This research focused on the evaluation of the potential use of a soil-isolated bacteria, identified as Staphylococcus equorum, for microbial-induced calcite precipitation (MICP) and copper removal. Isolated bacteria were characterized considering growth rate, urease activity, calcium carbonate precipitation, copper tolerance as minimum inhibitory concentration (MIC) and copper precipitation. Results were compared with Sporosarcina pasteurii, which is considered a model bacteria strain for MICP processes. The results indicated that the S. equorum strain had lower urease activity, calcium removal capacity and copper tolerance than the S. pasteurii strain. However, the culture conditions tested in this study did not consider the halophilic feature of the S. equorum, which could make it a promising bacterial strain to be applied in process water from mining operations when seawater is used as process water. On the other hand, copper removal was insufficient when applying any of the bacteria strains evaluated, most likely due to the formation of a copper–ammonia complex. Thus, the implementation of S. equorum for copper removal needs to be further studied, considering the optimization of culture conditions, which may promote better performance when considering calcium, copper or other metals precipitation.

Copper-molybdenum grades of important mining deposits have progressively decayed, which is associated with high levels of clay minerals which affect froth flotation. The depressing effect of clay minerals on copper sulfides was previously reported but there are no systematic studies on the effect on molybdenite flotation in seawater. The objective of this work was to study the effect of kaolinite on molybdenite flotation in seawater and to evaluate the use of sodium hexametaphosphate (SHMP) as dispersant. The results of this work show that kaolinite depresses molybdenite flotation which is more significant in seawater at pH > 9. All the experimental data validate the hypothesis that kaolinite covers molybdenite, reducing its flotation recovery. The depressing effect of kaolinite on molybdenite flotation in seawater is enhanced by the magnesium and calcium hydroxo complexes at pH > 9, which induce heterocoagulation between kaolinite and molybdenite, thus reducing recovery. The attachment of the positively charged hydroxo complexes of magnesium and calcium to the molybdenite and kaolinite surfaces is diminished by SHMP. This reagent increases the repulsive forces between molybdenite and precipitates and as a result, molybdenite becomes more hydrophobic and recovery increases.

Polyacrylamides (PAM) are used as flocculants in the copper-molybdenum mining industry to improve the settling rate of flotation tailings. These types of reagents are recirculated to flotation in the water that is recovered from the thickeners, and as a result of this practice they can cause depression of flotation of some important minerals such as molybdenite. The objective of this work was to study the effect of a PAM of 11.9% of degree of anionicity on the flotation of molybdenite. The effect of the anionic PAM on molybdenite flotation was studied under different levels (three) of flocculant mechanical shearing. The flotation data was discussed along with intrinsic viscosity, adsorption, induction time, and electrophoretic mobility measurements. It was found that the non-sheared PAM (NS–PAM) had the strongest depressing effect on molybdenite flotation, followed by the moderately sheared PAM (MS–PAM). The depressing effect of the strongly sheared PAM (SS–PAM) was negligible. The flotation data correlated with the induction time measurements that showed that molybdenite became more hydrophilic in the presence of the NS–PAM. The SS–PAM has no effect on the induction times. Further work is ongoing to understand the effect of PAM on molybdenite flotation in the presence of clay minerals and different aqueous media.

The widely used technology for the selective flotation of copper and molybdenite using sodium hydrosulfide (NaSH) to depress copper sulfides creates environmental issues related to the potential emissions of toxic hydrosulfide gas (H₂S) and bad odors. Previous studies showed that molybdenite flotation can be depressed by the action of lignosulfonates, but no significant progress has been made in studying the effect that these reagents have on the foaming/frothing phenomena in flotation. The objective of this work was to investigate the foaming properties of three samples of lignosulfonates through measurements of surface tension, foamability, bubble size distributions, and water recovery. A sugared sodium lignosulfonate (NaLS), a calcium lignosulfonate (CaLS), and a sample prepared by sulphomethylation of kraft lignin (KLS) were tested. It was found that all lignosulfonates displayed surface activity that decreased with pH and was related to the degree of anionicity and molecular weight. The NaLS lignosulfonate showed the highest dynamic foamability index (DFI) value, compared to that of the CaLS and KLS samples. The lignosulfonates tested in this study strongly affected bubble size. Water recovery tests performed using flotation experiments in a two-phase system showed that the KLS and NaLS samples had the strongest effect, which correlated with the surface tension, foamability, and bubble size results.

Enargite (Cu₃AsS₄), a copper–arsenic sulfosalt, represents a critical challenge in copper mineral processing due to its high arsenic content, which poses significant environmental, metallurgical, and economic issues. Its flotation behavior closely resembles that of other copper sulfides such as chalcopyrite and chalcocite, complicating selective separation at early beneficiation stages. This review presents a comprehensive examination of enargite’s surface chemistry and electrochemical behavior, focusing on the influence of oxidation, pH, and pulp potential on surface reactivity, charge distribution (zeta potential), and hydrophobicity. Detailed insights into the formation of surface oxidation layers, passivation mechanisms, and contact angle variations are provided to elucidate collector-mineral interactions. Advances in selective flotation techniques are also discussed, including the use of depressant reagents, controlled redox environments, and reagent conditioning strategies. Special attention is given to flotation in seawater, where ionic strength and multivalent ions significantly influence mineral-reagent interactions and flotation outcomes. Galvanic interactions between enargite and other sulfide minerals are identified as critical factors affecting floatability and selectivity. The review consolidates findings from recent experimental and electrochemical studies, highlighting promising approaches to enhance enargite rejection and copper concentrate purity. It concludes with perspectives on future research aimed at optimizing flotation processes and developing sustainable solutions for processing arsenic-bearing copper ores.

Nanobubbles have recently been proposed as a promising technology to enhance mineral flotation; however, their behavior in real ores with complex mineralogy remains poorly understood. This study evaluates the effect of nanobubbles on the flotation of copper sulfide ores from Chilean porphyry deposits with contrasting clay contents. Two representative samples were analyzed: a low-clay-content ore (M1) and a high-clay-content ore (M2). Flotation tests were carried out in a 2.7 L forced-air cell, using kinetic experiments with and without nanobubbles and frother addition. The mineralogical composition was characterized by XRD and QEMSCAN, while SEM-EDS was used to analyze surface morphology and particle associations. The results showed that nanobubbles improved copper and molybdenum recoveries in M1 up to 7.5 and 20%, respectively, increasing both kinetics and final recovery, which was supported by SEM observations of clean surfaces and compact agglomerates. In contrast, in M2 the use of nanobubbles decreased flotation efficiency due to enhanced slime coating and the formation of non-selective agglomerates, which reduced the hydrophobicity of sulfide surfaces. Overall, this study demonstrates that the efficiency of nanobubbles strongly depends on ore mineralogy, offering advantages in clean systems but limitations in clay-rich ores, and highlights the need for mineral-specific strategies for their successful industrial application.