Flotation of pyrrhotite to produce magnetite concentrates with a sulphur level below 0.05% w/w

Abstract

Northland Resources is developing several magnetite mineral resources in northern Europe. The Tapuli, Sahavaara and Pellivuoma mineral resources are in Sweden and the Hannukainen resource is in Finland. Three of these resources (Sahavaara, Pellivuoma and Hannukainen) require flotation to remove more than 98% by mass of the sulphur in the feedstock to produce a saleable magnetite concentrate with a sulphur level below 0.05% w/w. The detrimental sulphur containing mineral is monoclinic pyrrhotite and its removal requires flotation. Previous published results related to pyrrhotite flotation from magnetite concentrate, e.g. on a magnetite deposit in Peru, only required the process to produce a final magnetite concentrate with a sulphur level below 0.4% w/w. There is currently no known published information on a process that floats pyrrhotite to achieve a magnetite concentrate with less than 0.05% w/w of sulphur.Extensive bench-scale tests were conducted on samples from Sahavaara, Pellivuoma and Hannukainen. Low-intensity magnetic separation (LIMS) tests showed that LIMS upgraded the magnetite and the sulphur in the pyrrhotite at the same ratio.The final flotation reagent regimes and conditions for each deposit were different being related to differences in mineralogy and grind size. The pH ranged from natural to pH of 4. Large dosage rates of xanthate collectors and long flotation times were needed. Flotation feed percent solids of between 45% and 50% w/w was required. Future work will modify these reagent regimes and flotation conditions in the full-scale plants to further optimise the flotation processes.