Evaluation of a sequential extraction for the speciation of thorium in soils from Baotou area, Inner Mongolia

Sequential extraction procedures were widely applied for speciation of radioactive elements. In this study, the sequential extraction procedure developed by Martinez-Aguirre was employed for quantification of different chemical forms of thorium in the soil. The total amount of thorium in contaminated soil was much higher by four-fold than the local background value. The soil properties affect the amount of thoriurn and distribution of fractions in contaminated soil. Results showed that the proportion of thorium in soils from Baotou was found as the residual fraction (F5 + F6) > absorbed fraction (F3), coprecipitated fraction (F4) > carbonates fraction (172) and exchangeable fraction (F1) that could be available to plants. The recovery, calculated by ratio of the sum of the six fractions to the pseudo-total content of thorium, was in the range from 96% to 110%. A comparison was carried out between the sequential extraction and the single extraction to evaluate the selectivity of the extractants. It was found that the amount of thorium of absorbed fraction (H) was higher in the single extraction than that estimated in the sequential extraction, possibly duo to transform of the labile form. While for non-residual fraction analysis, the single extraction scheme was a desirable alternative to the sequential extraction procedure.

Liquid-liquid extraction of cerium(IV) from nitric acid media by di-(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP)

In this paper, the extraction of Ce(IV) from nitric acid solutions is investigated using di-(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP, B) in heptane as extractant. Ce(IV) can be extracted effectively from nitric acid solution, whereas it is poorly extracted from sulfuric acid solution. Compared with some other organophosphorus esters, DEHEHP has moderate extractablity for Ce(IV). The extraction efficiency varies with diluent in the order: aliphatic hydrocarbons > nitrobenzene > aromatic hydrocarbons > carbon tetrachloride > chloroform. Regeneration and loading capacities of DEHEHP have also been examined. Ce(IV) extraction in HNO3 solutions as well as extraction of HNO3 and H2O have been systematically studied. The Ce(IV) extraction increases with an increasing of HNO3 concentration and exhibits the maximum distribution ratio at 1-1.5 mol/L HNO3. Nitric acid, as a source of nitrate ion, enhances the extraction of metal ion. But it also competes with metal ions for extractant molecules by its own extraction under high acidities. The proposed extraction process is described by the following equilibrium equations

Electrooxidative polymerization of phenothiazine derivatives on screen-printed carbon electrode and its application to determine NADH in flow injection analysis system

The electrooxidation polymerization of phenothiazine derivatives, including azure A and toluidine blue 0, has been studied at screen-printed carbon electrodes in neutral phosphate buffer. Both compounds yield strongly adsorbed electroactive polymer with reversible behavior and formal potentials closed to 0.04 V at pH 6.9. The modified electrodes exhibited good stability and electrocatalysis for NADH oxidation in phosphate buffer (pH 6.9), with an overpotential of more than 500 mV lower than that of the bare electrodes. Further, the modified screen-printed carbon electrodes were found to be promising as an amperometric detector for the flow injection analysis (FIA) of NADH, typically with a dynamic range of 0.5-100 muM.

Kinetics of cerium(IV) extraction with DEHEHP from HNO3-HF medium using a constant interfacial cell with laminar flow

Studies of the extraction kinetics of cerium(IV) into n-heptane solutions of di(2-ethylhexyl)-2-ethylhexyl phosphonate DEHEHP from HNO3-HF solutions have been carried out using a constant interfacial cell with laminar flow. The experimental hydrodynamic conditions were chosen so that the contribution of diffusion to the measured rate of reaction was minimized. The data were analyzed in terms of pseudo-first order constants. The effects of the stirring rate, specific interfacial area, and temperature on the extraction rate showed that the most probable reaction zone is in the aqueous homogeneous phase. The results were compared with those of the system without HF. It was concluded that the presence of HF decreases the extraction rate of cerium. The addition of HF increases the activation energy for the forward reaction from 21.2 to 55.3 kJ/mol and for the reverse process from 57.9 to 79.0 kJ/mol. According to the experimental data correlated as a function of the concentration of the relevant species involved in the extraction reaction, the corresponding rate equation was deduced as follows:-d[Ce]/dt = k[Ce] center dot B-0.62 center dot HF-0.58 center dot [NO3-](0.57)

Three-phase extraction study in the Cyanex923-n-heptane/HNO3 system

The present paper reports a study of the extraction of HNO3 with Cyancx923 (C923)-n-heptane. A third phase appears at different aqueous HNO3 concentrations for various initial C923 concentrations. Data analysis indicates that almost all of HNO3 and H2O are extracted into the middle phase. More HNO3 and water at a fixed ratio are solubilized in the reverse micelles or microemulsion in the third phase, which leads to a sharp increase of their concentration. The effect of temperature on the phase behavior of the three-phase system has also been investigated.

