Range Of Initial Concentrations Research Articles

A green method for extracting molybdenum (VI) from aqueous solution with aqueous two-phase system without any extractant

Abstract An aqueous two-phase system (ATPS) of TX-100 + (NH4)2SO4 + H2O without using any extractant was reported for the selective extraction and separation of molybdenum (VI) from aqueous media. The effects of aqueous pH, initial molybdenum concentration, phase-forming ammonium sulfate and TX-100 concentration, extracting temperature on the extraction of molybdenum were investigated. The experimental results indicate that the extraction rate and distribution coefficient of molybdenum have remarkable relationship with molybdenum species in aqueous phase and reach the maximum of 97% and 75 at pH = 3.00. The extraction rate of molybdenum decrease with increasing temperature within 298.15–343.15 K, and its distribution coefficient decrease with increasing temperature within 303.15–343.15 K, and the thermodynamic analysis of extracting process indicates that polymolybdate anion transferring from salt-rich phase to TX-100-rich micellar phase is a spontaneous and exothermic process. The high distribution coefficient and extraction rate of molybdenum are obtained in the broad initial molybdenum concentration range of 0.1–30 g L−1 in aqueous phase. The extraction mechanism reveals that there is no significant interaction between polymolybdate anion and ethylene oxide unit in TX-100 molecule by Fourier Transform Infrared Spectroscopy (FT-IR) and zeta potential of TX-100 micellar phase slightly changes from positive to negative after extracting polymolybdate anion, and from negative to positive again after adding charge modifier making for separation of molybdenum and metal cations by Dynamic Light Scattering (DLS), which can be deduced that polymolybdate anion is extracted into TX-100 micellar core depending on salting-out effect of phase-forming ammonium sulfate and relatively high hydrophobic nature of polymolybdate anion by micelle solubilization. The stripping rate of molybdenum can be easily achieved to 95% in single stage stripping. Some metal cations (Fe(III), Co(II), Ni(II), Cu(II), Zn(II)) are remained in salt-rich phase and separated from molybdenum under the suitable conditions by adding charge modifiers.

Immobilized particle coating for optimum photon and TiO2 utilization in scaled air treatment photo reactors

This study reports the critical importance of the particle state in TiO2 immobilized photocatalysis. To address this, TiO2 coatings are prepared using two methods: an Air Assisted Spray with an Automatized Spinning Coating (TiO2-AAS-ASC) and a Spread Coating (TiO2-SCM). The state of the TiO2 particles is investigated using SEM and local gravimetry. It is proven that the TiO2-AAS-ASC displays homogeneity, limited particle agglomeration, close to optimum thickness and stability under flow. Furthermore, the prepared coatings are evaluated in terms of photoactivity using acetone in air mineralization in the 24–49μmol/L initial concentration range. This allows Quantum Efficiency evaluations based on absorbed photons and hydroxyl radical consumed. It is proven that the TiO2-AAS-ASC exhibits a close to expected optimum photoactivity and QYs in the 0.4–0.5 range. Furthermore, when the TiO2-AAS-ASC is assessed in terms of QY per unit weight of photocatalyst (QY/W), it shows a value 3 times higher than the TiO2-SCM. This high photon utilization is close to the best possible level expected for an optimized TiO2 coating.

Batch growth kinetic studies for elimination of phenol and cyanide using mixed microbial culture

The efficiency of a mixed microbial culture to eliminate phenol and cyanide from aqueous solution was estimated in a batch process. The influence of initial concentration of phenol and cyanide on the microbial growth was calculated for the range of initial concentration between 50 and 1500mg/L of phenol and 5–150mg/L of cyanide. A maximum specific growth rate of 0.0663h−1 was observed at 250mg/L of phenol and 0.143h−1 at 25mg/L of cyanide concentration in the growth medium. The specific growth rate of the culture followed substrate inhibition kinetics. Monod, Haldane, Edward, Yano and Koga, Luong, Han-Levenspiel, and Powell growth kinetic models were used to determine the growth kinetics of mixed culture. Edward, Luong and Han and Levenspiel models were established as best fit to the specific growth rate data for phenol. However, for cyanide Haldane and Edward models were found to be best with lowest Marquardt’s percent standard deviation (MPSD) values. The degradation kinetics of phenol and cyanide was found to follow a three-half order model at all initial concentrations with lowest MPSD value.

