Influence of Muscovite Content on the Flotation of Pyrite and Arsenopyrite

Abstract

Muscovite is a hydrophilic, platy micaceous mineral, classified as a phyllosilicate. Previous research identified that micas and clays can have a deleterious effect on the flotation of sulfide minerals; for example, the presence of muscovite is associated with an increase in pulp viscosity, the formation of slime coatings and high recovery of muscovite through entrainment. The majority of previous studies relating to the effect of mica and clays on sulfide minerals were conducted using copper ores. Barrick Gold Corporation has a sub-economic refractory gold orebody with a high content of muscovite. The flotation circuit designed for this project has a high capital cost, due to the high throughput and the relatively long residence time required to recover the gold-bearing sulfide mineral. In addition, muscovite is readily recovered to the concentrate, which affects downstream processes.The effect of the presence of muscovite on the flotation of pyritic gold-bearing minerals has not been reported in the literature. This work investigates the effect of muscovite on pyrite and arsenopyrite floatability at laboratory-scale using a synthetic ore consisting of pyrite, arsenopyrite, quartz (silica) and muscovite. The experimental program applied a Central Composite Rotatable Design (CCRD) to identify the potential causes for the detrimental effect of muscovite. The aim was to identify the most significant factors affecting to the floatability of pyrite and arsenopyrite in this synthetic system, with the factors investigated being frother dosage (ppm), the percentage of solids, the percentage of muscovite in the gangue, pH and muscovite size distribution (P80).In order to investigate the underlying mechanisms behind the effects observed in the CCRD, zeta potential measurements were done to investigate the formation of slime coatings, viscosity measurements of the pulp monitored any changes in viscosity, and Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) were used to investigate changes in surface chemistry of the pyrite and arsenopyrite. The froth height of selected experiments was measured to detect changes on froth stability.The results of the CCRD analysis indicated that the factors that significantly affected the kinetics of arsenopyrite and pyrite are the positive interaction of pH with frother and the interaction of %solids with muscovite size distribution which is a negative term. It can be speculated that positive effect of the term pH x frother dosage on the flotation rates of arsenopyrite and pyrite is due to the combined effect of the frother and pH on the froth stability, as limited tests showed that the increase of pH increases the froth height.The results showed that the proportion of muscovite in the gangue has no effect on the flotation rate of arsenopyrite. Furthermore, the effect of the proportion of muscovite in the flotation kinetics of pyrite is not deleterious and has low significance, according to the regression.No direct correlation was found between the measured viscosity and the flotation rate of pyrite or arsenopyrite. In addition, the proportion of muscovite in the gangue does not affect significantly pulp viscosity. Therefore, the presence of muscovite may not affect the flotation kinetics through an increase in pulp viscosity.No evidence of muscovite slime coatings on the pyritic minerals was found by the zeta potential measurements. The ToF-SIMS and XPS analyses indicated that the increase in the particle size distribution of muscovite was related to an increase of the levels of K and Al, which originate from the muscovite lattice, on the surface of pyrite. A corresponding decrease of the level of Cu and collector, in the presence of coarser muscovite, leads to a decrease of particle hydrophobicity of pyritic minerals. The leaching of K and Al from muscovite was found to be size-dependent, increasing with the increase in muscovite particle size, which explains the effect of muscovite P80 on the kinetics of arsenopyrite and pyrite. These results suggest that the reason for the deleterious effect of the interaction term %solids x muscovite P80 is due to the increase in K and Al ions on the pyritic minerals surfaces. As the percentage of solids increases, more muscovite is available for leaching and less solution is available to carry those ions; therefore, the concentration of K and Al ions increases significantly, leading to the slower flotation kinetics.In conclusion, contrary to the expected, the deleterious effect of muscovite on the flotation rate is not caused by physical mechanisms, such as the increase of viscosity or the formation of slime coatings on the surface. The dominant deleterious effect of muscovite is due to the chemical modification of the surfaces of pyritic minerals by K and Al ions from its lattice.