Studies on the adsorption of flotation collectors on iron oxides

Sammanfattning: Iron ore pellets are an important refined product used as a raw material in steel manufacturing. In order to meet the requirements of the blast furnace process for steel production, the iron ore is upgraded in a number of steps including, among others, flotation. The induced hydrophobicity of the iron ore concentrate caused by adsorption of the flotation collector may affect the pellet strength both in wet and dry state. In order to minimize the influence of the collector on pellet properties it is important to understand the mechanism by which the collector interacts with iron oxides and what factors may affect this interaction.In this work, the adsorption of a commercial fatty acid type collector Atrac 1563 as well as four model compounds on synthetic iron oxides was studied in-situ using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The effect of collector concentration, ionic strength, calcium ions and sodium silicate on the collector adsorption was investigated. The mechanism of adsorption of anionic collectors on iron oxides at pH values above the point of zero charge was found to be similar to that of non-ionic collectors. At pH values above the point of zero charge, sodium cations were found to increase collector adsorption on magnetite by reducing electrostatic repulsion while negatively charged silicate species were shown to reduce collector adsorption by blocking magnetite surface sites. Calcium ions were found to significantly enhance the adsorption and possibly induce precipitation of the collector on magnetite even in the presence of sodium silicate suggesting that a high concentration of calcium in the process water could possibly enhance the contamination of the iron ore with the flotation collector, which has been previously shown to have a negative effect on both flotation and pelletization processes.