Manganese is a widely used element in the steel industry; its main source is a mineral named rhodochrosite (MnCO₃). For industrial usage, rhodochrosite is reduced to different manganese oxides by means of nodulation furnaces. In this study, rhodochrosite was thermally analyzed at temperatures ranging from 100 °C to 1200 °C. XRD (Powder X-ray diffraction), XRF (X-ray fluorescence), AAS (Atomic Absorption Spectrometry), and FESEM-EDX (Field Emission Scanning Electron Microscopy-Energy Dispersive X-ray Spectrometry) were used to characterize the mineral and the residues were analyzed by XRD and FTIR (Fourier-transform infrared spectroscopy) to determine the stoichiometry of the thermal decomposition reactions. Three mass losses were observed, the first attributed to the transformation from carbonate to manganese (III) oxide, the second to the reduction to manganese tetroxide, and the third to the decomposition of calcium carbonate (CaCO₃) present as a contaminant in the studied mineral. Thermal decomposition kinetics shows that the first mass loss required 17.91 kJ mol⁻¹, indicating a control by mass transport-controlled process. For the second and third mass loss, the apparent activation energy of 112.41 kJ mol⁻¹ and 64.69 kJ mol⁻¹ was obtained respectively, indicating that both mass loss events were rate-controlled.

Jarosites are widely used in the hydrometallurgical industry of zinc to eliminate iron and other impurities contained in the concentrates. However, these compounds can also incorporate elements of significant environmental concern such as Tl⁺, Hg²⁺, Pb²⁺, Cd²⁺, Cr(VI), and As(V). In this work, the characterization of a synthetic mercury jarosite and its thermal decomposition kinetics are reported. XRD and FTIR analyses confirm that a mercury jarosite—Hg_0.40(H₃O)_0.2]Fe_2.71(SO₄)_2.17(OH)_4.79(H₂O)_0.44—was successfully synthesized. Four mass loss events were observed by thermogravimetric analysis at 290 °C, 365 °C, 543 °C, and 665 °C. The third event corresponds to mercury decomposition into mercury oxide, whilst the forth is related to the jarosite to hematite transformation determined by X-ray diffraction starting at around 600 °C. According to the kinetic parameters (activation energy and frequency factor) of the thermal decomposition process, the fourth stage required the highest energy (Ea = 234.7 kJ∙mol⁻¹), which corresponds to elimination of sulfur and oxygen from the jarosite lattice. Results show that jarosite-type compounds have the capability to incorporate heavy metals into their structure, retaining them even at high temperatures. Therefore, they can be used as a remediation strategy for heavy metals, such as mercury and others elements of environmental concern.

The materials used to conduct kinetic study on the leaching of silver in the S₂O₃²⁻-O₂-Cu²⁺ system were mining residues (tailings) from the Dos Carlos site in the State of Hidalgo, Mexico, which have an estimated concentration of Ag = 71 g∙ton⁻¹. The kinetic study presented in this paper assessed the effects of the following variables on Ag dissolution rate: particle diameter (d₀), temperature (T), copper concentration [Cu²⁺], thiosulfate concentration [S₂O₃²⁻], pH, [OH⁻], stirring rate (RPM), and partial pressure of oxygen (PO₂). Temperature has a favorable effect on the leaching rate of Ag, obtaining an activation energy (Ea) = 43.5 kJ∙mol⁻¹ in a range between 288 K (15 °C) and 328 K (55 °C), which indicates that the dissolution reaction is controlled by the chemical reaction. With a reaction order of n = 0.4, the addition of [Cu²⁺] had a catalytic effect on the leaching rate of silver, as opposed to not adding it. The dissolution rate is dependent on [S₂O₃²⁻] in a range between 0.02 mol·L⁻¹ and 0.06 mol·L⁻¹. Under the studied conditions, variables d₀, [OH⁻] and RPM did not have an effect on the overall rate of silver leaching.

