Preparation of alpha-sources of U(VI) and Th(IV) by the electrodeposition technique in the presence of Ca2+ and some trivalent metals

Comparative study of different analytical methods for the determination of 238U, 234U, 235U, 230Th and 232Th in NORM samples (Southern Catalonia)

Uranium and thorium isotopes from sludge samples taken from an area of influence of a dicalcium phosphate factory, located close to the Ebro River reservoir in Flix, and from mineral raw materials (coal and phosphate) which were deposited in Tarragona Harbour (Catalonia) have been measured. To do that, several procedures to determine these isotopes have been applied and compared in terms of accuracy, precision and total analysis time. In particular, digestion procedures, such as one based on conventional acidic digestion or another based on the use of microwave digestion, have been tested. Moreover, different radiochemical separation procedures have been applied. In this regard, one method based on liquid-liquid extraction using TBP/Xylene and another based on the use of extraction chromatography using UTEVA resins have been compared. Firstly, the different proposed methods were tested by analyzing a phosphogypsum sediment and a moss-soil sample from two different intercomparison exercises. The microwave digestion - UTEVA method provided the best results (recoveries higher than 82% for uranium and thorium isotopes) and was then applied to the NORM samples. The obtained results showed that the higher uranium and thorium activities values were found in phosphate raw material and in the more superficial samples located in sludge sediments next to the dicalcium phosphate factory.

Preparation of U(VI) and Th(IV) α-sources from calcium nitrate solutions by combining solvent extraction and electrodeposition procedures

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).

Preparation of U(VI) and Th(IV) alpha-sources from sea and fresh water samples by combining coprecipitation, solvent extraction and electrodeposition procedures

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.

Use of combined solvent extraction-electrodeposition techniques to uranium and thorium isotopes analysis in industrial phosphoric acid, phosphate and phosphogypsum by alpha-particle spectrometry

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.

Determination of thorium concentrations and activity ratios in silicate rocks by alpha spectrometry

A detailed radiochemical procedure for alpha spectrometry measurements of thorium concentrations and of 230Th/232Th activity ratios in silicates is presented. The Th behaviour, during each step of the chemical process, was investigated by using a 234Th tracer, which is a gamma-ray emitter. The described chemical processing provides relatively high thorium yields, which varied between 56% and 88%, in the analysis of GB-1 (granite) and BB-1 (basalt) Brazilian geological standards. Also, the application of the established radiochemical method allowed a determination of both Th concentrations and activity ratios with high reproducibility, on the order of 2%. The estimation of the concentration result accuracy is also about 2%, which was calculated by using published data obtained from neutron activation analysis as reference values.

A method for the rapid radiochemical analysis of uranium and thorium isotopes in impure carbonates

A simple method combining solvent extraction and electrodeposition procedures is described for the determination of the isotopic composition and content of uranium and thorium in travertine samples. The actinide elements are extracted with diethyl ether from a calcium nitrate solution. The isolation of the elements and the alpha source preparation are performed in two steps after the sample digestion. The acid leaching of samples is performed using both partial and total dissolution methods. High recoveries of both uranium and thorium and good alpha-spectra are obtained with both partial and total dissolution methods.

Determination of uranium concentrations and activity ratios in silicates by alpha spectrometry: application to the volcanic rocks from the Trindade and Martin Vaz Islands (Brazil)

A detailed radiochemical procedure for alpha spectrometry measurements of uranium concentrations and of 234U/238U activity ratios in silicates is presented. The described chemical processing is characterized by relatively high uranium yields, in the range of 51-89%. The application of this chemical procedure to geological standards allowed estimating a reproducibility of the alpha spectrometry uranium measurements on the order of 3.5%. As an application example. the procedure was used in the analysis of quaternary volcanic rocks from the Trindade and Martin Vaz Islands, Brazil.