A study on the dissolution rates of K-Cr(VI)-jarosites: kinetic analysis and implications.

BACKGROUND: The presence of natural and industrial jarosite type-compounds in the environment could have important implications in the mobility of potentially toxic elements such as lead, mercury, arsenic, chromium, among others. Understanding the dissolution reactions of jarosite-type compounds is notably important for an environmental assessment (for water and soil), since some of these elements could either return to the environment or work as temporary deposits of these species, thus would reduce their immediate environmental impact. RESULTS: This work reports the effects of temperature, pH, particle diameter and Cr(VI) content on the initial dissolution rates of K-Cr(VI)-jarosites (KFe3[(SO4)2 - X(CrO4)X](OH)6). Temperature (T) was the variable with the strongest effect, followed by pH in acid/alkaline medium (H3O(+)/OH(-)). It was found that the substitution of CrO4 (2-)in Y-site and the substitution of H3O(+) in M-site do not modify the dissolution rates. The model that describes the dissolution process is the unreacted core kinetic model, with the chemical reaction on the unreacted core surface. The dissolution in acid medium was congruent, while in alkaline media was incongruent. In both reaction media, there is a release of K(+), SO4 (2-) and CrO4 (2-) from the KFe3[(SO4)2 - X(CrO4)X](OH)6 structure, although the latter is rapidly absorbed by the solid residues of Fe(OH)3 in alkaline medium dissolutions. The dissolution of KFe3[(SO4)2 - X(CrO4)X](OH)6 exhibited good stability in a wide range of pH and T conditions corresponding to the calculated parameters of reaction order n, activation energy E A and dissolution rate constants for each kinetic stages of induction and progressive conversion. CONCLUSIONS: The kinetic analysis related to the reaction orders and calculated activation energies confirmed that extreme pH and T conditions are necessary to obtain considerably high dissolution rates. Extreme pH conditions (acidic or alkaline) cause the preferential release of K(+), SO4 (2-) and CrO4 (2-) from the KFe3[(SO4)2 - X(CrO4)X](OH)6 structure, although CrO4 (2-) is quickly adsorbed by Fe(OH)3 solid residues. The precipitation of phases such as KFe3[(SO4)2 - X(CrO4)X](OH)6, and the absorption of Cr(VI) after dissolution can play an important role as retention mechanisms of Cr(VI) in nature.

Cyanide-Free Copper-Silver Electroplated Coatings on Carbon Steel Exposed to 5% NaClO Bleacher.

This work deals with the development of cyanide-free copper-silver electroplated coatings on AISI-1075 steel and its corrosion behavior under a 5% NaClO solution (commercial household bleach). A cyanide-free bath based on sodium thiosulfate was employed to obtain the silver coatings using current densities from 0.2 to 5.0 mA/cm2 and different concentrations of EDTA (additive). The evolution of the open circuit potential with time showed that silver is anodic with respect to copper, so there were no intense attacks in the silver pores. Adhesion measurements were made on both coatings by the tape test. The behavior against corrosion was evaluated by polarization resistance (Rp) in samples with the best coating adhesion. The best results were obtained with a silver coating of about 20 µm in thickness deposited on copper coating previously polished with colloidal silica. The best performance was attributed to the formation of AgCl as demonstrated by x-ray diffraction and scanning electron microscopy.

Rosuvastatin adjunctive therapy for rifampicin-susceptible pulmonary tuberculosis: a phase 2b, randomised, open-label, multicentre trial.

