for 2 days. The results indicate that magnetite concentrates of pelletizing fineness already start to oxidize to gamma-hematite during drying at 105 degreesC, although 105 degreesC is recommended by ISO 7764 and ISO 3087 and given as the maximum allowable drying temperature in ISO 3082. The importance of drying time for the amount of magnetite oxidized should also be recognized, but is not mentioned in the ISO standards. The sensitivity of magnetite particles for oxidation during drying could not be predicted by measuring the BET surface area. A simple isothermal TGA run gives exact experimental data and is recommended as a standard procedure before choosing the drying temperature for magnetite concentrate samples. Oxidation during storage at room temperature was observed as well. The Fe2+ content in a standard LuossavaaraKiirunavaara (LKAB) pellet feed decreased by 0.3% Fe2+ during 4 years of storage at room temperature. Oxidation during storage was completely hindered when the samples were stored in a freezer at -50 degreesC. Therefore, freezer storage is recommended for all magnetite reference materials. These materials are used over several years and are especially susceptible to oxidation because they are usually finely ground and high in Fe2+ content. The results also show that if the magnetite sample has partly oxidized to gamma-hematite, the oxidation curve obtained by TGA will overestimate the Fe2+ content of the sample, if background correction is necessary. (C) 2004 Elsevier B.V. All rights reserved.