Nuclear decontamination of cementitious materials by electrokinetics: An experimental study

The objective of this paper is to evaluate the efficiency of an electrokinetic method of radionuclide removal from a cement-based material. This work is a two-part process. In the first part, a sample of mortar was uniformly contaminated for use as a reference. In order to ensure a uniform contamination, the ingress of the radioelement (cesium) was controlled by an external electrical field. The second part of this work concerns the removal of cesium from the contaminated mortar samples. This second, decontamination, phase was driven by the same electrical field. No electroosmosis was detected. Both phases were characterized by analyses of cesium and calcium concentrations in cathodic and anodic solutions, and by measurements of cesium content in the samples at the end of each phase. In addition to the electrical current, pH, and conductivity were measured during the experiments. Finally, the efficiency of the electrokinetic method was described in terms of decontamination factor, leading to promising results.     

Experimental study and mathematical model of nanoparticle transport in porous media

Two types of polysilicon nanoparticles (PN) were used in oil fields to improve oil recovery and enhance water injection respectively in this work. The physical properties of the nanoparticles were studied experimentally, and pore characteristics of sandstone were investigated by mercury injection experiments. The adsorption experiments of lipophobic and hydrophilic polysilicon nanoparticles (LHPN) were conducted to testify wettability change (from oil wetting to water wetting) of sandstone surface, and the nanoparticles attached to pore walls were observed by a transmission electron microscope (TEM). A mathematical model to describe the nanoparticles transport carried by two-phase flow in random porous media was presented and a numerical simulator was developed to simulate two application examples of the nanoparticles in oilfields. An important discovery is that water-phase permeabilities of these sandstones increase from 1.6 to 2.1 times of their original values. However, there are decreases in their absolute permeabilities because of nanoparticle adsorption on pore surfaces and nanoparticle capture at pore throats. The important parameters such as the distributions of porosities and permeabilities, the changes in water injection capability and oil recovery are obtained successfully by numerical simulation approach. Furthermore, the permeabilities obtained from numerical simulation have a good match with experimental data. The conclusion that polysilicon nanoparticles are effective agents for enhancing water injection capability or improving oil recovery can be safely drawn.     

Improving on electrokinetic remediation in spiked Mn kaolinite by addition of complexing agents

During the electrokinetic treatment of kaolinite polluted with Mn, metal ions migrated to the cathode side, but the alkaline front generated by the reduction of water at the cathode provoked their precipitation as Mn hydroxide. It prevented their collection in the cathode chamber. Most Mn precipitated in a thin soil layer close to the cathode (68%), and only 26% of the initial Mn was found in the cathodic solution. Solubility of manganese can be enhanced with the addition of organic compounds (EDTA, oxalic acid and citric acid) that form complexes or chelates with Mn²⁺ ions. Besides, the complexing agents tested in this work are environmentally benign and do not provoked negative effects in soil. The addition of EDTA and oxalic acid to the spiked Mn kaolinite improved metal removal from kaolinite. Thus, 38% of Mn was colleted at the cathode chamber when oxalic acid was used as complexing agent. EDTA was more effective since 42% of Mn reached the cathode. The rest of the Mn remained into the kaolinite, mainly in the last section, close to the cathode. When citric acid was added to kaolinite, the behaviour of the electrokinetic treatment was totally different. Mn was completely removed and no accumulation was detected into the kaolinite. All contaminated metal was recovered in the cathodic solution. This good result was attributed to the complexing activity of citric acid and to the high electro-osmotic flow induced by the presence of citric acid into the kaolinite sample.     

The effect of convection in the external diffusion layer on the results of a mathematical model of multiple ion transport across an ion-selective membrane

A previously published macrohomogeneous mathematical model of the simultaneous transport of multiple ions across an ion-selective membrane under current load based on the Nernst–Planck equation was extended. A significantly more realistic model is proposed and realised. The change with the most significant impact on the results of the model is consideration of convective mass transfer in the external diffusion layers adjacent to the membrane surfaces. This change results in a reduction of the concentration maximum previously observed in the membrane interior and highlights the importance of the external diffusion layers for ion transport across an ion-selective membrane. Hitherto this has often been underestimated.     

