Adsorption of lanthanoid ions on calcite

Abstract

The adsorption of 14 trivalent lanthanoid ions and yttrium ion (denoted by Ln3+) on calcite surfaces was investigated under various solution conditions of pH (pH = 6.8-7.8) and calcium ion concentration (pCa = -log[Ca2+]= 2.0 and 3.0), and different surface conditions of calcite crystals (well-developed and rough surfaces). The lanthanoid ions were equilibrated in a solution of ionic strength 0.1 mol dm-3(NaCl) saturated with calcite at 25.0 degrees C using excess (solid) calcite crystals suspended in solution. The concentrations of the lanthanoid ions on the calcite crystals (C(cry)/mol kg-1) and in solution (C(soln)/mol dm-3) were determined by means of inductively coupled plasma-mass spectrometry (ICP-MS). It is found that the distribution ratio (D=C(cry)/C(soln) decreases as the atomic number of the lanthanoid increases showing the so called Tetrad Effect. D values increase with increasing pH, whereas they are independent of the calcium ion concentration (i.e., carbonate ion concentration). These results indicate that lanthanoid ions are adsorbed on the calcite surface together with hydroxide ions, i.e., the adsorption of hydroxo-complexes. The heavy lanthanoid ions (Er3+ to Lu3+) are adsorbed as monohydroxo-complexes, (Ln(OH)2+), whereas those of the light lanthanoids are predominantly adsorbed as dihydroxo-complexes (Ln(OH)2+). Other lanthanoids show competitive adsorption reactions of mono- and dihydroxo complexes. Both successive adsorption constants of hydroxo complexes increase with decreasing atomic number of the lanthanoid. The rough surface of calcite is quite active and the distribution ratio of the lanthanoid ions on the rough surface is much higher than that on the well-developed crystalline surface. Rates of adsorption of lanthanide ions were measured and mechanisms are being discussed

Tetrad effect in the adsorption of the lanthanides on zeolite Y

“…Their diameter, 7.4 Å, is sufficient for easy diffusion of hydrated tripositive lanthanide ions and nitrate ions to the internal structure of the adsorbent. If we take into account that the radii of the tripositive lanthanides are in the range 1-1.25 Å [12], whereas the diameter of the water molecule and the ionic radius of the NO − 3 ion are 2.82 [40] and 1.79 Å [41], respectively, then we can see that the outer sphere nitrato lanthanide complex Ln(H 2 O) x NO 2+ 3 can accommodate to the zeolite Y pore structure. …”

“…Four parts were distinguished within the series: 57-60, 60-64, 64-68, and 68-71. Sawada et al [12] observed the tetrad effect in the distribution constants of the lanthanides on calcite.…”

p-Aminobenzoic acid (pABA) sensitization of LaF3:Tb3+ nanoparticles and its applications in the detection of explosive materials

“…The reason for the shrinking phenomenon of the unit cell volume is due to the smaller ionic radius of Tb 3+ (0.923 Å) as compared to that of La 3+ ion (1.032 Å). 39 The above observation further conrms the successful substitution of Tb 3+ ions in the crystalline LaF 3 lattices. All the above analysis indicates that Tb 3+ ions have been successfully doped into the lattice of LaF 3 nanomaterials.…”

Spectral and laser properties of Er:Yb:Sr_3Lu_2(BO_3)_4 crystal at 15–16 μm

“…Although the Er:Yb:SYB crystal, which combines the advantages of the YAB and YCOB crystals, can be grown by the Czochralski method and has large absorption cross-section and broad absorption band around 976 nm, the segregation coefficient of Yb 3+ ions is only 0.75 in this crystal [7]. The segregation coefficient less than 1 may be originated from the difference of ionic radii between Y 3+ (0.900 Å) and Yb 3+ (0.868 Å) ions [8] and the high Yb 3+ doping concentration in the crystal. Thus, lattice distortion and defects may exist in the Er:Yb:SYB crystal after the introduction of high Yb 3+ doping and then affect the performance of the 1.5-1.6 μm laser.…”

“…This is because that the radius of Lu 3+ ions (0.861 Å) is much closer to that of Yb 3+ ions (0.868 Å) [8]. Therefore, the crystal Sr 3 Lu 2 (BO 3 ) 4 (SLuB) may provide preferable condition for the doping of Er 3+ and Yb 3+ ions.…”