Growth characteristics of freeze-tolerant baker's yeast Saccharomyces cerevisiae AFY in aerobic batch culture.

Saccharomyces cerevisiae AFY is a novel baker’s yeast strain with strong freeze-tolerance, and can be used for frozen-dough processing. The present study armed to clarify the growth characteristics of the yeast AFY. Aerobic batch culture experiments of yeast AFY were carried out using media with various initial glucose concentrations, and the culture process was analyzed kinetically. The growth of the yeast AFY exhibited a diauxic pattern with the first growth stage consuming glucose and the second growth stage consuming ethanol. The cell yield decreased with increasing initial glucose concentration in the first growth stage, and also decreased with increasing initial ethanol concentration in the second growth stage. In the initial glucose concentration range of 5.0–40.0 g/L, the simultaneous equations of Monod equation, Luedeking–Piret equation and pseudo-Luedeking–Piret equation could be used to describe the concentrations of cell, ethanol and glucose in either of the two exponential growth phases. At the initial glucose concentrations of 5.0, 10.0 and 40.0 g/L, the first exponential growth phase had a maximal specific cell growth rate of 0.52, 0.98 and 0.99 h−1, while the second exponential growth phase had a maximal specific cell growth rate of 0.11, 0.06 and 0.07 h−1, respectively. It was indicated that the efficiency of the yeast production could be improved by reducing the ethanol production in the first growth stage.

Automated Prediction of Catalytic Mechanism and Rate Law Using Graph-Based Reaction Path Sampling.

In a recent article [ J. Chem. Phys. 2015 , 143 , 094106 ], we introduced a novel graph-based sampling scheme which can be used to generate chemical reaction paths in many-atom systems in an efficient and highly automated manner. The main goal of this work is to demonstrate how this approach, when combined with direct kinetic modeling, can be used to determine the mechanism and phenomenological rate law of a complex catalytic cycle, namely cobalt-catalyzed hydroformylation of ethene. Our graph-based sampling scheme generates 31 unique chemical products and 32 unique chemical reaction pathways; these sampled structures and reaction paths enable automated construction of a kinetic network model of the catalytic system when combined with density functional theory (DFT) calculations of free energies and resultant transition-state theory rate constants. Direct simulations of this kinetic network across a range of initial reactant concentrations enables determination of both the reaction mechanism and the associated rate law in an automated fashion, without the need for either presupposing a mechanism or making steady-state approximations in kinetic analysis. Most importantly, we find that the reaction mechanism which emerges from these simulations is exactly that originally proposed by Heck and Breslow; furthermore, the simulated rate law is also consistent with previous experimental and computational studies, exhibiting a complex dependence on carbon monoxide pressure. While the inherent errors of using DFT simulations to model chemical reactivity limit the quantitative accuracy of our calculated rates, this work confirms that our automated simulation strategy enables direct analysis of catalytic mechanisms from first principles.

Magnetic graphene oxide based nano-composites for removal of radionuclides and metals from contaminated solutions

Magnetic graphene oxide based composites of the nano-particle size of <10 nm were synthesized, characterized and used in sorption experiments. The adsorption of Cs(I), Co(II), Ni(II), Cu(II) and Pb(II) to nano-composites was studied in a wide range of initial concentrations and analyzed by Langmuir and Freundlich models. In addition, the effects of pH and coexisting ions on the adsorption of Cs to Prussian blue based composites were investigated. The maximum adsorption capacities of studied elements varied from 29 to 641 mg g−1. The obtained Langmuir and Freundlich constants indicated the dominating physisorption mechanism and favorable adsorption conditions.

