Uranium sorption from phosphoric acid solutions using selective ion exchange resins: Part II. Kinetic studies

Experiments have shown that the sorption of uranium from strong phosphoric acid solutions onto four D2EHPA/TOPO based ion exchange resins and one aminophosphonic acid resin is particle diffusion controlled in the uranium concentration range 42–780 μM. Interdiffusion coefficients of about 10^?12 m²s^?1 were obtained for D2EHPA/TOPO resins and 0.14 × 10^?12 m²s^?1 with the aminophosphonic acid exchanger at 20°C in 3 M H₃PO₄. Both homogeneous particle diffusion, based on Fick's Law, and the ash layer diffusion model fitted the kinetic measurements.     

The reaction of Cu(II) with LIX 65N in homogeneous solution

The nature of the complexes formed between Cu(II) and LIX 65N (H₂L) in ethanol has been studied by UV-visible spectrophotometry and the kinetics of the reaction between Cu(II) and H₂L by stopped-flow spectrophotometry at 25°C. The major complex, Cu(HL)₂, has a formation constant β₂ = [Cu(HL)₂]/[Cu][HL^?]² of log β₂ = 26.5 l² mol^?2 in 0.04 M NaClO₄. An additional complex, probably Cu(HL)⁺, can be detected in the absence of added NaClO₄. A third complex, identified as Cu₂(HL)₂²⁺, was observed at higher copper concentrations with formation constant K_d = [Cu₂(HL)₂]/[Cu(HL)₂][Cu] 1.7 × 10⁴ l mol^?1 in 0.04 M NaCIO₄. The rate of reaction of Cu(II) with H₂L to form Cu(HL)₂ obeys the rate equation, d[Cu(HL)₂]/d t = K_rate[Cu]¹[H₂L]¹[H⁺]⁰ where K_rate has the value of 2.9 × 10⁴ l mol^?1 s^-1 in the absence of added electrolytes.     

Etude spectrophotometrique de solutions aqueuses chlorurees de chlorure cuivreux,a concentrations elevees

The behaviour of CuCl was investigated from 10^?3M up to quasi saturation by absorption spectrophotometry between 200 and 1000 nm, in aqueous solutions of (NaCl + HCl), 1 to 5 M, at pH 0 and 25°C. The spectra show a shoulder at 230–235 nm and two bands, respectively at 195–215 nm and at 273–290 nm (273 to 275 nm for solutions of up to 4 M Cl^? and 5 M Cl^? solutions with (CuCl) < 0.6 M, and 275 to 290 nm for 5 M Cl^? solutions with (CuCl) < 0.6 M. The shoulder corresponds to the complex ion CuCl₂^?; the band at 273–275 nm to the complex ion CuCl₃^2? and the one at 275–290 nm to the stepwise formation of the dinuclear complex ion Cu₂Cl₄^2?. The equilibrium constant for the reaction CuCl₂^? + Cl^? ?CuCl₃^2? was determined to be 0.45. At 273–275 nm, the Lambert-Beer law is satisfied for all concentrations of dissolved copper up to quasi saturation when the Cl^? (Na⁺ + H⁺) concentration does not exceed 4 M. A diagram showing the concentrations of the complex copper species in terms of CuCl and (NaCl + Hcl) concentrations has been established.     

Colorimetric estimation and some physicochemical properties of purified Cyanex 272

A technique for the colorimetric estimation of purified Cyanex 272 has been developed. The technique consists of the digestion of pure sample or its aqueous solution with concentrated nitric acid (70%)–perchloric acid (70%) mixture for 1 h. The oxidizing mixed acid quantitatively converts Cyanex 272 to a clear solution of orthophosphate that can be easily estimated by the molybdenum-blue colorimetric method at 830 nm. The method is sensitive with a molar extinction coefficient of ∼2.6×10⁴ and reproducible within ±2%. Applying this technique of analysis, the dimerization constant (K₂), distribution or partition coefficient (K_d) and ionization constant (K_a) of the purified Cyanex 272 (bis-2,4,4-trimethylpentylphosphinic acid, BTMPPA) have been estimated to be 190, 53 and 5.52×10⁻⁴, respectively.     

