O efeito da granulometria na decrepitação durante a decomposição térmica de calcários e carvão

The use of fluidized bed combustors to burn coal is largely studied to permit the addition of limestone to capture SO2. The particle size for coal and limestone is an important parameter in this process. Thermogravimetry (TG) is used to elucidate the combustion and sulfation processes, but the experimental parameters must be evaluated to be representative in fluidized bed combustors. In the present study the effect of particle size is analyzed in the calcination of limestones and the combustion of coal through the thermogravimetric curve for limestone and derivative thermogravimetric curve for coal. Small peaks representing mass losses between 400 and 500 ºC are observed due to the jumping of particles out of the crucible. This effect, recognized as decrepitation is observed for mid-sized particles provoked by the release of water vapor trapped within their lattice.

Estudo termogravimétrico do efeito da temperatura e da atmosfera na absorção de dióxido de enxofre por calcário

Thermogravimetry was applied to investigate the effects of temperature and atmosphere on conversion of sulfur dioxide (SO2) absorbed by limestone. Ranges of temperature and particle size were studied, typical of fluidized-bed coal combustion. Isothermal experiments were performed at different temperatures (between 750 and 950 ºC) under local atmospheric pressure (~ 697 mmHg) in dynamic atmospheres of air and nitrogen. The maximum conversion was 29% higher in nitrogen atmosphere than in air atmosphere. The optimum conversion temperature was found at 831 ºC in air atmosphere and at 894 ºC in nitrogen atmosphere.

Determinação dos parâmetros de arrhenius da reação de sorção do dióxido de enxofre por calcário

Sulfur emission in coal power generation is a matter of great environmental concern and limestone sorbents are widely used for reducing such emissions. Thermogravimetry was applied to determine the effects of the type of limestone (calcite and dolomite), particle size (530 and 650 µm) and atmosphere (air and nitrogen) on the kinetics of SO2 sorption by limestone. Isothermal experiments were performed for different temperatures (650 to 950 ºC), at local atmospheric pressure. The apparent activation energies, as indicated by the slope of the Arrhenius plot, resulted between 3.03 and 4.45 kJ mol-1 for the calcite, and 11.24 kJ mol-1 for the dolomite.

Descrições de técnicas da química na produção de bens de acordo com os relatos dos naturalistas viajantes no Brasil colonial e imperial

European naturalists explored Brazil in long scientific expeditions and published accounts that make up a rich and still largely untapped historiographic source for the understanding of the history of chemistry. The production of indigo dye, the manufacture of limestone, extraction and purification of saltpeter and the production of salt are discussed. Lime was used to whitewash walls and, mixed with whale oil, as cement to glue stones in buildings of the colonial period. It was prepared by burning seashells in specifically designed ovens. Saltpeter was produced by reacting naturally occurring calcium and magnesium nitrate with potassium-rich wood ashes to yield KNO3. NaCl was obtained by evaporating seawater under the sun. Indigo, a native plant, was cultivated and processed to produce the renowned dye, which was exported to Europe.

Processos físico-químicos em drenagem ácida de mina em mineração de carvão no sul do Brasil

Acid mine drainage generated from coal mine showed a pH of 3.2, high concentrations of SO4(2-), Al, Fe, Mn, Zn and minor As, Cd, Co, Cr, Cu, Ni and Pb. The major reduction in the concentration occurred for Al, As, Cr, Fe and Pb after the treatment with CaO. The evolution of these acid waters within the tributary stream showed decreasing concentration for all soluble constituents, except Al. This natural attenuation was controlled by pH (6.4 to 10.8) as a result of concurrent mixing with tributary stream and reaction with local bedrock that contains limestone. Aluminum increasing concentration during this evolution seems to be related to an input of Al-enriched waters due to the leaching of silicate minerals in alkaline conditions.

Metodologia para o estudo da porosidade de dolomita em ensaio de sulfatação interrompida

The aim of this work is to propose a methodology to evaluate the evolution of the pore blockage of limestone during the sulfation reaction. The experiments were performed for a national limestone (dolomite) with average particle size of 545 μm in interrupted sulfation tests were conducted at seven different times and at three different temperatures of the process. The empirical data were obtained from porosimetry tests to establish BET surface area, volume and average size of pore and distribution of pore sizes of the sulfated samples. Thermogravimetric tests were performed to evaluate the preparation methodology of the samples used in the porosimetry tests.

Interpretação do mecanismo de difusão no processo gás-sólido da reação de dessulfurização

The present paper aims to interpret the SO2 diffusion mechanism process for two different limestones: a calcite and a dolomite. In previous study, the apparent activation energies for sulfation reaction were between 3.03 and 4.45 kJ mol-1 for the calcite, and 11.24 kJ mol-1 for the dolomite. Using nitrogen porosimetry it was possible to observe that the dolomite presents mesopores of 0.03 μm, while the calcite presents mesopores of 0.01 μm. The evaluation of limestones porous structure together with their kinetic parameters, allowed concluding that the diffusion mechanism follows Fick law and Knudsen law for dolomite and calcite, respectively.

