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First-Principles Methods as a Powerful Tool for Fundamental and Applied Research in the Field of Optical Materials
Published in Ru-Shi Liu, Xiao-Jun Wang, Phosphor Handbook, 2022
Mikhail G. Brik, Chong-Geng Ma, Tomoyuki Yamamoto, Michal Piasecki, Anatoli I. Popov
Figure 1.6 shows how the calculated lattice constants in this group of materials depend on the lanthanide atomic number. The obtained numerical values of the lattice constants are represented by the filled symbols; they were approximated by the linear functions of the Ln ions atomic number Z (solid lines). The linear fitting equations are given for each line. Available experimental data are shown by the open symbols for some elpasolites; good agreement demonstrated between the calculated and measured lattice constants in these cases serves as a proof of reliability of the predicted structural data for other (unexamined experimentally yet) considered elpasolites. The lattice constants decrease linearly with the lanthanide atomic number, which is due to the well-known lanthanide contraction (decrease of the ionic radii of rare-earth ions) with increasing atomic number. On the other hand, the lattice constants increase with increased anion atomic number, if keeping the same cations. The calculated band gaps of all 60 elpasolites in this group are plotted in Figure 1.7.
Sustainable Electronics Waste Management in India
Published in Abhijit Das, Biswajit Debnath, Potluri Anil Chowdary, Siddhartha Bhattacharyya, Paradigm Shift in E-waste Management, 2022
The conventional methods such as fractional crystallization and fractional precipitation used in the past were slow and tedious. Presently, the solvent extraction and ion exchange methods are being used. These methods worked on the basis of the lanthanide contraction, i.e. ionic radius is decreasing across the lanthanide series of elements, from lanthanum to lutetium. The heavy members of the series will, therefore, create stronger binding with solute and solvent molecules compared to light members, which allows preferential binding to ion exchange resins, or extraction of the complex into the organic phase. Lamps are initially crushed and phosphor powder is collected. Then the powers are subjected to solvent extraction and followed by the precipitation of the metals and calcination of the precipitate to obtain the pure rare earth oxides. The sulfuric acid is used for acid leaching and DEHPA is used by solvent extraction. The recycling process developed by C-MET, Hyderabad from spent phosphors of CFL and fluorescent lamp is capable extracting > 96 percent purity of yttrium. The batch scale up gradation and further purity improvement is in progress under the CoE.
Solids: comparison with experiment
Published in Michael de Podesta, Understanding the Properties of Matter, 2020
This orbital results in the additional electronic charge residing inside the atom rather than near the outside of the atom. This has two consequences for the density of the lanthanides. First, as the charge density in the outer part of the atom is not changed, the bonding to neighbouring atoms (which is both metallic and covalent) is broadly unaffected. If this was the only effect then the density of elements would increase as the mass of atoms increased, while the separation between atoms would remain roughly constant. Second, the effect of the each extra nuclear charge pulls all the orbitals a little closer to the nucleus. This makes the orbitals, and hence the atom itself, become systematically smaller as one proceeds across the series, an effect known as the lanthanide contraction.
Study on leaching behavior differences of rare earth elements from coal fly ash during microwave-assisted HCl leaching
Published in International Journal of Coal Preparation and Utilization, 2023
Hangchao Chen, Zhiping Wen, Jinhe Pan, Lei Zhang, Xin He, Dmitry Valeev, Changchun Zhou
During the experiment, it was found that the leaching efficiency of LREY was higher than that of HREY, which may be related to the ionic radius of REY. This result is consistent with the previous finding listed in Table 4. The ionic radius of the rare earth element is mentioned in Table 5, the phenomenon that the trivalent ion radius of lanthanide elements decreases with the increase in atomic number is called lanthanide contraction. The correlation between ionic radius and leaching efficiency of REY was studied. The results of the correlational analysis are presented in Figure 12 and Table S2. The Pearson correlation coefficients (r) ranged from 0.947 to 0.975, which showed a strong linear correlation. It can be seen that the increase in rare earth ionic radius leads to the increase in leaching efficiency of the sample, for reasons that remain unclear; therefore, some speculative discussion is in order.
Hydrometallurgical processes for heavy metals recovery from industrial sludges
Published in Critical Reviews in Environmental Science and Technology, 2022
Viraj Gunarathne, Anushka Upamali Rajapaksha, Meththika Vithanage, Daniel S. Alessi, Rangabhashiyam Selvasembian, Mu. Naushad, Siming You, Patryk Oleszczuk, Yong Sik Ok
One of the most utilized hydrometallurgical techniques for the removal of metal ions present as impurities in leach liquor is adsorption. The removal of Tungsten (W), which is present in leach liquor as an impurity, to facilitate efficient recovery of Mo is one of the most critical applications of adsorption. The separation of these two metal ions is difficult because of their almost equal ionic radii due to the phenomenon of lanthanide contraction. The study conducted by Srivastava et al. (2012) showed the separation of W from a mixed liquor solution that was obtained from the leaching of the hydro-desulphurization catalyst using manganese and ferric compounds. The results indicated approximately 90% adsorption of W and 100% adsorption of V and Co on freshly prepared adsorption material of hydrous ferric oxyhydroxide with optimal conditions of 0.5 M W/Fe ratio, 50 °C temperature, and a reaction period of 2 h. However, the loss of Mo was noted as 10%. A similar study conducted by Zhang et al. (2014) to separate W from mixed Mo solution using microporous resin D301 (analogous to Amberlite IRA-94) showed better selectivity for W at near-neutral pH. The W adsorption rate was enhanced with the increase in temperature and decrease in the particle sizes of resin. The adsorption kinetics of W was explained by the pseudo-second order adsorption model, and diffusion was recognized as the mechanism that regulated the adsorption rates for W and Mo.
Mixed-ligand lanthanide complexes constructed by flexible 1,3-propanediaminetetraacetate and rigid terephthalate
Published in Journal of Coordination Chemistry, 2019
Mao-Long Chen, Xiong Tang, Tian-Hui Lu, Xin-Qi Zhan, Zhao-Hui Zhou
The radii of lanthanide ions (Å), selected bond distances (Å), coordination numbers (C.N.) of lanthanide ions and dentate numbers (D.N.) of 1,3-pdta ligands for 1–6 and previously reported [Sm(1,3-Hpdta)(H2O)]n·4nH2O [31] are listed in Table 2. In addition, the denticity number (D.N.), in this article, signifies the number of all coordination bonds including bridged bonds. From the table, we find an obvious lanthanide contraction effect for the lanthanide ions whose radii decrease from 1.356 to 1.247 Å. The average Ln − Oc (Oc stands for the carboxyl oxygen from 1,3-pdta or 1,3-Hpdta ligand) bond distances decrease from 2.532 to 2.378 Å with the increase of the lanthanide number. The biggest difference of average Ln − Oc bond distances is 0.154 Å, which is bigger than the difference of the radii of the lanthanide ions (0.109 Å). The bond distances of Ln–N and Ln–Ow also decrease with the increase of lanthanide number. In order to highlight these trends, the bond distances (Å) of Ln − Oc, Ln–N and Ln–Ow are presented in a chart graph (Figure S5) to give a clear visualization. The coordination numbers (C.N.) of lanthanide ions and denticity numbers (D.N.) of 1,3-pdta or 1,3-Hpdta ligands also show a similar relationship.