The influence of strain amplitude on the transient current behaviour in corrosion fatigue of Fe-26Cr-1Mo

Corrosion fatigue damage and its electrochemical characteristics of high purity ferritic stainless steel (Fe-26Cr-1Mo) under symmetrical tension and compression strain control have been investigated in 1M H₂SO₄ and 3.5 % NaCl solution by using three-electrode technique at imposed passive potential. The tests were carried out at the total strain amplitudes of 4 × 10^?3, 8 × 10^?3, 1.0 × 10^?2 and 1.2 × 10^?2. The effects of the strain amplitude on the electrochemical dissolution and plastic deformation on the surface were studied particularly. At low strain amplitude (Δε_t = 4 × 10^?3), the passivity-maintaining current was small and stable because of the small slip activity. The maximum current at the tensile half cycle, l_t^p, was always bigger than l_c^p, or sometimes equal to l_c^p, the maximum current at the compressive half cycle in 3.5 % NaCl. At high strain amplitude (Δε_t = 1.2 × 10^?2), the enhanced deformation on the surface induced the increasing dissolution. The increasing anodic current reflects the breakdown of the surface film, and only one current peak occurs within one cycle. At intermediate strain amplitude (Δε_t = 8 × 10^?3), the current behaviour was very stable after cyclic hardening in 3.5%, NaCl, but periodical jumpings of current during cycling were observed in the saturation region in 1 M H₂SO₄.     

Polymeric pseudocrown ethers. III. The complexation with iron(III) in phosphoric—hydrochloric acid mixtures

Polymeric pseudocrown ethers, incorporating oxyethylene and oxypropylene units, extract FeCl₄^? from mixed hydrochloric and phosphoric acids. The complexation depends on hydrochloric acid concentration and becomes efficient when the HCl concentration exceeds 4 M. The regeneration of the polymers is accomplished with water. Column tests have been shown to separate iron very efficiently from phosphoric acid, which is recovered quantitatively. In comparison, Amberlyst A-21, a weak-base anion exchanger, shows affinity for phosphoric acid, making the separation between iron and phosphorus difficult.     

Kinetics of dissolution of synthetic heazlewoodite (Ni3S2) in nitric acid solutions

The dissolution rate of heazlewoodite in nitric acid solution has been determined. The effects of nitric acid concentration, temperature, particle size, stirring intensity and addition of Cu²⁺ ions have been investigated. Solid residues after leaching were examined by SEM, X-ray diffraction and chemical analysis. In the solutions containing less than 2.0 M HNO₃, dissolution was observed to be completely inhibited after 30 min leaching time, and the rate of hydrogen sulphide production was faster than its oxidation to S⁰ and HSO₄^?. In 3 M HNO₃, an abrupt increase in dissolution rate of Ni₃S₂ was found. Two different regions of the dissolution of heazlewoodite were observed below and above 50°C. At temperatures below 50°C, the dissolution rate was very slow, even in 3.0 M HNO₃ solution, and H₂S gas was evolved. Above 50°C, the dissolution rate rapidly increased. Over the temperature interval 60–90°C in 3.0 M HNO₃ dissolution followed a linear rate law, and the activation energy was found to be 42.1 kJ mol^?1. Most of the oxidized sulphide ion was found in the solution as sulphate. The leaching rate was independent of stirring speed. The rate-controlling step of the Ni₃S₂ dissolution is the oxidation of hydrogen sulphide to elemental sulphur or sulphate ions on the Ni₃S₂ surface. Addition of small amounts of Cu²⁺ ions to the nitric acid acted as catalyst for the dissolution of Ni₃S₂. Bubbling air through the leach suspension increased the dissolution rate of Ni₃S₂ in solutions containing less than 2.0 M HNO₃.     

Temperature dependent behaviors of electro-elastic properties of NdCa4O(BO3)3 crystal with monoclinic symmetry

Rare-earth calcium oxyborate crystals (RECa₄O(BO₃)₃, RECOB, RE: rare-earth elements) are a kind of multifunctional crystal materials. In this work, the temperature dependent behaviors of the electro-elastic constants of NdCOB crystal were investigated over the temperature range of –80–200 ℃, and their temperature coefficients were evaluated. It is found that NdCOB crystal possesses minimal variation of relative dielectric permittivities (<3%). The temperature coefficient of frequency for ZY cut with width shear vibration mode is in the order of 0.07 × 10^?4/℃. The temperature coefficients of the elastic compliances are obtained to be in the range of ?33.0 × 10^?4/℃–32.2 × 10^?4/℃. Particularly, the s₄₄ and s₆₆ were found to show low temperature coefficients of the elastic compliances, i.e. 1.0 × 10^?4/℃ and ?0.4 × 10^?4/℃, respectively, indicating the existence of zero temperature coefficient of frequency crystal cut. Furthermore, the electromechanical coupling factors and piezoelectric coefficients as a function of temperature were studied. The electromechanical coupling factor k₂₆ and piezoelectric coefficient d₂₆ are determined to be ～30.8% and ～15.2 pC/N at room temperature, respectively. The large piezoelectric response and zero temperature coefficient of frequency indicate the potential usage of NdCOB crystal for piezoelectric frequency devices over a wide temperature range.     

