A new hydrometallurgical process for extracting rare earths from apatite using solvent extraction with P-350

In this paper, a new process is proposed to recover rare earths from nitric acid leaching of apatite without interfering with the normal route for fertilizer production using solvent extraction with dimethyl heptyl methyl phosphonate CH3P(O)(OC8H17)(2) (P-350, B). In the present work, the leaching conditions are studied. In selected condition, apatite was dissolved in 20% (v/v) nitric acid solution at 60-70 degrees C while agitating. The most suitable acidity for extraction is 0.4 M HNO3. More than 98% of rare earths in apatite can be recovered using countercurrent extraction process with six stages when phase ratio = 0.5, and defluorination is unnecessary. The influences of phase ratio, stage number, acidity and salting-out agent on extractabilities Of P-350 are studied. The results show that rare earths can be separated with P-350 from Ca, P, Fe and other impurities. Mixed rare earth oxides (REO) of which purity is more than 95% with yield over 98% can be obtained.

The extraction of rare earths using mixtures of acidic phosphorus-based reagents or their thio-analogues

The solvent extraction of rare earths from chloride solution has been investigated using mixtures of 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (HEHEHP, P507) and organophosphorus acids [di-(2-ethylhexyl)phosphoric acid (HDEHP, P204), isopropylphosphonic acid 1-hexyl-4-ethylocryl ester (HHEOIPP), bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272), bis(2,4,4-trimethylpentyl)monothiophosphinic acid (Cyanex 302), and bis(2,4,4-trimethypentyl)dithiophosphinic acid (Cyanex 301)]. Results show that the extractability of the selected extractants for rare earths decreases in the order: HEHEHP/HDEHP > HEHEHP/Cyanex 301 > HEHEHP/HHEOIPP > HEHEHP/Cyanex 302 > HEHEHP/Cyanex 272. A possible explanation of the different extractabilities is given based on the structure of the extractants. Furthermore, the possibilities of the separation of adjacent rare earths with these mixtures were investigated according to the extractabilities; the results show the possibility of separating the rare earths.

Studies on the synergistic extraction of rare earths with a combination of 2-ethylhexylphosphonic mono-2-ethylhexyl ester and trialkylphosphine oxide

The synergistic extraction of rare earths (La, Nd, Gd, Y and Yb) with a mixture of 2-ethylhexyl 2-ethylhexylphosphonate (EHEHPA) (HA) and trialkylphosphine oxide (Cyanex 923) (B) from a hydrochloride medium was investigated. The mixed system significantly enhances the extraction efficiency for lighter lanthanides and the synergistic enhancement coefficients for La (4.52), Nd (3.35), Gd (2.08), Y (1.31) and Yb (1.08) decrease with decreasing ionic radius of the rare earths. The extraction equilibrium of La, Nd and Gd indicate that La and Nd were extracted as MA(3)(.)B, whereas Gd was extracted as Gd(OH)A(2)(HA)(2)B-.. The equilibrium constants, thermodynamic functions such as Delta G, Delta H and Delta S and formation constants of the extracted species were determined. The stripping properties were also studied.

Synergistic extraction of rare earths(III) from chloride medium with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 and di-(2-ethylhexyl)-2-ethylhexylphosphonate

The synergistic effect of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 (HPMBP, HA) and di-(2ethylhexyl)-2-ethylhexylphosphonate (DEHEHP, B) in the extraction of rare earths (RE) from chloride solutions has been investigated. Under the experimental conditions used, there was no detectable extraction when DEHEHP was used as a single extractant while the amount of RE(III) extracted by HPMBP alone was also low. But mixtures of the two extractants at a certain ratio had very high extractability for all the RE (III). For example, the synergistic enhancement coefficient was calculated to be 9.35 for Y3+, and taking Yb3+ and Y3+ as examples, RE3+ is extracted as RE(OH)A(2).B. The stoichiometry, extraction constants and thermodynamic functions such as Gibbs free energy change Delta G (-17.06kJmol(-1)), enthalpy change Delta H (-35.08kjmol(-1)) and entropy change Delta S (-60.47JK(-1)mol(-1)) for Y3+ at 298 K were determined. The separation factors (SF) for adjacent pairs of rare earths were calculated. Studies show that the binary extraction system not only enhances the extraction efficiency of RE(III) but also improves the selectivity, especially between La(III) and the other rare earth elements.

