Top PDF Influence of chemical reaction kinetics on electrokinetic remediation modelling results

A numerical model describing transport of multiple species and chemical reactions during electrokinetic treatment is presented. The transport mechanisms included in the model were electromigration and electroosmosis. The chemical reactions taken into account were water electrolysis at the electrodes, aqueous species complexation, precipitation, and dissolution. The model was applied to simulate experimental data from an acid-enhanced electrokinetic treatment of a Pb-contaminated calcareous soil. The kinetics of the main pH buffering process (i.e., calcite dissolution) was taken into account and its time-dependent behavior was described by a rate law. The influence of kinetics was evaluated by comparing the results from a set of simulations in which calcite dissolution was implemented considering thermodynamic equilibrium and another set in which the same reaction was described by the rate law. The results show that the prediction capability of the model significantly improves when the kinetic rate is taken into account.

While the simulation results presented in previous works [12] were carried out using a tailor made code fully written in Matlab®, the numerical procedure presented in this work was achieved by coupling two specialized software packages; namely COMSOL Multiphysics and PHREEQC. COMSOL was used for the solution of the finite element integration of the transient Nernst- Planck-Electroneutrality system of algebraic and partial differential equations, while the algebraic system of chemical equilibrium equations, accounting for the formation of aqueous complexes, precipitation and dissolution reactions, were computed using the PHREEQC [28]. It should be noted that the transient dissolution/precipitation reaction of calcite was also included in the PHREEQC script as a kinetic reaction module. The coupling between COMSOL and PHREEQC was attained using an envelope Matlab® script, as shown in Fig. 2, which is also used to initialize the system and postprocess the results.

Electrokinetic mass transport processes may have great influence on the availability of the inorganic nutrients when biological and electrochemical treatments are combined for the remediation of a polluted soil. The well-known electromigration process attains the transport of the ionic species toward the anodic or the cathodic electrodes. Depending on the duration the treatment and on the intensity of the electric field applied, this transport can even lead to the depletion of nutrients from the soil matrix. If exhaustion is achieved, the biological removal of pollutant from the soil is inhibited. Therefore, the combination of the biological and the electrokinetic processes may lead to worse results as compared with both single technologies, applied separately. However, if the electrokinetic processes are well controlled, there is an increase in the possibilities of interaction among the different components electrokinetically mobilized, and which take part in the biological degradation process, and hence the efficiency will be higher. Likewise, it is hypothesized than the oxygen produced in the electrolytic water oxidation reaction can be dragged by the water transported by the electro-osmosis process. If this process has high efficiency, an increase in the aerobic degradation process in the in situ treatment can also be achieved.

There are very few theoretical studies on the combustion of droplets considering finite chemical kinetics. Lorell, Wise and Carr 9 studied the problem by taking an overall reaction rate and solving numerically the differential equations of the process. However, they took a constant and rather large value of the droplet radius, they did not consider the influence of pressure and they studied the problem for the case of equal molecular weights of all chemical species. Under such conditions results obtained by assuming an infinite reaction rate are not very different from those derived considering finite chemical kinetics.

containing toothpastes. However, this dental products supply a high concentration of ionic fluoride directly to the biological fluids increasing the risk of toxicity and dental fluorosis. 5 In this sense future perspectives of fluoride utilization are found in optimizing the control and/or slow release of fluoride in the oral environment. For this reason, a toothpaste with a controlled release of mineral ions based on an ion- exchange system, specifically an ion-exchange resins mixture that releases calcium, fluoride, phosphate and zinc ions (named NMTD), was developed. The application of ion-exchange materials has advantages in comparison with the conventional chemical reagents. These materials do not introduce undesirable ions into the solution, ion release is carried out only by the ion-exchange mechanism, they are characterized by practically neutral pH values and they can absorb bacteria on the surface. Once again, it is essential to formulate an adequate toothpaste matrix compatible with the function of anticarious treatment of dental tissues of the ion-exchange resins mixture, which is going to be encapsulated.