Surface complexation model of uranyl sorption on Georgia kaolinite

The adsorption of uranyl on standard Georgia kaolinites (KGa-1 and KGa-1B) was studied as a function of pH (3–10), total U (1 and 10 μmol/l), and mass loading of clay (4 and 40 g/l). The uptake of uranyl in air-equilibrated systems increased with pH and reached a maximum in the near-neutral pH range. At higher pH values, the sorption decreased due to the presence of aqueous uranyl carbonate complexes. One kaolinite sample was examined after the uranyl uptake experiments by transmission electron microscopy (TEM), using energy dispersive X-ray spectroscopy (EDS) to determine the U content. It was found that uranium was preferentially adsorbed by Ti-rich impurity phases (predominantly anatase), which are present in the kaolinite samples. Uranyl sorption on the Georgia kaolinites was simulated with U sorption reactions on both titanol and aluminol sites, using a simple non-electrostatic surface complexation model (SCM). The relative amounts of U-binding >TiOH and >AlOH sites were estimated from the TEM/EDS results. A ternary uranyl carbonate complex on the titanol site improved the fit to the experimental data in the higher pH range. The final model contained only three optimised log K values, and was able to simulate adsorption data across a wide range of experimental conditions. The >TiOH (anatase) sites appear to play an important role in retaining U at low uranyl concentrations. As kaolinite often contains trace TiO₂, its presence may need to be taken into account when modelling the results of sorption experiments with radionuclides or trace metals on kaolinite.     

Analytical study of effects of finger-growth velocity on reaction characteristics of reactive miscible viscous fingering by using a convection-diffusion-reaction model

Reactive miscible viscous fingering occurs when a reactive and miscible less-viscous liquid displaces a more-viscous liquid. Effects of bulk finger-growth velocity on reaction characteristics of miscible viscous fingering with a chemical reaction were studied analytically by using a convection-diffusion-reaction model. The model assumes the existence of a distinct interface between both liquids, assumes the existence of a two-dimensional, steady, stagnated flow field in the less-viscous liquid, and assumes an infinite chemical reaction rate. The model was then used to determine the reaction characteristics, such as the location of the reaction surface and the profile of the product, as functions of the velocity and initial reactant concentrations. The results reveal that the effects of the velocity on the reaction characteristics can be divided into low-, intermediate-, and high-velocity regions. In the low-velocity region, the reaction characteristics strongly depend on the reactant concentrations. In the intermediate-velocity region, the dependence of the reaction characteristics on the reactant concentrations decreases with increasing velocity. In the high-velocity region, the reaction characteristics are nearly independent of the reactant concentrations. Experiments confirm the existence of these three velocity regions predicted by the model.     

Effect of different treatments on electrokinetic remediation of Zn,Pb and Cd from a contaminated calcareous soil

Electrokinetic remediation is a promising method to decontamination of the heavy metals from soils.In this paper,the remediation of a contaminated calcareous soil with Zn,Cd and Pb sampled from around Zanjan province of Iran,was investigated using electrokinetic method.In this paper,the soil contain a high concentration of Zn (1400 mg·kg-1),Cd (15 mg·kg-1) and Pb (250 mg·kg-1).Electrokinetic decon-tamination consists of two series of experiments as follows:(1) the effect of five treatments including the use of distilled water,acetic acid and EDTA electrolyte solutions,and approaching anodes systems,and the circulation flow of electrolyte at two different voltage gradient (i.e.1.33 and 2.66 V·cm-1),and(2) the effect of moisture content (saturated,FC and 0.7FC,FC indicated soil moisture at "Field Capacity") with a voltage gradient of 1.33 V·cm-1.After applying electric current for 5 days,the results of experiments indicated that the removal efficiency of heavy metals can be increased by raising the volt-age gradient.In this matter,the highest remediation can be observed among different treatments in EDTA(Ethylene diamine tetra acetic acid) treatment (40.11％,43.10％ and 24.7％ for Zn,Cd and Pb,respectively).Moreover,the heavy metals removal at the saturated moisture was at the highest level so that 32.62％cadmium,31.33％ zinc and 18.82％ lead being removed after 120 h of electric current application.By decreasing moisture to 0.7FC,the removal percentage for the three heavy metals obtained 20.97％,18.44％ and 12.25％,respectively.Furthermore,Cd had the highest removal,and Zn and Pb were next among the three heavy metals in question.     

Optimization of electroless Ni-Zn-P deposition process: experimental study and mathematical modeling

A mathematical model based on mixed potential theory was developed which was used to optimize a non-anomalous Ni-Zn-P electroless deposition process developed by us at USC. The model was developed by assuming an adsorption step in addition to the electrochemical steps. The concentrations of the Zn and Ni complex were estimated by solving the material balances in addition to the electroneutrality condition and the equilibrium relations. The composition of the coating was estimated from the partial current densities of all charge transfer reactions, which occur at the electrode-electrolyte interface. The model results showed that the adsorption plays a significant role in the alloy deposition process. From the model results, it was seen that the addition of Zn ions to the bath inhibits the deposition rate by changing the surface coverage of the adsorbed electroactive species on the electrode surface. The model indicated that an increase of pH of the bath increases the alloy deposition rate.     

