The assessment of mineral surface hydrophobicity at the industrial scale is a challenge. In some industrial situations, such information is indirectly obtained from other proxy variables. A well-known example of this is observed in the Cu-Mo selective flotation operation, where sodium hydrosulphide is used to change the redox potential and, controlling this value, determine when Cu-sulphide floatability is inhibited. Preliminary experiments indicate that this reagent may also promote the formation of solid precipitates, reducing its impact on the redox potential. This study aims at designing a simple strategy at the laboratory scale to report and quantify NaSH losses due to parallel, irreversible, and/or fast reactions, such as precipitation. Experiments carried out using process water coming from a Cu-Mo selective flotation plant in Chile show that departing from different pH conditions and the addition of hydrosulphide ions effectively triggers the precipitation of specific metal ions, decreasing its availability to reduce the redox potential of the aqueous solution. For this specific case scenario and water quality, around 5% of the NaSH dosed precipitated. An SEM-EDX analysis of the produced solid phase shows that it is composed of mainly iron sulphide and hydroxide, along with other metal hydroxides. More importantly, it was found that dosing the reagent at the same concentration, but in the form of small increments, allows reaching the redox potential more efficiently, reducing to some extent the precipitate production and the unnecessary NaSH consumption in up to 30% of the NaSH dosed. Preliminary 1-D modelling of the process, based on mass transport coupled with reaction mechanisms, provided a first indication of the best dosing conditions for this reagent. The latter is expected to contribute to the development of better and improved reagent dosage technologies in froth flotation environments.

The presence of arsenic-bearing minerals in ores, notably enargite (${Cu}_{3}As{S}_4$), remains an unresolved issue for copper beneficiation processes, including those for porphyry copper deposits. In particular, several operational challenges remain for the selective flotation of enargite from copper–sulphide ores, as well as the selective leaching of arsenic from enargite in copper concentrates. This study addresses these challenges from the standpoint of mediator science, where structures with specific elemental compositions observed by several authors at the surface of enargite and chalcopyrite, under different conditions and analytical techniques, are compiled and analysed. Most probable surface species, observed using technologies measuring the outmost surface layer and occurring onto the mentioned minerals, are identified and compared to species predicted by classic thermodynamic calculations. The results indicate that for chalcopyrite the major species formed in acidic conditions is elemental sulphur, while copper oxide and iron oxides and oxy-hydroxides species predominate with increasing pH. For the case of enargite, a similar situation is observed at low pH values, although slightly acidic conditions appear as a less examined condition for this mineral. Some of the observed species were found to be consistent with thermodynamic predictions, while others are notably absent. Particularly, for the case of enargite researchers have reported the formation of arsenic (III) oxide at pH values as high as 13, and observation not predicted by Pourbaix diagrams. Thus As₂O₃ could be considered a metastable species at highly alkaline conditions, which opens an option to beneficiation from froth flotation. Interestingly, at the same pH condition, iron oxide and oxyhydroxides species predominate at the surface of chalcopyrite. Therefore, applying the mediator concept, the initial alkaline flotation of sulphide ores turns into an oxide flotation case.

The concept of mineralogy, originally defined as a geological science focused on the study of minerals within the Earth’s crust, encompasses all measurable characteristics of these materials. Significant progress has been made in understanding physical properties such as hardness and roughness. However, knowledge of surface chemical composition and its relationship to surface reactivity remains limited, particularly in systems where metal sulphides play an important role. It is well established that the composition of a bulk solid often bears little resemblance to that observed at a solid-fluid interface. This discrepancy poses major challenges for mineral systems, as determining and quantifying the correct elemental and “mineral” composition of an interface is difficult, even in relatively simple situations such as the exposure of sulphide minerals to atmospheric conditions. In such cases, complex and frequently non-stoichiometric surface structures may form, making them difficult to define and interpret. This chapter seeks to describe some of these scenarios, highlighting the role of so-called “mediators,” which are ultimately responsible for mineral surface reactivity. The analytical techniques used to characterise these mediators are shown to be crucial for interpreting their influence. For example, QEMSCAN and XPS analyses applied to the same chalcopyrite sample demonstrate that the depth of analysis is critical. The observation that iron species dominate the outermost surface during oxidation supports qualitative models previously proposed by other authors. In addition, this chapter discusses challenges associated with mineral processing and extractive metallurgy and concludes by outlining potential trends and approaches to address these issues.

This work describes the development of a core–shell magnetic nanoadsorbent (Fe₃O₄@TiO₂) designed for the selective recovery of rare earth elements (REEs) from electronic waste. The synthesis involved the co-precipitation of magnetite coated with an anatase-phase TiO₂ layer, subsequently functionalized with organophosphorus groups using glycolic acid and phosphoric acid. This surface modification, verified via FT-IR spectroscopy and zeta potential analysis, provided the material with a high density of active sites. Adsorption studies with lanthanum revealed that the process follows pseudo-second-order kinetics, reaching equilibrium in only 15 min with a theoretical model-calculated capacity of 19.4 ± 0.8 mg/g at pH 5. The material demonstrated high stability and reusability, maintaining 75% of its adsorption capacity after five cycles with a corresponding H₂SO₄ desorption efficiency of 58–60%. Finally, the nanoadsorbent was validated on real LCD screen leachates following an upstream pH 5.0 pre-neutralization and filtration stage designed to remove massive baseline concentrations of iron and copper. Although residual copper and chromium acted as the primary competitors within the remaining complex matrix, the material effectively partitioned REEs (Gd, Y, Ce, Pr, Nd, and Sm) present at ultra-low trace levels (μg/L), demonstrating its potential for urban mining and the circular economy.