Flotation of Uranium from uranium ores in Canada: Part II — Cupferron adsorption on uranium oxide,quartz, illite and a uranium ore from elliot lake

Measurements are reported for the equilibrium adsorption of cupferron from solutions by uranium oxide, quartz, illite, a mixture of these three, pitchblende, pyrite and brannerite ore. The cupferron concentration ranged from 1 to 6 g/L, and the pH was 7 and 8. Most isotherms followed the Langmuir model, although Freundlich behaviour was observed for illite and pitchblende. Most adsorption was pH independent except for illite and pitchblende. The adsorption isotherms for a mixture of uranium oxide, quartz and illite in the same proportions as in the naturally occurring ore agreed with the adsorption on the pyrite-free ore at pH 8 but not pH 7. We attribute the discrepancy to the use of illite as the model clay. The specific adsorption of cupferron on quartz and illite is lower by a factor of about 50 and 5, respectively, than the adsorption on uranium oxide. Specific adsorption less than 1 mg cupferron per gm of pyrite free ore does not float the mineral. The corresponding equilibrium concentration of cupferron is 0.5 g/L. A qualitative model is given, and the implications of this work for practical operations are presented.     

Functional graphene oxide nanosheets modified with cyclodextrins for removal of Bisphenol A from water

A novel type of functional graphene oxide nanosheets (GNs) modified with β-cyclodextrins (β-CDs) have been developed by coating dopamine-functionalized cyclodextrin (DACD) molecules on GNs for removing Bisphenol A (BPA) molecules from water. The DACD molecules with both β-CD groups for achieving adsorption property and dopamine (DA) groups for achieving adhesion property are synthesized by grafting DA onto carboxymethyl-β-cyclodextrin (CmβCD). The proposed DACD molecules can be firmly coated on the surfaces of various inorganic and organic substrates. Due to the large specific surface area of GNs, DACD-coated GNs (DACD@GNs) are proposed for efficient adsorption separation of BPA molecules from water. Due to the host-gust complexation between the BPA molecules in water and β-CDs on DACD@GNs, the fabricated DACD@GNs exhibit excellent adsorption performances. The adsorption kinetics can be explained via the pseudo-second-order model effectively. The experimental adsorption capacity of DACD@GNs is 11.29 mg·g^-1 for BPA. Furthermore, after the adsorption process, the DACD@GNs can be easily separated from aqueous solutions via vacuum filtration with porous membranes, and then regenerated by simply washing with ethanol. The proposed strategy in this study can be used for effectively functionalizing the surfaces of various substrates with functional β-CDs, which is highly promising in applications in the field of adsorption separations, especially water treatments.     

含盐溶液汽液平衡预测(Ⅰ)——Pitzer模型的扩展及其在多元体系中的应用

本文提出一种新的预测含盐溶液汽液平衡的方法.对Pitzer(1980)模型进行扩展后,将其简化成单参数形式,推广至多元电解质溶液;经过适当假定,得到计算含盐挥发性强电解质和水体系及含盐水醇体系的活度系数公式,这些公式仅含二元相互作用参数;由二元溶液的活度关联出该参数后,可用于含盐体系各种温度下汽液平衡的预测.关联了40个二元电解质水溶液及7个电解质甲醇溶液298.15K时的简化Pitzer方程的单参数;用以推算6个水盐体系和2个甲醇盐体系在320-403K的蒸汽压,得到满意的结果,182个数据点的平均偏差小于0.65kPa;用以预测5个不同类型的含盐三元体系的等温、等压汽液平衡,所得的平均偏差对于汽相组成、沸点、压力分别为0.015、1K和1.92kPa.     