Antocianinas em extratos vegetais: aplicação em titulação ácido-base e identificação via cromatografia líquida/espectrometria de massas

Anthocyanins extracted from picao, quaresmeira, petunia, flamboyant, purple ipe, lobeira, pata de vaca, jaboticaba, purple cabbage and jambul were evaluated as natural acid-base indicators. Anthocyanins in extracts were identified using HPLC/MS. Clear, rapid change in color at final-point titration was observed for extracts but only picao showed strong change in pH. Indirect determination of carbonate in limestone using a natural indicator was performed and results compared with phenolphthalein indicator and potentiometer titration. Optimal results were obtained with picao but other extracts showed good accuracy and precision.

SUBSTRATE, LIME, PHOSPHORUS AND TOPDRESS FERTILIZATION IN MACAW PALM SEEDLING PRODUCTION

ABSTRACT The macaw palm [Acrocomia aculeata (Jacq.) Lood. ex Mart] has been domesticated to subsidize biodiesel production programs in Brazil. However, little is known about the seedling production of this species. This study aimed to evaluate substrate mixtures, limestone and phosphorus rates for substrate amendment and topdressing frequency in macaw palm seedlings. Three trials were conducted in a greenhouse up to six months of nursery cultivation. Trial 1: determination of percent mineral and organic fractions of seven substrate mixtures. Trial 2: evaluation of four limerates for soil amendment versus four phosphorus rates. Trial 3: evaluation of N, K and Mg topdressing frequency. Significant differences were found in the three trials for most of the variables (plant height, leaf number, shoot dry mass, root dry mass, vigor and bulb diameter). The main results obtained were as follow: Trial1 - the best seedling growth was observed in substrates with at least 25% organic matter. Trial2 -lime rates ranging from 0.50 to 1.25 kg associated with 3 to 4 kg of single superphosphate per m3 of substrate provided the best seedling growth. Trial 3 - topdressing fertilization provided better development of seedlings regardless of frequency.

Groundwater recharge estimate at Alto Rio Grande - MG watershed

Springs are outcrops of aquifers surface, and the water cycle in this environment pass through the recharge, generally defined as the amount of water added to the aquifer, which may occur locally from rainwater infiltration. This study uses the Water Table Fluctuation (WTF) method to estimate the direct recharge and a groundwater balance to estimate the deep recharge on unconfined aquifers. The WTF method employs data of the aquifer water levels and its specific yield to estimate the direct recharge. The groundwater balance considers the direct recharge estimated by the WTF method, as the water input in the system and outputs as the base flow and deep recharge. The recharge was estimated at four areas at the watershed of Alto Rio Grande city, Minas Gerais (MG) state, in Brazil. The direct recharge estimate was 121.11; 64.62; 83.99; 152.46 (mm/year) for the L1, L2, M1 and M2 areas. The effect of the presence of forest in the recharge area can prevail over slope of relief, allowing more direct recharge, even in sources with steeper relief. The runoff from the springs in the study period exceeded the direct recharge, indicating a situation in which the saturated zone feeds the vadose zone. The annual flow was above the direct recharge pointing a situation of over exploitation of the aquifer, a non sustainable situation. The specific yield of the aquifers could also have been underestimated.

Floristic composition, diversity and structure of the "cerrado" sensu stricto on rocky soils in northern Goiás and southern Tocantins, Brazil

The "cerrado" sensu stricto is a savanna woodland physiognomy which occupies most of central Brazil, with the degree of canopy cover varying from 10% to 60% at a site with trees reaching up to seven meters high. It occurs mostly on deep and well-drained soils but can also be found on shallower ones. The diversity and structure of the "cerrado" sensu stricto on shallow and rocky Cambisols and Litosols were studied here. Sixteen 20 x 50 m² plots were sampled in a random design over patches of this vegetation in northern Goiás State and southern Tocantins. All stems from 5 cm diameter at 30 cm from the ground level were measured. Vouchers were collected and deposited at the IBGE herbarium. A total of 87 species in 65 genera and 33 families were found. Diversity index was 2.87 nats ind-1, density was 836 stems ha-1 with a basal area of 8.4374 m² ha-1. Sørensen's index indicated higher similarities between plots at the same site indicating a geographical gradient influencing the floristic composition of the "cerrado" sensu stricto on rocky soils. Czekanowski's index confirmed this trend. TWINSPAN classification final groups were defined by preferential species of more fertile soils, in opposition to those typical of dystrophic soils and to common species to gallery forests occurring on sloping terrains with gullies.

