Navegando por Autor "LIMA, Paula Elissa Antonio de"

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Desconhecido
Caulim calcinado: estudo cinético da dissolução do alumínio em meio ácido e aplicação como precursor na produção de sílica porosa
(Universidade Federal do Pará, 2016-12-19) LIMA, Paula Elissa Antonio de; NEVES, Roberto de Freitas; http://lattes.cnpq.br/9559386620588673
A kinetic study of metakaolin (calcined kaolin) dissolution was carried out using kaolin for paper coating derived from the Rio Capim region (Pará State, Northern Brazil). The kaolin was calcined at 700ºC for 2 hours, in order to obtain metakaolin, and then leached with sulfuric, hydrochloric and nitric acid at 95ºC, 80ºC and 70ºC ± 3°C. The leachings were performed using excess acid of 5%. Samples were collected every 15 minutes for 3 hours and subjected to aluminum analysis by the EDTA titrimetric method. Final aluminum extraction of 97.42%, 97.99% and 95.9% was obtained with sulfuric, hydrochloric and nitric acid, respectively. Hydrochloric acid was faster than nitric and sulfuric acid, which showed a similar dissolution behavior. Kinetic models of homogeneous (Integral Method, Method of Half-Lives and Method of Initial Rates) and heterogeneous (Shrinking Core Model) reaction were used. The Shrinking Core Model for spherical morphology with a constant size showed better fit. The leaching process is chemically controlled, with leaching reaction of the first order with respect to aluminum from metakaolin, the first order with respect to sulfuric, hydrochloric and nitric acid concentration and activation energies of 87.78 kJ/mol, 90.60 kJ/mol and 91.58 kJ/mol, respectively. Previous research, using excess acid above 50%, are consistent with the data found in this study carried out with only 5% excess acid. The study about the application of calcined kaolin as a precursor in the porous silica production was carried out with the solid obtained in the leaching process with sulfuric acid. The leached material was a microporous solid, with 86.7% of silica, high specific area (297.13m²/g) and humidity adsorption capacity compatible with commercial silica.
Desconhecido
Investigação da reatividade e da cinética de dissolução do metacaulim em ácido sulfúrico
(2013-06) LIMA, Paula Elissa Antonio de; ANGÉLICA, Rômulo Simões; SCHELLER, Thomas; NEVES, Roberto de Freitas
A study about reactivity and dissolution kinetics of metakaolin was carried out using kaolin for paper coating derived from the Rio Capim region, Pará state, northern Brazil. The kaolin was burned at 600, 700, 800, 900 and 1000 ºC during 2 h in order to obtain metakaolin, followed by leaching with sulfuric acid at constant temperatures within the 50-95 ºC ± 3 ºC range. In the leachings, amounts of sulfuric acid corresponding to 10% above the stoichiometric values were used with respect to aluminum present in the material. Samples were collected in predetermined intervals every 15 min until a total time of 3 h, which were subjected to aluminum analysis by the EDTA titrimetric method. The results showed that the reactivity of burned kaolin decreased with the increase of burning temperature and that the dissolution kinetics of aluminum from metakaolin obtained by burning at 700 ºC followed the methods of homogeneous reaction used: integral method, method of half-lives and method of initial rates. 96.25 kJ/mol of activation energy was found as well as leaching reaction of the first order with respect to aluminum from metakaolin and the first order with respect to acid concentration. Researches carried out previously, using one of the reagents with excess above 90% and models of heterogeneous reaction, are consistent with the data found in this paper developed with only 10% excess.
Desconhecido
Metacaulim: investigação da reatividade e da cinética de dissolução do alumínio em ácido sulfúrico
(Universidade Federal do Pará, 2012-12-11) LIMA, Paula Elissa Antonio de; NEVES, Roberto de Freitas; http://lattes.cnpq.br/9559386620588673
A research about reactivity and dissolution kinetics of metakaolin was carried out using kaolin for paper coating derived from the Rio Capim region (Pará State, Northern Brazil). The kaolin was calcined at 600, 700, 800, 900 and 1000ºC during 2 hours in order to obtain metakaolin, followed by leaching with sulfuric acid at constant temperatures within the range of 50-95ºC ± 3ºC. In the leachings, amounts of sulfuric acid corresponding to 10% above the stoichiometric values were used with respect to aluminum present in the material. Samples were collected in predetermined intervals every 15 minutes until a total time of 3 hours, which were subjected to aluminum analysis by the EDTA titrimetric method. The kaolin and products of calcinations and leachings were characterized by XRD, XRF, DTA-TG, SEM, BET analysis as well as granulometric and real density analysis. The results showed that the initial material was a mesoporous solid, in which the calcination process at 700ºC increased the number of mesopores in the material and sulfuric leaching process at 95ºC promoted the formation of a microporous solid with a high specific area (297.13 m²/g) and consisting essentially of amorphous silica. The calcination at temperatures above 800ºC indicated the beginning of the structure consolidation process. The reactivity of metakaolin was reduced with the increase of calcination temperatures in the range studied. The dissolution kinetics of aluminum in the metakaolin, obtained by calcination at 700ºC, followed the methods of homogeneous (Integral Method, Method of Half-Lives and Method of Initial Rates) and heterogeneous (Shrinking Core Model) reaction used. 96.85 kJ/mol of activation energy was found as well as leaching reaction of the first order with respect to aluminum from metakaolin and the first order with respect to acid concentration. Researches carried out previously, using one of the reagents with excess above 90%, are consistent with the data found in this study developed with only 10% excess.