Separation of heavy rare earth elements with extraction resin containing 1-hexyl-4-ethyloctyl isopropylphosphonic acid

This paper presents the results of the adsorption of heavy rare earth ions (Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), Lu(III) and Y(III)) from hydrochloric acid solutions at 30 degreesC by the extraction resin containing 1-hexyl-4-ethyloctyl isopropylphosphonic acid (HEOPPA), which has higher steric hindrance, higher selectivities and lower extraction and stripping acidity than di(2-ethylhexyl)phosphoric acid (DERPA) or 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH/EHP). The dependence of acid concentration, flow rate and amounts of rare earth ions sorbed on the separation of Er-Tm, Tm-Yb and Er-Tm-Yb mixtures has been studied. The baseline chromatographic separation of Er-Tm-Yb mixture has been observed. Satisfactory results with purity and yield of Tm2O3>99.71% and >71.25%, Er2O3>99-81% and >94.17%, and Yb2O3>99.74% and >89.83%, respectively, have been obtained. The parameters such,as resolution, separation factors and efficiencies have been determined as a function of acidity, loading of rare earth elements and flow rates. The stoichiometry of the extraction of rare earth ions has been suggested as well.

Three-phase extraction study of Cyanex 923-n-heptane/Ce4+-H2SO4 system

Phase behavior of the extraction system, Cyanex 923-heptane/Ce4+-H2SO4 has been studied and compared with Cyanex 923-heptane/H2SO4 System. Cerium(IV) is mainly extracted into the third phase, and its concentration in the third phase first increases with the increasing aqueous acid concentration, reaches maximum and then decreases. At higher acidity, cerium(IV) is hardly extracted in the third phase. The phase behavior and change of the contents of acid and water are similar to those in the acid system. The acid concentration increases with increase of the aqueous acid in the whole extraction region while the water content first decreases with it and then increases after the third phase formation. The third phase has a characteristic lamellar structure formed by the aggregates of Cyanex 923 (.) (H2SO4)(2) (.) H2O as those in the case of acid system. The third phase loaded Ce(IV) has been used to prepare ultrafine CeO2 powder conveniently by precipitation with oxalic acid, and powders with size mostly smaller than 100 nm can be obtained.

SOLVENT-EXTRACTION OF TERBIUM(III,IV) PERIODATE COMPLEXES WITH QUATERNARY AMINE

The differences between the solvent extraction of Tb(III) and Tb(IV) periodate complexes with quaternary amine were studied carefully for the first time. The effects of extractant concentration, phase ratio, the pH value of stock solution, salting-out agent, extractant form, diluent, and extraction time were comprehensively investigated. Under optimal conditions the separation factor between Tb(IV) and Tb(III) periodate complexes is over 5.5.

ELECTROCATALYTIC OXIDATION AND FLOW-INJECTION DETERMINATION OF REDUCED NICOTINAMIDE COENZYME AT A GLASSY-CARBON ELECTRODE MODIFIED BY A POLYMER THIN-FILM

G chemically modified electrode (CME) was prepared by electrochemical copolymerization of pyrrole and Methylene Blue. The resulting CME exhibits effective electrocatalytic activity towards the oxidation of reduced nicotinamide coenzymes (NADH and NADPH),

AN EXPERT SYSTEM FOR SOLVENT-EXTRACTION OF RARE-EARTHS

An expert system for solvent extraction of rare earths has been developed using LISP. The goal of this project was to mimic the chemists' inferential abilities to assist in the process of solvent extraction of rare earths. The system includes frequently used extractants, separation of specific rare earths, recommendation of procedures for the separation of mixtures of rare earths using (2-ethylhexyl)phosphonic acid 2-ethylhexyl monoester, selection of parameters for counter-current extraction and methods for evaluation of the technique, and the economics of the processing. The expert system runs on an IBM-PC/XT.

Ontogenetic development of digestive enzymes and effect of starvation in miiuy croaker Miichthys miiuy larvae

