Trivalent lanthanum

Similar types of electric double layer may also be formed at the phase boundary between a solid electrolyte and an aqueous electrolyte solution [7]. They are formed because one electrically-charged component of the solid electrolyte is more readily dissolved, for example the fluoride ion in solid LaFs, leading to excess charge in the solid phase, which, as a result of movement of the holes formed, diffuses into the soUd electrolyte. Another possible way a double layer may be formed is by adsorption of electrically-charged components from solution on the phase boundary, or by reactions of such components with some component of the solid electrolyte. For LaFa this could be the reaction of hydroxyl ions with the trivalent lanthanum ion. Characteristically, for the phase boundary between two immiscible electrolyte solutions, where neither solution contains an amphiphilic ion, the electric double layer consists of two diffuse electric double layers, with no compact double layer at the actual phase boundary, in contrast to the metal electrode/ electrolyte solution boundary [4,8, 35] (see fig. 2.1). Then, for the potential... 

The electrodeposition of lanthanum. La, has been attempted in neutral and acidic EMICI-AICI3 ionic liquids [70, 71]. Lanthanum trichloride, LaCl3, is soluble in the acidic ionic liquid. The solubility of LaCl3 in the acidic ionic liquid containing AICI3 at 66.7 mol% is reported as 45 mmol kg at 25°C. The deposition of metallic La is not conhrmed, while the reduction of a trivalent lanthanum species is suggested in the presence of SOCI2. The electrodeposition of Al-La alloys has been also examined in the acidic ionic liquid where the content of La in the Al-La alloys is less than 0.1 at%. 

Starting from the nitrates, it proved possible to synthesise 18-membered (2 -I- 2) macrocyclic compounds from 2,6-dfp and en for all the members of the lanthanide series (except Pm) [23-25]. For trivalent lanthanum, cerium, praseodymium and europium, products containing the tetraimine macrocyclic ligand L649 are formed, for example Ln(L649)(N03)j, whereas for the heavier and smaller ions (Nd " —> Lu +, besides Eu ) formation of L650 is preferred (Eq. 3.5). 

Table 17.14 The colors of trivalent lanthanum and lanthanide ions in water solution and of common oxide powders...

In fact, the contribution of electronic conductivity can be ignored because it is quite small. The major contribution to Cp arises from the lattice (vibrational) component Cy, which varies linearly as a function of molar volume V in a series of isomorphous compounds. For the com-poimds imder study, Cy can therefore be estimated using volume-weighted interpolation (Westrum et al., 1989) and data on isomorphous diamagnetic substances as reference values. For instance, the Cy heat capacities measured for trivalent lanthanum, gadolinium, and lutetium compoimds were used as reference values. Subsequently, the Cm and Csch contributions were determined by subtracting the sum of the Cy and Cd contributions from the experimental Cp values. 

Blanchard et al. (1999) and Blanchard Brennecke (2001) extracted aromatic and aliphatic compounds into a CO2 phase from IL [bmim][PF6]. Examples include separation of naphthalene from the [bmim] [PFg] [Blanchard Brennecke, 2001] and methanol [bmim][PF6] using pressurized CO2 [ Scurto et al, 2002]. A two-step extraction system (water/RTIL/CO2) for trivalent lanthanum and europium was reported by Mekki et al. (2006) where the metal ions were extracted from the aqueous phase into SCCO2 via a RTIL/fluorinated P-diketonate mixture with high extraction efficiencies. 

Mekki et al. (2006) reported a two-step extraction system (water/RTIL/C02) for trivalent lanthanum and europium. The metal ions were extracted from the aqueous phase into SCCO2 via a RTIL/fluorinated P-diketonate mixture with high extraction efficiencies. 

Novikov GI, Baev AK (1962) Vapor pressure of chlorides of trivalent lanthanum, cerium, praseodymium, and neodymium. Zh Neorg Khim 7 1340-1352... 

Lopez-Gonzalez, H., Solache-Rfos, M., Jimenez-Reyes, M., Ramirez-Garcia, J.J., and Rojas-Hernandez, A. (2005) Effect of chloride ions on the hydrolysis or trivalent lanthanum, praseodymium and lutetium in aqueous solutions of 2 M ionic strength. J, Solution Chem., 34, 427 —441. 

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

Lanthanum is a naturally occurring trivalent rare earth element (atomic number 57). Lanthanum carbonate quickly dissociates in the acidic environment of the stomach, where the lanthanum ion binds to dietary phosphorus, forming an insoluble compound that is excreted in the feces. Lanthanum has been shown to remove more than 97% of dietary phosphorus... 

