The effect of superstructure on the zeta potential, xanthate adsorption, and flotation response of pyrrhotite

Abstract

Pyrrhotite (Fe(1–x)S; 0 < × ≤ 0.125) is a complex sulfide gangue mineral in base metal mining operations, having several superstructures. Of these, magnetic/4C (Fe7S8) and non-magnetic/5C (Fe9S10) superstructures are commonly found together and have demonstrated different flotation behaviour both in lab-scale and industrial settings. Currently, much of the literature data supports the theory that non-magnetic pyrrhotite is more floatable than magnetic pyrrhotite. The present study aimed at assessing the differences between the superstructures by investigating their zeta potentials (pH 2–11), n-amyl xanthate collector adsorption (pH 7, 8.5, and 10), and microflotation (pH 7–11) response (with and without sonication pre-treatment). Overall, zeta potential analysis demonstrated similar superstructure behaviour (minerals alone and in the presence of Ni2+, Cu2+, and xanthate collector) when their surfaces are “fresh” (i.e. minimal contact with oxygen). The results also supported xanthate adsorption by an initial physisorption mechanism. Collector adsorption studies demonstrated that xanthate uptake was much higher for magnetic than non-magnetic pyrrhotite for all pH conditions tested (7, 8.5, and 10). Based on this, it was proposed that different proportions of Fe(OH)[S][X] and Fe(OH)[S][X2] (dixanthogen) are present on the superstructures and that non-magnetic pyrrhotite likely contains more dixanthogen. Microflotation investigations showed that when surface oxidation products have been removed (via sonication) and sufficient xanthate is present (permitting adequate dixanthogen), magnetic and non-magnetic pyrrhotite superstructures behave virtually the same. It was acknowledged that in real systems (i.e. industrial operations) where surface oxidation is inevitable, superstructure flotation will differ significantly due to their different reactivities towards oxygen.