示踪剂运移数学模型求解方法研究

随着测试目的的明确和井间示踪的发展,示踪测试解释方法也不断完善和发展。目前,不考虑地质模型进行井间示踪测试解释的方法主要为界标法,结合地质模型进行解释的方法主要有三种:解析方法、数值模拟法、半解析方法。三种方法各有优缺点。从油藏工程的角度,基于流线方法和不稳定渗流场,构建了更为完善的井间示踪产出浓度计算求解半解析方法体系,包括压力场求解、质点追踪方法和流场分解方法等,将三维问题的求解处理为一维问题解的组合形式。     

Experimental study of gas–liquid mass transfer coupled with chemical reactions by digital holographic interferometry

This work deals with the development of a new experimental tool and an original procedure to study the gas–liquid absorption process coupled with chemical reactions in the liquid phase. This absorption is realized inside a Hele-Shaw cell and digital holographic interferometry is used to visualize the formation and the development of the diffusion layer during the mass transport in the liquid phase in the vicinity of the gas–liquid interface. An image processing code is developed to extract quantitative information from the raw experimental results. The experimental results are compared to a mass transfer model in the liquid phase of the Hele-Shaw cell and some physico-chemical parameters of this model are estimated from this comparison using on a non-linear least-square fitting method. The developed procedure is used to study the gaseous CO₂ absorption in NaHCO₃–Na₂CO₃ aqueous solution. Calibration curves are determined and experiments are realized for several couples of NaHCO₃–Na₂CO₃ initial concentrations. The estimated values of the physico-chemical parameters for each experiment are presented and they are compared to the values calculated from correlations found in the literature. A reasonable agreement is observed, which tends to show that the methodology is promising and could be applicable to other systems.     

Validation of a mathematical model for predicting high pressure carbon dioxide inactivation kinetics of Escherichia coli spiked on fresh cut carrot

Inactivation kinetics of Escherichia coli spiked on fresh cut carrot and exposed to high pressure carbon dioxide (HPCD) treatment at several conditions of pressure (6, 8, 10, and 12 MPa) and two conditions of temperature (26 and 35 °C) were obtained as a function of the treatment time (up to 30 min).The Weibull model was applied to fit the inactivation kinetics and calculate δ and n model parameters for each pressure and temperature. The results demonstrated that the model was able to fit with good agreement the inactivation curves (high R² and low RMSE values). In a second attempt, the model parameters were correlated with CO₂ density resulting in a linear relationship. Validation of the proposed model was also performed at 6.6 and 10 MPa, 26 °C and at 8 MPa, 35 °C providing log reduction residual values (observed value–predicted value) lower than 0.50 and showing a good agreement between the experimental and the predicted inactivation data.The model proved to be a powerful tool to fit and predict, in the proposed operative range, the inactivation kinetics of E. coli spiked on fresh cut carrot treated by HPCD. The results demonstrated the potential of a relative simple correlative model for the interpretation of the inactivation data and for HPCD process design and optimization.     

A primary, secondary and pseudo-tertiary mathematical model of a chlor-alkali membrane cell

A theoretical study of current density and potential at the anode, membrane and cathode, of a chlor-alkali membrane cell where the electrode blades are placed vertically, is presented. A representative unit cell is modelled in primary, secondary and pseudo-tertiary current distribution models. It is shown that electrolyte and membrane resistance has the greatest effect on current distribution. Furthermore, it is shown that there is a surprisingly small influence of mass transport on current distribution, on the assumption that the diffusion layer is of constant thickness. In converse to this, it is shown that mass transport affects the anode overpotential distribution to the extent that conclusions can be made about the occurrence of side-reactions and where they occur. Finally, it is shown that it is possible to estimate tertiary behaviour with a secondary current distribution model, by using an analytic expression at the anode surface.     

Chromatographic separation of bupivacaine racemate by mathematical model with competitive langmuir isotherm

HPLC (High Performance Liquid Chromatography) was utilized for the chiral separation of racemic bupivacaine, and mathematical modeling with competitive Langmuir isotherm was performed to determine the optimum feed condition. For each racemic compound, the isotherm parameters a, b and mass transfer coefficients k were obtained by parameter estimation and maximum likelihood method. The agreement of elution profiles between the experimental data and the calculated values was fairly good. In order to find the optimum separation condition, simulations were carried out to determine the feed conditions such as concentration and injection volume. To preparatively separate racemic bupivacaine, the desirable injection volumes were 0.05 ml at 2.0 mg/ml of the concentration of racemic mixture or 0.01 ml at 20 mg/ml.     

