Surface characterization of microwave-treated chalcopyrite

The application of microwave radiation as an assisted grinding technique has shown great potential to improve comminution. Besides fracturing, the treatment also leads to phase transformations at the grain boundaries of the minerals, changing their surface properties and affecting downstream processes, such as flotation. Therefore, the study of the effects of microwave treatment on a mineral's surface properties is important for the industrial application of microwave assisted grinding. In this work, the surface properties of untreated and microwave-treated chalcopyrite were investigated by XRD, XPS, ATR-FTIR, SEM, BET/BJH, IGC, ELS (zeta potential) and microflotation. While short exposure times were found to favor the formation of copper polysulphides (CxFeySn) at the mineral surface, longer treatments converted CuFeS2 into iron oxides/hydroxides/oxyhydroxides and sulfate at the surface and, enriched C(x)Fe(y)S(n )underneath the oxidation layer. A shift in the zeta potential curves to less negative values was observed after treatment, reaching an IEP around pH 4.5. The collectorless floatability of chalcopyrite initially improved after exposure as its surface energy decreased. However, the samples' surface became energetically more active after longer treatment times, and the flotation recovery decreased. Microwave treatment also increased the mineral's specific surface area (SSA) and porosity; and changed the pore size distribution.