Assessing surface-level processes during column leaching: A spatiotemporal and multilevel approach combining XPS and SEM-EDS

Surface-level processes play a significant role during leaching. However, few studies have been devoted to studying the surface of samples as part of column leaching experiments. This study proposes a methodology to access information from the surface-level processes that occur during column leaching, aiming to aid the design of economically and environmentally sustainable heap leaching operations. The methodology combines the use of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) to investigate changes occurring at the surface. These two techniques have different surface sensitivities and thus allow the tracking of surface changes spatially (at different depths) and temporally (throughout the leaching period). The methodology also considers dividing a leaching column into a group of columns arranged in series. This allows extracting solid and solution samples from separate locations within the system without disrupting the process, thus yielding more information from a single experiment.

A case study of the proposed methodology is presented, for which a simulated bioleaching column experiment of a low-grade chalcopyrite ore was performed. The case study illustrates the usefulness of combining the two surface techniques, as their different surface sensitivities allowed the detection of two layers forming over the surface of the sample: (1) an intermediate layer rich in sulphates (later confirmed to be mostly jarosite) and (2) a thin surface layer rich in silicon (seemingly silica gel).