摘要:

The distribution of neodymium(III) between acidic aqueous nitrate solutions and organic solutions of di(2-ethyl-hexyl)phosphoric acid (D2EHPA) in hexane has been studied for different extractant and metal ratios at constant aqueous ionic strength 0.1 M (Na+,H+-NO3). The distribution data have been evaluated by both graphical and numerical analysis, in order to determine the speciation in the organic phase. The results obtained suggest the formation of two complexes in the organic phase: NdA3-3HA, which is predominant when the extractant/metal ratio is higher than one, and NdA3, which is the main species when the ratio is equal to one. For lower concentrations of extractant it has been found that the possible formation of species at the interface creates difficulties in the modelling of the extraction process.

ISSN:0736-6299    

DOI:10.1080/07366299908934623

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The kinetics of europium extraction into D2EHPA is studied in a stirred cell. For the range of concentrations investigated (10−6kmol/m−3≤ [Eu3+] ≤ 10−4kmol/m3; 0.01 kmol/m3≤ [H+] ≤ 0.15 kmol/m3; 0.001 kmol/m3≤ [(HX)2] ≤ 0.05 kmol/m3) extraction rate increases linearly with stirring speed, i.e. mass transfer is limited by diffusion. An increase in proton concentration or a decrease of complexant concentration reduces fluxes but does not change the extraction regime. Based on the found equilibrium constant and individual mass transfer coefficients, extraction rates are calculated showing good agreement with experimental data. The influence of concentrations on extraction rate is explained by the gradient between bulk concentration and interfacial concentration as the driving force for mass transfer in an extraction system controlled by diffusion.

ISSN:0736-6299    

DOI:10.1080/07366299908934624

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Using UV spectroscopy, we have studied the thermodynamics of extraction of metal picrates M+Pic−(M+= Li+, Na+K+, Rb+, Cs+Tl+and Ag+) and M2+(Pic−)2(M2+= Ca+, Sr+,Ba+, Pb+, and UO22+) from water to a chloroform or to a dichloromethane solution. The extractant molecules are mono-podands R-O-(CH2-O-CH2-)n-O-R containing an ether chain and terminal phosphoryl groups: R = (Ph)2P(O)-C6H4-; n = 3,4 (I - H) and R = (Ph)2P(O)-CH2-C6H4-, n = 1, 3, 4 (III - V). We found that podand displays a remarkable Ba2+/Ca2+extraction selectivity. All podands extract alkali and alkaline earth picrates in dichloromethane (as dissociated ion pairs) better than in chloroform (as non-dissociated ion pairs). Based on Molecular Dynamics simulations of the complexes IM2+and IM2+(Pic−)2in the gas phase and in chloroform we suggest that the high selectivity of I for Ba2+is due to (i) the formation of the complex with an “optimal” pseudocavity for Ba2+, in which six donor atoms of the ligand and four oxygens of the Pic−counter-ion coordinate to the cation. and, (ii) the smaller dehydration energy of Ba2+compared to other alkaline earth cations. The relative free energies of extraction obtained from simulations on the IM2+(Pic−)2complexes are in good agreement with the experimental data

ISSN:0736-6299    

DOI:10.1080/07366299908934625

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Extraction of microquantities of Sc, Mn(II), Ni, Co, Cu, Zn, Ga, Y, Pd, Cd, In, La, Eu, Tl(III). Pb, Bi, Th, and U(VI) from aqueous solutions of HNO3by solutions of phosphoryl-containing podands in dichloroethane has been studied. The influence of the podand molecule structure on the process of extraction is considered. The stoichiometry of the complexes extracted into the organic phase has been established.

