BACTERIAL LEACHING OF URANIUM ORE FROM FIGUEIRA-PR, BRAZIL, AT LABORATORY AND PILOT-SCALE

A bacterial leaching program was carried out in order to evaluate the potential of applying this process to leach uranium from the ore of Figueira-PR, Brazil. The experiments were carried out in shake flasks, column percolation (laboratory and semipilot scale) and in heap leaching. In shake flasks and in column percolation experiments at laboratory scale, bacterial activity on the ore was confirmed: approximately 60% of uranium was leached, against around 30% in sterilized controls. Column percolation experiments at semipilot scale and heap leaching (850 tons of ore) showed uranium extractions of approximately 50%. In both experiments, a complementary sulfuric acid attack, after the bacterial leaching phase, was necessary to reach this level of uranium extraction.

High current-density anodic electro-dissolution in flow-injection systems for the determination of aluminium, copper and zinc in non-ferroalloys by flame atomic absorption spectrometry

An automatic Procedure with a high current-density anodic electrodissolution unit (HDAE) is proposed for the determination of aluminium, copper and zinc in non-ferroalloys by flame atonic absorption spectrometry, based on the direct solid analysis. It consists of solenoid valve-based commutation in a flow-injection system for on-line sample electro-dissolution and calibration with one multi-element standard, an electrolytic cell equipped with two electrodes (a silver needle acts as cathode, and sample as anode), and an intelligent unit. The latter is assembled in a PC-compatible microcomputer for instrument control, and far data acquisition and processing. General management of the process is achieved by use of software written in Pascal. Electrolyte compositions, flow rates, commutation times, applied current and electrolysis time mere investigated. A 0.5 mol l(-1) HNO3 solution was elected as electrolyte and 300 A/cm(2) as the continuous current pulse. The performance of the proposed system was evaluated by analysing aluminium in Al-allay samples, and copper/zinc in brass and bronze samples, respectively. The system handles about 50 samples per hour. Results are precise (R.S.D < 2%) and in agreement with those obtained by ICP-AES and spectrophotometry at a 95% confidence level.

The influence of aluminium on the overall properties of SnO2-based varistors

The influence of aluminium on the development of the microstructure and on the electrical behaviour of the SnO2 center dot Co3O4 center dot Nb2O5 typical varistor system was studied. Two sources of Al were used, alumina (Al2O3) and boehmite (AlO(OH)). The microstructural features were characterised with scanning (SEM) and transmission (TEM) electron microscopies. The different phases present in the studied samples were also studied with XRD, EDS and electron diffraction patterns of selected areas (SAED). Particles containing Sri, Co, Al, and O were unveiled with TEM. Impedance spectroscopy measurements and current density versus electric field characteristics revealed superior electrical properties for samples with AlO(OH). The higher non-linearity (alpha = 19) was achieved with the addition of 0.1% mol of boehmite. The influence of the secondary phases on the electrical properties is also addressed in this work.

Influence of pH and precipitation temperature on the structural characteristics of aluminium hydroxides prepared form nitrate aqueous solutions

Aluminium Hydroxides were precipitated from Aluminium Nitrate and Ammonium Hydroxide, at the temperatures 64 degrees C (hot) and 25 degrees C (cold), under the pH conditions 5, 7 and 9. The samples were characterized by X-Ray Diffraction (XRD) and Differential Thermal Analysis (DTA). The hydroxide precipitated at pH 9 and 64 degrees C is built up by pseudoboehmite and a minor share of others apparently amorphous hydroxides. The crystallinity of the hot yielded pseudoboehmite diminishes with the pH. The crystallite size was evaluated as about 40 Angstrom for the best crystallized sample. The cold precipitated product is apparently composed by amorphous or very poorly crystallized hydroxides. Upon heating, the cold precipitated hydroxides, and the low pH and hot precipitated hydroxide, release their structural water before the occurrence, about 430 degrees C, of the transition of the pseudoboehmite to gamma-alumina, and exhibit a shifting (towards low temperature side) and a broadening in the peak of the transition to alpha-alumina, which occurs at 1200 degrees C in the pseudoboehmite pattern. The yielded pseudo-boehmite peptized by HNO3, addition and gelified by evaporation in a critical concentration approximately 0.17 gcm(-3).

Controlled growth of anodic aluminium oxide films with hexagonal array of nanometer-sized pores filled with textured copper nanowires

Anodic aluminium oxide (AAO) films exhibiting a homogeneous morphology of parallel pores perpendicular to the surface were prepared in a two-step anodization process and filled with copper by electrochemical deposition. The optimum growth conditions for the formation of freestanding AAO films with hexagonal compact array of cylindrical pores were studied by field emission scanning electron microscopy and small angle X-ray scattering. The results show well-defined periodic structures with uniform pores size distribution for films with pore diameters between 40 and 70 nm prepared using different voltages and temperatures during the second anodization step. X-ray photoelectron spectroscopy and X-ray diffraction analysis of AAO films filled with copper show the formation of nanowires with high structural order, exhibiting a preferential crystalline orientation along the (2 2 0) axis and only small fraction of copper oxides. The best results for textured Cu nanowires were obtained at a reduction potential of -300 mV. (C) 2009 Elsevier Ltd. All rights reserved.