BACKGROUND: Shorter treatments are needed for drug-susceptible tuberculosis. Adjunctive statins increase bactericidal activity in preclinical tuberculosis models. We investigated the safety and efficacy of adjunctive rosuvastatin in people with tuberculosis. We tested the hypothesis that adjunctive rosuvastatin accelerates sputum culture conversion within the first 8 weeks of treatment of rifampicin-susceptible tuberculosis. METHODS: This phase 2b, randomised, open-label, multicentre trial conducted in five hospitals or clinics in three countries with high tuberculosis burden (ie, the Philippines, Viet Nam, and Uganda) enrolled adult participants aged 18-75 years with sputum smear or Xpert MTB/RIF positive, rifampicin-susceptible tuberculosis who had received less than 7 days of previous tuberculosis treatment. Participants were randomly assigned via a web-based system to receive either 10 mg rosuvastatin once per day for 8 weeks plus standard tuberculosis therapy (rifampicin, isoniazid, pyrazinamide, and ethambutol; rosuvastatin group) or standard tuberculosis therapy alone (control group). Randomisation was stratified by trial site, history of diabetes, and HIV co-infection. Laboratory staff and central investigators involved in data cleaning and analysis were masked to treatment allocation, but study participants and site investigators were not. Both groups continued standard treatment to week 24. Sputum samples were collected once per week for the first 8 weeks after randomisation, and then at weeks 10, 12, and 24. The primary efficacy outcome was time to culture conversion (TTCC; days) in liquid culture by week 8, assessed in randomised participants who had microbiological confirmation of tuberculosis, took at least one dose of rosuvastatin, and who did not show resistance to rifampicin (modified intention-to-treat population), for which groups were compared with the Cox proportional hazards model. The main safety outcome was grade 3-5 adverse events by week 24, assessed in the intention-to-treat population, for which groups were compared with Fisher's exact test. All participants completed 24 weeks of follow-up. This trial is registered with ClinicalTrials.gov (NCT04504851). FINDINGS: Between Sept 2, 2020, and Jan 14, 2021, 174 participants were screened and 137 were randomly assigned to the rosuvastatin group (70 participants) or control group (67 participants). In the modified intention-to-treat population of 135 participants, 102 (76%) were men and 33 (24%) were women. Median TTCC in liquid media was 42 days (95% CI 35-49) in the rosuvastatin group (68 participants) and 42 days (36-53) in the control group (67 participants; hazard ratio 1·30 [0·88-1·91], p=0·19). Grade 3-5 adverse events occurred in six (9%) of 70 in the rosuvastatin group (none were considered related to rosuvastatin) and four (6%) of 67 in the control group (p=0·75). There were no serious adverse events that were considered to be related to rosuvastatin. INTERPRETATION: Adjunctive rosuvastatin at 10 mg once per day was safe but did not produce substantive benefits on culture conversion in the overall study population. Future trials could explore the safety and efficacy of higher doses of adjunctive rosuvastatin. FUNDING: National Medical Research Council, Singapore.

Raw data of silver extraction from sodium-silver jarosite using three different lixiviants in alkaline medium.

This article presents the raw data of silver concentration ([Ag]) obtained as a function of time (t) from silver leaching experiments, which were conducted using a synthetic sodium-silver jarosite and different complexing agents: thiosulfate, thiocyanate, and cyanide. Leaching experiments were performed under different conditions of temperature, pH and lixiviant concentration. The data refer to the article "Silver leaching from jarosite-type compounds using cyanide and non-cyanide lixiviants: a kinetic approach" (Islas et al., 2021), in which they were used to determine the leaching kinetics of jarosite-type compounds. The datasets were obtained experimentally from batch experiments. Concentration of silver, [Ag], was determined in each experiment as a function of time by atomic absorption spectroscopy. The information presented in this article can be useful for engineering students interested in mineral processing; particularly, for the calculation of kinetic parameters of silver leaching process. The data could also help in the formulation, implementation, or optimization of strategies for extraction of valuable metals from residues generated by the hydrometallurgical industry.

Thallium(I) sequestration by jarosite and birnessite: Structural incorporation vs surface adsorption.

