Browsing by Author "Lima, Geraldo Magela de"

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    Capture of CO2 by vermiculite impregnated with CaO.
    (2022) Pereira, Matheus Henrique Simplício; Santos, Cláudio Gouvêa dos; Lima, Geraldo Magela de; Bruziquesi, Carlos Giovani Oliveira; Oliveira, Victor de Alvarenga
    Vermiculite samples were impregnated with different amounts of calcium oxide by the con- ventional thermal heating technique and subject to CO2 capture experiments in thermal analysis equipment. The amount of CO2 captured by calcium oxide increased from 13 g of CO2 per mol of CaO to 16.8 g of CO2 per mol of CaO when the experiments were carried out with pure calcium oxide and vermiculite impregnated with CaO (1:1), respectively. Integral isoconversional methods of Kissinger-Akahira-Sunose (KAS) and Osawa-Flynn-Wall (OFW) were used for the kinetic study of the process and good correlation coefficients were achieved. The apparent activation energy values showed that for low conversions (a < 0.3) the controlling step of the process is a mixed step where the chemical reaction and the dif- fusion of the reagents into the vermiculite have rates of the same order of magnitude (20 kJ < Ea < 40 kJ). For higher conversions values (a > 0.3) the apparent activation energy values suggest that the slow step is a chemical step (Ea> 40 kJ).
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    Magnetic separation studies of a lateritic nickel ore.
    (2021) Ramírez, Rafael Leonardo Silva; Santos, Claudio Gouvea dos; Lima, Geraldo Magela de; Pereira, Matheus Henrique Simplício; Oliveira, Victor de Alvarenga
    Hydrogen reduction and thermal treatment experiments were carried out in the laboratory using a transition zone lateritic nickel ore. The products of the pyrometallurgical operations were subjected to magnetic separation. The ore and samples produced after the thermal processing (reduction and thermal treatment) were characterized by X-ray diffractometry (XRD), thermogravimetric analysis (TG), scanning electronic microscopy (SEM), and energy dispersive spectrometry (EDS). The qualitative identification of the main mineral transformations was performed and the influence of these thermal transformations in the magnetic properties of the sample was studied. When the reduction experiments were performed at 800 ° C, with a magnetic flux of 97.5 ± 10.6 mT, the nickel content increased by up to 33 % (recovery of ≈ 75 %) in the magnetic fraction. During the formation of magnetite in the reduction experiments, carried out at 400°C, the sample became very magnetic and, consequently, the unit operation of magnetic separation was not selective. It was possible to remove magnesium from all samples, regardless of the thermal treatment or reduction temperature used. The contents of this element were adjusted to the characteristic values of a limonitic ore.
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    Tin and organotin coordination polymers and covalently bonded supramolecular materials - the last 15 years of research.
    (2020) Santos, Cláudio Gouvêa dos; Lima, Geraldo Magela de
    The objective of this paper is to summarise the main achievements concerning the tin and organotin supramolecular chemistry in the last 15 years. Since the last review several compounds have been doc umented in the literature together with new synthetic approaches and potential applications. It is divided in two parts, according to the forces sustaining the repeating units along with the supramolecular struc tures. The first topic comprises details about R2Sn and R3Sn-based polymers supported by N H, O-H O, C-H O, C-H p, among other weak intermolecular interactions. The second part is dedicated to cover data regarding R2Sn, R3Sn and Sn(II)-containing structures and miscellaneous Sn(II) polymers constructed by the multidimensional Sn-O, Sn-N, or other covalent bonds. Among the ligands stand carboxylates, sul fonates, phosphonates, sulphur and phosphorous mixed electron donors and other Lewis bases contain ing sulphur atoms or heterocyclic groups. The dimensionality of R2Sn or R3Sn-containing polymers is influenced by the geometry at the Sn(IV), the bulkiness of the organic group attached to it, as well as by the nature of the ligands. The architecture of Sn(II) supramolecular structures depends also on the existence of stereochemically active electron lone pairs in Sn(II) species. The antitumoral or biocide stud ies employing organotin polymers revealed excellent activities towards different isolates. Other potential applications of organotin and Sn(II) polymers were also investigated, for example photo-luminescence or semiconducting properties, in electrochemistry, or as single-source precursors for the production of tin materials or nanowires, among others.
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    Tin(IV) compounds derivatives of reaction between Organotin(IV), SNCL4 and rutin trihydrate : characterization and hypolipidemic effects.
    (2004) Mello, Vanessa Joia de; Maia, José Roberto da Silveira; Oliveira, Tânia Toledo de; Ardisson, José Domingos; Nagem, Tanus Jorge; Ardisson, José Domingos; Patricio, Patrícia Santiago de Oliveira; Lima, Geraldo Magela de
    Equimolar reactions involving SnClPh3, SnCl2Ph2, SnCl3Ph and SnCl4 and rutin trihydrate (Quercetin-3- rutinoside) produced organotin(IV) polymers, which have been characterized by infrared spectroscopy, 'H, n C and "9Sn NMR, Mössbauer spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and microanalysis. The NMR ('Η, 13C) and "9Sn Mössbauer spectroscopy have revealed dephenylation of the starting organotin(IV) materials. The overall data have revealed a six-coordination for the Sn(IV) centre in solution as well as in solid state. DSC and GPC techniques have confirmed the formation of macromolecules for those adducts with an average molar mass higher than 7.0x10' g/mol. The hypolipidemic effect of total cholesterol reduction in male New Zealand rabbits was comparable to calcic atorvastatin, a commercial drug for treatment of hyperlipidemic patients.