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  • Author: A. Elyahyaoui x
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Summary

A simple method combining coprecipitation, solvent extraction and electrodeposition for determining uranium and thorium in sea water and fresh water samples is developed. It offers a considerable saving in time, minimising chemical treatment and costs. The analytical procedure consists of enrichment of U and Th by coprecipitation with iron(III) hydroxides and subsequent extraction by diethylether solution and electrodeposition of each actinide in the extracting organic phase in which it was separated.

The dependence of the coprecipitation, the extraction-electrodeposition and the overall yields of the above mentioned elements is examined in relation to the initial aqueous solution acidity and various amounts of iron carrier. At an initial pH between 6 and 10, quantitative coprecipitation of U and Th requires use of an Fe(III) quantity which depends on the acidity of these solutions. This quantity varies, under explored conditions, between 10 and 110mg/L. At a starting pH of 11, this coprecipitation becomes almost independent of Fe(III) amounts.

The proposed procedure was used to analyse the content of U and Th isotopes in water samples. Recoveries of 60%-93% are obtained for uranium and 63%-86% for thorium. Good resolutions (37-56.5keV) are also achieved under optimum conditions. These resolutions allow to make accurate determination of U and Th isotopes in various water samples.

Summary

A method combining liquid-liquid extraction and electrodeposition procedures is carried out to determine isotopic composition of uranium and thorium in technical wet phosphoric acid, phosphate rock and phosphogypsum leachates, by α-particle spectrometry. Extraction experiments are performed with diethylether from 5.57 M calcium nitrate solution with nitric acid concentration of 2 M. Uranium is extracted in the pH range 0.6-0.8 and thorium is extracted after acidification with 2 M HNO3. Alpha-sources are obtained by a selective electrodeposition of U(VI) or Th(IV) directly from the extracting solution without applying back-extraction or purification steps. The dependence of the electrodeposition and the overall recovery of U and/or Th are examined as a function of the amount of phosphate ions (C PO₄³⁻) in the electrolyte and of the aqueous phase, respectively. In all cases a decrease of the deposition yield with C PO₄³⁻ is observed. An improvement in the uranium overall recovery is achieved from 7.57 to 9.57 M nitrate solution and PO4 3- concentration lower than 0.8 M. The method proposed is applied to technical wet phosphoric acid, phosphate rock and phosphogypsum leachates. Recoveries of 74%-93% are obtained for uranium and 54%-69% for thorium. Good resolutions (37-52 keV) are also achieved under optimum conditions. These resolutions allow to make accurate determination of U and Th isotopes in the above mentioned samples.

Summary

A simple method of preparing α-sources for alpha spectrometric analysis of uranium and thorium is investigated by combining solvent extraction and electrodeposition procedures. Extraction of these actinides is performed by diethyl ether from calcium nitrate solution with various nitric acid concentrations. Recoveries of 90–100% are obtained for uranium and 83.5% for thorium. Good resolutions are also achieved under optimum conditions.

The dependence of the overall yield of U(VI) and Th(IV) is examined in relation to the aqueous phase acidity. A procedure combining solvent extraction and electrodeposition is proposed for a selective α-source preparation of U(VI) and Th(IV). Uranium is first extracted at pH range about 1 to 2. At this acidity, thorium remains in the aqueous phase and may be subsequently extracted from this after acidification with 2 M HNO3. A second decontamination of a specific nuclide is achieved by a selective electrodeposition using electrolyte consisting of about 70% ethanol, 0.45 M hydrochloric acid, 0.09 M acetic acid and 108 µg Fe2O3, with concentrations above 0.48 M in HCl for U(VI) or 0.06 to 0.09 M in HNO3 for Th(IV).

The paper presents a case study for the application of environmental tritium to assess the mean residence time of water in the Tafilalet aquifer. This aquifer corresponds geologically to a tectonic depression with Quaternary fill. The Tafilalet area depends mainly on agriculture and herding. Groundwater is the main source of water supply for domestic, agriculture, and herding purposes.

The data on the distribution of tritium in subsurface water indicate the modern water of the Tafilalet aquifer. The tritium transport modelling indicates that Quaternary alluvial waters are likely to have short mean residence times of a few years (14 to 32 years). The study addresses several difficulties concerning the detailed quantitative interpretations of the results, which must be the focus of future work.