The ontogenetic development of the digestive enzymes amylase, lipase, trypsin, and alkaline phosphatase and the effect of starvation in miiuy croaker Miichthys miiuy larvae were studied. The activities of these enzymes were detected prior to exogenous feeding, but their developmental patterns differed remarkably. Trypsin activity continuously increased from 2 days after hatching (dah), peaked on 20 dah, and decreased to 25 dah at weaning. Alkaline phosphatase activity oscillated at low levels within a small range after the first feeding on 3 dah. In contrast, amylase and lipase activities followed the general developmental pattern that has been characterized in fish larvae, with a succession of increases or decreases. Amylase, lipase, and trypsin activities generally started to increase or decrease at transitions from endogenous to exogenous feeding or diet changes, suggesting that these enzymatic activities can be modulated by feeding modes. The activities of all the enzymes remained stable from 25 dah onwards, coinciding with the formation of gastric glands and pyloric caecum. These results imply that specific activities of these enzymes underwent changes due to morphological and physiological modifications or diet shift during larval development but that they became stable after the development of the digestive organs and associated glands was fully completed and the organs/glands functioned. Trypsin and alkaline phosphatase were more sensitive to starvation than amylase and lipase because delayed feeding up to 2 days after mouth opening was able to adversely affect their activities. Enzyme activities did not significantly differ among feeding groups during endogenous feeding; however, all activities were remarkably reduced when delayed feeding was within 3 days after mouth opening. Initiation of larvae feeding should occur within 2 days after mouth opening so that good growth and survival can be obtained in the culture.

Sedimentation rates and provenance analysis in the Southwestern Okinawa Trough since the mid-Holocene

As a high-sedimentation rate depocenter along the path of the Kuroshio Current, the southwesternmost part of the Okinawa Trough is a key area to understand the Kuroshio history and sediments transportation. A 34.17-m-long sediment core was obtained by the advanced piston corer of Marco Polo/IMAGES XII MARION DUFRESNE during the May 2005 from the Southern Okinawa Trough at site MD05-2908. The recovered sediments were analyzed by AMS C-14 dating, coarse size fraction (> 63 mu m) extraction and moisture content determination in order to study its sedimentation flux and provenance. The depth-age relationship of core MD05-2908 was well constrained by 17 C-14 dating points. The sediments span across the mid-Holocene (6.8 ka B.P.) and have remarkablely high sedimentation rates between 1.8 and 21-2 m/ka, which is well consistent with the modern observations from sediment traps. We identified five 70-200 a periods of abnormally rapid sedimentation events at 6790-6600 a B.P., 5690-5600 a B.P., 4820-4720 a B.P., 1090-880 a B.P., and 260-190 a B.P., during which the highest sedimentation rate is up to 21-2 m/ka. In general, the lithology of the sediments were dominated by silt and clay, associated with less than 5% coarse size fraction (a parts per thousand << 63 mu m). As the most significant sediment source, the Lanyang River in northeastern Taiwan annually deliver about 10Mt materials to the coastal and offshore region of northeast Taiwan, a portion of which could be carried northward by currents toward the study area. Therefore, we concluded that the 5 abnormally rapid sedimentation events may be related to intensified rainfall in Taiwan and thus increased materials to our study area at that time. However, a few extreme-rapid sedimentation events cannot be explained by normal river runoff alone. The large earthquakes or typhoons induced hyperpycnal discharge of fluvial sediment to the ocean may also act as a potential source supply to the Okinawa Trough.

Nonvolatile photorefractive holograms in LiNbO3 : Cu : Ce crystals

We report experimental and theoretical studies of nonvolatile photorefractive holographic recording in LiNbO3:Cu:Ce crystals with two illumination schemes: (1) UV light for sensitization and a red interfering pattern for recording and (2) blue light for sensitization and a red pattern for recording. The results show that the oxidized LiNbO3:Cu:Ce crystals can provide high, persistent refractive-index modulation with weak lightinduced scattering. The optimal working conditions and the prescription for doping and oxidation-reduction processing that yields the maximum refractive-index modulation are discussed. (C) 2000 Optical Society of America OCIS codes: 050.7330, 190.5330, 090.2900.

A wideband sensitive holographic photopolymer

A novel wideband sensitive dry holographic photopolymer sensitized by rose bengal (RB) and methylene blue (MB) is fabricated, the holographic storage characteristics of which are investigated under different exposure wavelengths. The result shows that the sensitive spectral band exceeds 200 nm in visible light range, the maximum diffraction efficiency under different exposure wavelengths is more than 40% and decreases with the decrease of exposure wavelength, the exposure sensitivity is not change with the exposure wavelength. This photopolymer is appropriate for wavelength multiplexing or multi-wavelength recording in digital holographic storage.

碱金属氟化物对掺Yb~(3+)氟磷酸盐玻璃析晶稳定性和光谱性质的影响

研究了碱金属氟化物对掺Yb3+氟磷玻璃的光谱性质和析晶稳定性能的影响。运用倒易法计算了Yb3+的发射截面。结果显示,LiF的引入对吸收和发射截面的提高作用较大并出现最佳引入量极值,其次为KF。碱金属氟化物的引入可提高二元体系的析晶稳定性能,使玻璃网络结构得到改善;拉曼光谱显示二元体系中引入YbF3后玻璃网络结构得到增强,而在引入碱金属氟化物的三元体系中掺杂YbF3后破坏了网络完整性,降低系统析晶稳定性能。