Flotation recovery–by–size comparison of pyrrhotite superstructures with and without depressants

Abstract

This paper is a continuation of a lab–scale flotation scoping study completed on a Ni–Cu sulfide ore that incorporated the use of diethylenetriamine/sodium metabisulfite (DETA/SMBS) pyrrhotite depressants. The scoping test work showed depressive effects on both hexagonal (Hex Po; Fe9S10) and monoclinic (Mono Po; Fe7S8) pyrrhotite superstructures with DETA/SMBS. This work investigates pyrrhotite superstructure flotation, with a focus on recovery–by–size with/without depressants (DETA/SMBS). From the baseline rougher test (pH 9.2), it was observed that Hex Po floated primarily in intermediate size classes (10–100 μm) while Mono Po floated largely in finest sizes (<10 μm). The likely contributing factors for this flotation difference were substantial surface passivation sustained by Mono Po over Hex Po which also permitted a larger degree of surface activation for Hex Po by Cu2+ and Ni2+ ions. Baseline scavenger tests (pH 8) showed similar superstructure flotation across all size classes, suggesting that mildly alkaline conditions did not cause significant surface passivation on Mono Po and thus did not hinder xanthate collector uptake by either superstructure, yielding similar floatabilities. This combination of DETA (150 g/t) and SMBS (300 g/t) was found to be very effective at depressing both superstructures for an ore containing 28% pyrrhotite (42% of which was Hex Po), especially in the intermediate and coarse size classes (>30 μm). After DETA/SMBS conditioning, both Mono Po and Hex Po recovery–by–size was identical, flotation was largely observed in the fine fraction (<10 μm) – regarded as weakly floatable Po. The major factors that caused measurable differences in the superstructure flotation responses: alkaline conditions (pH > 9); presence of activating ions (e.g. Cu2+ and Ni2+) and superstructure reactivity towards oxygen.