928 resultados para 640305 Production of unrefined precious metal ingots and concentrates


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The chemical fractionation and bioleaching of Mn, At, Zn, Cu and Ti in municipal sewage sludge were investigated using Thiobacillus ferrooxidans as leaching microorganism. As a result of the bacterial activity, ORP increase and pH reduction were observed. Metal solubilization was accomplished only in experimental systems supplemented with energy source (Fe(II)). The solubilization efficiency approached similar to80% for Mn and Zn, 24% for Cu, 10% for At and 0.2% for Ti. The chemical fractionation of Mn, At, Zn, Cu and Ti was investigated using a five-step sequential extraction procedure employing KNO3. KF, Na4P2O7, EDTA and HNO3. The results show that the bioleaching process affected the partitioning of Mn and Zn, increasing its percentage of elution in the KNO3 fraction while reducing it in the KF, Na4P2O7 and EDTA fractions. No significant effect was detected on the partitioning of Cu and Al. However, quantitatively the metals Mn, Zn, Cu and At were extracted with higher efficiency after the bacterial activity. Titanium was unaffected by the bioleaching process in both qualitative and quantitative aspects. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

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In order to obtain cellulases that improve the detergency of laundry detergent products, two alkalophilic microorganims, Bacillus sp B38-2 and Streptomyces sp S36-2, were isolated from soil and compost by incubating samples in enrichment culture medium containing CMC and Na2CO3 at pH9.6. It was found that they secrete a constitutive extracellular alkaline carboxymethyl cellulase (CMCase) in high quantity. The maximum enzyme activity was observed between 48hr to 72 hr at 30-degrees-C for the Streptomyces and between 72hr to 96hr at 35-degrees-C for the Bacillus. The optimum pH and temperature of the crude enzyme activities ranged from 6.0 to 7.0 at 55-degrees-C for the Streptomyces and 7.0 to 8.0 at 60-degrees-C for the Bacillus. Two crude CMCases activities were termostable at 45-degrees-C for 1hr and the both crude enzyme activities of the Bacillus as of the Streptomyces were stable at pH 5.0 to 9.0 after pH treatments in various buffer solutions at 30-degrees-C for 24hr.

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The effects of Alchornea glandulosa ethyl acetate fraction (AGF) on hydrogen peroxide (H2O2), nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) production in peritoneal macrophages activated with lipopolysaccharide (LPS) or phorbol myristate acetate (PMA) were investigated. Analysis by thin layer chromatography (TLC) of AGF showed several constituents, including flavonoids, which may have anti-inflammatory activity. Inhibitory effects of the fraction in H2O2 and NO production ranged from 8.59 +/- 7.84% to 70.56 +/- 4.16% and from 16.06 +/- 3.65% to 38.73 +/- 3.90%, respectively. The TNF-alpha production was only partially inhibited in the tested concentrations (12.21 +/- 6.23%-15.16 +/- 0.96%). According to these results, it is suggested that AGF has anti-inflammatory activity. This medicinal plant may have therapeutic potential in the control of inflammatory disorders.

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Tin oxide, SnO2. is a very used compound in industry and one of its uses is as varistor. For the current requirements of the technology is necessary a strict control of the chemical purity and the particle size of the raw material; for that reason the great interest that exists at the moment to develop synthesis methods that allow to get these requirements. In this work, ceramic powders of the Sn-Co-Nb-Ti-Al system using the controlled precipitation and polymeric precursor (Pechini) methods were synthesized. The raw material obtained was characterized using X-ray diffraction (XRD), thermal analysis (DTA/FG) and scanning electron microscopy (SEM). The sintering samples shown a good varistor behavior with non-linear coefficient (alpha) values similar to 22, and Er 2083 V/cm(2). (c) 2007 Elsevier Ltd. All rights reserved.

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Antimicrobial peptides (AMPs) are effector molecules of innate immune systems found in different groups of organisms, including microorganisms, plants, insects, amphibians and humans. These peptides exhibit several structural motifs but the most abundant AMPs assume an amphipathic alpha-helical structure. The alpha-helix forming antimicrobial peptides are excellent candidates for protein engineering leading to an optimization of their biological activity and target specificity. Nowadays several approaches are available and this review deals with the use of combinatorial synthesis and directed evolution in order to provide a high-throughput source of antimicrobial peptides analogues with enhanced lytic activity and specificity.

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The objective of this paper was to evaluate the relevance of environmental and genetics effects on milk production of buffalo cows in Brazil. The data were based on the Buffalo Genetic Improvement Program - PROMEBUL, using information of 1,911 cows (107 Jafarabadi, 101 Mediterranean, 1,056 Mu/Tab and 647 crossbred females) with parturition between 1982 and 2003. The mathematic model for evaluating milk production included the fixed effects of herd, parturition year (1982 to 2003) and month (January to December), calf's sex (male or female), genetic group (Jafarabadi, Mediterranean, Murrah, and crossbreed), number of milking (one or two), lactation order (1 to 12) and duration of lactation (as a linear effect). The mean milk production in herds was 1,590.36 +/- 609.25 kg. All sources of variation were significant (P<0.05) for the studied characteristics, except calf's sex. The mean milk production per genetic group was 1,651.4; 1,592.2; 1,578.3 and 1,135.5 kg, for Murrah, Mediterranean, Crossbred and Jafarabadi, respectively. The duration of lactation was the most important source of variation over milk production, followed by the year of parturition, herd, parturition order, genetic group and month of parturition.

