Sayra Ordoñez

This study presents a fixed-bed column packed with zeolite, activated carbon, and carbon nanotubes synthesized by chemical vapor deposition, which were used to adsorb heavy metals (As and Pb) from water. Water containing 50 mg/L of the target heavy metal was filtered through the column. The materials were characterized before and after their use in the column by X-ray diffraction (XRD) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). The analyses confirmed the structural stability and functional efficiency of each adsorbent material. A removal efficiency of 100% was achieved within the first 15 min for both metals, decreasing to 45% for As and 95% for Pb. The experimental data were evaluated using the Thomas, Yoon–Nelson, and Adams–Bohart models. For arsenic, an R² value of 0.934 was obtained, whereas better fits were observed for Pb, with all three models achieving R² values greater than 0.98. Dynamic adsorption analysis indicated that the mass and height of the fixed bed are suitable for the operating concentration. The column arrangement proved to be more efficient for Pb retention than for As retention.

Mercury in jarosites is crucial for environmental management and metallurgy. These minerals can incorporate highly toxic heavy metals from mining waste into their structure. This study analyzes the decomposition of mercury jarosite in a Ca(OH)₂ medium, focusing on its topological, kinetic, and modeling characteristics. Topological analysis, XRD and SEM−EDS were performed. ICP−OES was used to analyze the mercury and sulfur ions diffusing from the mercury jarosite into the Ca(OH)₂ solution. The kinetic model that best fit the data was that of spherical particles of constant size with an unreacted core under chemical control. The XRD results did not show new crystallographic phases. SEM−EDS showed a partially decomposed particle indicating a halo and core. The experimental conditions included temperatures from 298.15 to 333.15 K, concentrations of 0.0071–0.23210 mol L⁻¹ Ca(OH)₂, particle diameters of 25–53 µm, and pH of 11.12–12.85. During the induction period, reaction orders of 1.04 and 0.44 were obtained, along with an activation energy of 77.580 kJ mol⁻¹. For the progressive conversion period, the reaction orders were 0.59 and 0.15, with an activation energy of 52.124 kJ mol⁻¹. The overall kinetic modeling showed favorable results, supporting the evolutionary process of the mercury jarosite decomposition reaction in an alkaline medium under different conditions. This allows prediction of when mercury could be released back into the environment in alkaline soils or lime barriers.

Thallium is one of the most toxic elements on the planet, and one alternative method for its precipitation is through jarosite-type compounds. Therefore, in this work, the kinetics of thallium jarosite were evaluated in an alkaline medium (NaOH and Ca(OH)₂). Experiments were conducted to assess the effect of medium concentration from 0.03 M to 5.5 × 10⁻⁴ M and the effect of temperature from 20 °C to 60 °C. The sigmoidal curves showed an induction period, during which there was no release of sulfur or thallium ions into the solution, nor the formation of solid byproducts, according to the X ray diffraction (XRD) results. Similarly, a progressive conversion period was observed, evidenced by the release of sulfur and thallium ions into the solution and the formation of amorphous solids. Finally, a stability zone is reached, indicating that the decomposition reaction has ended, as there are no changes in the concentration of sulfur and thallium ions in the solution. The reaction was monitored by determining S using Inductively Coupled Plasma (ICP). The experimental results for the progressive conversion period show a better fit to the chemically controlled shrinking core kinetic model. The reaction order for the kinetics in NaOH medium is 1.09 for the induction period and 0.89 for the progressive conversion period, while for Ca(OH)₂ medium it is 0.78 for the induction period and 0.47 for the progressive conversion period. The activation energies for the progressive conversion period in the two proposed media are 91.87 kJ mol⁻¹ in NaOH and 71.14 kJ mol⁻¹ in Ca(OH)₂, indicating that the controlling mechanism in both systems is the chemical reaction. For the induction period, the activation energies are 101.52 kJ mol⁻¹ and 79.45 kJ mol⁻¹, respectively, indicating that the chemical reaction also controls the initiation of the reactions. The high activation energy in both reaction media suggests that high concentrations of OH⁻ and high temperatures are required to initiate the decomposition reaction. Thallium jarosite precipitates a large amount of thallium and requires high energy to decompose, so it could be a viable alternative in thallium retention.

The results of the effect of the three Ba:Ti molar ratios (MR) (1:1, 2:1, 4:1) and four sintering temperatures (1250, 1275, 1300, 1325 °C) on the structural and electrical properties of BaTiO₃ (BT)-type ceramics synthesized by the hydrothermal method are shown. The BT phase formed was analyzed by x-ray diffraction (XRD), Raman spectroscopy (RS), dielectric and ferroelectric measurements and high-resolution scanning electron microscopy (HRSEM). For the samples synthesized using a Ba:Ti MR of 4:1 and at all sintering temperatures analyzed, XRD results confirmed the presence of the tetragonal ferroelectric phase, BT. In the same way, these results corroborated the results obtained by the RS technique. Dielectric properties measured at 100 kHz and 1 MHz over a temperature range of 30 °C–200 °C indicated a relative permittivity value of 4280 at 1 MHz and 4200 at 100 KHz at a Curie temperature of 110 °C in both cases for the sample synthesized at with a Ba:Ti MR ratio of 4:1 and sintered at 1300 °C. Ferroelectric measurements for the samples showed a best remnant polarization (Pr) of 3.5 µC/cm² for the sample synthesized with a Ba:Ti MR ratio of 4:1 and sintered at 1325 °C. The HRSEM results showed grains composed of Ba, Ti, and O homogeneously distributed in the BT structure, and a trend of increasing average grain size with increasing sintering temperature was observed.

