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A microfluidic platform to extract uranium from HNO3 (nitric acid) medium using tri-isoamyl phosphate (TiAP) dissolved (30% v/v) in ionic liquid ([BMIM]PF6) is reported. PTFE microbore tubes serve as the microchannels. The quality of dispersion inside the translucent tubes was observed using a camera. The images obtained are used to understand the observed experimental trends. Overall volumetric mass transfer coefficient was determined considering the microchannel as a differential contactor with co-currently flowing phases. The effects of contact time, flow velocity, organic to aqueous (O/A) ratio and microchannel diameter on mass transfer performance are studied. Effect of different coiling configurations on mass transfer performance was compared. Under optimum conditions, 95.3% of uranium present in the feed (corresponding stage efficiency being 99.2%) could be extracted within a contact time of about 200 s in a single contact. Corresponding (KLa) was 0.024 s−1. Coiling was found to have a significant effect on values of KLa especially at low residence times.

Large-scale continuous synthesis of ionic liquid [BMIM]Br in solvent-free mode is carried out in a 862 μm diameter microbore tube. A 750 μm diameter T-junction is used to mix the two reactant streams. The effects of reaction temperature, residence time and flow velocity on product yield, space-time-yield (STY), production rate (PR) and specific power consumption are studied. Product yield is observed to increase with an increase in residence time and reaction temperature. The conditions which maximize STY and PR while ensuring that the overall reaction is kinetically controlled and yield is close to 100% are obtained. Maximum STY of 213.1 g/min-L could be attained at reaction temperature of 90 °C and a residence time of 4.93 min. At the same conditions maximum PR of 7.1 kg/day could be attained with 100% yield, the specific power consumption being 27.67 W/kg. Plug flow reactor (PFR) model is found to reproduce experimental data better compared to a laminar flow reactor (LFR) model. Performance of a simple T-junction micromixer is compared with commercially available micromixers and is found to be at par with them.

Considering the beneficial aspects of ZnO doping in silicate and borosilicate glasses for bioactive glass, nuclear waste vitrified glass and many other applications, the combined experiments and molecular dynamics (MD) simulations were performed over wide range of composition. First principles ab-initio MD (AIMD) simulations confirmed the transferability of B-K-S potential model for multi-component glasses. A significant change in glass structure was monitored from short range order parameters: pair correlation function, coordination number, as well as intermediate range order parameters: bond/angle distribution profiles, structure factor and probability of X-O-X\ (X,X\ = Si, B, Zn) connections. Order of connectivity illustrated that hydrolysis of glass will slow down with addition of ZnO in the glass matrix. Successively, the effect of microscopic structure on observable glass properties: chemical durability, mechanical strength, thermal stability and characteristic vibrational spectra was analyzed. Results show good match of MD estimated trend for Young Modulus, glass transition temperature, and leaching data with the experimental observations, hereby, confirm the transferability of applied potential parameters for multi-component (n≥4) glasses. Both the experiments as well as MD simulations report the enhanced chemical durability of glass withZnO addition. Low R (Na2O/B2O3) and high K (SiO2/B2O3) of ZnO doped sodium borosilicate (Zn-NBS) glass surface compared to bare NBS represents the more stable structure of glass surface for Zn-NBS than NBS. During contact with water, Na+ ions were less likely to leach out from glass to aqueous solution for Zn doped glasses. The enhanced chemical resistivity of Zn-NBS was also established from the increasing activation energy for diffusion of Na ions. Likewise, the ring statistics as well as Na cluster size also supported the reduced chemical reactivity of Zn added glasses. The systematic study of linkage between network formers, ring statistics, diffusion dynamics and ion/water migration provides significant understanding of glass dissolution mechanism. Also, results predict the beneficial impact of ZnO doping for improved strength of glass skeleton, which would eventually control the glass degradation due to micro cracking. The combined studies from experiments and MD simulations disclose many interesting microstructure and dynamics due to the presence of ZnO in the glass.