Radiocarbon dating and the 36Cl/Cl evolution of three Great Artesian Basin wells at Dalhousie, South Australia

The use of 14C (half-life = 5,730 years) in modeling the evolution of the 36Cl/Cl ratios in groundwater is reported for the first time. The complexity of the Cl–36Cl system due to the occurrence of different Cl and 36Cl sources and the difficulty of the determination of the initial groundwater 36Cl/Cl ratios have raised concerns about the reliability of using 36Cl (half-life = 301 thousand years, a) as a groundwater-dating tool. This work uses groundwater 14C age as a calibrating parameter of the Cl–36Cl/Cl decay-mixing models of three wells from the southwestern Great Artesian Basin (GAB), Australia. It aims to allow for the different sources of Cl and 36Cl in the southwestern GAB aquifer. The results show that the initial Cl concentrations range from 245 to 320 mg/l and stable Cl is added to groundwater along flowpaths at rates ranging from 1.4 to 3.5 mg/l/ka. The 36Cl content of the groundwater is assumed to be completely of atmospheric origin. The samples have different Cl–36Cl/Cl mixing-decay models reflecting recharge under different conditions as well as the heterogeneity of the aquifer.

Simultaneous removal of phenol and cyanide from aqueous solution by adsorption onto surface modified activated carbon prepared from coconut shell

The present study is devoted to the elimination of phenol and cyanide from binary component aqueous solution by adsorption onto copper impregnated coconut shell activated carbon (Cu-CSAC). Effects of initial concentration, adsorbent dose, pH, temperature and contact time on phenol and cyanide elimination have been examined. At an optimum temperature 30°C, pH 8, and the adsorbent dose of 40g/L, 71.43% phenol and 86.8% cyanide were removed from binary aqueous solution comprising 300mg/L of phenol and 30mg/L of cyanide. The isotherm modeling study is carried out by accompanying batch experiments at range of initial concentration 100–1000mg/L of phenol and 10–100mg/L of cyanide. Three mono component isotherm model and six binary component isotherm models were considered. The model parameters were predicted by using non-linear regression analysis technique. It was observed that the experimental data indicate a better fit with an Extended Freundlich isotherm model for adsorption of phenol and cyanide in the binary component system. The adsorption efficiency of Cu-CSAC was observed to be 239.85mg/g of phenol and 5.30mg/g of cyanide. The mechanism of adsorption process was found chemisorption followed by Pseudo second order kinetics. Thermodynamic studies indicated the adsorption process onto Cu-CSAC as endothermic nature and reversible.

Removal of methylene blue from industrial wastewater in Palestine using polysiloxane surface modified with bipyrazolic tripodal receptor

Different pollutants from industries leach every day to soil and ground waters without treatment. The product N,N-bis (3,5-Dimethylpyrazol-1-yl methyl)-3-aminopropyl Polysiloxane (Si-C 3 H 6 NPz 2 ) was successfully prepared. The FTIR results confirmed that the dimethylpyrazole units have been immobilized onto the surface of the modified silica gel. The adsorption experiments were conducted for a wide range of solution pH, adsorbent dosage, temperature, initial concentration and contact time. It was observed that the percentage removal of methylene blue dye decreased with an increase initial concentration and temperature while it increased with increase in solution pH, contact time and adsorbent dose. Over 82% removal efficiency of methylene blue dye was achieved after 180 min at solution pH around 10, 20°C temperature, 0.25 g weight of dose and initial concentration of 15 mg/L of 50mL MB dye solution. Negative ∆G° values (-17.17 to -17.25 KJ/mol) indicate that the adsorption is favorable and spontaneous at these temperatures. The negative value of ∆H° (-16.66 KJ/mol) reflects an exothermic adsorption and indicates that the adsorption is favored at low temperature. The value of ∆H° was higher than those corresponding to physical adsorption. This would suggest that the adsorption process is chemical in nature. The small positive value of ∆S° (+1.78 J/mol.K) suggests that some structural changes occur on the adsorbent and the randomness at the solid/liquid interface in the adsorption system increases during the adsorption process. The results of the present study show that the prepared compound has a negative biological activity against Pseudomonas aeruginosa, Staphylococcus aurous, and Escherichia coli.

