An investigation into the floatability of a pentlandite–pyroxene system

Abstract

Mineral surface oxidation, slimes coating and inadvertent activation can detrimentally affect flotation and the separation of sulphide minerals. Surface oxidation and slime coatings will reduce hydrophobicity and collector adsorption selectivity. Inadvertent activation of gangue minerals by metal ions is frequently suspected of playing a detrimental role in selective flotation. In this study, the floatability of a pentlandite–pyroxene system was investigated in synthetic process water at pH 6 and pH 9 using zeta potential, microflotation and time of flight secondary ion mass spectrometry (ToF-SIMS) techniques. The aim was to maximise pentlandite recovery and simultaneously minimise the percentage pyroxene reporting to the concentrate. The results obtained showed that inadvertent activation by heavy metal ions, Cu(II) and Ni(II), contributes significantly to the true flotation of pyroxene. The microflotation tests revealed that pyroxene rejection is greatly improved by the addition of diethylenetriamine (DETA) in combination with sodium polyphosphate, this being particularly noticeable at pH 6. The mechanism responsible for the observed selectivity is explained by the ability of DETA to deactivate Ni(II), Cu(II) and possibly other ions through formation of stable chelates. The addition of polyphosphate introduced a more negative surface charge onto the minerals investigated thus preventing the formation of valuable-gangue mineral aggregates.