Potentialities and practical limitations of absolute neutron dosimetry using thin films of uranium and thorium applied to the fission track dating

Neutron dosimetry using natural uranium and thorium thin films makes possible that mineral dating by the fission-track method can be accomplished, even when poor thermalized neutron facilities are employed. In this case, the contributions of the fissions of (235)U, (238)U and (232)Th induced by thermal, epithermal and fast neutrons to the population of tracks produced during irradiation are quantified through the combined use of natural uranium and thorium films.If the Th/U ratio of the sample is known, only one irradiation (where the sample and the films of uranium and thorium are present) is necessary to perform the dating. However, if that ratio is unknown, it can be determined through another irradiation where the mineral to be dated and both films are placed inside a cadmium box.Problems related with film manufacturing and calibration are discussed. Special attention is given to the utilization of thin films having very low uranium content. The problems faced suggest that it may be better to substitute these films by uranium doped standard glasses calibrated with thicker uranium films (thickness greater than 1.5 x 10(13) mu m).

Solid-state compounds of 4-methoxybenzylidenepyruvate and cinnamylidenepyruvates with thorium (IV) - Preparation and thermal studies

By close control of experimental variables affecting precipitation, solid-state compounds of the type Th(OH)(m)L4-m.nH(2)O, where L stands for 4-methoxy-benzylidenepyruvate, cinnamylidenepyruvate or 4-dimethylaminocinnamylidene-pyruvate; m=0 to 3 and n=0.5-3 were isolated. Chemical analysis, TG, DTG, DSC and X-ray powder diffractometry have been employed to characterize and to study the thermal behavior of these compounds in dynamic air atmosphere. In all cases, hydration water is slowly lost between 30 and 160degreesC; a continuous, slow rate, mass loss is observed thereafter and beyond 280-400degreesC the rate of decomposition/oxidation increased rapidly, to give ThO2 as the final product, beginning at 412-510degreesC. The results associated with the hydroxo-compounds indicate that the loss of constitution water (OH ions) and the decomposition / oxidation of the organic moieties occur as simultaneous process.

Durango apatite fission-track dating using length-based age corrections and neutron fluence measurements by natural thorium thin films and natural U-doped glasses calibrated through natural uranium thin films

In this work, we present an approach for neutron fluence measurements based on natural thorium thin films and natural uranium-doped glasses calibrated through natural uranium thin films to be used for dating with the Fission-Track Method (FTM). This neutron dosimetry approach allows the employment of FTM even when dating is carried out using low neutron themalization facilities. Besides, it makes possible the determination of the Th/U ratio of the mineral to be dated. Durango apatite which is often employed in FTM as an age standard was analyzed. This apatite presented a fairly high Th/U ratio, 29.9 +/- 1.7. Th fissions were 18%, 12% and 10% of the total for irradiations where thermal to fast neutron flux ratios were 2.4, 4.4 and 5,2, respectively. These results show that Th fission must be considered for this apatite, when not well-thermalized irradiation facilities are used. The ratio between spontaneous and induced track length, L(S)/L(1), close to 0.89, indicates a certain amount of rejuvenation of the age of Durango apatite. Therefore, its apparent age should be corrected, the application of a technique based on track-length measurements produced a corrected age of 29.7 +/- 1.1 Ma, consistent with the independent reference age of this apatite (31.4 +/- 0.5 Ma). This result represents a support for viability of the neutron dosimetry approach studied in this work for FTM.(C) 2002 Elsevier B.V. B.V. All rights reserved.

The behavior of dissolved uranium in groundwaters of the Morro do Ferro thorium deposit, Brazil

Groundwater samples were collected for several months in boreholes drilled at Morro do Ferro, a thorium and rare earth deposit located on the Poços de Caldas Plateau, Minas Gerais State, Brazil. An aquifer system has developed in the weathered mantle due to in situ intense alteration. The weathered zone includes a thick argillaceous laterite greater than 100 m thick. The U content and 324U/238U activity ratio were measured in the groundwater samples and in spoil samples of a borehole drilled in the ore body. Some possible mechanisms related to the mobilization of uranium are considered such as complexation with humic substances and adsorption by clays. © 1989.