Oxidation of Solid Phase and Ionic Strength Effect to the Cesium Adsorption on Pumice Tuff

In-situ oxidation of solid phase was considered to investigate adsorption behavior under different geochemical parameters like pH, initial concentration and ionic strength. Pumice tuff, a potential host rock for low and intermediate radioactive wastes, has been affected by the redox zone. The characterization of the fresh and oxidized tuff was performed by X-ray diffractometer, scanning electron microscope and mercury intrusion porosimetry. In order to compare the difference of distribution coefficient (Kd) in fresh and oxidized pumice tuffs, a batch adsorption study was carried out at the range of pH (4 - 12), ionic strength (0.003, 0.1, 1.0 and 3.0 mol/dm3) and initial cesium concentration (10&#454, 10&#455, 10&#456 and 10&#457 mol/dm3). Based on experimental Kd values, ionic strength was found to be the most influential factor, whereas the effects of pH, initial Cs concentration and weathering condition of pumice tuff were negligible. The recalculated Kd values suggest that the existing surface complexation model is applicable to explain the sorption coefficients through the wide range of solution conditions.

Pre-concentration of Ta(V) by solvent extraction before determination of trace amounts of Ta in Nb and Nb compounds

The paper presents the results of a study on the efficiency of the separation of Ta(V) and Nb(v) from fluoride solutions by solvent extraction with methyl isobutyl ketone with a view to applying the extraction process to the purification of Nb from Ta and for the pre-concentration of Ta prior to its determination in Nb and its compounds over a wide range of initial concentrations.

A Study on Astrazon Black AFDL Dye Adsorption onto Vietnamese Diatomite

In the present paper, the adsorption of Astrazon Black AFDL dye onto Vietnamese diatomite has been demonstrated. The diatomite was characterized by XRD, SEM, TEM, EDS, and nitrogen adsorption/desorption isotherms. The results show that diatomite mainly constituted centric type frustules characterized by pores as discs or as cylindrical shapes. The adsorption kinetics and isotherms of dye onto Vietnam diatomite were investigated. The experimental data were fitted well to both Freundlich and Langmuir in the initial concentration range of 400–1400 mg L−1. The average value of maximum adsorption capacity,qm, calculated from Freundlich equation is statistically similar to the average value of maximum monolayer adsorption capacity calculated from Langmuir equation. The thermodynamic parameters evaluated from the temperature dependent on adsorption isotherms in the range of 303–343 K show that the adsorption process was spontaneous and endothermic. The Webber and pseudo-first/second-order kinetic models were used to analyze the mechanism of adsorption. The piecewise linear regression and Akaike’s Information Criterion were used to analyze experimental data. The results show that the dye adsorption onto diatomite was film diffusion controlled and the goodness of fit of experimental data for kinetics modes was dependent on the initial concentration.

Green synthesis of α-Fe2O3 nanoparticles for arsenic(V) remediation with a novel aspect for sludge management

A simple, single step and eco-friendly approach was taken for synthesizing iron oxide nanoparticles using Aloe vera leaf extract. The nanoparticles were characterized by various techniques and used for arsenic(V) remediation in synthetic system with an initial concentration range of 2–30mg/L. The effect of pH, particle dosage and initial arsenic concentration on arsenic adsorption was investigated using response surface methodology involving five levels Central Composite Design (CCD) considering adsorption capacity as the response. The nanoparticles showed a high sorption capacity of 38.48mg/g in the experimental range of concentration compared to other inorganic oxide based adsorbents.A novel approach was adopted for utilization of arsenic contained sludge. As(V) sorbed nanoparticles were used in the preparation of colored soda lime silicate glass. The basic properties such as density, thermal and optical properties were measured for the experimental glass sample and compared with samples containing commercial Fe2O3.The overall study indicates that the green synthesized iron oxide nanoparticle is a prospective candidate for arsenic remediation in contaminated water. The arsenic contained sludge may be used in preparation of coloured glasses which have wide application in making container bottles and building glasses.

Adsorption reaction and diffusion based-models with solid-phase concentration-dependent coefficient for adsorption of reactive dye

ABSTRACTThe adsorption behavior for tartrazine removal was studied in batch and fixed-bed column operations with the commercially available anion exchange resin. The breakthrough curves were simulated according to mathematical models that considered the mass transfer resistance, such as the film diffusion, pore diffusion, and a combination of both. Analyses of adsorption reaction models in a batch experiment could be an efficient way to select an adsorption model in a fixed-bed operation, because in this study, such models represented the film and pore diffusion phenomena in a separate initial concentration range. The simulation analysis showed that the adsorption process could be controlled by a combination of film and internal particle resistance, and the tartrazine adsorption process was strongly affected by the internal mass transfer resistance. The concentration-dependent rate expression was used to improve the prediction accuracy of both the film and pore diffusion models, and its application to conventional mathematical models could not define meaningful segments in the adsorption process, but could provide a most useful and accurate way of quantitatively estimating the mass transfer effect.