Copper–Chlorine cycle has been identified as the most prospective among the low temperature thermochemical cycles for hydrogen production. The cycle consists of two thermal reaction steps, one electrochemical step and a physical separation step. The two thermal reaction steps, hydrolysis and thermolysis are carried out in series for water splitting and oxygen production, respectively. The solid product from hydrolysis step Cu2OCl2 enters the thermolysis step where it undergoes decomposition to CuCl and O2. In the present work, thermolysis experiments were carried out in a laboratory scale horizontal furnace reactor with CuO–CuCl2 equimolar mixture and Cu2OCl2 in the temperature range of 470–575 °C. Experiments in furnace reactor show that, under otherwise same conditions, similar conversions are obtained with Cu2OCl2 as well as with the equimolar mixture of CuO–CuCl2. It was also observed that the conversion increased with an increase in CuCl2 percentage in the reaction mixture. From the experimental data, an attempt has been made to provide insights into the reaction mechanism and kinetics. These results are expected to be useful for the design and scale-up of the thermolysis reactor.

Liquid-liquid two-phase flows are central to solvent extraction processes. In a columnar solvent extraction contactor, the turn-down ratio can be increased by imposing oscillatory flow over steady ...

The fusion of valuable material properties has led to the acceptance of sodium borosilicate (NBS) glasses for nuclear waste immobilization. Although popular, the mechanisms associated with these properties are still only partially discovered and need further exploration. Bearing this in mind, the combination of experiments, molecular dynamics (MD) simulations and the Dell, Yuan and Bray model have been used to understand the role of composition variation for structural and physical aspects of vitrified borosilicate glasses. Experiments have been conducted to evaluate the macroscopic glass parameters of density (ρ), glass transition temperature (Tg) and thermal expansion coefficient (TEC). Experimentally observed trends for ρ, Tg and TEC with composition have been found in good agreement with the MD results. MD studies also provide a microscopic understanding of the glass structure and phenomena associated with the change in the glass composition. A detailed view of local structure and medium-range connectivity for the borosilicate glasses has been explored. Owing to a large B4 population, the results showed the abundant presence of BO4-BO4 connections, we hereby omit the generally accepted "B[4] avoidance rule" for glass. The relative propensity for connecting SiO4/BO3/BO4 structural motifs is in line with the predictions made by the Dell, Yuan and Bray model. Furthermore, the effects of composition on the mechanical integrity of NBS glasses, including the elastic nature, plastic distortion, yielding, breaking stress, and brittle fracture, have been explored by MD simulations. In addition, the glass dynamics have been evaluated by diffusion coefficient and the results suggest that Na+ is likely to be more mobile in the case of NBS1 as compared to NBS2 and NBS3 due to significant disruption in the glass network introduced by a larger amount of Na2O network modifier. Also, the diffusivity was reduced with increasing B2O3 due to the altered role of Na+ ions from network modifiers to charge compensators. The combined study of experiments, MD simulations and the Dell, Yuan and Bray model establish the correlation between the microscopic structure and macroscopic properties of NBS glasses with varied composition, which might be of great scientific use for future glasses in various applications including nuclear waste immobilization.

Computational Fluid Dynamics (CFD) is used to predict continuous phase axial dispersion coefficient for liquid-liquid two-phase flow in a pulsed-sieve plate column (PSPC). The CFD model is based on...

Tungsten (W) has shown promise to be the most favored plasma facing material in nuclear fusion with deuterium (D) and tritium (T) as fuel. In order to identify a better material, atomistic understanding of the behavior of D/T with W is highly desirable. Here, we report the mechanistic pathways of diffusion of H, D and T in bcc W employing density functional theory (DFT) using PBE and PBE-D3 functional and harmonic transition state theory. The activation diffusion barrier was determined using nudge elastic band techniques. The zero point energy (ZPE) was incorporated by phonon calculations to include the isotope effects. The surface adsorption of H, D and T is predicted to be exothermic, whereas surface to sub-surface and bulk absorption is endothermic but the vacancy induced absorption in bulk W was predicted to be exothermic. H, D and T atoms were observed to be diffused preferably from tetrahedral site to the nearest tetrahedral site. The calculated diffusion coefficients, rate constants, permeability constants and solubility are found to be higher for H compared to its heavier isotopes D and T. The trends of diffusion, permeation and solubility for H, D and T are well in agreement with the experimental results. The diffusion values predicted for H isotopes in bcc W from PBE-D3 method is quite close to the experimental values compared to PBE method. But, the calculated and experimental ratio of diffusivity, permeability and solubility of any two H isotopes follow the similar trend and no considerable change is noticed between PBE and PBE-D3 methods. Further, the calculated diffusion coefficients are shown to be one order of magnitude lower than Cr and two orders than Fe and thus might be the basis for considering W as plasma facing materials. The present study might be useful in modeling the behavior of tritium in W metal for which data is either scattered or least available.