The effect of grain size and cross-head velocity on the lower yield strength during inhomogeneous discontinuous yielding in iron and steel

The validity of the relation, \(\underline {Ag} \) , has been checked with experimental results on the lower yield strength, σ _aF of various irons and steels determined at room temperature over wide ranges in cross-head velocity,V _c, and grain boundary intercept or grain diameter,l. Good agreement was found with the proposed relation form ^*=4, wherem ^* is the dislocation velocity-effective stress exponent, and α=1/3. σ _i , the internal stress, ranged between 5000 and 13,000 psi andN ^αθK’ between 4.3×10^?15 and 19.3×10^?15. In the original relation, the value of α was one andK’ was given asK, which was assumed to be a material constant. The modification which became necessary indicates that possibly the density of mobile dislocations and/or the resistance of grain boundaries to propagating Lüder’s bands depend on Lüder’s band velocity and strain. The validity of the relation at very high and very low cross-head velocities or strain rates is discussed. The relation should apply in an intermediate range of cross-head or dislocation velocities wherem ^* should remain constant and should show an apparent decrease at both higher and lower velocities. The basis for this prediction is discussed and results are presented at low strain rates.     

Polymeric pseudocrown ethers. II. Complexation with acids in aqueous and organic solvents

A macroreticular polystyrene incorporating polyoxyethylene (14) units (Pseudocrown-14) was shown to complex strongly with both protic and Lewis acids. The distribution coefficients depend on the dielectric constant of the solvent. In non polar organic solvents such as benzene or chloroform, the capacity of the polymer for acid reaches the theoretical value of 13.60 mmole hydrogen ions per gram polymer. Column tests have shown that the polymers can be used to reduce acidity in solutions to 10^?4M or less, and that the polymers can be fully regenered using polar solvents such as methanol or water. The comparison of HBr complexation with pseudocrown-14 and linear or macrocyclic ethers, shows that pseudocrown-14 behaves similarly to a macrocyclic crown ether.     

Absorption behavior of lattice oxygen in Ce_(0.8)Y_(0.2)O_(2-δ) at intermediate temperature

The absorption behavior of lattice oxygen for Ce_(0.8)Y_(0.2)O_(2-δ)(YDC) crystal was investigated. Combined with TG-DSC, XRD, Raman and XPS characterization, lattice oxygen absorption occurs at intermediate temperature(from 500 to 800 ℃),which is related to the oxygen vacancies consumption,and no phase change is observed in this process. In electric conductivity relaxation(ECR) experiment, prolonged oxygen diffusion process is observed above 600 ℃, which may be caused by oxygen absorption process. And through ECR experiments,the bulk diffusion coefficient D_(chem) and surface exchange coefficient K_(ex) for YDC dense sample are measured as 6,5×10~(-5)-2×10~(-4)cm~2/s and K_(ex)=2×10~(-4)-9×10~(-4)cm/s at intermediate temperature range.     

The influence of growth rate and temperature on high cycle fatigue of Al−Al3Ni

High-cycle fatigue tests have been conducted on specimens of an Al?Al₃Ni eutectic alloy, unidirectionally solidified at selected rates from 1.39×10^?4 cm/s to 0.3 cm/s. Tests were conducted in air at 298, 458 and 683 K. Room temperature fatigue lives were independent of growth rate at low solidification rates (1.39×10^?4–8.33×10^?3 cm/s, but were markedly improved in samples grown at 0.3 cm/s. Materials grown at 8.33 × 10^?3 cm/s exhibited fatigue lives similar to those of the lower growth rates, despite gross misalignment due to cellular growth. At 0.5T _m (458 K) and 0.75T _m (683 K), the fatigue lives of the material grown at low solidification rates were dependent on growth rate. The dependence of fatigue life on growth rate at elevated temperatures appears to be due primarily to differences in cyclic creep rates as a result of varying interfiber spacings. Crack initiation and propagation mechanisms were established by metallographic and fractographic examination. Dislocation substructure-fiber interactions were studied by transmission electron microscopy.     