Kinetic studies on radio-selenium uptake by ion exchange resin

ABSTRACTKinetic studies on the sorption of radioactive Se (IV) ion on Amberlite MB9L have been carried out under a wide range of temperature, pH, initial concentration, and resin weight. Analyses of the experimental data by two theoretical models commonly used to explain the ion exchange kinetics and shrinking core model (SCM), and homogeneous diffusion model (HDM) against exponential diffusion decay model (EDM) show a greater preference of EDM over HDM and SCM at all reaction conditions. The obtained regression coefficient values in case of HDM and SCM are in general not high enough to give a satisfactory fit for the experimental data. The estimated values for EDM parameters provides a good satisfactory fit for the yielded adsorption results as the corresponding linear regression values are high. The sorption process is found to be accompanied with fast film diffusion and slow diffusion between the reacted layer and the shrinking un-reacted core within the ion exchange resin. It also shows that ion exchange as the controlling step offers the lowest probability due to the highest obtained diffusion parameters over the normal tested reaction conditions.

BatchHeavy MetalsBiosorption by Punica granatum Peels: Equilibrium andKinetic Studies

This research was conducted to study the feasibility of using fruit peels as biosorbent for removal of Pb+2, Cu+2 and Zn+2 ions from simulated wastewater. A waste biomass of Pomegranate Peel or Punicagranatum L. (P. granatum L.) was chosen as neutral biosorbent in this study.Fourier transformation infrared (FTIR) was used to characterize the surface of PGP, the results confirm that amino, carboxylic, hydroxyl and carbonyl group on the surface of PGP. Different parameters such as initial concentration range between (25-200) mg/L, pH (3-7), contact time (1-2) hour, amount of sorbent (0.1- 4) gm, agitation speed range (200- 500) rpm and temperature (25- 50oC), influencing the sorptive process were examined. Sorption equilibrium isotherm and kinetic data fit well by the Langmuir isotherm and the pseudo-second-order kinetic model, respectively. Sorption processes were spontaneous and exothermic in nature according to the thermodynamic results and the equilibrium was attained within 60 minute. The amount of sorbed metal ions was calculated as 9.9, 9.5 and 7.75 mg/g dry PGP for Pb+2, Cu+2 and Zn+2ions, respectively, at pH 5; temperature 25oC; contact time 1hr and 4 gm of peels.&#x0D;

L-cystein modified bentonite-cellulose nanocomposite (cellu/cys-bent) for adsorption of Cu2+, Pb2+, and Cd2+ ions from aqueous solution

ABSTRACTIn this study, L-cystein modified bentonite-cellulose (cellu/cys-bent) nanocomposite was synthesized and characterized by XRD, FTIR, SEM with EDS, TGA, and TEM techniques. In order to optimize the process the effect of various operational parameters such as pH, adsorbent dosage, contact time, and temperature were also investigated. The adsorption experiments were carried out in initial concentrations range of 20-100 mg L−1and the adsorbent affinity for metal ions was found to be in order of Cu2+ > Pb2+ > Cd2+. The optimum pH for adsorption of Cu2+ and Cd2+ was observed at 5 while for Pb2+ it was pH 6. Based on the Langmuir model, the maximum adsorption capacity of Cu2+, Pb2+, and Cd2+ at 50ᴼC was found to be 32.36, 18.52, and 16.12 mg g−1, respectively. The Langmuir isotherm and pseudo-second order model were found to be better fitted than the other isotherms and kinetic models. The results of thermodynamic parameters confirmed the process to be endothermic and spontaneous in nature.

Concentration dependence of biotransformation in fish liver S9: Optimizing substrate concentrations to estimate hepatic clearance for bioaccumulation assessment.