Following the Hohenberg–Kohn theorem (HKT) [62] to represent and describe molecules and their corresponding chemical reactivity, the electron density corresponds to an appropriate choice because it is a local function defined within the exact many body theory, and it is also an experimentally accessible scalar field. As Martín-Pendás et al. [63] remark: “The best known approach is based on choosing the electron density, ρ (r), as basic variable. This is the simplest invariant scalar that can be constructed from orbitals, and the joint use of the theorems of Hohenberg and Kohn [62] and Mezey [64] guarantees that such a scalar must carry chemical information both globally and locally.” The global point of view has crystallized in what we know today as conceptual density functional theory [65], which has provided a sound physical foundation to electronegativity and electronegativity equalization, frontier orbital theory, etc. The local image, in turn, evolved independently, giving rise to topological theories of the chemical bond [66]. These powerful approaches work in synergy with the relief that a theory based on an experimentally available magnitude [67] incites in non-theoreticians.

In order to calculate the overall estrogenicity of the adipose tissue extracts, samples were tested in the E-Screen bioassay, which measures the proliferative effect of xenoestrogens on MCF-7 breast cancer cells by comparing cell yield between cultures of MCF-7 cells treated with estradiol and those treated with different concentrations of xenobiotics or extracts (Soto et al., 1992). Each adipose tissue extract was resuspended in 5 mL Dulbecco's modified Eagle's medium without phenol red, supplemented with 10% charcoal dextran-treated human serum, and was then tested in the E-Screen bioassay for estrogenicity at dilutions of 1:1, 1:5, and 1:10, using a slight modification of the originally described technique. Each sample was assayed in triplicate with a negative (vehicle) and positive (estradiol) control in each plate. The proliferative effect of the adipose tissue extract was referred to the maximal effect obtained with estradiol, transformed into estradiol equivalents (Eeq) units by reading from a dose–response curve, and expressed in Eeq units per gram of lipid.

Even though the application of external mechanical forces has been linked to chemistry since its beginning as science (e.g. maceration and grinding of raw materials), it has been only in the last years that it has received attention as a possibility to induce chemical reactions or change physical chemistry properties. Since the introduction of the surface force apparatus in the early 1970’s, a new and proliferous experimental field in the researching of the interaction of external forces with molecular systems has bloom. The capacity to measure not only the macroscopic properties of some bulk material under stress, but the ability to follow the breaking of a covalent bond into single molecules, has endowed us with chemical information that was not possible to obtain before, clearing the way to design new simulations. For an extended discussion of the state of the art in Mechanochemistry see: (Balaz, et al. 2013, Beyer and Clausen-Schaumann 2005).

Mortar specimens were prepared according to the factorial experimental design using chemical admixtures and self-healing agents as experimental factors. Two chemical admixtures were used: calcium lignosulfonate 23.5%, a common plasticizer, and sodium lauryl ether sulfate 4%, a common air-entraining agent. Self-healing agents BC, B, and C were used. Twelve mixtures were prepared in triplicate. Table 1 shows the combination and nomenclature used to prepare these mortar specimens. Each specimen consisted of 4x4x16 cm prisms with shear and flexural reinforcement to allow controlled crack formation upon loading. They were prepared with Type I Ordinary Portland Cement, water, siliceous sand, LWA and chemical admixtures (Table 2). Chemical admixtures were dosed according to supplier’s recommendations: 0.5% of cement weight for the plasticizer and 120 mL per 100 kg cement for the air-entraining agent.

Crapiste, G.H. y Rotstein, E. (1997). Design and Performance Evaluation of Dryers. Cap. 4 (pág. 125-165) en Handbook of Food Engineering Practice (Editores: Valentas, K.J.; Rotstein, E. y Singh, R.P.), CRC Press, Boca Raton y New York.