Non-linear modeling of kinetic and equilibrium data for the adsorption of hexavalent chromium by carbon nanomaterials:Dimension and functionalization

The adsorption capacities for the removal of hexavalent chromium from aqueous solutions by six carbon nanomaterials have been evaluated. Single-walled and multi-walled carbon nanotubes as received and after oxidation treatment, graphene oxide and reduced graphene oxide are the materials with different dimension and functionalization compared in this research. Carbon nanotubes have been modified using hydrogen peroxide as oxidizing agent under microwave radiation. The oxidation treatment on carbon nanotubes has a positive effect increasing the adsorbent–adsorbate interaction. Rate-controlling mechanisms and equilibrium data are analyzed using non-linear models. Non-linear method is proposed as the most suitable method for determining the kinetic and equilibrium parameters. The values of adsorption energy(E) obtained from the Dubinin–Radushkevich isotherm,have been found around 0.371 and 0.870 k J·mol~(-1), indicating physical adsorption. Therefore, the pseudo-second order model represents better the kinetic experimental data. The results show that the Langmuir isotherm provides a slightly better fit to the experimental data compared with the Freundlich isotherm, indicating homogeneous distribution of active sites on carbon nanomaterials and monolayer adsorption. The separation factors RLare found in the range of 0–1, suggesting that the adsorption process is suitable for all adsorbents. The mechanisms for hexavalent chromium removal have been proposed as electrostatic interactions and hydrogen bonding.     

含盐溶液汽液平衡预测

本文提出一种新的预测含盐溶液汽液平衡的方法。对Pitzer(1980年)模型进行扩展后,将其简化成单参数形式,推广至多元电解质溶液;经过适当假定,得到计算含盐挥发性强电解质和水体系及含盐水醇体系的活度系数公式,这些公式仅含有二元相互作用参数;由二元溶液的活度关联出参数后,可用于含盐体系各温度下汽液平衡的预测。关联了四十个二元电解质水溶液及七个电解质甲醇溶液298.15K时的简化Pitzer方程的单参数;用以推算六个水盐体系和二个甲醇盐体系在320-403K的蒸汽压,得到满意的结果,182个数据点的平均偏差小于0.65kPa;用以预测五个不同类型的含盐三元体系的等温、等压汽液平衡,所得的平均偏差对于汽相组成、沸点、压力分别为0.015、1K、1.92kPa。     

铝基锂吸附剂制备及其吸附性能研究

以氯化锂、无水氯化铝为原料,通过正交实验优化反应合成条件,采用“一步法”制备LiCl·2Al（OH）₃·nH₂O型铝基锂吸附剂。分别探究了吸附时间、吸附温度、溶液初始pH、溶液初始Li⁺浓度对吸附性能的影响,对吸附前后的无机铝吸附材料做了表征,并考察了吸附剂的离子选择吸附性及稳定性能。结果表明：最佳吸附条件为在45 ℃下pH=7的锂溶液中吸附2 h,吸附容量高达到8.66 mg/g。XRD、FT-IR表征结果表明：所制吸附材料有良好的稳定性。且该吸附剂对Li⁺分配系数（K=10.06）远高于其他金属阳离子,吸附材料经5次循环使用后,吸附容量仍能保持原来的91.5%。在西藏龙木错盐湖卤水中,对锂的吸附量达到5.24 mg/g。吸附平衡数据拟合结果表明：铝基锂吸附剂符合Langmuir等温吸附模型,吸附是发生在吸附剂表面的单层吸附;吸附过程符合伪二级动力学,是典型的化学吸附过程。     

MULTICOMPONENT LIQUID PHASE ADSORPTION IN BATCH PART II EXPERIMENT ON CARBON ADSORPTION FROM SOLUTIONS OF PHENOL, O-CRESOL, AND 2,4-DICHLOROPHENOL

Experiments were conducted on carbon adsorption from solutions of phenol, o-cresol, and 2,4-dichlorophenol in various combinations. The equilibrium data were found in general agreement with predictions based on the ideal adsorbed solution (IAS) theory. The kinetic measurements suggest that the adsorption process can be described by the film-surface diffusion (FSD) model. By using the algorithms developed in Part I and based on the rate and equilibrium data obtained from single adsorbate adsorption measurements, concentration histories of the individual adsorbate of carbon adsorption from solutions containing phenol, o-cresol and 2,4-dichlorophenol can be predicted with sufficient accuracy.     

