Improving flotation hydrodynamics to maximize nickel recovery from tailings

The REFLUX™ Flotation Cell (RFC™) was used to investigate the flotation of a nickel tailings stream containing significant levels of dissolved solids, slow floating nickel minerals, and ultrafine hydrophilic silicates. Slow floating minerals are known to lead to excessive gangue entrainment and low upgrade. The performance of the RFC™ was investigated with reference to that observed for a batch mechanical cell. The flotation feed system displayed complexity including sensitivity to aging of the tailings, coupled with acute sensitivity to the effects of dilution. The work suggests dilution of the tailings feed leads to the dissolution of surface species formed during aging, essential for hydrophobicity and indeed nickel recovery. These observations point to the need for new work on the interplay between the water chemistry and the mineral surfaces. Although the nickel recovery was only of order 30 %, the recovery of the hydrophobic components from a single stage RFC™ was closer to 80 %. Moreover, the silica content of the feed was reduced from 37 % to ∼1 % through a powerful counter-current washing of the rising bubbles, delivering a hydrophobic-hydrophilic selectivity exceeding ∼10. The product flux, measured relative to that achieved using a mechanical cell at the same feed concentration, was more than 6-fold. This work demonstrated the efficacy of the RFC™ hydrodynamics in upgrading slow floating minerals using a reduced footprint while rejecting the hydrophilic ultrafine particles.