Reproductive phenology, pollination and seed dispersal syndromes on sandstone outcrop vegetation in the "Chapada Diamantina", northeastern Brazil: population and community analyses

Vegetation on rock outcrops in the "Chapada Diamantina" (soil islands) is often aggregated and surrounded by nude rock surfaces, thus creating natural units with well defined limits. The flowering and fruiting cycles of plants on 58 soil islands at altitudes between 1,100 and 1,140 meters above sea leavel were analyzed at Mãe Inácia Peak (12°27' S and 41°28' W) in the "Chapada Diamantina", Bahia, Brazil. The presence/absence of flowering and fruiting species on each soil island, and their respective cover areas were analyzed at both the population and community levels, and the phenophases of flowering and fruiting were observed during 24 successive months. The analyses of pollination and seed dispersal syndromes indicated that animals are more important in pollination than in seed dispersal (which is predominantly by anemochory and autochory). The flowering and fruiting of plants with animal pollination syndromes were correlated with rainfall and temperature. The flowering season varied during the year according to the pollination syndrome involved: entomophily was predominant from summer through autumn, ornithophily was predominant during winter, and anemophily in the spring. The staggered timing of flowering and fruiting among different species provides a nearly continuous supply of resources for the local fauna.

Tropical inselbergs: habitat types, adaptive strategies and diversity patterns

Inselbergs are isolated rock outcrops that rise abruptly above the surrounding plains. Granitic and gneissic inselbergs are geologically and geomorphologically old and occur throughout a broad spectrum of climatic zones. They form microclimatically and edaphically dry growth sites that support a highly specialized vegetation. Based on physiognomic criteria a number of habitat types can be distinguished that are widespread on inselbergs (e.g. ephemeral flush vegetation, monocotyledonous mats, rock pools). Three hot spots of global inselberg plant diversity can be identified which are both rich in species and endemics: a) southeastern Brazil, b) Madagascar and c) southwestern Australia.

Rock outcrop habitats in the Venezuelan Guayana lowlands: their main vegetation types and floristic components

The Guayana Shield, located in north-eastern South America, consists of a highly complex and composite mosaic of landscape elements. Amongst these, inselbergs are very conspicuous, because of their peculiar shape and their unusual associated vegetation. Geologically, these rock outcrops are part of the underlying ancient igneous-metamorphic basement and occur mainly in the lowlands of the periphery of the shield. As azonal habitats, inselbergs harbour a highly specialized flora. The characteristic vegetation is composed of lithophytic and savanna-like plant communities, as well as low dry forests. As a whole, the vegetation of an inselberg may be interpreted as a mosaic of marginal habitats. Therefore a large number of taxa find suitable niches in a quite condensed space. Gradients of soil depth and water availability are the main factors determining the floristic composition. A preliminary floristic inventory of the Venezuelan inselberg flora comprises 614 vascular plant species. 24% of them are endemic to the Guayana region, 15% are endemic to inselbergs of the Guayana region. The distribution patterns of these latter, eco-endemic species allows to distinguish a northern and a southern inselberg district. The two districts overlap in the Átures area, in the surroundings of Puerto Ayacucho, where a true centre of endemism is located. The distinction into two districts is emphasised by different phytogeographic relations. The southern inselberg district shows connections to the "tepui" flora, whereas the northern district reveals phytogeographic relations to the Caribbean region as well as to the Brazilian Shield. Possible explanations for the floristic interchange across the equator are discussed.

Species composition and biogeographic relations of the rock outcrop flora on the high plateau of Itatiaia, SE-Brazil

We studied the flora of vegetation islands on rock outcrops on the Itatiaia Plateau (22°21'S and 44°40'W), at 2,400 m.a.s.l. A total of 114 vascular plant species, which correspond to ca. 20%-25% of the currently inventoried flora of the plateau, were sampled in 197 small vegetation islands (total area of 0.034 ha). Xerophytes and hydrophytes were often found side by side due to environmental heterogeneity at a small scale, explaining in part the high species diversity. Rock outcrops may support floras quite distinct from those in neighbouring habitats, due to the action of strong environmental filters, but in Itatiaia the geographic distribution patterns among rupicolous plants appear to mimic those described for the whole flora around it, with 15.1% of narrow endemic species and six strictly rupicolous plants. Underlining the "temperate" nature of the high elevation climate in Itatiaia, the sampled flora was dominated by species of the families Asteraceae and Poaceae, and the number of CAM (crassulacean acid metabolism) species was very low. A few endemic species of tropical origin - Pleurostima gounelleana (Beauv.) Men. (Velloziaceae) and Fernseea itatiaiae (Wawra) Baker (Bromeliaceae) - play a crucial role in this vegetation, as pioneer mat-formers facilitating later establishment of numerous other species. Hemicryptophytes prevail in the sampled flora, while therophytes are exceptionally rare and mainly consist of opportunistic species associated with disturbances. Numerous microhabitats and strong environmental gradients in these high elevation rock outcrops afford opportunities for establishment of a highly diversified flora. These island-like environments may represent an important refuge for grassland species from fire and other disturbances in the surrounding grasslands.