CO在成型催化剂上脱除NOx的反应动力学模型

采用实验和模拟相结合的方法研究了NO_x在固定床反应器中的吸附还原过程。选取商业常用的堇青石和TiO₂为主要的成型催化剂基体材料，以铜铁铈复合型金属氧化物为活性成分，制备了蜂窝成型催化剂，对蜂窝催化剂的吸附性能和脱硝还原活性进行测定。建立了固定床反应器中CO脱除NO_x的反应动力学模型，由于CO法脱硝反应的解耦分解，脱硝反应模型也由吸附模型和还原模型组成。吸附模型由固相和气相的微分质量平衡方程建立，还原模型由一组微分方程组成。通过固定床NO_x吸附曲线和不同温度下NO_x的转化率对模型中的关键参数进行了拟合，得到了CO在成型催化剂上脱除NO_x的反应动力学模型，该模型与实验数据吻合较好。在此基础上，模拟了其他条件下吸附过程的穿透曲线和还原反应的转化率。此模型能较好地揭示CO在蜂窝催化剂上还原NO_x的反应动力学，为CO法成型催化剂脱除NO_x的实验或者工程提供理论指导。     

Small angle neutron scattering from ionomer gels

Small angle neutron scattering intensities for sols and gels of the physically associating ionomer 1.39 mol% sodium sulphonated polystyrene with molecular weight 10⁵ g/mole in xylene have been obtained over a broad wavevector (q) and concentration range. In the low q and concentration range the scattering behaviour of this ionomer/solvent system can quite readily be interpreted using the open association aggregation model. In more concentrated solutions and at higher q, however, interpretation of the scattering behaviour for polymers associating via an open association mechanism (OAM) is more difficult, particularly if, as in this investigation, the single chains and aggregates have varying densities and fractal parameters. In this study various methods have been developed to interpret the low and high q scattering from systems whose extent of aggregation can be modelled using the OAM. Using these methods it has been possible to confirm that the open association model can be used to interpret the extent of aggregation of the above ionomer in xylene even after the solutions appear to be gelled. Single ionomer chains within both the dilute solutions and gels were found via modelling to have a radius of gyration of 60 Å, which compares with dimensions of 25 Å and 93 Å calculated for a solid sphere of polystyrene or an unperturbed polystyrene Gaussian coil, respectively. The aggregates, however, all had radii of gyration comparable with what would be expected for polystyrene of the aggregate molecular weight in an unperturbed state. These results suggest that gelation of ionomer solutions at particular concentration thresholds is not due to an abrupt change in the aggregate structures at some critical concentration but occurs as a result of interactions between the very large aggregates that the OAM predicts should gradually form as the ionomer concentration increases.     

On the interaction of oxygen with platinum

The cyclic voltammograms were obtained on both bright polycrystalline Pt and Pt---O alloy bead electrodes in both 2 N H₂SO₄ and 1 N HF solutions saturated with purified N₂. The samples were scanned between 0 and 1500 mV vs nhe at rates from 100 to 17 mV s⁻¹. In rigorously purified systems, the chief effect of polarizing Pt above 1 V is the charging of Pt with dissolved oxygen. Such a Pt--- O alloy has different electrochemical properties than Pt. On Pt there are two adsorption and desorption sites for hydrogen and possibly two adsorption sites for sulfate ions. A third hydrogen desorption site exists on Pt---O alloy.     

