Pyrochlore flotation from silicate gangue minerals: Amine adsorption mechanisms and the effect of modifying reagents

Abstract

In this study, zeta potential measurements, micro flotation, Fourier Transform Infrared Spectroscopy (FT-IR), and X-Ray Photoelectron Spectroscopy (XPS) were used to evaluate the floatability of pyrochlore, quartz, and microcline in the presence of three different pH modifiers: hydrochloric, oxalic, and fluorosilicic acid. The results showed that oxalic acid acted as a pyrochlore depressant through precipitation of calcium oxalate at the mineral surface, hindering collector adsorption. Comparatively, fluorosilicic acid helped maintain the hydrophobicity of all minerals in high calcium-content water, but was confirmed to have a true activating effect on microcline only (not pyrochlore, as previously reported in the literature). When flotation pH was below the mineral’s isoelectric point (IEP), all three modifiers reduced floatability, and relative mineral floatability was a function of: (1) the strength of interaction between collector and the individual mineral surface, and (2) collector concentration. At low collector concentrations, below the mineral’s IEP, mineral floatability was as follows: microcline ≥ pyrochlore > quartz; explaining why it may be more challenging to reject microcline from the pyrochlore concentrate, compared with quartz. XPS results confirmed that amine adsorption on the surface of pyrochlore is stronger than previously reported. Adsorption involved a chemical interaction between the amine and niobium sites on the mineral surface, explaining why pyrochlore maintains its hydrophobicity below its IEP. Overall, it is hoped that this work will help existing operations better understand and control their flotation circuits and aid in the development of effective pyrochlore flotation reagent schemes.