Surface chemical characterization of different pyrite size fractions for flotation purposes

A surface chemical approach of different pyrite size fraction is developed in this paper in the prospect of addressing the well-known coarse pyrite flotation challenge for environmental purposes. This work aims at exploring the effect of particle size on pyrite surface chemistry through the study of three pyrite size fractions up to 425μm. Pyrite surface evolution was investigated through dry crushing, air oxidation and aqueous conditioning using X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared spectroscopy (DRIFT) as complementary surface characterization tools. XPS, which characterized the outmost surface (about 40Å depth), indicated that pyrite size fraction did not impact its surface chemistry after crushing. However, DRIFT which characterizes the whole oxidation layer, led to the conclusion that ferric sulfate was more abundant in the finer fraction than in the two coarser fractions. Those two surface characterization tools allowed a thorough insight into the three-dimensional oxidation product structures of pyrite from different size fractions. The surface evolution of coarse fractions had the same surface evolution trend when submitted to aging and conditioning processes than the fine pyrite size fraction, studied in previous works, in terms of surface species speciation and their relative proportion. Those results led to a better understanding of particle size impacts on pyrite surface chemistry. ► XPS coupled to DRIFTS reveals a heterogeneous oxidation layer organized as clusters. ► DRIFT high quality spectra were obtained with pyrite size fraction up to 425μm. ► Particle size influences surface chemistry speciation and coverage after crushing. ► Coarse fraction had less sulfate containing less ferric sulfate than fine fraction. ► All fractions had similar surface evolution trend when conditioned at different pHs.