Jarosite and birnessite secondary minerals play a pivotal role in the mobility, transport and fate of trace elements in the environment, although geochemical interactions of these compounds with extremely toxic thallium (Tl) remain poorly known. In this study, we investigated the sorption behavior of Tl(I) onto synthetic jarosite and birnessite, two minerals commonly found in soils and sediments as well as in mining-impacted areas where harsh conditions are involved. To achieve this, sorption and desorption experiments were carried out under two different acidic conditions and various Tl(I) concentrations to mimic natural scenarios. In addition, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and inductively coupled plasma (ICP) analyses were conducted to determine the performance of both minerals for Tl(I) sequestration. Our results indicate that both phases can effectively remove aqueous Tl by different sorption mechanisms. Jarosite preferentially incorporates Tl(I) into the structure to form Tl(I)-jarosite and eventually the mineral dorallcharite (TlFe3(SO4)2(OH)6) as increasing amounts of Tl are employed. Birnessite, however, favorably uptakes Tl(I) through an irreversible surface adsorption mechanism, underlining the affinity of Tl for this mineral in the entire concentration range studied (0.5-5 mmol L-1). Lastly, the presence of Tl(I) in conditions where aqueous molar ratio Tl/Mn is ∼0.25 inhibits the formation of birnessite since oxidation of Tl(I) to Tl(III) followed by precipitation of avicennite (Tl2O3) take place. Thus, the present research may provide useful insights on the role of both jarosite and birnessite minerals in Tl environmental cycles.

A novel, rapid technique for clearing leaf tissues.

PREMISE: Clearing leaves is a highly useful practice for many taxonomic, ecological, physiological, and eco-physiological aspects of research. Using traditional methods, the procedure for clearing a leaf (referred to as diaphanization) can take several days or even weeks. In our laboratory we developed a technique, originally used for dissociating wood, that yields excellent epidermal and leaf venation preparations clearly showing the details of epidermal cells, hydathodes, trichomes, leaf margins, and leaf venation, in a maximum of three days. METHODS AND RESULTS: A solution originally used to macerate wood (Franklin's solution) was used to accelerate the process of clearing leaves. Using this approach, it is possible to obtain clear images of the leaf adaxial and abaxial epidermal surfaces and leaf venation. Our technique works with both fragile and sturdy leaves, as well as with thin roots and stems. A few examples are presented. CONCLUSIONS: Franklin's solution is very simple to prepare and easy to manipulate. This new technique has the advantage of separating the leaf epidermal layers and venations, which can then be clearly observed.

Solid-phase distribution and mobility of thallium in mining-metallurgical residues: Environmental hazard implications.

Thallium (Tl) and its compounds are non-essential and highly toxic for living organisms, even at low concentrations. In this paper, we analyzed the presence and geochemical distribution of Tl in different mining-metallurgical and sediment samples collected from several mining zones of Mexico. A modified BCR sequential extraction procedure was also applied to the samples to investigate the geochemical behavior and potential environmental risk of Tl according to types of ore deposit and mineral processing method applied. Results revealed the presence of Tl in the majority of the mining-metallurgical samples, with labile concentrations reaching up to values of 184.4 mg kg-1, well above the environmental standards. A comparison of Tl partitioning in different samples showed that Tl was usually found associated with labile fractions instead of entrapped in the environmentally-passive residual fraction. Specifically, high levels of Tl were extracted from the exchangeable/acid-extractable and poorly-crystalline reducible fractions, suggesting its association with both soluble and amorphous Fe-Mn oxyhydroxides, respectively. Besides, Tl was also frequently found associated with the crystalline reducible fraction, presumably bonded to manganese oxides and jarosite-like minerals. Lastly, little amounts of Tl were extracted from the oxidizable fraction. Considering the fractionation of Tl in these mining-metallurgical samples, they may pose a significant environmental hazard. This study provides useful insights into the potential sources of Tl pollution in Mexico and emphasizes the need for further research to determine the extent of its impact and to develop effective remediation protocols to protect the environment from Tl toxicity.