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The experiment was installed in Lageado Experimental Farm with aim to verify the influence of organic fertilisation (0, 4, 8 and 12 kg of manure/m(2) - with four replications) on leaves and essential oil production of Ocimum gratissimum. The harvesting was done twice (May - autumn and August - winter), and the leaves were separated for extraction of essential oil by Clevenger apparatus. The leaf production and oil content were calculated on dry mass basis. The results showed no statistical difference for organic fertilisation, although significant difference was verified for seasons. The main constituents of essential oil were eugenol and 1,8- cineole. The amount of the eugenol was higher in autumn, while the presence of other components including 1,8-cineole, beta-selinene and trans-caryophyllene were more dominant at wintertime.

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In this work, a hydrophilic clay, Na-montmorillonite from Wyoming, USA, was rendered organophilic by exchanging the inorganic interlayer cations for hexaclecyltrimethylammonium ions (HDTA), with the formulae of [(CH3)(3)N(C16H33)](+) ion. Based on fact that organo-clay has high affinities for non-ionic organic molecules, 1,3,4-thiadiazole-2,5-dithiol was loaded oil the HDTA-montmorillonite surface, resulting in the 1,3,4-thiadiazole-2,5-dithiol-HDTA-montmorillonite complex (TDD-organo-clay).The following properties of TDD-organo-clay are discussed: selective adsorption of heavy metal ions measured by batch and chromatographic column techniques, and utilization as preconcentration agent in a chemically modified carbon paste electrode (CMCPE) for determination of mercury(II).The main point of this paper is the construction of a selective sensor, a carbon paste electrode modified with TDD-organo-clay, its properties and its application to the determination of mercury(II) ions, as this element belongs to the most toxic metals. The chemical selectivity of this functional group and the selectivity of voltammetry were combined for preconcentration and determination. (c) 2005 Elsevier B.V. All rights reserved.

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This work describes the application of partial least squares (PLS) regression to variables that represent the oxidation data of several types of secondary metabolite isolated from the family Asteraceae. The oxidation states were calculated for each carbon atom of the involved compounds after these had been matched with their biogenetic precursor. The states of oxidation variations were named oxidation steps. This methodology represents a new approach to inspect the oxidative changes in taxa. Partial least square (PLS) regression was used to inspect the relationships among terpenoids, cournarins, polyacetylenes, and flavonoids from a data base containing approximately 27,000 botanical entries. The results show an interdependence between the average oxidation states of each class of secondary metabolite at tribe and sub tribe levels.

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The brown alga Pilayella littoralis was used as a new biosorbent in an on-line metal preconcentration procedure in a flow-injection system. Al, Co, Cu and Fe were determined in lake water samples by inductively coupled plasma optical emission spectrometry (ICP-OES) after preconcentration in a silica-immobilized alga column. Like other algae, P. littoralis exhibited strong affinity for these metals proving to be an effective accumulation medium. Metals were bound at pH 5.5 and were displaced at pH < 2 with diluted HCl. The enrichment factors for Cu-II, Fe-III, Al-III and Co-II were 13, 7, 16 and 11, respectively. Metal sorption efficiency ranged from 86 to 90%. The method accuracy was assessed by using drinking water certified reference material and graphite furnace atomic absorption spectrometry (GFAAS) as a comparison technique. The column procedure allowed a less time consuming, easy regeneration of the biomaterial and rigidity of the alga provided by its immobilization on silica gel. (C) 2003 Elsevier B.V. All rights reserved.

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The in vitro gas production of four single roughages and their paired combinations (1:1 on dry matter basis) were evaluated. Two roughage samples (100 mg) per treatment were fermented with ruminal fluid during a 48 h incubation period. Total 48 h gas volumes of fermentation dry matter (DM), neutral detergent fiber (NDF) and soluble compounds in neutral detergent (NDS) were for sugarcane = 16.8, 11.2, 6.9 mL; sugarcane + corn silage = 20.1, 12.6, 9.1 mL; sugarcane + 60-day elephantgrass = 16.5, 17.6 mL; sugarcane + 180-day elephantgrass = 13.8, 8.2, 5.9 mL; corn silage = 18.8, 16.8, 4.7 mL; corn silage + 60-day elephantgrass = 16.3, 15.4, 2.4 mL; corn silage + 180-day elephantgrass = 16.1, 11.8, 4.2 mL; 60-day elephantgrass = 16.9, 19.0 mL and 180-day elephantgrass = fermented 10.7, 12.2 mL, respectively. The NDS gas production was not possible to estimate for sugarcane + 60-day elephantgrass, 60-day elephantgrass and 180-day elephantgrass. The present data shows that the curves subtraction method can be an option to evaluate the contribution of the soluble fractions in roughages to digestion kinetics. However, this method underestimates the NDS gas contribution when roughages are low in crude protein and soluble carbohydrates. It is advisable to directly apply the two-compartmental mathematical model to the digestion curves for roughage DM, when determining the NDS gas volume and the digestion rate. This method is more straightforward and accurate when compared to the curve subtraction method. Non-structural carbohydrates combined with fiber and protein promoted a positive associative effect in sugarcane + corn silage (50:50) mixture. Therefore, it can be concluded that the soluble fraction of roughages greatly contributes to gas production. (C) 2004 Elsevier B.V. All rights reserved.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)