The further step on this research is to understand the main cause of the estuarine breezes in Lisbon through the calculation of the energy balance both in the city and in the estuary. For this purpose, several temperature and humidity dataloggers will be installed in different sites of Lisbon and radiance measurements will take place on the summer of 2004.

ABSTRACT. A study was conducted in the experimental area of INCA, Havana province, on a compacted Red Ferralitic soil. A split plot design with four replications was used in order to evaluate four biofertilization systems in two cropping sequences: soybean (Glycine max L.)-corn (Zea mays)-sweet potato (Ipomea batata L) and soybean-sunflower (Helianthus annus)-sorghum (Sorghum vulgaris). Seeding started in 1998 spring with 32 plots of 100 m 2 (10x10 m). Biofertilizer was applied by seed pelletization before sowing. Soybean was inoculated with Bradyrhizobium japonicum (ICA 8001 strain) and Glomus clarum, whereas the remaining crops of each sequence were inoculated with Glomus clarum and Burkholderia cepacia. For each crop, yield, mycorrhizal colonization and endophyte weight percentages were evaluated, while soil evaluations were performed on real density (Dr), bulk density (Da), texture, degree of aggregation, stability coefficient and dispersion index. Results showed a notable influence of biofertilization system and both crop sequences on the degree of aggregation and some indicators of soil physical properties evaluated.

Nevertheless, in the area in which clinical data are most scarce –molecular diagnosis in non-respiratory VDPSOHV VXFK DV VWHULOH ERG\ ÁXLGV HVSHFLDOO\ XULQH &6)DQGSOHXUDOÁXLGVDQGJDVWULFDQGWLVVXHDVSLUDWHV LQFOXGLQJIRUPDOLQÀ[HGVDPSOHV²SDUWLFLSDWLRQLVUH- quired by multiple institutions to carry out an optimal clinical study design to evaluate PCR in extrapulmonary VDPSOHV3URWRFROVVKRXOGEHGHYHORSHGWRVWDQGDUGL]H VDPSOHSURFHVVLQJZLWKDVXIÀFLHQWQXPEHURISURWRFROV at each site to obtain an adequate quantity of positive UHVXOWVDQGWREHDEOHWRYDOLGDWHWKHVH 46,47

For all the CL spectra recorded, two main peaks around 3.34 and 3.31 eV are observed. The other peaks, with lower intensity, correspond to phonon replicas of the 3.31 eV peak. In wurtzite-type ZnO, the peaks located between 3.32 and 3.36 eV are attributed to bound exciton transitions, being the most prominent lines labeled as I4, I6, and I9. 32 The spectral resolution of our CL equipment could not resolve adequately these bound exciton transitions because the spectra were acquired at 80 K, being thus observed a relatively broad band around 3.34 eV, which includes the different bound excitonic transitions and the free exciton emission in the high energy flank. The origin of the peak around 3.31 eV remains contro- versial. It has been associated with the first LO phonon replica of the free exciton (1LO-FX); 33,34 with a DAP

• The influence of the minimum element size on crack opening and closure results has been analysed considering a three-dimensional model. The error can be minimized when a minimum element size is established as δ<0.015 for K ttop and δ<0.03 for K ncop

The main production method of unsaturated hydrocarbons is cracking of petroleum hydrocarbons including heavy liquid fractions i.e., crude oil [5]. However, steam reforming processes take place at high temperature which results in the formation of a few percent of alkadienes and/or alkynes as impurities, i.e. 0.3 to 6.0% of residual butadiene in butenes, 0.5 to 3% of acetylene in ethylene and 2 to 8% of propyne and propadiene in propene [6], [7]. These impurities contained into the alkene cuts can easily poison the catalysts employed for polymerization reactions [2]. An example is illustrated by B.J.Burger et al. when 2-butyne impurity altercates the catalyst during 2-butene polymerization [8]. Thus, to avoid catalyst poisoning, impurity level must be controlled and not exceeded 10 ppm [9]. In essence, there are three alternatives to eliminate or reduce the alkynes and dienes impurities:

Figure 5 shows the considerable increase of water absorption taking place when grinding fineness decreases. It is noticed that specimens elaborated with grinding fineness of 297 m at firing temperatures of 800°C and 900°C, they achieve the maximum water absorption value allowed by Cuban regulation NC 359- 2005 for standard red ceramic bricks (18%). By increasing temperature at 1000°C, water absorption values considerably decrease for the three fluxing agent fineness sizes, because at this temperature and, due to the calcite addition, the material vitrification takes place thus diminishing pores amount (Betancourt et al., 2007). Figures 4 and 5.

In the case of external irradiation of film coated tubing, the electron–hole (e–h) pairs are photogenerated more intensely close to the interface film-tubing (x = 0); these carriers have to migrate to the surface of the film (x = d) in order to contribute to the photocatalytic process. Thus, the film thickness constitutes a crucial parameter that determines the photocatalytic activity of the film. Consequently, relative activity should increase as a function of film thickness, only in the case where the film thickness (d) is small or approximately to the diffusion length (L) of the photogenerated species. In this circumstance, almost all of the e–h pair photogenerated in the volume of the film were able to diffuse to the film surface, contributing to photocatalytic reaction [34]. Therefore, in this thickness interval (d ≤ L), as the photogenerated carriers increase with film

In comparing values to those obtained in previous studies about the EKF technology in smaller scales (Risco et al., 2015, 2016e), it can be drawn that average temperature during the prototype test is 29.4 C which is more than 10 C above the average temperature maintained in the mockups (18.2 and 19.3 C for the oxy fl uorfen and the 2,4-D tests, respectively). In those lower-scale cases-of- study, the increase of temperature was much lower, which it can be easily explained because of the lower ohmic loses associated to the closer position between electrodes. Another difference is worth to be pointed out. In the mockup, the portion of soil surrounded by electrodes (so-called electrokinetic zone) showed a temperature which was almost 4 higher than the external zone, although this increase was found to be not high enough to lead to signi fi cant changes in the volatilization properties. This is just the opposite behaviour of what it is observed in the prototype, in which the temperature in the zone surrounded by the electrodes is lower. This fact points out that, although the same processes are occurring (in this case, the electric heating, which is more intense in the nearness of electrodes), and the same energy transport mechanisms are affecting to soil, the different sizes of the evaluation facilities lead to a completely different temperatures distribution map. Regarding the lab-scale plant (results not shown), no signi fi cant differences in the temperature were observed over the tests. In this case, the very low resulting current intensities (in the range from 10 to 20 mA) helps to explain that any small increase in temperature could be compensated by the evaporative cooling and also by the exchange R. L opez-Vizcaíno et al. / Chemosphere 166 (2017) 549e555

The solubility of SPNA was measured similarly to the procedure reported by Panteli et al. 37 Approximately 15–20 mg of SPNA and 1 mL of buffer were placed in a 1.5 mL Eppendorf safe-lock micro test tube. The sample was stirred for 48 h at 1400 rpm and left to settle for 24 h at 303.15 K in a climate chamber. If the upper phase was turbid after that time, the tube was centrifuged at a controlled temperature of 303.15 K in a preheated benchtop centrifuge from Fisher Scientifics for 1 min. Samples from the liquid phase were taken with a 200 mL pipette from Eppendorf and dissolved in buffer in a 1 : 200 ratio. Samples were analysed in an Eppendorf UV-Vis Biospectrometer at 315 nm using molar extinction coefficients listed in Table 9. Extinction coefficients were determined for reaction conditions and are thus valid for 303.15 K and a pH of 8 in a 100 mmol kg 1 Tris–HCl buffer. As the pH remained constant over the reaction period possible protonation or deprotonation effects were not accounted for.