Precipitation of ALn(CO3)2, xH2O and Dy2(CO3)3, xH2O compounds from aqueous solutions for A+ = Li+, Na+, K+, Cs+, NH4+ and Ln3+ = La3+, Nd3+, Eu3+, Dy3+

Double carbonates of lanthanide (Ln) and alkaline or ammonium (A) ions, noted ALn(CO3)(2), xH(2)O, were precipitated from concentrated A(2)CO(3) aqueous Solutions at roorn temperature and atmospheric pressure. Twelve hydrated compounds out of the twenty targeted ones have been obtained: Li(Nd or Eu) (CO3)(2), NaLa(CO3)(2), KNd(CO3)(2),XH2O, Cs(La or Nd)(CO3)(2), NH4(Nd, Eu or Dy)(CO3)(2), Dy-2(CO3)(3) from concentrated A(2)CO(3) solutions and Na(Nd, Eu or Dy)(CO3)(2) from concentrated AHCO(3) solutions. Although the trivalent lanthanide ions are often considered as analogs in Solution, differences in their precipitation behaviour was observed, which is believed to have a kinetic origin in relation to the small differences in their ionic radii. The solid compounds were characterised by elemental analyses, thermogravimetry (TG), X-ray diffraction (XRD) and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS). The powder diffraction patterns of nine solids were fitted using the tetragonal P4/mmm Laue class: LiNd(CO3)(2), xH(2)O: a = (12.16 +/- 0.02)A, c = (9.21 +/- 0.02)A, LiEu(CO3)(2), 3H(2)O: a = (12.201 +/- 0.007) A, c = (9.23 +/- 0.01)A, KNd(CO3)(2), xH(2)O: a = (13.28 +/- 0.04) A, c = (10.00 +/- 0.04) A, CsLa(CO3)(2), xH(2)O: a = (10.82 +/- 0.02) A, c = (8.18 +/- 0.02) A, CsNd(CO3)(2), xH(2)O: a = (10.81 +/- 0.07) A, c = (8.16 +/- 0.07) A for NaLn(CO3)(2), xH(2)O: a = (11.10 + 1.75r(Ln)(3+))A and c = (8.60 + 1.13r(Ln)(3+)) A,where r(Ln)(3+) is the ionic radius of Ln(3+) for a coordination number of 8 (r(La)(3+) = 1.16A, r(Nd)(3+) = 1.12A, r(Eu)(3+) = 1.07 A and r(Dy)(3+) = 1.03A). It is proposed that all the NaLn(CO3)(2), xH(2)O compounds are of very similar structure, as evidenced by their XRD patterns and by the linear variations of the lattice parameters with r(Ln)(3+). The small differences in the lattice parameters can induce large modification of the precipitation pathways. Conversely, structural changes were evidenced within the A(+) series for ANd(CO3)(2), xH(2)O, Dy-2(CO3)(3), xH(2)O was also obtained as a by-product. Its lattice parameters are in good agreement with Eu-2(CO3)(3), 3H(2)O ones. (C) 2008 Elsevier Inc. All rights reserved.