Extraction of rare earths(III) from nitrate medium with di-(2-ethylhexyl) 2-ethylhexyl phosphonate and synergistic extraction combined with 1-phenyl-3-methyl-4-benzoy l-pyrazolone-5

The extraction of trivalent rare earths ( RE) from nitrate solutions with di-(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP, B) and synergistic extraction combined with 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP, HA) were investigated. The extraction distribution ratios demonstrate a distinct "tetra effect," and Y lies between Tb and Dy when DEHEHP is used as a single extractant for RE. According to the corresponding separation factors (SF12) for adjacent pairs of rare earths, it could be concluded that DEHEHP could be employed for the separation of La from the other rare earths, and Y from light rare earths. The present work has also found that mixtures of HPMBP and DEHEHP have an evident synergistic effect for RE(III). Taking Y( III) as an example, a possible synergistic extraction mechanism is proposed. The enhancement of extraction in the binary system can be explained due to the species Y(NO3) (.) A(2) (.) HA (.) B formed. The synergistic enhancement coefficients ( R), extraction constants, formation constants and thermodynamic functions of the reaction were calculated.

Mechanism of phase transformation and formation of barium hexaferrite doped with rare-earths in sol-gel process

The phase-transformation in sol-gel preparation of barium hexaferrite and the formation of barium hexaferrite doped with La3+ Were studied by chemical phase analysis, X-ray diffraction and infrared spectrometry analysis. The experimental results show that phase transformation reactions of FeCO3, Fe2O3 and BaFe2O4, barium hexaferrite and gamma-Fe2O3 take place in the heat treatment of gel. While the doping lanthanide ion replace barium ion, an equivalent quantity of Fe3+ are reduced to Fe2+ to maintain the charge equilibrium.

AFM studies of DNA structures on mica in the presence of alkaline earth metal ions

As counterions of DNA on mica, Mg2+, Ca2+, Sr2+ and Ba2+ were used for,clarifying whether DNA molecules equilibrate or are trapped on mica surface. End to end distance and contour lengths were determined from statistical analysis of AFM data. It was revealed that DNA molecules can equilibrate on mica when Mg2+, Ca2+ and Sr2+ are counterions. When Ba2+ is present, significantly crossovered DNA molecules indicate that it is most difficult for DNA to equilibrate on mica and the trapping degree is different under different preparation conditions. In the presence of ethanol, using AFM we have also observed the dependence of B A conformational transition on counterion identities. The four alkaline earth metal ions cause the B-A transition in different degrees, in which Sr2+ induces the greatest structural transition.

Extraction mechanism of rare earths with sec-octylphenoxy acetic acid by two-phase titration technique

The compositions of the extracted complexes of La, Gd, Er and Y with sec-octyl-phenoxy acetic acid in heptane and the related apparent extraction equilibrium constants K-M were determined using two-phase titration technique. The stoichiometric compounds for La, Gd, Er and Y should be LaA(3) . 2.5HA, GdA(3) . 3HA, ErA(3) . 3.1HA and YA(3) . 4.3HA respectively. And their pK(M) are 3.43, 3.46, 3.08 and 2.58 respectively.

Preparation of borates doped with divalent rare earth ions (RE2+) in air and spectroscopy of divalent rare earth ions (RE2+ = Sm, Eu, Tm, Yb)

The spectroscopic feature of divalent Sm2+, Eu2+, Tm2+ and Yb2+ is discussed in this paper. Especially the spectroscopic properties of some berates containing tetrahedral BO4 group such as SrB4O7, SrB6O10 and BaB8O13 doped with these divalent ions are reported. When the divalent alkaline earth ion in these berates is replaced partially by the above trivalent rare earth ion, the charge carried in the produced defects can be used as reductant to reduce the doped rare earth ion into divalent state at high temperature even in air. Therefore, a convenient and safe method is provided to prepared phosphors doped with these divalent rare earths.

The electrical and magnetic properties of lanthanide alkaline-earth transition-metal oxides

Five Ln(2)SrMCuO(6.5) oxides (M = Co, Ln = Y and Ho; M = Fe, Ln = Y, Ho, and Dy) were synthesized, and their crystal structures, IR spectra, and physical properties were studied. They have almost the same structure and crystallize in orthorhombic systems. Below room temperature, Y2SrFeCuO6.5, a known layered oxide, shows antiferromagnetic behavior, but the four new oxides are paramagnetic. Y2SrFeCuO6.5 fits the Curie-Weiss law in the temperature range 300-100 K, but Y2SrCoCuO6.5 shows complex magnetic behavior because of the disproportion of some Co+3 to Co+2 and Co+4 The five oxides are all p-type semiconductors in the measured temperature range and have large electrical resistivities at room temperature.