Liquid–liquid solvent extraction process consists of dispersion of one phase into another in the form of fine drops and allowing the solute of interest to migrate from one phase into the other. Sub...

Computational fluid dynamics – population balance (CFD-PB) simulations are performed to predict Sauter mean drop diameter and dispersed phase holdup for liquid–liquid two-phase flow in a pulsed dis...

Hydrolysis of CuCl₂ is the water splitting step of the Cu–Cl thermochemical cycle, where CuCl₂ reacts with steam to produce Cu₂OCl₂ and HCl. In the present work, this gas–solid reaction was investigated to understand the mechanism and kinetics. Experiments were conducted in a semibatch fluidized bed reactor to study the effect of temperature (275–375 °C), steam mole fraction (0.4–0.9), and reaction time (0–3 h). The challenges due to the hygroscopic nature of the reactant, product agglomeration, and multiple side reactions to achieve smooth and consistent reactor performance were overcome by the addition of inert additives during fluidization. The analysis of the mechanism showed that the desired product Cu₂OCl₂ is formed initially and further undergoes decomposition to CuO and CuCl₂. Also, with increasing temperatures, the yield of Cu₂OCl₂ decreases because of the formation of CuCl from reactant decomposition. The results indicate that a minimum steam mole fraction of 0.5 is required to prevent the formation of side product CuCl in the temperature range of 300–325 °C. The minimum steam requirement for maximum yield to Cu₂OCl₂ was found to increase with increase in temperature.

Kinetics of solvent extraction of zirconium, from raffinate generated in zirconium purification plant, have been studied, using tributyl phosphate as the extractant solvent. The system being a liqu...

Experiments are carried out to study the separation of liquid-liquid dispersion generated at a microfluidic junction by using an in-line phase separator. The phase separator comprises a metallic mesh sandwiched between two flow channels. Dispersion generated at the microfluidic junction is fed to the upper flow channel of the in-line phase separator. Continuous phase permeates through the metallic mesh into the lower flow channel and gets separated from the dispersed phase. The effects of operating parameters (flow rates of the aqueous and organic phases), flow channel geometry and mesh properties (pore size and thickness) on phase separation are studied. After identification of operating window in which complete phase separation is achieved, mass transfer experiments are performed to demonstrate intensified uranium extraction using a micromixer and in-line phase separator.

Isotope effect is a quantum mechanical phenomenon and thus poses a challenge for the separation of isotopes of an element of interest, especially for heavy elements. Isotopic fractionation of zinc is also quite difficult and challenging but is necessitated due to various applications of its isotopes ranging from nuclear medicine to nuclear power reactors. Here, we developed the dibenzo-18-crown-6 (DB18C6) ether-functionalized poly(methacrylic acid) (PMA) resin by exploiting the ion and isotope recognition ability of the crown ether using DFT/MD simulations followed by experiments for isotopic fractionation of zinc. The PMADB18C6 adsorbent was prepared and suitably characterized. Both computational and experimental findings demonstrate that the adsorption and isotope separation of zinc with PMADB18C6 are due to the molecular recognition effect of the "O" dipole of the crown ether. Furthermore, both MD simulations and experiments suggest Langmuir type adsorption isotherms. The adsorption of Zn2+ ions on the PMA resin is predicted to be endothermic, whereas it is exothermic on the PMADB18C6 resin, as revealed from the experimentally observed enthalpy change. A small scale fixed bed column study was demonstrated to test the scale-up application. The values of the experimental separation factors: 1.0013 for 66/64 and 1.0027 for 68/64 confirm the computationally predicted results of 1.00088 and 1.0010, respectively, thus establishing the combined strength of the theory and experiments for the identification of efficient fractionating agents for a complex quantum isotope effect which eventually helps in planning further experiments in view of medicinal and technological applications of zinc isotopes.