Preparation and evaluation of α-Al2O3 supported lithium ion sieve membranes for Li+ extraction

Spinel lithium manganese oxide ion-sieves have been considered the most promising adsorbents to extract Li⁺ from brines and sea water. Here, we report a lithium ion-sieve which was successfully loaded onto tubular α-Al₂O₃ ceramic substrates by dipping crystallization and post-calcination method. The lithium manganese oxide Li₄Mn₅O₁₂ was first synthesized onto tubular α-Al₂O₃ ceramic substrates as the ion-sieve precursor (i.e. L-AA), and the corresponding lithium ion-sieve (i.e. H-AA) was obtained after acid pickling. The chemical and morphological properties of the ion-sieve were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Both L-AA and H-AA showed characteristic peaks of α-Al₂O₃ and cubic phase Li₄Mn₅O₁₂, and the peaks representing cubic phase could still exist after pickling. The lithium manganese oxide Li₄Mn₅O₁₂ could be uniformly loaded not only on the surface of α-Al₂O₃ substrates but also inside the pores. Moreover, we found that the equilibrium adsorption capacity of H-AA was 22.9 mg·g^-1. After 12 h adsorption, the adsorption balance was reached. After 5 cycles of adsorption, the adsorption capacity of H-AA was 60.88% of the initial adsorption capacity. The process of H-AA adsorption for Li⁺ correlated with pseudo-second order kinetic model and Langmuir model. Adsorption thermodynamic parameters regarding enthalpy (ΔH), Gibbs free energy (ΔG) and entropy (ΔS) were calculated. For the dynamic adsorption- desorption process of H-AA, the H-AA exhibited excellent adsorption performance to Li⁺ with the Li⁺ dynamic adsorption capacity of 9.74 mg·g^-1 and the Mn²⁺ dissolution loss rate of 0.99%. After 3 dynamic adsorption-desorption cycles, 80% of the initial dynamic adsorption capacity was still kept.     

Derivatization of cellulose in lithium chloride and N-N-dimethylacetamide solutions

The derivatization of cellulose in mixtures of lithium chloride and N,N-dimethylacetamide (LiCl/DMAc) is described. A wide range of cellulose derivatives, including cellulose esters, carbamates, sulphonates and ethers, have been synthesized in homogeneous solution using the LiCl/DMAc solvent. In most cases, a high degree of substitution was achieved, and the degree of substitution could be controlled accurately. Compared to current heterogeneous synthesis of cellulose derivatives, reactions conducted in homogeneous solutions of LiCl/DMAc have many advantages: (1) reactions may be conducted at moderate temperatures; (2) less reagent is required; (3) less degradation of the cellulose occurs; and (4) substitution is uniformly controllable.     

Nitric oxide reduction at noble metal electrodes: a voltammetric study in acid solution

Features of the electrochemical reduction of nitric oxide on platinum, palladium, rhodium and ruthenium in aqueous perchloric acid solutions (0.33–1.0 M) are compared. The results from voltammetric studies (ie linear potential sweep and rotating disc electrode) using the bulk metal electrodes are described and compared with residual current voltage plots in acid electrolyte alone. In general, three nitric oxide reduction peaks are observed on the metals. The most anodic peak, at ca E = 0.15 V vs sce is attributed to the one-electron reduction of nitric oxide to an adsorbed NOH intermediate on a bare metal surface (ie one free of oxides or adsorbed hydrogen). The other two peaks occur in potential regions where adsorbed hydrogen is present on the metal surface (ca E = 0.0 and −0.20 V, respectively). The co-adsorbed hydrogen complicates the analysis and precludes an unambiguous interpretation of these two peaks. However, they apparently reflect nitric oxide reduction to nitrogen, hydroxylamine and/or ammonia. In a cathodic scan on the rhodium electrode, a current plateau is seen instead of the first (most anodic) peak, a probable consequence of oxide film formation with subsequent chemical complications. On the ruthenium electrode the first two (most anodic) peaks are not observed probably due to a relatively stable oxide layer. Reaction selectivities at metal black gas diffusion cathodes operating in an electrogenerative (ie galvanic) mode with perchloric acid electrolyte are compared with the voltammetric results at the corresponding bulk electrodes. Dinitrogen formation is observed on the platinum and rhodium black electrodes as suggested from voltammetric results. A series-parallel reaction sequence is proposed to explain the results. Limitations of using simple voltammetric techniques for predicting behavior of large scale preparative electrochemical reactors are discussed.     