In vitro bioassays to estimate biotransformation rate constants of contaminants in fish are currently being investigated to improve bioaccumulation assessments of hydrophobic contaminants. The present study investigates the relationship between chemical substrate concentration and in vitro biotransformation rate of 4 environmental contaminants (9-methylanthracene, pyrene, chrysene, and benzo[a]pyrene) in rainbow trout (Oncorhynchus mykiss) liver S9 fractions and methods to determine maximum first-order biotransformation rate constants. Substrate depletion experiments using a series of initial substrate concentrations showed that in vitro biotransformation rates exhibit strong concentration dependence, consistent with a Michaelis-Menten kinetic model. The results indicate that depletion rate constants measured at initial substrate concentrations of 1 μM (a current convention) could underestimate the in vitro biotransformation potential and may cause bioconcentration factors to be overestimated if in vitro biotransformation rates are used to assess bioconcentration factors in fish. Depletion rate constants measured using thin-film sorbent dosing experiments were not statistically different from the maximum depletion rate constants derived using a series of solvent delivery-based depletion experiments for 3 of the 4 test chemicals. Multiple solvent delivery-based depletion experiments at a range of initial concentrations are recommended for determining the concentration dependence of in vitro biotransformation rates in fish liver fractions, whereas a single sorbent phase dosing experiment may be able to provide reasonable approximations of maximum depletion rates of very hydrophobic substances.

The dynamics of multiple populations in the globular cluster NGC 6362

We investigate how the Milky Way tidal field can affect the spatial mixing of multiple stellar populations in the globular cluster NGC 6362. We use $N$-body simulations of multiple population clusters on the orbit of this cluster around the Milky Way. Models of the formation of multiple populations in globular clusters predict that the second population should initially be more centrally concentrated than the first. However, NGC 6362 is comprised of two chemically distinct stellar populations having the same radial distribution. We show that the high mass loss rate experienced on this cluster's orbit significantly accelerates the spatial mixing of the two populations expected from two body relaxation. We also find that for a range of initial second population concentrations, cluster masses, tidal filling factors and fraction of first population stars, a cluster with two populations should be mixed when it has lost 70-80 per cent of its initial mass. These results fully account for the complete spatial mixing of NGC 6362, since, based on its shallow present day mass function, independent studies estimate that the cluster has lost 85 per cent of its initial mass.

Stability of buffer-free freeze-dried formulations: A feasibility study of a monoclonal antibody at high protein concentrations

We studied the stability of freeze-dried therapeutic protein formulations over a range of initial concentrations (from 40 to 160mg/mL) and employed a variety of formulation strategies (including buffer-free freeze dried formulations, or BF-FDF).Highly concentrated, buffer-free liquid formulations of therapeutic monoclonal antibodies (mAbs) have been shown to be a viable alternative to conventionally buffered preparations. We considered whether it is feasible to use the buffer-free strategy in freeze-dried formulations, as an answer to some of the known drawbacks of conventional buffers.We therefore conducted an accelerated stability study (24weeks at 40°C) to assess the feasibility of stabilizing freeze-dried formulations without “classical” buffer components. Factors monitored included pH stability, protein integrity, and protein aggregation. Because the protein solutions are inherently self-buffering, and the system’s buffer capacity scales with protein concentration, we included highly concentrated buffer-free freeze-dried formulations in the study.The tested formulations ranged from “fully formulated” (containing both conventional buffer and disaccharide stabilizers) to “buffer-free” (including formulations with only disaccharide lyoprotectant stabilizers) to “excipient-free” (with neither added buffers nor stabilizers). We evaluated the impacts of varying concentrations, buffering schemes, pHs, and lyoprotectant additives.At the end of 24weeks, no change in pH was observed in any of the buffer-free formulations. Unbuffered formulations were found to have shorter reconstitution times and lower opalescence than buffered formulations. Protein stability was assessed by visual inspection, sub-visible particle analysis, protein monomer content, charge variants analysis, and hydrophobic interaction chromatography. All of these measures found the stability of buffer-free formulations that included a disaccharide stabilizer comparable to buffer-based formulations, especially at protein concentrations up to and including 115mg/mL.