Isotopic evidence for the late Brasiliano (500-550 Ma) ore-forming mineralization of the Araes gold deposit, Brazil

The Araes gold deposit, located in eastern Mato Grosso State, central Brazil, is hosted in Neoproterozoic volcanosedimentary rocks of the Paraguay belt, which formed during collision of the Amazonian craton and the Rio Apa block. Ar-40/Ar-39 geochronology and Pb and S isotopic analyses constrain the timing and sources of mineralization. Three biotite flakes from two samples of metavolcanic host rock yield Ar-40/Ar-39 plateau ages between 5941 and 531 Ma, interpreted as cooling ages following regional metamorphism. Clay minerals from a hydrothermal alteration zone yield an Ar-40/Ar-39 integrated age of 503 +/- 3 Ma. Galena grains from ore-bearing veins yield values of Pb-206/(204)pb from 17.952 to 18.383, Pb-207/Pb-204 from 15.156 to 15.811, and Pb-208/Pb-204 from 38.072 to 39.681. Pyrite grains from ore-bearing veins yield values of Pb-206/Pb-204 from 18.037 to 18.202, Pb-207/Pb-204 from 15.744 to 15.901., and Pb-208/(204)pb from 38.338 to 38.800. Pb isotope variations may be explained in terms of mixing a less radiogenic lead component (mu similar to 8.4) from mafic and ultramafic basement host-rocks (Nova Xavantina metavolcanosedimentary rocks) and a more radiogenic lead component (mu similar to 9.2) probably derived from supracrustal rocks (Cuiaba sedimentary groups). Sulfur isotope compositions are homogeneous, with delta S-34 values ranging from -1.1 parts per thousand to 0.9 parts per thousand (galena) and -0.7 parts per thousand to 0.9 parts per thousand (pyrite), suggesting a mantle-derived reservoir for the mineralizing solutions. Based on the Ar, Pb, and S isotope data, we suggest that the precious metals were remobilized from metavolcanic host rocks by hydrothermal solutions during Brasilide-Panafrican regional metamorphism. The Arabs gold deposit probably formed during a late stage of the orogeny, coeval with other mineralization events in the Paraguay Belt.

Bacterial leaching of uranium ore from Figueira-PR, Brazil, at laboratory and pilot scale

A bacterial leaching program was carried out in order to evaluate the potential of applying this process to leach uranium from the ore of Figueira-PR, Brazil. The experiments were carried out in shake flasks, column percolation (laboratory and semipilot scale) and in heap leaching. In shake flasks and in column percolation experiments at laboratory scale, bacterial activity on the ore was confirmed: approximately 60% of uranium was leached, against around 30% in sterilized controls. Column percolation experiments at semipilot scale and heap leaching (850 tons of ore) showed uranium extractions of approximately 50%. In both experiments, a complementary sulfuric acid attack, after the bacterial leaching phase, was necessary to reach this level of uranium extraction.

Finite element analysis of warpage in laminated aluminium alloy plates for machining of primary aeronautic parts

The aim of this paper consists in presenting a method of simulating the warpage in 7xxx series aluminium alloy plates. To perform this simulation finite element software MSC.Patran and MSC.Marc were used. Another result of this analysis will be the influence on material residual stresses induced on the raw material during the rolling process upon the warpage of primary aeronautic parts, fabricated through machining (milling) at Embraer. The method used to determinate the aluminium plate residual stress was Layer Removal Test. The numerical algorithm Modified Flavenot Method was used to convert layer removal and beam deflection in stress level. With such information about the level and profile of residual stresses become possible, during the step that anticipate the manufacturing to incorporate these values in the finite-element approach for modelling warpage parts. Based on that warpage parameter surely the products are manufactured with low relative vulnerability propitiating competitiveness and price. © 2007 American Institute of Physics.

La industria del aluminio de América Latina y el Caribe: opciones tecnológicas y oportunidades para el crecimiento = The aluminium industry of Latin America and the Caribbean: technological options and opportunities for growth

Incluye Bibliografía

Opciones tecnológicas y oportunidades para el desarrollo: un estudio comparativo entre el aluminio y el estaño = Technological options and opportunities for development: a comparative study between aluminium and tin

Incluye Bibliografía

Report of the Meeting on Technological Options and Opportunities for Development: the Aluminium and Tin Industries in Latin America and the Caribbean = Informe de la Reunión sobre Opciones Tecnológicas y Oportunidades para el Desarrollo: las Industrias del Aluminio y el Estaño en América Latina y el Caribe

Contiene discurso de inauguración, presentación y comentario de los documentos presentados y recomendaciones de la reunión en que se trataron las opciones tecnológicas para el desarrollo de las industrias del aluminio en América Latina y el Caribe.

Profile and possibility of a multinational ore marketing enterprise: the case of Latin America

Includes bibliography

Latin American supply and major world market demand for the principal metals, 1970-1990: aluminium, copper, iron, nickel, lead, zinc, tin

Includes bibliography