Caracterización clínica de pacientes con gangrena de Fournier del Hospital General Docente "Dr. Agostinho Neto", 2008-2018 / Clinical characterization of patients with Fournier's gangrene at the Hospital General Docente "Dr. Agostinho Neto", 2008-2018 / Caracterização clínica de pacientes com gangrena de Fournier no Hospital Geral de Ensino "Dr. Agostinho Neto", 2008-2018

RESUMEN Introducción: La gangrena de Fournier se define como una forma específica de fascitis necrotizante Tipo I, que constituye una emergencia urológica, poco frecuente y de elevada mortalidad. Objetivo: Caracterizar la gangrena de Fournier en los pacientes atendidos en el servicio de Urología del Hospital General Docente "Dr. Agostinho Neto" en el periodo enero 2008 - diciembre 2018. Método: Se realizó un estudio descriptivo de variables demográficas y clínicas (edad, sexo, mortalidad, comorbilidad, causas desencadenantes, sitio primario de la infección, sitio de extensión de la infección, estadía hospitalaria) en 20 pacientes. La historia clínica fue la fuente de información primaria. Los datos fueron procesados mediante el programa estadístico SPSS versión 20.0, y se utilizó la estadística descriptiva para determinar las frecuencias absolutas y relativas (porcentajes) y media. Resultados: El 100 % correspondió a varones con un promedio de edad de 64,0 años (27-92); la mortalidad fue del 40 %. La diabetes mellitus fue la comorbilidad más frecuente en 10 pacientes (50,0 %), 12 (60,0 %) tenían más de un proceso comórbido. Las lesiones cutáneas constituyeron la causa primaria en 11 (55,0 %), y los escrotos fueron el principal sitio de origen de la infección en el 55,0 %. El promedio de estadía hospitalaria fue de 37,7 días (7-75 días). Conclusiones: La correcta evaluación de las variables demográficas y clínicas es necesaria para establecer un correcto diagnóstico y plan de tratamiento.

ABSTRACT Introduction: Fournier's gangrene is defined as a specific form of Type I necrotizing fasciitis, which constitutes a rare urological emergency with high mortality. Objective: To characterize Fournier's gangrene in patients treated in the Urology service of the Hospital General Docente "Dr. Agostinho Neto" in the period from January 2008 to December 2018. Method: A descriptive study of demographic and clinical variables (age, gender, mortality, comorbidity, triggering causes, primary site of infection, site of extension of the infection, hospital stay) was carried out in 20 patients. The medical history was the primary source of information. The data were processed using the statistical program SPSS, version 20.0, and descriptive statistics were used to determine the absolute and relative frequencies (percentages) and mean. Results: 100% corresponded to men with an average age of 64.0 years (27-92); mortality made a 40%. Diabetes mellitus was the most frequent comorbidity, in 10 of the patients (50.0%); 12 patients (60.0%) had more than one comorbid process. Skin lesions were the primary cause in 11 (55.0%), and the scrotum was the main site of origin of infection in 55.0%. The mean hospital stay was 37.7 days (7-75 days). Conclusions: The correct evaluation of the demographic and clinical variables is necessary to establish a correct diagnosis and treatment plan.

RESUMO Introdução: A gangrena de Fournier é definida como uma forma específica de fasceíte necrosante tipo I, que se constitui em uma rara emergência urológica com alta mortalidade. Objetivo: Caracterizar a gangrena de Fournier em pacientes atendidos no serviço de Urologia do Hospital Geral Universitário "Dr. Agostinho Neto" no período de janeiro de 2008 a dezembro de 2018. Método: Estudo descritivo de variáveis demográficas e clínicas (idade, sexo, mortalidade, comorbidade, causas desencadeantes, sítio primário de infecção, extensão do sítio de infecção, internação) em 20 pacientes. O histórico médico foi a principal fonte de informação. Os dados foram processados no programa estatístico SPSS versão 20.0, e a estatística descritiva foi utilizada para determinar as frequências absolutas e relativas (percentuais) e a média. Resultados: 100% corresponderam a homens com idade média de 64,0 anos (27-92); a mortalidade foi de 40%. Diabetes mellitus foi a comorbidade mais frequente em 10 pacientes (50,0%), 12 (60,0%) apresentaram mais de um processo comórbido. Lesões cutâneas foram a causa primária em 11 (55,0%), e o escroto foi o principal sítio de origem da infecção em 55,0%. O tempo médio de internação foi de 37,7 dias (7-75 dias). Conclusões: A correta avaliação das variáveis demográficas e clínicas é necessária para estabelecer um correto diagnóstico e plano de tratamento.