Navegando por Autor "SCHELLER, Thomas"

Agora exibindo 1 - 4 de 4

Acesso aberto (Open Access)
Caracterização mineralógica e geoquímica e estudo das transformações de fase do caulim duro da região do Rio Capim, Pará
(2003-12) CARNEIRO, Bruno Santana; ANGÉLICA, Rômulo Simões; SCHELLER, Thomas; CASTRO, Elton Anderson Santos de; NEVES, Roberto de Freitas
The Capim region (Pará State, northern Brazil) is the most important kaolin district in the Amazon region, with the largest Brazilian reserves of high whiteness kaolin for the paper coating industry. The main ore (soft kaolin horizon) is located at a depth of about 20 m, being covered by a hard, iron-rich kaolin level, also called flint or semi-flint kaolin, besides a sandy-clay overburden. The beneficiation of this kaolin produces large volumes of wastes, composed mainly of coarse-grained kaolinite, deposited in basins that occupy extensive areas. The main objective of this work is to carry out mineralogical and geochemical studies of the hard kaolin, and to evaluate its thermal transformations through calcination up to 1500 oC. The results show a mineralogical composition dominated kaolinite. The evaluated thermal transformations allows us to describe a series of chemical reactions from kaolinite to metakaolinite and further development of spinel, cristobalite and mullite. For the two analyzed samples, such transformations can start at different temperatures as a result of the different chemical compositions, mainly the iron contents.
Acesso aberto (Open Access)
Determinação da composição isotópica de estrôncio em águas naturais: exemplos de sua aplicação em águas subsuperficiais da zona costeira na região Bragantina-PA
(2007) BORDALO, Adriana Oliveira; MOURA, Candido Augusto Veloso; SCHELLER, Thomas
Analytical procedures used for determining the concentrations and isotope composition of strontium in subsurface waters, by mass spectrometry, are described. Sampling was performed in coastal plateaus, salt marsh and mangrove environments in the coastal region of Pará. Coastal plateau waters have δ87Sr between 1.51 and 6.26‰ and Sr concentration bellow 58 ppb. Salt marsh waters show δ87Sr between 0.55 and 0.90‰ and Sr concentration between 93 and 114 ppm, while mangrove waters have δ87Sr around zero and Sr concentration above 15 ppm. Differences in the 87Sr/86Sr ratio in these subsurface waters are detected, as well as seasonal variations in the coastal pleteau waters.
Acesso aberto (Open Access)
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.
Acesso aberto (Open Access)
Síntese e caracterização de óxido hidróxido de manganês do tipo manganita (γ -MnOOH)
(2008-06) FIGUEIRA, Bruno Apolo Miranda; ANGÉLICA, Rômulo Simões; SCHELLER, Thomas
Manganese oxyhydroxide (g - MnOOH) of the manganite type has been synthesized by a simple route with K-birnessite prepared by the sol-gel method. The hydrothermal treatment of the lamellar birnessite type structure facilitates the formation of tunnel structures where the size of the tunnels depends on the synthesis conditions (pH, temperature and time). The evidence of manganite formation under the synthesis conditions were made by X-ray diffraction, scanning electron microscopy, thermogravimetry, differential thermal analysis and infrared spectroscopy.