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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 (CuxFeySn) at the mineral surface, longer treatments converted CuFeS2 into iron oxides/ hydroxides/oxyhydroxides and sulfate at the surface and, enriched CuxFeySn 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.

Flotation is the most commonly used beneficiation method for rare earth (RE) ores. Due to the dissolution characteristics of the RE minerals and the gangue minerals, they may behave similarly in a flotation system. Previous work has shown that dissolved mineral species from gangue could precipitate/adsorb at the mineral surface affecting the minerals’ flotation behavior. In this work, the effect of dolomite supernatant on the surface of bastnasite, monazite and dolomite are presented. Zeta potential measurements, complemented with flotation tests, were conducted with and without the presence of the supernatant using benzohydroxamate as the collector. XPS results confirmed the surface speciation, and DFT simulations detail the possible mineral - collector, mineral - precipitated species and precipitated species - collector interactions. The results show that carbonate precipitates and Ca2+ from the supernatant could adsorb onto the mineral surface through covalent bonding, both affecting the zeta potential and reducing collector adsorption. Another important finding of this study is the potential loss of the collector in the solution due to complexation with ions from the supernatant. These findings confirm that an effective rare earth mineral separation through flotation does not rely solely on the strength of collector-mineral interaction, but rather is highly dependent on the chemistry of the flotation solution. Taking advantage of, or controlling, the surface reactions should be the main target to developing a more efficient and cost-effective flotation process. Different measures have been proposed to reverse/reduce the detrimental effects of the dolomite supernatant to RE mineral flotation.