The fundamental understanding of adsorption, absorption, diffusion, and permeation of hydrogen and its isotopes is of paramount importance in controlling the hydrogen-induced embrittlement and also...

Pulsed disc and doughnut columns (PDDCs) and pulsed sieve plate columns (PSPCs) are widely used for liquid-liquid extraction processes in nuclear fuel cycle. In this study, experiments are performed to understand the effects of operating parameters (continuous phase velocity, dispersed phase velocity and pulsing velocity) on Sauter mean diameter and drop size distribution in PDDC and PSPC. Experiments are conducted in aqueous continuous mode of operation using 3N nitric acid as the aqueous phase and 30% TBP in dodecane as the organic phase. Previously reported correlations for estimating drop diameter in PSPC and PDDC are evaluated with the experimental data of this study. Correlations based on modification of previously reported correlations are proposed for estimating Sauter mean drop diameter in PSPC and PDDC.

Numerical simulations of liquid–liquid counter-current two-phase flow in pulsed disc and doughnut columns (PDDCs) are performed. The simulation methodology comprises two steps. In the first step, t...

Selection of suitable glass composition for vitrification of high-level radioactive wastes (HLWs) is one of the major challenges in nuclear waste reprocessing. Atomic and molecular level understand...

Understanding the phenomena of formation of single drops is necessary to understand the hydrodynamics in solvent extraction equipment which are used for separation of nuclear materials. In this work, the phenomena of aqueous phase and organic phase drop formation at submerged nozzles are compared by conducting experiments with 30%TBP (v/v) in dodecane as the organic phase and nitric acid as the aqueous phase. Two different nozzles and three different nitric acid concentrations are used. For each nozzle and nitric acid concentration, velocity of the dispersed phase is varied. Drops of aqueous phase formed at downward oriented nozzles submerged in organic phase are observed to be smaller than the drops of organic phase formed at upward oriented nozzles submerged in aqueous phase. Correlations to estimate drop diameter are proposed. Keywords: Dodecane, Drop formation, Nozzle, Nuclear fuel cycle, Solvent extraction, TBP

A 2D computational model coupling two-phase CFD and population balance equations is used to predict dispersed phase holdup and Sauter mean drop diameter in a pulsed sieve plate column which is relevant for solvent extraction in nuclear fuel cycle. Spatial and temporal variations of drop diameter are captured by the model. Population balance equations consider both drop breakage and coalescence in the column. Standard breakage and coalescence kernels are used to model breakage and coalescence rates. The model is validated using reported experimental data of dispersed phase holdup and Sauter mean drop diameter. In the first round of simulations standard Kumar-Hartland drag model is used to model the interphase momentum exchange. The average absolute relative error in estimation of dispersed phase holdup and Sauter mean diameter are found to be 13.6% and 8.5%, respectively. Optimization of the model constants of Kumar-Hartland drag model is done to reduce the error in dispersed phase holdup prediction to 5.6%.

Solvent extraction is an important separation process having many applications in chemical process industry, wastewater treatment, and separation of nuclear materials in the front-end and b...

The phenomenon of drop formation at a single plain hole and a single nozzle hole in a plate submerged in a quiescent continuous phase is studied by carrying out numerical simulations. Phase...

CFD simulations of Pulsed Disc and Doughnut Columns (PDDCs), which are used in solvent extraction based separation processes, are preformed to predict dispersed phase holdup in two-phase flow. Flow field is obtained by using Euler-Euler approach embedding continuity and momentum equations along with equations of the standard k-e mixture model of turbulence. The dispersed phase is assumed to be monodispersed. The momentum equation of the dispersed phase is modified to account for the effect of collisions among drops on dispersed phase holdup. The model is validated with in-house experimental data for different geometric and operating conditions. Predictions of CFD model are found to be better than the predictions of the reported correlations for estimating dispersed phase holdup in PDDCs. The validated computational approach is used for parametric analysis to understand the dependence of dispersed phase holdup and other hydrodynamic variables on operating and geometric parameters and scale-up methodology.