Complexation of some trivalent lanthanides, scandium(III) and thorium(IV) by benzylidenepyruvates in aqueous solution

The protonation constants of 4-methylbenzylidenepyruvate (4Me-BP) and 4-isopropylbenzylidenepyruvate (4IP-BP) as well as the stability constants of their binary 1:1 complexes with Cu(II), La(III), Pr(III), Sm(III), Eu(III), Yb(III), Sc(III) and Th(IV) have been determined spectrophotometrically in aqueous solution at 25°C and ionic strength 0.500 M, maintained with sodium perchlorate. For all metal ions considered, the stability changes move in the same direction as the pKa of the ligands. Linear free energy relationships, as applied to oxygen donor substances, suggest the -COCOO- moiety as the metal binding site of the ligands. The results are discussed mainly taking into account that benzylidenepyruvates, besides the α-keto canonical form, may display other forms in aqueous solution with changing pH and the possible occurrence of extra intra-ligand charge polarization, induced by metal ions.

4-Dimethylaminocinnamylidenepyruvic acid: Synthesis, characterization and complexation with trivalent lanthanides, yttrium(III), scandium(III), thorium(IV) and uranium(VI) in aqueous solution

4-Dimethylaminocinnamylidenepyruvic acid (H-DMCP)and its sodium salt (Na-DMCP) have been synthesized and characterized. The protonation constant of DMCP as well as the stability constants of its binary 1:1 complexes with trivalent lanthanides (except Pm), Yttrium(III), Scandium(III), Thorium(IV) and Uranium(VI) were determined in an aqueous medium at 25°C and ionic strength 0.500 M. The mode of coordination of this ligand is discussed.

Geochemical Study of the Itabirite Iron Ores of the Alegria Mine - Quadrilátero Ferrífero, Minas Gerais, Brazil

The iron ores of Alegria mine are composed of itabirites enclosing minor bodies of high-grade ores. The itabirites are classified according to mineralogical composition in five types: martite-rich, goethite-rich, specularite-rich, magnetite-rich and anphibolite-rich ores. The hematites are martite-rich, magnetite-rich, specularite-rich and more rarely, amphibolite-rich. Other classification criteria of the ores are based on the physical properties and the degree of compaction. As such, the itabirites and hematites can be classified as hard, friable and soft types. The mineralogical/textural evolution of the ores is linked to the pressure and temperature conditions that accompanied the tectonic processes in anphibolite facies and the different degrees of subsequent surficial weathering processes. Petrographic and microstructural studies indicate that the magnetite and amphibole bearing itabirites represent the parent rocks that created the other itabirites and that the specularite itabirites and the hard martite types are related to silica dissolution and redeposition in zones of high and low strain. Most of itabirites ores correspond to chert oxide facies banded iron formation, except the goethite and amphibole bearing itabirite that resemble a silicate or oxide-silicate facies with minor carbonate impurities. The great mass and pods of soft martite itabirites are probably shaley oxide facies BIFs with little volcanic contribution. Trace element contents of the Alegria's itabirites show strong dissimilarities with BIFs associated with volcanism (Algoma type), but closely ressemble to the Lake Superior type, with high content in Cr, Co and low V, Ni, Cu and Zn. Although the absolute contents of REE present in the Alegria's itabirites are, in general very low, the pattern when normalised by NASC is similar to the great majority of the Archean and Paleoproterozoic BIFs elsewhere in the world, and characterised by positive Eu anomaly.

Complexation of some trivalent lanthanides, scandium(III) and thorium(IV) by benzylidenepyruvates and cinnamylidenepyruvate in aqueous solution

The protonation constants of benzylidenepyruvate, 2-chloro-, 4-chlorobenzylidinepyruvate and cinnamylidenepyruvate as well as the stability constants of their binary 1:1 complexes with Cu(II), La(III), Pr(III), Sm(III), Lu(III), Sc(III) and Th(IV) have been determined spectrophotometrically in an aqueous medium at 25 °C and ionic strength 0.500 M, held with sodium perchlorate. Coordination centres in the aforementioned ligands are suggested. © 1995.

