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

Abstract

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.