Production of nanoparticles of copper compounds by anodic dissolution of copper in organic solvents

The anodic behaviour of copper was investigated in ethanol solution containing LiClO₄, LiCl electrolyte and water. The type of electrolyte and the water content influences the mechanism of the anodic process and the formation of anodic products. In LiClO₄ electrolyte the dissolution of copper is related to the oxidation of Cu(I) to Cu(II). In solutions of LiCl the etching of copper begins with the creation of soluble complexes of Cu(I) with chloride ions and solvent molecules. At potentials above 0.4 V the formation of alkoxides was observed in both solutions, characterized by a yellow tint. On the other hand, above 0.8 V (i.e. above the equilibrium potential of alcohol oxidation) copper dissolution is accompanied by the formation of a blue colloidal suspension of Cu (II) copper salt. Anodic etching of copper in solutions containing 3% H₂O at potentials higher than 0.4 V leads to the formation of colloidal suspension of copper oxide nanoparticles.     

The adsorption of an epoxy acrylate resin on aluminium alloy conversion coatings

A thermodynamic study of the adsorption of an epoxy acrylate resin used for UV-cured coatings on two different anticorrosion pretreatments on aluminium alloys relevant to aerospace industry has been undertaken. Aluminium alloy Al2219 specimens, treated with an inorganic chromate based conversion coating (Alodine 1200S) and an organic titanium based conversion coating (Nabutan STI/310), were immersed in solutions of different concentrations of the resin and adsorption isotherms were determined by assessing the uptake of the adsorbate, as a function of solution concentration, by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results show different behaviour for the two substrates, which can be attributed to the organic component of the titanium based coating. In the case of the inorganic conversion coating a clear plateau is achieved at relatively low concentrations and at a lower level of adsorption than for the hybrid coating. The data for both the coatings conform well to the Langmuir model, the organic coating, as well as showing a higher level of adsorption of the resin, also presents oscillatory behaviour at low concentration, which is shown to be complementary to the behaviour of the reactive diluent included with the epoxy acrylate to aid processing. A discussion of this competitive adsorption of the epoxy resin and the diluent on the different substrates is presented, based on considerations of the chemistry of the systems under investigation.     

A study of coprecipitated Mn–Zr oxides and their behaviour as oxidation catalysts

Mn–Zr mixed oxide samples with the general formula Mn_xZr_1−xO_y, where x=0,0.1,0.2,0.5,0.8,0.9,1, have been prepared by a conventional coprecipitation procedure and characterised by X-ray diffraction (XRD), TG-DTA analyses, FT-IR and UV–VIS-diffuse reflectance (DR-UV–VIS) spectroscopies, BET specific surface measurements and surface acidity by pyridine adsorption techniques. It was found that Mn stabilises the metastable phase tetragonal zirconia and gives rise to low-concentration solid solutions (up to about 10% of Mn), remaining as Mn(IV) within the structure. Their catalytic behaviour was tested by the phenanthrene combustion and the isopropanol oxidation reactions. All samples were found to be active in the total oxidation of phenanthrene at quite a low temperature of 523–673 K. They are also very active in the oxidation of isopropanol, giving rise to acetone with high selectivity at partial conversion and producing CO₂ with total selectivity at total conversion. These materials are relevantly more active than Mn–Ti catalysts and approach the activity of pure Mn oxides, but with higher thermal stability.     