BENEFICIATION OF HIGH-MgO SEDIMENTARY PHOSPHATE ORES

Dolomite [CaMg(CO3)2] is an intolerable impurity in phosphate ores due to its MgO content. Traditionally, the Florida phosphate industry has avoided mining high-MgO phosphate reserves due to the lack of an economically viable process for removal of dolomite. However, as the high grade phosphate reserves become depleted, more emphasis is being put on the development of a cost effective method for separating dolomite from high-MgO phosphate ores. In general, the phosphate industry demands a phosphate concentrate containing less than 1%MgO. Dolomite impurities have mineralogical properties that are very similar to the desired phosphate minerals (francolite), making the separation of the two minerals very difficult. Magnesium is primarily found as distinct dolomite-rich pebbles, very fine dolomite inclusions in predominately francolite pebbles, and magnesium substituted into the francolite structure. Jigging is a gravity separation process that attempts to take advantage of the density difference between the dolomite and francolite pebbles. A unique laboratory scale jig was designed and built at Michigan Tech for this study. Through a series of tests it was found that a pulsation rate of 200 pulse/minute, a stroke length of 1 inch, a water addition rate of 0.5gpm, and alumina ragging balls were optimum for this study. To investigate the feasibility of jigging for the removal of dolomite from phosphate ore, two high-MgO phosphate ores were tested using optimized jigging parameters: (1) Plant #1 was sized to 4.00x0.85mm and contained 1.55%MgO; (2) Plant #2 was sized to 3.40mmx0.85mm and contained 3.07% MgO. A sample from each plant was visually separated by hand into dolomite and francolite rich fractions, which were then analyzed to determine the minimum achievable MgO levels. For Plant #1 phosphate ore, a concentrate containing 0.89%MgO was achieved at a recovery of 32.0%BPL. For Plant #2, a phosphate concentrate containing 1.38%MgO was achieved at a recovery of 74.7%BPL. Minimum achievable MgO levels were determined to be 0.53%MgO for Plant #1 and 1.15%MgO for Plant #2.

The Recovery of Copper in Sulphide Ores by Roasting, Leaching, and Electrolysis

Sulphide ores of copper are insoluble in dilute sulphuric acid leaching solutions, but a very high extraction can be obtained if the copper ore is in the oxidized condition. The problem is to convert the sulphide into the oxide form. This can be done by giving the sulphide ore an oxidizing-sulphatizing roast. Copper sulphate is soluble in water, so acid will be saved in the leaching process if copper sulphate is present. The iron in the copper sulphide ores is present as pyrite, or in combinations as bornite, or chalcopyrite.

Supergene Enrichment of Silver Ores with Special Reference to those from Neihart, Montana.

In the development of a technique it was necessary to learn the fundamentals of ore microscopy as applied to the various minerals of silver, which included the use of reflected polarized light, etch reactions, micro­chemical analysis, and sight recognition of mineral. In addition it was necessary to become familiar with the accepted criteria of sequence, replacement, and other textural phenomena.

Microscopic Study of Montana Silver Ores.

A microscopic investigation of the Montana silver minerals was conducted. This study consisted mainly of identifying the silver and silver-bearing minerals and of determining their paragenetic rela­tionships. The increasing amount of research in which the reflecting microscope is employed is evidence of the great value of this method of approach in the solution of problems of paragenesis of the opaque minerals.

A Metallurgical Study of Gold Ores

Gold is widely distributed in the earth's crust in small quantities. Gold is found in nature in two forms; the element itself and the compound gold telluride. In all cases, silver in some proportion is an alloying constituent.

A Study and Application of the Process of Supergene Enrichment of Silver Ores.

In many deposits of silver ores the grade of the ore de­creases considerably a few hundred feet below the surface. It is believed that in many cases the better ores owe their richness in part to the process of sulphide enrichment. It is recognized, however, that many rich silver ores are hypogene deposits that have been affected very little, if any, by processes of enrichment.