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AbstractThis work was carried out with the aim to establish the effect of some impurities on the coprecipitation of gadolinium with calcium phosphate and gypsum. The tests were performed using the radioactive tracer technique to monitor the fate of gadolinium in various phosphoric and sulpho-phosphoric media containing fluoride and silicate ions as impurities. In 10-2to 10-1M NH4H2PO4solution, the Gd(III) at a concentration of 10-4M is almost entirely precipitated as amorphous phosphate. However, the presence of H2SO4at CH2SO4= 0.1 M, reduces the coprecipitation to less than 8 at. %, on average. The fluoride ions in solution, even at CHF= 0.1 M, induce a reduction of coprecipitation of 10 to 30% according to HF concentration. In the media containing 10-2to 10-1M NH4H2PO4and 10-1M H2SO4, the effect of HF is almost negligible in the absence of Si(IV); nevertheless, the presence of fluorosilicate in solution may contribute to the enhancement of the coprecipitation of the REE. The sulphuric acid (0.1 M) in phosphoric media (0.74 = CH3PO4= 4.44 M), leads to a significant coprecipitation of the REE (1.3 ± 0.2 = DGd= 3.1 ± 0.5), whilst the addition of HF (0.1 M) to these media enhances the solubility of the REE (DGd= 0.06 ± 0.01).XRD, IR spectroscopy and elemental analyses of the solid phases in conjunction with the variation of the distribution coefficient Dindicate that the coprecipitation of the REE is likely controlled by heterovalent substitution of REE in gypsum and its precipitation as phosphate or fluorosilicate.

Abstract: A method is described for the analysis of thorium by neutron activation. The sample is brought into solution and quantitative extraction of233Pa is carried out in 1M HNO3 using 0.5M HTTA in benzene. Extraction mechanisms are discussed. The use of a low-power reactor (100 kWth) enables determination of thorium at a lower concentration limit of 50 ng for periods of irradiation, cooling and measurement of 3 hours, 24 hours and 300 seconds, respectively.

Abstract: A method is described for the analysis of uranium by neutron activation. The sample is brought into solution and the neptunium present is reduced to oxidation state (IV); quantitative extraction of239Np in the acidified aqueous phase (0.4thermal) enables determination of uranium at a lower concentration limit of 33 ng for periods of irradiation. cooling and measurement of 3 hours, 24 hours and 900 seconds, respectively.