Synthesis of C2H4 by partial oxidation of CH4 over LiCl/NiO

Alkali halide added transition metal oxides produced ethylene selectively in oxidative coupling of methane. The role of alkali halides has been investigated for LiCl-added NiO (LiCl/NiO). In the absence of LiCl the reaction over NiO produced only carbon oxides (CO₂ + CO). However, addition of LiCl drastically improved the yield of C₂ compounds (C₂H₆ + C₂H₄). One of the roles of LiCl is to inhibit the catalytic activity of the host NiO for deep oxidation of CH₄. The reaction catalyzed by the LiCl/NiO proceeds stepwise from CH₄ to C₂H₄ through C₂H₆ (2CH₄ → C₂H₆ → C₂H₄). The study on the oxidation of C₂H₆ over the LiCl/NiO showed that the oxidative dehydrogenation of C₂H₆ to C₂H₄ occurs very selectively, which is the main reason why partial oxidation of CH₄ over LiCl/NiO gives C₂H₄ quite selectively. The other role of LiCl is to prevent the host oxide (NiO) from being reduced by CH₄. The catalyst model under working conditions was suggested to be the NiO covered with molten LiCl. XPS studies suggested that the catalytically active species on the LiCl/NiO is a surface compound oxide which has higher valent nickel cations (Ni^(2+δ)+ or Ni³⁺). The catalyst was deactivated at the temperatures>973 K due to vaporization of LiCl and consumption of chlorine during reaction. The kinetic and CH₄---CD₄ exchange studies suggested that the rate-determining step of the reaction is the abstraction of H from the vibrationally excited methane by the molecular oxygen adsorbed on the surface compound oxide.     

Molecular dynamics of poly(ethylene oxide) in concentrated solution

Incoherent quasi-elastic neutron scattering measurements on aqueous poly(ethylene oxide) solutions show that as the concentration of water is increased to 1:1 mole ratio of water to ethylene oxide monomer units, the polymer chain mobility is not enhanced. Increased mobility is only observed when the water content is increased beyond this ratio. The activation energy for viscous flow shows a similar behaviour, it is unchanged as the system is diluted from the melt to the 1:1 solution and as more water is added it falls sharply. Similar studies on the system poly(ethylene oxide)/toluene show that chain mobility is enhanced and the activation energy for viscous flow falls continuously, at all concentrations. The difference is attributed to the formation of polymer-water hydrogen bonded complexes in aqueous solution. High resolution data for the aqueous systems suggest that the molecular dynamics obey the scattering law predicted for the Zimm model. In the melt the behaviour changes towards the limit given by the Rouse model.     

Electrosorption of tri(n)octylphosphine oxide from methanol and water-methanolic solutions on a polarized mercury electrode

The adsorption of tri(n)octylphosphine oxide on the mercury electrode in methanolic and water-methanolic solutions of LiCl has been examined from electrocapillary measurements. In methanolic solutions this substance shows the typical characteristic features of an organic adsorbate. The isotherms are congruent only with respect to potential on the negative side of the electrocapillary maximum and in this region a Frumkin isotherm is obeyed with an interaction parameter equal to α = 0.3 corresponding to intermolecular attraction. On the positive side the isotherms are non congruent with respect to both the electrical variables, while the system may be described by a Frumkin isotherm either with constant Γ_s = 1.03 × 10^?10 mole cm^?2 and α decreasing with the increase of the positive charges on the electrode or with constant α = 0.3 and decreasing Γ_s.In water-methanolic solutions the adsorption of tri(n)octylphosphine oxide increases, due mainly to the decrease of its solubility. In parallel a clear dependence of Γ_s on the amount of water in solutions is detected. Γ_s is seen to increase with the water content of the solutions probably due to a partial overlap of the hydrocarbon chains of this substance.     

MgO/Mg(OH)2热化学储热反应的第一性原理研究

以MgO/Mg(OH)₂储热系统为研究对象,以微观储热机理为切入点,建立相应储热材料的分子晶体结构模型,采用第一性原理密度泛函理论,分析不同吸附距离和吸附构型对吸附稳定性的影响,并进一步研究了掺杂对储热的影响。研究发现,对于不同吸附距离,因为物理吸附和化学吸附共同作用,导致吸附能不同,最佳吸附距离为0.15 nm;Mg原子在高对称的镁顶位,即超晶胞第一层中央的镁原子,具有很强的失电子能力,所以失去的电子数最多,存在更强的化学键,分子与表面的作用力更强,是最稳定的吸附位点;掺杂Li、Na、K原子有利于氧化镁储热。本研究某种程度上揭示了热化学储热系统的微观机理,这对后续研究双组分吸附、掺杂的原子对晶体本身的影响等改性处理改善反应物性质的方法研究有很好的参考价值。