Floatability studies of wavellite and preliminary results on phosphorus removal from a Brazilian iron ore by froth flotation

Along with other deleterious elements, phosphorus is an extremely harmful element found in iron ores used as a raw material in the steel making process. It is responsible for increasing its hardness and brittleness while decreasing its ductility. Reducing the phosphorus content in ores when the apatite is the main phosphorous mineral can be easily achieved through reverse flotation making use of anionic collectors to float the apatite and sodium silicate to depress the iron oxides. However, the phosphorus removal from iron ores other than igneous formations has been a challenge for most of the iron ore operations. This research aims to make a preliminary study of wavellite’s floatability and to evaluate the reduction of phosphorus content by froth flotation from a Brazilian iron ore with a P content of 0.82%. Microflotation experiments of wavellite using anionic, cationic and amphoteric collectors were carried out in the basic pH range. Sodium silicate was evaluated as a depressant, and the presence of this reagent did not change significantly the wavellite’s floatability. Dodecylamine showed the best floatability results, which were around 100% above pH 8. Bench flotation experiments confirmed the results of the microflotation experiments. During the bench experiments, flotation with amine as collector gave the lowest phosphorus content at the final iron concentrate. A concentrate containing 0.201% P with a mass recovery of 62.31% was achieved when a 150 g/t dosage of Flotigam EDA (an amine type collector) was used. In a bench experiment with Flotigam 2835 2L as collector led to a concentrate containing 0.312% P with a mass recovery of 90.24%. The collector Flotigam 2835 2L appeared to be more selective onto phosphates and aluminum silicates than the other amine.

The high floatability of wavellite with dodecylamine may be attributed to both chemical and electrostatic adsorption mechanisms. Precipitation of insoluble salts and formation of surface chemical complexes are the most likely hypothesis for the chemical interactions in this system.Figure optionsDownload as PowerPoint slideHighlights
► Wavellite presents a higher floatability with dodecylamine in alkaline pH.
► The high floatability values obtained in the pH range of 10.5–12 may be due to amine precipitation at the wavellite surface.
► At pH 8–10, the adsorption may be due to electrostatic forces.
► During the bench experiments amines attained the lowest phosphorus grades at the final concentrate.