Biochar is a carbonaceous and porous material with limited adsorption capacity, which increases by modifying its surface. Many of the biochars modified with magnetic nanoparticles reported previously were obtained in two steps: first, the biomass was pyrolyzed, and then the modification was performed. In this research, a biochar with Fe₃O₄ particles was obtained during the pyrolysis process. Corn cob residues were used to obtain the biochar (i.e., BCM) and the magnetic one (i.e., BCM_Fe). The BCM_Fe biochar was synthesized by a chemical coprecipitation technique prior to the pyrolysis process. The biochars obtained were characterized to determine their physicochemical, surface, and structural properties. The characterization revealed a porous surface with a 1013.52 m²/g area for BCM and 903.67 m²/g for BCM_Fe. The pores were uniformly distributed, as observed in SEM images. BCM_Fe showed Fe₃O₄ particles on the surface with a spherical shape and a uniform distribution. According to FTIR analysis, the functional groups formed on the surface were aliphatic and carbonyl functional groups. Ash content in the biochar was 4.0% in BCM and 8.0% in BCM_Fe; the difference corresponded to the presence of inorganic elements. The TGA showed that BCM lost 93.8 wt% while BCM_Fe was more thermally stable due to the inorganic species on the biochar surface, with a weight loss of 78.6%. Both biochars were tested as adsorbent materials for methylene blue. BCM and BCM_Fe obtained a maximum adsorption capacity (q_m) of 23.17 mg/g and 39.66 mg/g, respectively. The obtained biochars are promising materials for the efficient removal of organic pollutants.

In the present study, the aqueous-slurry decomposition kinetics of industrial jarosite in alkaline media for the recovery of silver by cyanidation was investigated. For this purpose, aqueous-slurry decomposition experiments, using both NaOH and Ca(OH)₂ as alkalinising agents, were carried out in order to (1) study the effect of pH (i.e. 8, 9, 10 and11), contact time and temperature (i.e. 30, 40, 60 and 70°C) on jarosite decomposition; (2) elucidate the rate-determining step of the process kinetics when using NaOH or Ca(OH)₂, by applying the shrinking core model and Arrhenius equation and (3) study the effect of the aqueous-slurry decomposition on the recovery of silver by cyanidation. Results showed that when NaOH was used, the decomposition process was controlled by the chemical reaction with an activation energy of 40.42 kJ mol⁻¹, whereas when Ca(OH)₂ was used, the decomposition was controlled by diffusion through a porous layer of CaCO₃ with an activation energy of 21.72 kJ mol⁻¹. The alkaline decomposition emerges as a necessary step in order to recover up to 74% of the silver contained in the jarosite by cyanidation.

The sludge from a wet-off gas cleaning system of the iron blast furnace (BF) contains significant amounts of iron; however, they cannot be recycled due to their high content of zinc and alkalis. These compounds are detrimental to the optimal performance of iron and steelmaking furnaces. In this work, a comparative laboratory study to reduce zinc and alkali contained in the blast furnace sludge (BFS) is presented. The effect of leaching parameters such as oxidant (i.e., ferric ion, oxygen or ozone), aqueous solution media (i.e., 0.2 M NH₄Cl, 0.2 M HCl and 0.1 M H₂SO₄) and temperature (i.e., 27 and 80 °C) on Zn and alkalis (Na₂O and K₂O) removal were studied by applying an experimental design. The results obtained show that Zn and K₂O removal of 85% and 75% were achieved under the following conditions: Ozone as an oxidant agent and 0.1 M H₂SO₄ as an aqueous medium, temperature had no significant effect. The results are supported by thermodynamic diagrams and the possible chemical reactions are mentioned. Although the results also indicate that leaching under the above conditions dissolves up to 9% of iron, this loss is much less than leaching without the oxidizing conditions generated by the ozone. The BFS obtained from this treatment could be recirculated to the iron or steelmaking processes to recover iron values.

This work examines the role of NaOH and Ca(OH)2 on the hydrothermal decomposition of industrial jarosite deposited by a Mexican company in a tailings dam. The industrial jarosite is mainly composed by natrojarosite and contains 150 g Ag/t, showing a narrow particle size distribution, as revealed by XRD, fire assay, SEM-EDS and laser-diffraction analysis. The effect of the pH, when using NaOH or Ca(OH)2 as alkalinizing agent was studied by carrying out decomposition experiments at different pH values and 60?C in a homogeneous size particle system (pH = 8, 9, 10 and 11) and in a heterogeneous size particle system (pH = 11). Also, the kinetic study of the process and the controlling step of the decomposition reaction when NaOH and Ca(OH)2 are used was determined by fitting the data obtained to the shrinking core model for spherical particles of constant size. These results, supported by chemical (EDS), morphological (SEM) and mapping of elements (EDS) analysis of a partially reacted jarosite particle allowed to conclude that when NaOH is used, the process kinetics is controlled by the chemical reaction and when Ca(OH)2 is used, the rate determining step is changed to a diffusion control through a layer of solid products.

Coal has been a valuable natural resource for Mexico not just for its relative abundance but for its critical role in the development of the steel and energy industries. It has been also important in the socioeconomic context of the northeast of the country. However, since years ago, coal mining is facing a transition due to the emergence of new energy sources and the public concern about global warming. A brief review on coal reserves, production and possible non-power uses was carried out to provide insight on the reserves in a global context, extraction patterns and alternatives that the Mexican coal industry has to evolve. For this purpose, Mexican coal reserves were overviewed and contextualized at a global level and total coal production figures from 1970 to 2021 were analyzed to identify fluctuations and differences in the amounts produced between coking and non-coking coal. Further, rare earth elements, carbon fiber and humic acid from coal were briefly reviewed with the aim of initiating a debate on the high value-added products that can be obtained and the technologies that can be adopted to develop the coal industry of Mexico. Coal proven reserves in Mexico are of 1211 million tonnes and, from 1970 to 2021, 428.11 million tonnes have been produced. Of the total cumulative production, 68.8% corresponds to non-coking coal and 31.2% to coking coal.