The mathematical model of the stripping voltammetry hydrogen evolution/dissolution process on Pd layer

The advanced two-plate mathematical model of electrochemical hydrogen evolution/dissolution process has been presented and discussed. The model, with Langmuir adsorption equation, has been experimentally verified by the use of the glassy carbon/Pd layer electrode system at different scan rates. The two cathodic-anodic stages of hydrogen evolution/dissolution process in 0.1 M and 0.001 M HCl solutions have been interpreted and discussed. The thickness of the layer and the way of deposition were also investigated. The fundamental kinetic problem of a change of electrode properties during electrode process as an effect of the elementary hydrogen presence in the solid electrode is presented and interpreted. The isopotential point phenomenon, an electrochemical analog of isosbestic point in absorption spectroscopy, was unexpectedly discovered as experimental effect of hydrogen adsorption and α variability.     

Multi-dimensional transient mathematical simulator of blast furnace process based on multi-fluid and kinetic theories

The ironmaking blast furnace is regarded as one of the biggest and most complex industrial reactors, because it includes various materials like gas, lump granular materials, liquids and powders and more than 30 major reactions and phase changes in a single reaction vessel. The mathematical simulator of this process developed in this study used the multi-fluid treatment as its framework, since the motions of these materials were governed by different flow mechanisms. The rates of the interactions among the phases and the chemical reactions were evaluated based on kinetic theories. The model successfully reproduced the fields of velocity, temperature and reaction in the furnace and its validity was confirmed. The simulator was also applied to a novel operation, namely the top gas recycling combined with the carbon-composite iron-ore charging and the waste plastics injection, and the advantages in furnace efficiency and environmental load were quantitatively indicated.     

Drying of sardine muscles: Experimental and mathematical investigations

The aim of this work was to study the effect of air drying process on the dehydration kinetics of sardine muscles (Sardina pilchardus). Experimental drying kinetics were measured at five air temperatures (40, 50, 60, 70 and 80 °C), two relative humidity and at a constant air velocity of 1.5 m/s. The sardine drying kinetics were accelerated by increasing air temperature and were showed down when increasing air humidity. Moisture desorption isotherms of sardine muscles were determined at three temperatures (40, 50 and 70 °C) by using the static gravimetric method. The equilibrium moisture contents of sardine muscles were used to treat mathematically the experimental drying kinetics. Experimental drying kinetics and desorption isotherms of sardine muscles were described by using empiric models available in the literature. Eight models (GAB, BET, Henderson–Thompson, Modified Chung & Pfost, Modified Halsey, Oswin, Peleg and Adam & Shove models) were compared in order to describe the desorption isotherms. The Peleg model showed the best fitting of experimental data. For the drying kinetics, the Page model allowed a better fitting than the Newton and the Henderson and Pabis models. The Page model was thus used for simulating the drying kinetics of sardine muscles between 40 and 80 °C.     

磷酸分解磷矿的化学过程及其模型

采用热法磷酸制成含 2 0 % P2 O5左右的磷酸 ,用以与云南上蒜磷矿进行分解反应。在实验条件下 ,研究了分解产物 Ca(H2 PO4) 2 在磷矿颗粒表面形成固体膜的特性。研究了磷矿粒度、反应时间、反应温度、初始磷酸浓度对磷矿分解率的影响。用扫描电镜观察了磷矿颗粒表面形成的固体膜的形貌特征。用粒径不变的缩芯模型来描述磷酸分解磷矿的过程。推导出了该过程的理论模型和实验数据的回归模型     

Experimental study and simulation of vibrated fluidized bed drying

The paper addresses numerical simulation for the case of convective drying of seeds (fine-grained materials) in a vibrated fluidized bed, analyzing agreement between the numerical results and the results of corresponding experimental investigation. In the simulation model of unsteady simultaneous one-dimensional heat and mass transfer between gas phase and dried material during drying process it is assumed that the gas-solid interface is at thermodynamic equilibrium, while the drying rate (evaporated moisture flux) of the specific product is calculated by applying the concept of a “drying coefficient”. Mixing of the particles in the case of vibrated fluidized bed is taken into account by means of the diffusion term in the differential equations, using an effective particle diffusion coefficient. Model validation was done on the basis of the experimental data obtained with narrow fraction of poppy seeds characterized by mean equivalent particle diameter (d_S,d = 0.75 mm), re-wetted with required (calculated) amount of water up to the initial moisture content (X₀ = 0.54) for all experiments. Comparison of the drying kinetics, both experimental and numerical, has shown that higher gas (drying agent) temperatures, as well as velocities (flow-rates), induce faster drying. This effect is more pronounced for deeper beds, because of the larger amount of wet material to be dried using the same drying agent capacity. Bed temperature differences along the bed height, being significant inside the packed bed, are almost negligible in the vibrated fluidized bed, for the same drying conditions, due to mixing of particles. Residence time is shorter in the case of a vibrated fluidized bed drying compared to a packed bed drying.