Detection of liquid-liquid interface is critical in solvent extraction equipment/contactors typically used in petroleum and hydrometallurgical industries. An instrumentation system, comprising of a self-calibrating ultrasonic sensor and a novel signal processing algorithm is reported. It can be used to estimate location of liquid-liquid interface along with speed of sound in both the liquids without any manual/user intervention. The algorithm involves use of discrete wavelet transform and matched filter. The system has been tested at laboratory scale under wide range of industrially relevant conditions. The system works for any pair of liquid without apriori knowledge of their acoustic characteristics, is insensitive to changes in temperature and/or compositions. It also works for dirty interfaces contaminated with particulate matter or emulsion. The above mentioned features truly impart the sensor system “deploy-and-forget” capabilities. The range, accuracy and resolution of the system, with respect to interface location, are 40–200 mm, 0.45% FS (Full-scale) and less than 1 mm, respectively.

Dispersion polymerization to synthesize polystyrene nanoparticles is implemented in a simple micro reactor for the first time. The reactor could be operated smoothly without any choking. The nanoparticles obtained using microfluidic approach (∼250 nm, 10% PDI) were much smaller and much more uniform as compared to those obtained in batch (`650 nm, 65% PDI). Residence time was seen to reduce particle size while it was not seen to have any impact on the polydispersity index.

The metal–organic frameworks (MOFs) have the potential as hydrogen storage materials due to large surface areas and presence of binding sites. To further enhance H2 storage capacities of MOFs, crown ethers have been incorporated to improve the interaction energies between the framework and binding molecules (H2). Therefore, the present study deals with the structure and energy of complexes of H2 with crown ethers (dibenzo-12-crown-4 and dibenzo-18-crown-6) and alkali metal ion decorated crown ethers at the DFT level of theory. The binding energy of H2 with only crown ethers was shown to be positive and thus not suitable for adsorption. But, after decoration with metal, namely Li and K, the binding energy of H2 was seen to be negative indicating feasibility for H2 adsorption. Increase in binding energy indicates an increase in stability of the complex, and as such, catenated crown ethers have a much improved hydrogen storage capacity allowing them to hold more molecules of hydrogen. Also, the binding energies are greater for Li+ systems compared to K+ systems, thus showing it as a better catenating agent than the latter. Also, Li+ incorporated DB18C6 in the MOF moiety has shown favorable H2 binding compared to Li+ incorporated DB18C6. The present computational results thus suggest that Li+-crown ether might be incorporated within MOF to enhance hydrogen storage capacity.

Niobium and tantalum are valued for their uses in nuclear, steel, aviation and electronics industries. This paper elucidates the development of a multistage counter-current separation process for obtaining pure niobium and tantalum from the hydrofluoric acid solution of Coumbite-Tantalite ore (leach liquor), with trioctyl amine (TOA) as the extractant solvent. Contrary to the conventionally used multistage process this novel route does not use any other acid in addition to hydrofluoric acid, resulting in the elimination of the generation of mixed fluoride waste. Reaction equilibrium constants for the reactions involving the extraction of hydrofluoric acid, niobium and tantalum have been determined and were used to generate equilibrium distribution curve of niobium and tantalum in the organic and aqueous phase. The number of counter-current stages required for an appropriate organic to aqueous phase volume (O/A) ratio was determined using McCabe-Thiele calculations. Selective extraction of 99% of tantalum from the leach liquor was achieved using 5 v/v% TOA and two counter-current stages for an O/A ratio of four. The tantalum lean raffinate was treated with commercial grade hydrofluoric acid to form the niobium feed solution having 16 M free acidity. Near complete extraction of niobium was achieved using a three stage counter-current process with O/A ratio of two and 10 v/v% TOA as the organic extractant. The calculations for the stage-wise variation of concentrations were validated by batch experimental simulation of counter-current processes.

This experimental study is focused on several aspects of microfluidic solvent extraction of uranium in setups comprising of microbore tube(s) connected to microfluidic junction(s). Extraction experiments are carried out using simulated lean aqueous phase having 550 ppm uranium in 1 M HNO3 as the feed. The organic phase consists of 30% (v/v) tributyl phosphate (TBP) in dodecane. The effects of flow rate on flow pattern, mass transfer and settling are studied. Performance of a straight microbore tube is compared with a coiled microbore tube of identical diameter and length. Two-stage extraction and stripping at total flow rate of 10 LPH are demonstrated using 20 parallel microbore tubes to highlight the ease of scale-up by numbering up.