Removal of iron and formation of copper(i) from solutions containing iron(ii) and copper(ii) by addition of chloride ion or acetonitrile

Solutions of Cu(II) and Fe(II) establish the redox equilibrium

$\text{Cu(II) + Fe(II)}\text{?}\text{K}\text{Cu(I) + Fe(III)}$

which is displaced to the right by addition of either Cl^? or acetonitrile (AN). Log K varies from ?10.5 in water to about ?2.5 in 4 M NaCl or AN, allowing iron to be removed selectively from copper (II) solutions either by solvent extraction with Versatic acid or by precipitation as goethite or j jarosite. To establish the required conditions Eh-pH diagrams have been developed for the CuH₂OCl and CuH₂OANSO₄²-systems at 25°C and 90°C. It is demonstrated that the catalytic effect of Cu(II) on the oxidation of Fe(II) to Fe(III) by O₂ is dependent on the concentration of Cl^? or AN and on the position of this redox equilibrium. Applications to removing iron from hydrometallurgical solutions are discussed and tested.     

Dislocation Structures in a Cyclically Deformed Single-Slip-Oriented Fe-35?wt?pct Cr Alloy Single Crystal Containing Fine Cr-Rich Precipitates

The dislocation structures induced by the cyclic deformation of a $ [\bar{1}49] $ single-slip-oriented Fe-35?wt?pct Cr alloy single crystals containing fine Cr-rich precipitates have been studied by transmission electron microscopy (TEM) over the plastic strain amplitude ?? _pl range of 5?×?10^?4 to 5?×?10^?3. Persistent slip bands (PSBs) with different structures, such as ladder-like structure, irregular ladders, elongated cells, etc., were observed to form at plastic strain amplitudes ranging from 5.0?×?10^?4 to 2.5?×?10^?3, and the volume fraction of PSBs increases with increasing ?? _pl. As ?? _pl is as high as 5.0?×?10^?3, dislocation cells dominate the microstructure, even though a small amount of irregular PSB ladder structures still exists and they tend to evolve as labyrinth-like structures. The instability of Cr-rich precipitates during cyclic straining was believed to facilitate the formation of PSBs and thus promote some similarities of cyclic deformation characteristics between the current body-centered cubic (bcc) Fe-Cr single crystals and face-centered cubic (fcc) metal crystals. Whatever the internal structure of PSBs is, they could always carry the majority of the plastic strain in the course of cyclic deformation, thus causing the occurrence of a stress plateau region in the cyclic stress?Cstrain (CSS) curve of Fe-Cr alloy single crystals.     

Thermal expansion in the Ni−Cr−Al and Co−Cr−Al systems to 1200°C determined by high-temperature X-ray diffraction

The effect of temperature on the lattice parameters of phases in twelve nickel-chromium-aluminum (Ni?Cr?Al) alloys and nine cobalt-chromium-aluminum (Co?Cr?Al) alloys was determined using high temperature diffraction (HTXRD). The temperature range was from 25 to 1200°C. The data for each phase of each alloy were computer fit to an empirical thermal expansion equation developed in this study: \(LP_T = LP_{25^\circ C} (1 + R)^{(1 + T/273)^{1.5} } \) and a value forR was derived for each. Excellent fits were obtained for nearly all cases. A comparison ofR values revealed that for a given phase (ψ/ψ′, β and α in Ni?Cr?Al and αCo and β in Co?Cr?Al),R was independent of alloy composition. In the Ni?Cr?Al systemR for γ/γ′ was 19.2×10^?4,R for β was 19.9×10^?4 andR for αCr was 13.4×10^?4. In the Co?Cr?Al system theR value for αCo was 20.9×10^?4 and theR for β was 17.8×10^?4. Of all of the phases only the αCr in the Ni?Cr?Al system had anR sufficiently low to reduce to an unimportant level the stress generated from thermal expansion mismatch between Al₂O₃ and substrate or coating and substrate with either Ni?Al or Co?Al coatings on a γ/γ′-δ substrate.     

Recovery of uranium from phosphoric acid by means of supported liquid membranes

U(VI) was transported at 23 ± 1°C from 5–6 M phosphoric acid solutions through liquid membranes of kerosene solutions of di(2-ethylhexyl) phosphoric acid and trioctyl phosphine oxide (D2EHPA/TOPO) supported on porous polytetrafluoroethylene to a solution of phosphoric acid of equal or greater molarity containing ferrous ion as a reducing agent. The ferrous ion could be omitted when the higher molarity acid was used. The uranium flux was proportional to the U(VI) concentration. The overall resistivity of the membranes to uranium flux had a diffusional component that was proportional to the membrane thickness and an interfacial component that resulted from rate-limiting uranium complexation/decomplexation kinetics. The interfacial component accounted for over 80% of the resistivity of a membrane 75 μm thick. Increasing the temperature to 60°C only slightly diminished the interfacial resistivity. A theoretical model was constructed that accommodated data obtained from uranium transport through the membranes and through quiescent layers of phosphoric acid and D2EHPA/TOPO in kerosene. The average uranium flux from simulated solutions of wet-process phosphoric acid at 90% uranium transfer was estimated to be 1.3 × 10^?11 mol cm^?2 sec^?1, or 0.09 lb ft^?2 yr^?1. The flux was judged to be too low for supported liquid membranes to be competitive with liquid/liquid extraction for recovery of uranium from wet-process phosphoric acid.     

