MODELING OF THE NITROGEN PARAMETER OF THE PARAÍBA DO SUL RIVER USING THE QUAL-UFMG METHOD
Background: Due to population growth and increased use of water resources, there has been a need to implement management measures to control and monitor river parameters. Aims: This study aims to demonstrate the application of mathematical modeling using the QUAL-UFMG model for studying nitrogen concentration in the Paraíba do Sul River located in Volta Redonda. Methods: Through mathematical modeling, it is possible to identify areas of greater impact, evaluate the effectiveness of control measures, and propose a strategy to improve water quality and preserve the balance of local aquatic ecosystems. Results: The results obtained during the study showed that the nitrogen parameters and their derivatives are within the pre-established limits set by CONAMA. Discussion: During the modeling, it was observed that there is a tendency for nitrate levels to increase along the points, indicating good self-purification of the river. Organic nitrogen values increase along the points, which is due to the contribution of sewage discharge along the course of the river, as organic nitrogen and ammonia have a physiological origin in domestic sewage. Conclusions: Through the QUAL-UFMG model, it was possible to validate the conducted analyses and create future projections of the water quality in the Paraíba do Sul River along the studied points.
Read ArticleOPTIMIZATION AND KINETICS STUDIES OF THE DISSOLUTION OF DOLOMITE IN SULPHURIC ACID (H2SO4) VIA BOX-BEHNKEN EXPERIMENTAL DESIGN
Background: The recovery of any valuable component from dolomite as a double carbonate mineral depends on its dissolution efficiency. Aim: This study aimed to optimize and provide a simplified novel approach to the kinetics of dolomite dissolution in sulphuric acid solution using the Box-Behnken experimental design. Methods: The dolomite sample was dissolved in a sulphuric acid solution at seventeen different experimental conditions. The residue containing impurities was removed via filtration, while precipitation was carried out at the optimum conditions. Results and Discussion: The relationship between the independent and dependent variables best fits into the two-factor interaction model with a coefficient of determination of 0.9492, adjusted R² of 0.9187, and predicted R² of 0.7514. The total residual sum of 3x10-13 and adequate precision of 18.769 show that the predicted dissolution efficiency is much closer to the experimental values. The analysis of variance revealed that the individual effect of acid concentration, temperature, and dissolution time all positively contribute to the dissolution. The interactive effect of acid concentration with temperature and the interactive effect of temperature with dissolution time also positively influences the dissolution efficiency. Following the dissolution of dolomite in sulphuric acid, a white precipitate was formed at room temperature, which dissolved back at a temperature of 70 oC, agitation speed of 900 revolutions per minute, and within 10 minutes. A predictive approach using a two-factor interactive model was applied to generate the kinetic data. Conclusions: The established model equation is suitable for predicting dolomite dissolution in sulphuric acid. The application of the shrinking core model to the generated data shows that the reaction between dolomite and sulphuric acid is film diffusion control with a first-order reaction (0.6587) and activation energy of 27.5 KJmol-1k-1.
Read ArticleCOMPARISON OF TWO STAINING METHODS FOR ANODIZING IN ALLOY 6063 ALUMINUM PROFILES
Background: Aluminum stands out for being a light, corrosion-resistant, and recyclable metal, achieving wide coverage in the market. When incorporated into alloying elements, it is possible to acquire other desirable characteristics. Alloy 6063, intended for architectural purposes, has aesthetic, structural, and strength functions. Anodized finishing is performed through an electrolytic process, ensuring a more resistant aluminum oxide film than that formed naturally. For decorative purposes, the anodic film coloration can be performed by several methodologies, in this case, for the coloration by organic adsorption, with the use of aniline, and the electrolytic coloration, composed of tin sulfate salts, both for obtaining the black color. Aim: Compare of two different staining methods on the surface of anodized profiles of aluminum alloy 6063. Methods: Profile samples were collected and tests were carried out to measure the thickness of the anodic layer, immersion tests with 3,5 percent sodium chloride, for 1000 hours, and neutral saline mist, for 600 hours. Results and Discussion: Both methodologies proved to be resistant to immersion tests with sodium chloride, as well as with neutral saline mist, and these tests are quite aggressive and provide corrosion of the material when not well treated. Corrosion points were only seen at the intersections performed, and in the rest of thearea, no points were detected. Conclusions: The result of both methodologies was positive, considering tht there was no corrosion in the tested samples, except in the intersections performed, as well as the maintenance of the color in both tested methodologies, which was not expected in the literature. For future work, it is suggested to deepen the study to perform electrochemical impedance spectroscopy tests for exaluate the strength of the anodic film and perform anodizing with the same parameters, however, with different anilines to analyze their behavior.
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