Computational Fluid Dynamics (CFD) simulations have been performed to understand the effects of different operating and geometric parameters on axial dispersion and pressure drop for single-phase flow in annular pulsed disc and doughnut columns (APDDCs) which are relevant for spent nuclear fuel reprocessing. The first step of the two-step computational approach involves solution of Reynolds Averaged Navier-Stokes (RANS) equations with standard k-e model of turbulence in 2D axisymmetric computational domain to obtain velocity and pressure fields. In the next step, dilute species transport equation is additionally solved to obtain residence time distribution (RTD) and axial dispersion coefficient. The computational approach has been validated by using experimental data of pulsed disc and doughnut columns (PDDCs) reported in literature. The validated computational approach has been used to perform parametric analysis to understand the effects of flow velocity, amplitude of pulsing, disc spacing, percen open area, the ratio of outer diameter and inner diameter of the annulus and flow cross-sectional area on pressure drop and axial dispersion coefficient.

Host-guest encapsulation has been widely applied for purification and seizing of the metal ions. Macrocyclic crown ethers are one of the most popular hosts in the field of host-guest chemistry, which on functionalization with polymers are employed as an effective adsorbent. In spite of their vast applications, the microscopic information about their sensing mechanism toward cations/molecules is very scarce. Therefore, the present study is focused on the molecular insights of ion-exchange mechanism within the cavity of crown ether-functionalized polymers using molecular dynamics (MD) simulations. This present study investigates the molecular-level events of chloromethylated polystyrene (CMPS) bearing dibenzo-18-crown-6 (DB18C6) in the aqueous and acidic environment, which has been found to be particularly successful in sensing of various alkali and alkali earth metal ions. A strategy has been envisaged to design a crown ether-based functionalized polymeric resin, which exhibits good match of properties with the in-house-synthesized resin. The MD studies well capture the experimentally observed Langmuir-type adsorption isotherms of Li+ ions on crown ether-grafted polymer resins. The presence of acid reduces the adsorption of Li+ ions due to the competition with H3O+ ions. In addition, the results revealed that the "adsorption in crown cavity" follows a dual residence time function. To the best of our knowledge, this is the first report on the adsorption isotherm of functionalized crown ether using MD simulations. The structure and dynamics of binding sites were explored using radial distribution functions and diffusion coefficients. All of these effects have been studied for different Li+-ion concentrations, acid concentrations, and counterions as well as different lengths of polymer chains and degrees of polymerization. Overall, the present study provides insights into and quantitative information about adsorption on the CMPS-DB18C6 resin, which might be useful in myriads of host-guest-based adsorption experiments.

A predictive two-phase CFD model requiring no experimental input is used to estimate dispersed phase holdup in a pulsed sieve plate column (PSPC). Drop diameter used in simulations is obtained from...

The Cu complex, which is the key chemical species in well-known Cu–Cl hybrid thermochemical cycles and also in numerous metal hydrometallurgical and sedimentary deposit processes, displays a wide variety of structural and dynamical characteristics that are further complicated by the presence of multiple oxidation states of Cu ions with different coordination chemistries, therefore they are difficult to explore from experiments alone. In this article, an attempt has been made to understand the coordination behavior of the Cu complex using MD simulations. The study provides compelling evidence of the experimentally observed multiple stoichiometries of Cu ions, i.e., 1:6:0, 1:5:1, and 1:4:2 for Cu+:H2O:Cl– and 1:6:0 for Cu2+:H2O:Cl–. The presence of the anionic Cu complex, [Cu+Cl2]−·2H2O, [Cu+Cl2]−·3H2O, [Cu2+Cl3]−·H2O, and [Cu2+Cl3]−·2H2O, was captured in the presence of excess chloride ions. Furthermore, the probability distribution profiles have been estimated to determine the most possible complex in the...