Dissolution of zinc ferrite samples in acids

The dissolution of rotating discs of synthetic zinc ferrite — the principal constituent of the ‘Moore Cake’ residue in zinc extraction plants — was studied in mineral acids, particularly in 1–5 N H₂SO₄ at 70–99°C. This dissolution was found to be directly proportional to the surface area, and the order of the zinc ferrite-sulphuric acid reaction with respect to proton activity, [H⁺], to be 0.6. The apparent energy of activation was established as 15 kcal/mole, and the chemical reaction on the solid surface as the rate-controlling step.What appeared to be ‘non-stoichiometric’ or preferential dissolution of zinc (over iron) from zinc ferrite was observed during the initial stages of reaction. This was attributed to the existence of trace amounts (undetectable by X-ray methods) of unreacted zinc oxide grains in the zinc ferrite matrix. This is, to our knowledge, the first time that electron microprobe analysis has been used to identify and analyse these grains. Prolonged sintering at 1200°C for 48 hours eliminated the ZnO phase.Dissolution of zinc ferrite in acid is stoichiometric. A typical dissolution rate is ～ 10^?8 mol cm^?2 sec^?1, which corresponds to almost complete extraction of zinc from ‘Moore Cake’ particles in 2–5 N H₂SO₄ solution at 95°C in 1–2 hours.     

Corrosion Behavior of Sn-3.0Ag-0.5Cu Lead-Free Solder in Potassium Hydroxide Electrolyte

The corrosion behavior of Sn-3.0Ag-0.5Cu (SAC305) solder alloy in 6?M potassium hydroxide electrolyte was investigated using polarization analysis. The results revealed that SAC305 is susceptible to corrosion because of the dissolution of the Sn phase. The corrosion potential (E _corr) and corrosion current density (i _corr) obtained from the sample was ?C1.108?V vs Hg/HgO and 1.795?×?10^?4?A cm^?2, respectively. In addition, microstructural and elemental characterization revealed the presence of tin oxide, Cu, and/or Ag-containing corrosion product on the surface of the corroded sample. The morphology of the samples was also observed to contain several pits, cracks, and pore-like structures.     

Acid dissolution of cupric oxide

The rates of dissolution of synthetic cupric oxide in solutions containing perchloric, sulfuric, nitric or hydrochloric acid were studied using sintered disks. In each case, the dissolution rate increased with elapsed retention time until an essentially constant value was reached. This phenomenon can be attributed to an increase in the disk’s effective surface area. The dissolution rate is of the first order with respect to a_H ⁺ for perchloric, nitric, and hydrochloric acids, while it is of a half order for sulfuric acid. High activation energies, ranging from 12.4 to 20.5 kcal/mol, and the independence of agitation speed on cupric oxide dissolution reaction rate suggest that chemical reactions are the major determinants of dissolution rates. The addition of electrolytes having anions common with the acids resulted in an acceleration of the dissolution rate due to increases in a_H ⁺ values. However, the addition of electrolytes of noncommon anions revealed a quite different effect on dissolution rate. This suggests that the adsorption and/ or complexing of anions on the cupric oxide surface may have had a significant role in the determination of the dissolution rates. The type of acid used determined the identity of the adsorbed anion.     

Poly(4- and 5-acrylamidosalicylic acids). Part V. Effect of counter anion and salicylate complex stability on cation exchange from aqueous solution

Poly(5-acrylamidosalicylic acid) acts as a monobasic acid with a dissociation constant of 3.13 × 10^?4 moles l^?1 derived from the direct titration of monomeric 5-acrylamidosalicylic acid. The polymer exhibits very low solubility in acid media but is appreciably soluble above pH 6, when it is almost wholly dissociated. Studies with acetate, chloride, nitrate and sulphate ions show that the exchange characteristics of the polymer are little affected by the nature of the counter anion present in the case of strongly bound cations, but exchange levels are markedly depressed by the presence of sulphate in the case of weakly bound cations. Possible reasons for this change in behaviour are discussed.