Investigation of the oxidation effects on the precious metal recovery at the Kevitsa llotation plant, Finland

This thesis investigates the effects of sulphide mineral oxidation on the recovery of precious metals (Au, Pd, and Pt) at the Kevitsa mine in Finland. Emphasis is placed on understanding the electrochemical and mineralogical dynamics that govern the flotation efficiency of these metals under varying conditions. Plant performance from 2021 to 2024 reveals distinct seasonal fluctuations in Nickel (Ni) and Platinum Group Metals (PGMs), especially palladium (Pd) and platinum (Pt) recovery in the Copper (Cu) and Ni circuit. This is attributed to the oxidation of pentlandite due to the changes in the quality of the recycled process water from the TSF in summer, when the temperature is high and slightly acidic. Pd and Pt showed an inverse recovery pattern between Cu and Ni circuits, suggesting redistribution of PGMs depending on redox and circuit-specific conditions.

Laboratory works conducted with sodium dithionite (Na2S2O4) as a reducing agent showed that reducing the pulp Eh to -250 mV during conditioning significantly enhanced Ni and Pd recovery by 40% and 26%, respectively, in the Ni cleaner 2 concentrate. This was later confirmed in a repeated test. Gold, palladium, and platinum will be referred to as PGMs throughout this thesis document.