A liquid-liquid two-phase flow based segmented microfluidics system comprising of a simple microfluidic junction and a PTFE microbore tube to synthesize BaSO4 nanoparticles is reported. The system is shown to be robust enough for continuous operation without any chocking. The effects of different operating parameters such as A/O ratio, initial concentration of precursors, precursor molar ratio and flow velocity on particle size and polydispersity index are studied. The above-mentioned parameters are important in synthesizing nanoparticles of precise and controlled size. Three different microfluidic junctions are evaluated for their influence on particle size and polydispersity index. Under optimum conditions, small and monodispersed BaSO4 nanoparticles (particle size and polydispersity index being 65 nm and 0.10, respectively) could be synthesized continuously using a cross microfluidic junction and microbore tube.

Polluted water sources due to enormously enhanced human population or rapid industrialization need to be treated as they have an adverse effect on human health. CNTs are becoming quite popular in the field of adsorption, which on functionalization with various functional groups can be employed as effective adsorbents. The present study explores the adsorption mechanism of Cd++/Hg++ with carboxyl (COOH), amine (CONH(CH2)2NH2) and sulfur (CONH(CH2)2SH) based CNTs, using molecular dynamics (MD) simulations. The study investigates the molecular level events of adsorption both in aqueous and acidic environments. The MD studies capture well the experimentally observed Langmuir type adsorption isotherms of metal ions for the CNTs. The presence of acid was found to reduce the adsorption of metal ions due to competition with H3O+ ions. The results establish the use of amine based CNTs over sulfur based CNTs for the adsorption of Cd++ ions. However, for the adsorption of Hg++, both amine based CNTs as well as sulfur based CNTs were found to be equally suitable. The simulation trajectories visualize the binding sites for adsorbed ions, which preferentially reside near the O atom for most of the functional groups and also near the N atom of the amine at higher concentration. In addition, the adsorption correlation function and corresponding residence time distribution were used to determine the strength of binding. Also, the rich structural and dynamical events were explored via RDF, CNs and diffusion coefficients. The higher the adsorption capacity of the functionalized CNTs, the lower the hydration number of the metal ions was estimated compared to the bulk value. In particular, the dynamics of the metal ions were found to support well the trend, followed by the primary hydration number as well as the order of the maximum adsorption capacity (qmax) exhibited by the different CNTs. The present study provides insights and quantitative information for the adsorption of metal ions with functionalized CNTs, which might be very useful for the exploration of the myriads of nano-adsorbent based experiments and thus future technology.

Experiments are conducted to understand the effects of important geometrical and operating parameters on continuous phase axial dispersion in liquid-liquid two-phase flow in air pulsed columns having sieve plate internals and disc and doughnut shaped internals. Water is used as the continuous phase. Dodecane containing 30% (v/v) tributyl phosphate is used as the dispersed phase. Among operating parameters, superficial velocities of the dispersed phase and continuous phase are varied. Pulsing velocity also is varied. Among geometrical parameters, column diameter, disc or plate spacing are varied while conducting the experiments. Correlations for estimating continuous phase axial dispersion coefficient reported in literature are evaluated using the experimental data of this study. A previously reported correlation to estimate axial dispersion of continuous phase is found to be good for the pulsed columns having sieve plates. A new correlation is proposed for the air pulsed columns having disc and doughnut internals.

This study reports a detailed comparison of dispersed-phase holdup and onset of different operating regimes in PSPC (pulsed sieve-plate column) and PDDC (pulsed disc-and-doughnut column) for 3 N ni...

Ammonium nitrate is one of the most common wastes generated in both front and back end of nuclear fuel cycle. Accurate and online estimation of ammonium nitrate concentration assumes importance in denitration processes for treatment of this waste. An ultrasonic based concentration estimation system is developed for online estimation of ammonium nitrate concentration in process vessels. A 5 MHz ultrasonic sensor is designed for this aim. The reflected signal is acquired and processed to measure the time-of-flight (TOF) across a known distance, which, in turn, is used to estimate the speed of sound in the medium. The effect of temperature on the results is studied in detail. A linear calibration equation is generated (R2∼0.995) which can predict concentration for measured value of TOF and temperature. Range, accuracy and resolution of the system are 0−150 g/L, 1.8 g/L and 1.5 g/L respectively. Moreover, the system is able to capture rapid dynamics of concentration change, updated every 25 ms. Applicability of the system is also tested with other nitrate bearing medium (sodium nitrate streams).