ISSN:0736-6299    

DOI:10.1080/07366299908934626

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The highly selective liquid-liquid extraction of the pertechnetate anion TcO4−from a nitrate matrix by the lipophilic redox-recyclable extractant HEP⩲NO3−[HEP = l,1′,3,3′-tetrakis(2-methyl-2-hexyl)ferrocene] has been investigated in comparison with the well known anion-exchange reagent tetra-n-heptyl ammonium nitrate (heptyl)4N+NO3−. Under conditions of low metal-anion loading, the distribution ratio D(TcO4−) was found to be insensitive to the alkali metal cation present as M+NO3−(M+= Li+, Na+, K+) and the initial concentration of TcO4−in the aqueous phase for both extractants. Also, slope analysis of the distribution data revealed approximate linear relationships between D(TcO4−) and the concentration of extractant in the organic phase (slope = 1.0) and the concentration of NaNO3in the aqueous phase (slope = −1) plotted on a full logarithmic scale, suggesting that the extraction of TcO4−occurs by a simple anion-exchange mechanism. Graphical analysis of partial loading data confirmed that both HEP+NO3−and (heptyl)4N+NO3−are predominantly monomeric in chlorobenzene under conditions of low metalanion loading. However, at an organic-phase TcO4−concentration of approximately 0.003 M, a sharp decrease in D(TcO4−) was observed, suggesting the formation of large aggregated species. At lower concentrations of TcO4−equilibrium modeling of the extraction data with the program SXLSQI was generally consistent with the simplest model of anion exchange, namely, that involving only the monomeric organic-phase ion pairs R+NO3−and R+TcO4−[R+= HEP+or (heptyl)4N+], To model extraction at aqueous nitrate concentrations as high as 3 M, it was found necessary 10 include the Pitzer mixing parameter θ(NO3−,·TcO4−), whose value (0.0435 ± 0.(039) upon refinement was found to be the same for both extractants.The logKexchvalues for TcO4−/NO3−anion exchange were found to be 3.84 ± 0.01 for HEP+NO3+and 3.69 ± 0.01 for (heptyl)4N+NO3−indicating that the selectivity for TcO4−over NO3−is approximately the same for both extractants, This is consistent with the hypothesis, based on electrostatic principles, that the selectivity in the observed anion-exchange process is favored by the large (and comparable) sizes of the cationic extractants, However, our analysis suggests that a further increase in cation size would not significantly improve TcO4−/NO3−selectivity in chlorobenzene, though selectivity could be so increased in diluents of lower dielectric constant.

ISSN:0736-6299    

DOI:10.1080/07366299908934627

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Remarkable phenomenon that the extraction of lanthanide(III) (Ln) with thenoyltnfluoroacetone (Htta) in benzene is highly enhanced by the addition of inert mer-tris(8-quinolinolato)cobalt(III) (Co(q)3) has been found out. The effect of (Co(q)3) was ascribed to the formation of a 1:1 complex of Ln(tta)3with Co(q)3, i.e., a binuclear complex, in the organic phase on the basis of the extraction-equilibrium analysis. The formation constants determined for La(tta)3. Eu(tta)3and Lu(tta)3with Co(q)3were as high as 104.96104.56and 104.97respectively. Furthermore, in the spectrophotometric study, not only the hypsochromic shift of the ligand absorption band of Co(q)3but an isosbestic point were observed by increasing the concentration of Ln(tta)3in benzene. The formation constants of the binuclear complexes were also determined spectrophotometrically and confirmed to be comparable with those obtained by the extraction method.

ISSN:0736-6299    

DOI:10.1080/07366299908934628

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

To design a new solvent extraction process, one needs to measure distribution ratios for the various components in the feed solution, determine the key components, and then develop a process flowsheet based on the criteria for the separation of the key components. By following a set of design rules based on the extraction factor and starting with the distribution ratios, we show how to develop the process flowsheet. These rules can also be used to determine the optimum organic-to-aqueous flow ratio and assess whether any of the components will be trapped (pinched) in the process.