During grinding with forged steel media, sulphides such as pyrite undergo surface changes due to the occurrence of oxidation–reduction reactions, which affect its depression during the concentration process. For this reason, in this work, the surface modification of pyrite during grinding was studied; FTIR, ICP-OES, XRD and SEM-EDS were used for the materials’ characterisation. It was found that the pyrite obtained during grinding showed magnetic susceptibility due to the absorption and superficial formation of magnetite Fe₃O₄, Fe–O bonds identified by FTIR at 598 cm⁻¹, and of other species, such as oxy-hydroxy-sulphates at 696 cm⁻¹ and goethite α-FeOOH at 875 cm⁻¹. This caused the reversal of the zeta potential magnitude (ζ) from positive to negative at pH 8.3 and 30 min of grinding. The ζ of the pyrite throughout the studied pH ranges was, overall, positive, i.e., +5 mV. However, at pH 10.5 and 15 min of grinding, the ζ turned negative. This was associated with the formation of Fe–CO₃ (−2) bonds in the siderite, which were identified with the absorption bands corresponding to 756, 1448 and 1493 cm⁻¹.

The increasing global demand for copper has driven the search for more efficient and sustainable extraction methods, particularly due to the environmental concerns associated with conventional processes. This study investigated the leaching of copper minerals MC (Cu₂O) and malachite (Cu₂CO₃(OH)₂) using glycine as an organic ligand in an alkaline medium, and evaluated the efficiency of hydrogen peroxide (H₂O₂) and ozone (O₃) as oxidizing agents. Chemical and mineralogical characterization using XRD, XRF, ICP, and SEM confirmed the predominance of MC and malachite, along with secondary phases such as hematite and calcite. Leaching experiments were carried out by varying glycine and oxidant concentrations at pH 10, with a reaction time of 240 min, agitation at 800 min⁻¹, a solution volume of 300 mL, and a mineral sample concentration of 0.33 g·L⁻¹. The results showed that O₃ exhibited low efficiency due to its limited solubility, whereas H₂O₂ achieved dissolution rates of 69.7% for MC in 150 min and 96.3% for MMin just 60 min. The glycine-H₂O₂ system optimized reaction time by 84% compared to conventional methods, emerging as a sustainable alternative due to the low toxicity and biodegradability of glycine.

Metallic elements of higher economic value, occurring in the mineralogy of Zimapán, are Pb, Zn, Cu, and Fe; said elements are sold as concentrates, which, even after processing, generally include significant concentrations of Mo, Cd, Sb, Ag, and As that can be recovered through different leaching methods. In this work, the influence of temperature in the complexation of silver contained in a concentrate of Zn using the technology of thiosulfate with oxygen injection was studied. Chemical and mineralogical characterization of the mineral concentrate from the state of Hidalgo, Mexico confirmed the existence of silver contained in a sulfide of silver arsenic (AgAsS₂) by X-ray Diffraction (XRD). The results obtained by Atomic Absorption Spectrophotometry (AAS) reported abundant metallic contents (% w/w) (48% Zn, 10.63% Fe, 1.97% Cu, 0.84% Pb, 0.78% As, and 0.25% Ag). These results corroborate the presence of metallic sulfides such as pyrite, chalcopyrite, and wurtzite; this last species was identified as the matrix of the concentrate by X-ray Diffraction (XRD) and Scanning Electron Microscopy-Energy-Dispersive X-ray Spectroscopy (SEM-EDS). Pourbaix diagrams were constructed for the AgAsS₂–S₂O₃²⁻–O₂ system at different temperatures, which allowed the chemical reaction of leaching to be established, in addition to determining Eh-pH conditions in which to obtain silver in solution. The highest recoveries of the precious metal (97% Ag) were obtained at a temperature of 333 K and [S₂O₃²⁻] = 0.5 M. The formation of silver dithiosulfate complex (Ag(S₂O₃)₂³⁻) was confirmed by the characterization of the leach liquors obtained from the experiments performed in the temperature range of 298 to 333 K using Fourier transform infrared spectroscopy (FTIR).