The treatment and safe disposal of mining tailings represent one of the main technical and environmental challenges in the contemporary mining industry. The present study aims to evaluate, at laboratory scale, three dewatering techniques applied to phosphate tailings: column thickener, hyperbaric filtration (horizontal filter press), and the direct application of a dewatering polymer. Based on the results obtained and the comparative analysis of Opex and Capex, the application of the dewatering polymer was selected for industrial-scale validation. The tailings sample presented an initial solids concentration of approximately 8.6% with very fine particle size, less than 70 microns. Under the best operating conditions for the aforementioned dewatering techniques, solids percentages by mass were obtained around ≈52% (thickening), ≈75% (filtration), and ≈40% (dewatering polymer). In all techniques, it was possible to obtain turbidity levels in the recovered water below 100 NTU, and a slight increase in the hardness of the overflows and filtrates was observed. According to the yield stress results, it was evident that the tailings were beginning to present characteristics of high-density slurry, paste, and cake with values of 40%, 48%, and 58% solids by mass, respectively.

Magnetite nanoparticles were synthesized using the green chemistry technique; ferric chloride was used as a precursor agent and Moringa oleifera extract was used as a stabilizer agent. A black powder, characteristic of magnetite, was obtained. X-ray diffraction was performed on the synthesis product and identified as magnetite (Fe₃O₄). Scanning electron microscopy characterization shows that nanoparticles have a spherical morphology, with sizes ranging from 15 nm to 35 nm. The synthesis of carbon nanotubes was carried out by the pyrolytic chemical deposition technique, from which multiwalled carbon nanotubes were obtained with diameters of 15–35 nm and of varied length. The decoration was carried out using the wet and sonification technique, where a non-homogeneous coating was obtained around the nanotubes. The thermal decomposition for both decorated and undecorated nanotubes presents two mass losses but with different slopes, where the activation energy for the decorated carbon nanotubes was 79.54 kJ/mol, which shows that the decoration gives more stability to the nanotubes since the activation energy of the undecorated nanotubes is 25.74 kJ/mol.

In this work, a kinetic study and modeling of the decomposition of a rock sample in an ascorbic acid medium with a high content of lepidolite phase were carried out, the results of which are of great importance due to the sample’s high lithium (Li) content. The rock sample was characterized by X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS), and the mineral species detected in the sample were lepidolite, at 65.3%, quartz, at 30.6%, and muscovite, at 4.1%, with a quantitative chemical analysis indicating the presence of elements such as Li, Si, K, Na, O, Al and, to a lesser extent, Fe and Ti; this highlights that the Li content present in the sample was 3.38%. Lithium was the element with which the chemical analysis of the kinetics was performed, resulting in decomposition curves comprising the induction period, progressive conversion and stabilization; this highlighted that the reaction progressed during the first two periods, obtaining a reaction order (n) of 0.4307 for the induction period and an activation energy (Ea) of 48.58 kJ mol⁻¹, followed by a progressive conversion period with n = 0.309 and Ea = 25.161 kJ mol⁻¹. This suggested a mixed control regime present in the lower temperature ranges, with a transition from chemical control to transport control present at high temperatures, with the study of the nature of the reaction and the concentration effect showing that chemical control predominates. The kinetic parameters and kinetic expressions for both periods were obtained, with the modeling showing that the calculated and experimental data do not present a major discrepancy.

En éste estudio de descomposición alcalina se empleó una jarosita de talio sintetizada de fórmula [Tl0.86 (H3O)0.14] Fe3.11 (SO4)2.11 (OH)6.11(H2O)0.44; de acuerdo a la caracterización utilizada, cuyas partículas son de geometría semiesféricas de un tamaño promedio de 38 µm. Los experimentos de la descomposición se realizaron en medio CaOH y de acuerdo a la curva de descomposición presenta; un periodo inducción, seguido de un periodo de conversión y una zona de estabilidad; indicando que la reacción a terminado al no haber cambios en la concentración de los iones SO42- y Tl+ que se liberan durante la descomposición de la jarosita de talio. Los puntos experimentales en la reacción de descomposición en CaOH, se adaptan preferentemente al modelo de núcleo decreciente de partículas esféricas de tamaño constante, donde la reacción química controla al proceso de descomposición y los productos sólidos de la descomposición total, corresponden a un compuesto amorfo de acuerdo a DRX. Mediante MEB-EDS fueron estudiados sólidos parcialmente descompuestos; presentando un núcleo sin reaccionar, un frente de reacción y una capa de ceniza.