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Journal of Thermal Analysis and Calorimetry
Authors: L. A. Perez-Maqueda, C. Maqueda, J. L. Perez-Rodriguez, J. Subrt, Z. Cerny, and V. Balek

, for the product prepared by acid leaching of the ground vermiculite has been recently reported [ 12 ]. The prepared sample contains amorphous phase (silica) and akaganeite (β-FeOOH). The presence of iron in the product obtained after acid treatment is

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The effects of acids on the removal of impurity from 2N grade silica have been studied using five leaching acids: 0.2 M-oxalic acid (pH 1.5 and 2.5), c-aqua regia, 2.5%—HCl/HF, and 1%—HNO3/HF. The presence of 39 impurities in the 2N grade silica and the reference material (RM, 5N grade silica) were investigated by neutron activation analysis (NAA), X-ray fluorescence (XRF), and inductively coupled plasma mass spectrometry (ICP-MS) methods. Major impurities of the 2N silica were Al, K, Fe, Na, Ti, Ca, Mg and P. The fractions of the eight major impurities were 99.2% and 90.9% of total impurity in the 2N and RM silica, respectively. Among the leaching acids, almost all of the major impurities were removed effectively by the 2.5% HCl/HF leaching acid. All the major impurities, except for phosphorous, as well as 21 minor and trace impurities could be determined by the NAA.

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Global fallout plutonium, most of which was produced by large thermonuclear tests injecting submicron particles into the stratosphere, can be readily extracted from soil by strong acid leaching. Some nuclear tests conducted at the Nevada Test Site (NTS) produced fallout in offsite regions that does not yield its total plutonium content to an acid leach. We theorize that those detonations occurred near the desert surface and incorporated fused silicate soil particles, many >1 m, into the mushroom cloud and stem. We have assembled a radiochemical procedure to insure the complete dissolution of plutonium in 50g of acid leached soil residue. The results of a complete analysis of the leachate and leached residue from soil collected near NTS and the eastern United States illustrate the impact of these particles on the plutonium values obtained by the two methods.

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, and the heating rate did not affect the properties and activities of the catalysts. All acid leaching were conducted under the room temperature for 24 h using 0.6 mol/L HNO 3 solution. The HNO 3 leaching operation was labeled B, and the steaming

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A series of leaching experiments with water and gradually harsher acid solutions have been carried out on a monazite.228Th/232Th,230Th/232Th, and234U/238U activity ratios in the acid fractions show a common variation pattern: high — low — close to bulk values, which can be explained in terms of preferential solution effect of recoil atoms. Compared with228Th, the preferential solution effect of234U is suppressed due to self-annealing of recoil tracks.

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A series of leaching experiments with H2O, HCl, HNO2 and HF were carried out on a sample of pitchblende from Africa. Anomalously high231Pa/235U ratios, which were not accompanied by similar enhancements of234U/238U and235U/238U ratios, were observed in some uranium fractions. The observed231Pa/235U ratios varied between the values of 0.035±0.005 and 2,000±300 (Ci/Ci). These results are interpreted as due, primarily, to the difference in the chemical properties of protactinium and uranium, rather than to the alpha-recoil effects.

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It was found that heating of diluted nitric or hydrochloric acids in many years stored glass beakers can result in mBq quantities of 210Po leached from beaker walls to the solution. In the case of freshly bought beakers acid leaching of 210Po was not observed. We suppose that acid leachable 210Po in old beakers is mainly due to implantation of radon progenies (from air) into superficial layers of glass beaker walls.

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Some results of the extraction of strontium and yttrium from soil samples by concentrated nitric acid are described. The concentration of Sr and Y in the solid was determined by XRF method. The results obtained allowed to elaborate the conditions of acid leaching and to propose an analytical procedure for the determination of 90Sr in samples without their total dissolution.

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Concentrations of U, Th, Ra, Pb, and Po were determined in native vegetation and underlying substrate (soil and tailings) at various sites around a conventional open pit, acid leach uranium production operation in the Western United States. Radionuclide concentrations in substrate and vegetation were generally elevated above background at all sites disturbed by mining and milling activities. Observed plant/soil CR values for vegetation growing on exposed, weathered tailings were ordered as follows:238U>230Th>210Po,226Ra>210Pb. We suspect that in the case of sulfuric acid leached tailings, Ra and Pb are sequestered as sulfates, which are highly insoluble relative to U and Th sulfates, resulting in reduced availability for plant uptake. Soil acidity and the saturation condition at the tailings impoundment edge tend to enhance radionuclide availability for plant uptake. The transport of radionuclides to foliage and subsequent retention and absorption may play a role in plant contamination.

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Simple nitric acid leaching and alkali fusion techniques for the determination of the total content of fallout239,240Pu in deep-sea sediment were compared. Leaching neither with boiling conc. HNO3 nor with boiling conc. HNO3+H2O2 was found to be sufficient. The sodium hydroxide fusion technique yielded reproducible analytical results and is proposed as an optimum dissolution method for quantitative determination of the total content of fallout239,240Pu in deep-sea sediment.

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