Americium metal has been obtained by heating americium oxide, Am203, with lanthanum at 1,200 °C americium, which is more volatile than other actinides, volatilizes and can readily be separated from other actinides. Am02 can be obtained by igniting most trivalent americium compounds (Budavari 1996 Cotton and Wilkinson 1980 UIC 1997). 

Fuger, J. and Cunningham, B. B. (1964). Microcalorimetric determination of the enthalpy of formation of the complex ions of trivalent plutonium, americium and lanthanum with EDTA, J. Inorg. Nucl. Chem. 27,1079. 

Lanthanum chromite is a p-type conductor so divalent ions, which act as electron acceptors on the trivalent (La3+ or Cr3+) sites, are used to increase the conductivity. As discussed above, the most common dopants are calcium and strontium on the lanthanum site. Although there is considerable scatter in the conductivities reported by different researchers due to differences in microstrucure and morpohology, the increase in conductivity with calcium doping is typically higher than that with strontium doping [4], The increase in conductivity at 700°C in air with calcium additions is shown in Figure 4.1 [1, 2, 28-44], One of the advantages of the perovskite structure is that it... 

Scandium, Sc yttrium, Y lanthanum, La trivalent lanthanides, Ln actinium, Ac ... 

The apparent failure of trivalent and tetravalent cations to enter plants could result from the interaction of the cations with the phospholipids of the cell membranes. Evidence for such interactions is provided by the use of lanthanum nitrate as a stain for cell membranes (143) while thorium (IV) has been shown to form stable complexes with phospholipid micelles (144). However, it is possible that some plant species may possess ionophores specific to trivalent cations. Thomas (145) has shown that trees such as mockernut hickory can accumulate lanthanides. The proof of the existence of such ionophores in these trees may facilitate the development of safeguards to ensure that the actinides are not readily transported from soil to plants. 

In studies of the concentrations of arsenic, bromine, chromium, copper, mercury, lead and zinc in south-eastern Lake Michigan, it was shown that these elements concentrated near the sediment water interface of the fine-grained sediments. The concentration of these elements was related to the amount of organic carbon present in the sediments (161). However, it was not possible to correlate the concentration of boron, berylium, copper, lanthanum, nickel, scandium and vanadium with organic carbon levels. The difficulty in predicting the behaviour of cations in freshwater is exemplified in this study for there is no apparent reason immediately obvious why chromium and copper on the one hand and cobalt and nickel on the other exhibit such variations. However, it must be presumed that lanthanium might typify the behaviour of the trivalent actinides and tetravalent plutonium. 

The rare earth (RE) ions most commonly used for applications as phosphors, lasers, and amplifiers are the so-called lanthanide ions. Lanthanide ions are formed by ionization of a nnmber of atoms located in periodic table after lanthanum from the cerium atom (atomic number 58), which has an onter electronic configuration 5s 5p 5d 4f 6s, to the ytterbium atom (atomic number 70), with an outer electronic configuration 5s 5p 4f " 6s. These atoms are nsnally incorporated in crystals as divalent or trivalent cations. In trivalent ions 5d, 6s, and some 4f electrons are removed and so (RE) + ions deal with transitions between electronic energy sublevels of the 4f" electroiuc configuration. Divalent lanthanide ions contain one more f electron (for instance, the Eu + ion has the same electronic configuration as the Gd + ion, the next element in the periodic table) but, at variance with trivalent ions, they tand use to show f d interconfigurational optical transitions. This aspect leads to quite different spectroscopic properties between divalent and trivalent ions, and so we will discuss them separately. 

Figure 6.1 An energy-level diagram for trivalent lanthanide rare earth ions in lanthanum chloride (after Dieke, 1968).

The trivalent rare-earth crystal structure sequence from hep - Sm type -> La type -> fee, which is observed for both decreasing atomic number and increasing pressure, is also determined by the d-band occupancy. Figure 8.11(a) shows the self-consistent LDA energy bands of fee lanthanum as a function of the normalized atomic volume fi/Q0, where Q0 is the equilibrium atomic volume. We see that the bottom of the NFE sp band moves up rapidly in energy in the vicinity of the equilibrium atomic volume as the free electrons are compressed into the ion core region from where they are repelled by orthogonality constraints (cf eqn (7.29)). At the same time the d band widens, so that the number of d electrons increases under pressure... 

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