This work shows the physicochemical behavior of two different diatoms from the country of Mexico (State of Jalisco and Hidalgo) with similar compositions. These were used to eliminate toxic cations from a synthetic solution containing 5.270 mg As 3+ /L; 4.280 mg Ag + /L; 3.950 mgNi 2+ /L; 4.090 mg Cr 6+ /L; and 4.081 mg Pb 2+ /L. These diatoms were used as filters, and the quantity of cations remaining in the solution after filtering was measured. According to the most important results found, for the recovery of metals, both minerals achieved arsenic, silver, lead, and nickel recoveries up to 95%, and lower than 10% for chromium. This could be due to the absence of an environment to reduce Cr 6+ to Cr 3+ . On the other hand, it was observed that there was no selectivity during the recovery of the other cations present in the solution. According to efficiency of interchange, the mineral from Hidalgo is slightly better than the mineral from Jalisco for the removal of arsenic, lead, and silver. For nickel, and particularly Cr 6+ , the efficiency is higher for the sample from Jalisco.

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Structural and morphological properties of hydronium-potassium jarosite microstructures were investigated in this work, and their electrical properties were evaluated. All the microstructures were synthesized at a very low temperature of 70 °C with a reduced reaction time of 3 h. An increase in the pH from 0.8 to 2.1 decreased the particle sizes from 3 µm to 200 nm and an increase in the aging time from zero, three, and seven days resulted in semispherical, spherical, and euhedral jarosite structures, respectively. The Rietveld analysis also confirmed that the amount of hydronium substitution by potassium in the cationic site increased with an increase in pH. The percentages of hydronium jarosite (JH)/potassium jarosite (JK) for pH values of 0.8, 1.1, and 2.1 were 77.72/22.29%, 82.44/17.56%, and 89.98/10.02%, respectively. Microstructures obtained in this work were tested as alternative anode materials and the voltage measured using these electrodes made with hydronium-potassium jarosite microstructures and graphite ranged from 0.89 to 1.36 V. The results obtained in this work show that with reduced particle size and euhedral morphology obtained, modified jarosite microstructures can be used as anode materials for improving the lifetime of lithium-ion batteries.

Most copper minerals are found as sulfides, with chalcopyrite being the most abundant. However; this ore is refractory to conventional hydrometallurgical methods, so it has been historically exploited through froth flotation, followed by smelting operations. This implies that the processing involves polluting activities, either by the formation of tailings dams and the emission of large amounts of SO2 into the atmosphere. Given the increasing environmental restrictions, it is necessary to consider new processing strategies, which are compatible with the environment, and, if feasible, combine the reuse of industrial waste. In the present research, the dissolution of pure chalcopyrite was studied considering the use of MnO2 and wastewater with a high chloride content. Fine particles (−20 µm) generated an increase in extraction of copper from the mineral. Besides, it was discovered that working at high temperatures (80 °C); the large concentrations of MnO2 become irrelevant. The biggest copper extractions of this work (71%) were achieved when operating at 80 °C; particle size of −47 + 38 µm, MnO2/CuFeS2 ratio of 5/1, and 1 mol/L of H2SO4.

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Abstract:In this study, four samples of recycled aggregates from the construction and demolition waste of Mexico City were characterized in order to find innovative uses for these types of materials. Gravel and sand from a recycling plant were analyzed, as well as aggregates produced in the laboratory from demolished concrete collected from landfills. The characterization was carried out by means of XRD (X-ray Diffraction), chemical microanalysis (EDS), X-ray fluorescence (XRF), pH measurement, and sieve analysis. The minerals present in the analyzed materials were feldspars, cristobalite and pyroxene, which corresponded to the natural aggregates, as well as variable amounts of calcite, a product of the carbonation of the cement paste adhered to these aggregates, and in a smaller proportion, calcium hemicarboaluminate, rosenhanite, and tobermorite. The quality (amount of cement) of the original concrete has a great influence on the granulometry and the chemical-mineralogical composition of the aggregates, since there will be different quantities and qualities of the cement paste adhered to the aggregates depending on their size. Finally, the pH values measured in all samples fluctuated between 10.15 and 12.08, suggesting that these materials can be used in soil stabilization or in agricultural applications.

Abstract:We report potentiodynamic studies to characterize copper, nickel and zinc leaching solutions from electronic waste. The metals were leached using oxygen and sulfuric acid (pH = 1.5). As is known, reduction potentials are determined using thermodynamics laws, and metal recovery strategies from electronic waste are usually considered according these thermodynamic values. Pourbaix-type diagrams are not appropriate to plan strategies in electrochemical processing. Therefore, knowledge of electrode potentials for the metal deposit/dissolution process is the basis for the selective recovery planning. For this reason, potentiodynamic studies, specifically cyclic voltammetry, are revealed as a good way to decide the best conditions for the process of electrochemical recovery of metals from electronic waste, which is also cost-efficient and has no interference from strange ions, such as lead, in this case.

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