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This 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 −2  to 10 −1  M NH 4 H 2 PO 4  solution, the Gd(III) at a concentration of 10 −4  M is almost entirely precipitated as amorphous phosphate. However, the presence of H 2 SO 4  at  C  H 2 SO 4   ≥ 0.1 M, reduces the coprecipitation to less than 8 at. %, on average. The fluoride ions in solution, even at  C  HF  ≤ 0.1 M, induce a reduction of coprecipitation of 10 to 30% according to HF concentration. In the media containing 10 −2  to 10 −1  M NH 4 H 2 PO 4  and 10 −1  M H 2 SO 4 , 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 ≤ C H 3 PO 4   ≤ 4.44 M), leads to a significant coprecipitation of the REE (1.3 ± 0.2 ≤  D  Gd  ≤ 3.1 ± 0.5), whilst the addition of HF (0.1 M) to these media enhances the solubility of the REE (〈 D  Gd 〉= 0.06 ± 0.01).

The effect of fluoride and silicate ions on the coprecipitation of gadolinium with calcium in phosphoric and sulpho-phosphoric media