Luminescence and energy transfer between Ce3+ and Mn2+ in alkaline earth borates

The luminescence of Ce3+ and Ce3+, Mn2+ co-doped BaB8O13 and SrB4O7 prepared in air is studied. The results show that tetravalent cerium ion can he reduced to trivalent state in the hosts and gives rise to efficient luminescence. Energy transfer between Ce3+ and Mn2+ is possible. Mn2+ ions can be efficiently sensitized by Ce3+ and exhibit green and red emissions which implied that Mn2+ occupied the crystallographic sites of cations and boron sites of the anoins, respectively. The intensity ratio of red to Been emission in matrix increases with the increasing of manganese concentration.

Main-chain photosensitive polyamic acids using alkaline aqueous solution as developer

In order to develop photosensitive polyimides (PSPIs) imaged in alkaline aqueous solution, a photosensitive diamine and relevant polymer containing conjugated double bonds in the main chain have been synthesized. The photosensitive characteristics and thermal stability of the polymers were investigated. These polymers possess good thermal stability and sensitivity to UV irradiation, and could be used to form a PSPI resist using alkaline aqueous solution as developer. (C) 1999 Society of Chemical Industry.

Luminescence and its temperature effects on Sm2+ in alkaline earth borates

The luminescence of Sm2+ in alkaline earth berates (BaB8O13, SrB4O7 and SrB6O10) is reported. The temperature effects on luminescence and decay time of Sm2+ are studied. Due to the thermal population, D-5(1) --> F-7(J) transitions of Sm2+ in BaB8O13, SrB4O7 and SrB6O10 are observed at room temperature. The f-d broad emission transitions of Sm2+ in SrB4O7 and SrB6O10 are observed at high temperature whereas no f-d transition is observed in BaB8O13.

Classification of valence changes of trivalent rare earth ions in alkaline earth borates using artificial neural networks

The investigations of classification on the valence changes from RE3+ to RE2+ (RE = Eu, Sm, Yb, Tm) in host compounds of alkaline earth berate were performed using artificial neural networks (ANNs). For comparison, the common methods of pattern recognition, such as SIMCA, KNN, Fisher discriminant analysis and stepwise discriminant analysis were adopted. A learning set consisting of 24 host compounds and a test set consisting of 12 host compounds were characterized by eight crystal structure parameters. These parameters were reduced from 8 to 4 by leaps and bounds algorithm. The recognition rates from 87.5 to 95.8% and prediction capabilities from 75.0 to 91.7% were obtained. The results provided by ANN method were better than that achieved by the other four methods. (C) 1999 Elsevier Science B.V. All rights reserved.

In situ UV-vis and CD thin-layer spectroelectrochemistry study of the electrochemical behavior of L-noradrenaline in alkaline solution

Electrochemical redox behavior of noradrenaline in alkaline solution on a glassy carbon electrode has been investigated by in situ UV-vis and CD spectroelectrochemistry by using a long optical path thin-layer cell. The experimental data were processed by using a double logarithmic method of analysis together with nonlinear regression which confirmed that the first step in both the oxidation of noradrenaline and reduction of noradrenochrome is a two-electron irreversible process governed by an EE mechanism. The kinetic parameters of the electrode reactions, i.e., charge transfer coefficient and the number of electrons transferred, alpha(1)n(1) = 0.11 and alpha(2)n(2) = 0.23, formal potentials modified with kinetics, E-1(0') = 0.65 (+/- 0.01) V and E-2(0') = 0.72V and standard rate cnstants, k(1)(0) = 7.0(+/-0.5)x10(-5) cm s(-1), for the first and second steps in the oxidation process of noradrenaline, and similarly, alpha(1)n(1) = 0.33, alpha(2)n(2) = 0.58, E-1(0') = 0.37(+/-0.01) V, E-0' = -0.25 (+/-0.01) V and k(1)(0) approximate to k(2)(0) = 1.06 (+/-0.05)x10(-4) cm s(-1) for the first and second steps in the reduction process of noradrenochrome were also determined.