ISSN:0736-6299    

DOI:10.1080/07366299908934629

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Resins having two types of ligands: guanidine and aminoguanidine on copolymers of vinylbenzyl chloride (VBC)/ methyl methacrylate (MM)/ divinylbenzene (DVB) and on styrene (S)/DVB have been investigated in respect to their selectivity towards dicyanoaurate anions Resins coded CH and CP displayed high selectivity and sorption of gold from its diluted solution. They sorbed 10 - 11 mg of gold/g and dicyanoaurate distribution coefficient reached 1890 and 2290, respectively. Resins have the following selectivity order when sorption was carried out from solution of 5.08 mg Au/dm3: resin U-BIS Zn>Ag>Au>Cu; resin CP Au>Zn»Cu»Ag; resin CH Au>Zn=Ag»Cu. Resins have weak affinity towards iron complexes.

ISSN:0736-6299    

DOI:10.1080/07366299908934630

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Spherically granulated sodium aluminosilicophosphate (APS) of the empirical formula Na4Al4PS18O46.518H2O was synthesized by a gel method. The APS was characterized by elemental analysis, X-ray diffraction, TGA and27AI,28Si and31P MAS NMR spectroscopy methods. Ion exchange of alkali, alkaline earth and some other divalent metal cations by APS was studied in batch conditions. It was found that the APS has a cation exchange capacity of 2.5 meq/g and exhibits rapid kinetics of ion exchange. The ion exchange isotherms of alkali, alkaline earth and some other divalent cations were determined and the corrected selectivity coefficients as a function of metal loading were analyzed. It was found that APS exhibits a high affinity for cesium ion, a moderate affinity for some heavy metal cations (Pb2+, Zn+) and a low affinity for alkali and alkaline earth metal ions. A testing of the APS in complex solutions suggests that it could be a promising exchanger for treatment of some specific nuclear waste and contaminated environmental and biological liquors from radioactive cesium and toxic heavy metal ions.

ISSN:0736-6299    

DOI:10.1080/07366299908934631

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Two novel metastable sodium niobium silicates of the empirical formula: Nal+x−yHy(Nb1−xSix)O3nH2O, where x=0.33−0.38, y<l+x, n=0,7-l.l (NbSi-Na, 6.0 Å phase), and Na3-xHxNb3Si2O13nH2O, where x<1.5, n=2.5−3.5 (NbSi-Na, 12.6 Å phase), and two novel potassium niobium silicates: K4−xHxNb4SijO22nH2O, where x<l, n=3.5-4.0 (NbSi-K., 10.0 Å phase), and K1−xHxNbSi4O11nH2O, where x<0.2, n=0.4-0.5 (NbSi-K, 6.05 Å phase), were synthesized in the homogeneous alkaline reaction system NbCl5- SiO2- NaOH (KOH) -H2O2- H2O under mild hydrothermal conditions. The compounds were characterized by elemental analysis, FTIR, TGA, MAS29Si NMR and X-ray diffraction. It was found that alkali metal niobium silicates have open framework structures. Their ion exchange affinity towards alkali, alkaline earth and some transition metal ions was studied. All alkali metal niobium silicates are moderately acidic ion exchangers. Both sodium niobium silicates show a distinct affinity for Cs+ion among alkali metal ions, whereas potassium niobium silicate, the NbSi-K, 10.0 Å phase, exhibits affinity for Rb+ion. The affinity of the sodium niobium silicate, NbSi-Na, 6.0 Å, toward strontium ion in neutral solutions is equal or superior to the best Sr-selective inorganic ion exchangers. The sodium niobium silicate (NbSi-Na, 12.6 Å phase) exhibits extremely high affinity for Pb2+ion in acidic and neutral media, and both sodium niobium silicates also show a moderate affinity for Hg2+ion in neutral and highly alkaline media. These exchangers could be promising for the treatment of some specific nuclear waste and contaminated environmental and biological liquors containing lead, mercury and radioactive strontium.

ISSN:0736-6299    

DOI:10.1080/07366299908934632

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor