Crossflow microfiltration (0.1 μm) of skimmed milk is widely used in the dairy industry to separate casein micelles from soluble proteins. The accumulated matter at the membrane surface turns into an irreversible deposit in critical hydrodynamic conditions (CHC) (J/τw)crit that irreversibly alters filtration performance. The aim of this work was to identify the milk constituents responsible for CHC and to evaluate the role of constituents (casein micelles, soluble proteins, minerals) on the microfiltration performance and deposit structure. An original methodology of filtration based on step-by-step τw variation at constant flux was used with dairy fluids of variable and controlled composition. Casein micelles were shown to be the milk constituents responsible for the apparition of the CHC, creating an irreversible deposit at the membrane surface. Soluble proteins had no effect on the set-up of the CHC, but their presence in milk increased by 20% the irreversible fouling. The presence of the mineral aqueous phase of milk played a role in CHC set-up and irreversible fouling. Calcium ions are supposed to create bonds in the deposit between the membrane and the micelles and between micelles themselves.
Photocatalytic purifiers, which are in development for treating gaseous effluents at flow rates generally higher than several tens of m3 h−1, usually employ TiO2-coated materials either as planar or folded fibrous filters, or as honeycomb monoliths. Our primary objective was to compare the photocatalytic efficacy of two types of these materials using a ca. 0.4 m3 close-loop, air tight, photocatalytic reactor we built at EDF. This loop – through which air can be flowed at rates from 16 to 1800 m3 h−1, i.e. 0.11–12.25 m s−1 – includes a paralleliped (560 mm × 295 mm × 200 mm) into which alternate banks of lamps and TiO2 coated-materials (entrance area = 408 cm2) can be accommodated. The materials tested were (i) an Ahlstrom-supplied, thin, non-woven tissue dried at room temperature after impregnation with both Degussa TiO2 P-25 and colloidal SiO2 used as a binder and (ii) an aluminum honeycomb-shaped material we coated with Degussa TiO2 P-25 and dried at room temperature. U-shaped lamps emitting at 254 nm and having an electrical power of 18 or 35 W were employed. The geometries of the materials and the spatial arrangements of the lamps and materials provided an irradiance of the materials as high and homogeneous as possible according to our modeling [Catal. Today 122 (2007) 66–77]. Methanol was chosen as the test pollutant because it is easily mineralized, which minimized the inhibition of the photocatalytic activity by intermediate products. In the recirculation regime, the initial rates of methanol removal observed for the folded tissue were multiplied by at least four – depending on the numbers of materials and banks of three 35 W lamps – when the honeycomb material was utilized. Several factors can add to cause this high increase in efficacy: distinct shapes and TiO2 supports, differences in photons scattering, and the reduced accessibility of reactants to TiO2 because of SiO2. Regarding energy consumption, the use of two photocatalytic materials sandwiching one bank of three 35 W lamps instead of one material in-between two banks of three lamps led to about the same efficacy. The honeycomb material was also tested with toluene at an initial concentration corresponding to the same amount of carbon as when methanol was the pollutant. The removal rate and CO2 formation rate were lower for toluene than for methanol, which can be easily explained by a lower reactivity with respect to oxidation, a smaller adsorbed amount and a higher competition with the more numerous degradation intermediate products. That comparison illustrates the need of trials for every effluent to be treated. Considerable differences in pressure drop between the two materials clearly demonstrated another interest of using honeycomb shapes, at least for the materials and configurations investigated. Furthermore, a deactivation, together with a yellowing, was noticed at high irradiance for the Ahlstrom tissue, which included cellulose fibers. Folding the material enables one to employ lower irradiances for minimizing this effect, while maintaining the efficacy because of the increase in the material area in the reactor, as well as slightly lowering the pressure drop.
The success of simulated moving bed (SMB) chromatography for separating difficult or nearly impossible mixture has drawn strong interest in improving its performance in recent years. In this work, experimentally verified mathematical model was used to find the best possible operating conditions for continuous separation of 1,1′-bi-2-naphtol racemate under specified product quality requirement. Equilibrium dispersive model for SMB systems coupled with non-linear equilibrium isotherm and lumped kinetic approximation constitute the mathematical model in simulating the system behavior. Single objective as well as multi-objective optimization with diverse objectives was carried out using a state-of-the-art AI-based non-traditional optimization technique, elitist non-dominated sorting genetic algorithm with jumping genes. The optimization results showed that significant improvement could be achieved depending on desired objectives. Equilibrium triangle theory was used to explain the optimization results.
Irradiated tellurium targets were purified by precipitation from 6 M HCl solution using 1,10-phenanthroline. The effect of molar ratio of the reactants (initial 1,10-phenanthroline:Te molar ratio) on the precipitation yield of radiotellurium was studied. It was found that, >99% of radiotellurium has been taken up by the precipitate formed with the initial 2 phenanthroline:1Te molar ratio along with different decontamination ratios from the other cross-radiocontaminants; ≥99.9% of 65Zn, 97.7 ± 1.2% of 75Se, ≥99.9% 110mAg, and 95.4 ± 2.5% of 124Sb. Traces of 51Cr, 54Mn, 59Fe, and 60Co have been detected only in the supernatant after the precipitation process. Un-irradiated tellurium was precipitated with 1,10-phenanthroline under the same conditions with the initial 2phenanthroline:1Te molar ratio and, then, the precipitate formed was characterized by IR spectroscopy and thermal analysis. The most probable chemical composition of this precipitate was [Te(phen)2Cl4]·3.4H2O.
A new simple and reliable method for rapid and selective extraction and determination of trace levels of Ag+ ion is developed. Silver ions are adsorbed quantitatively during passage of aqueous samples through octadecyl silica membrane disks modified with some recently synthesized mixed aza-thioether crowns containing 1,10-phenanthroline sub-unit. Almost all matrix elements were found to pass through the disk to drain. The retained Ag+ ions are then stripped from the disk with a minimal amount of thiosulfate solution as eluent and subsequently measured by atomic absorption spectrometry. The proposed method permitted large enrichment factors of about 200 and higher. The limit of detection of the proposed method is 100 ng Ag+ per 1000 ml. The method was applied to the recovery of Ag+ ions from different synthetic and water samples.
Two types of external lamp reactors were investigated for the titania catalyzed photodegradation of 1,2-dichlorobenzene (DCB) from a dilute water stream. The first one was a batch mixed slurry reactor and the second one was a semi-batch reactor with continuous feed recycle with titania immobilized on inert supports (quartz and low density polyethylene, LDPE). The batch reactor was used to study the intermediates and reaction kinetics of DCB degradation. Four intermediate products were observed in the degradation of DCB; these being 2-chlorophenol (CP), 2,3-dichlorophenol (DCP), 1,2-dihydroxybenzene (catechol) and, o-benzoquinone. A mechanism based on these observations is proposed. Increasing the pH of the solution increased the intial rate of photodegradation of DCB. Added oxidant (hydrogen peroxide) did not have any appreciable effect on the degradation of DCB. The Langmuir–Hinshelwood kinetic parameters for DCB, DCP and CP were obtained. The steady state removals and apparent rate constants were obtained for the plug-flow reactor with different supports and compared under similar conditions. The titania supported on LDPE showed a better rate of photocatalysis than titania supported on quartz, although the titania film thickness on LDPE was five times lower than on quartz. The modification of titania surface by adsorption of a non-photodegradable polyfluorinated surfactant vastly improved the rate of DCB degradation on both LDPE and quartz. The rate of photodegradation in the immobilized tubular reactor was mass transfer controlled for the flow regimes investigated, viz., Reynolds numbers, Re<550. The steady state removal was directly proportional to the radiant flux within the range 4–16 mW cm−2.
The surface of a semi-conducting surface, viz., titania was modified by adsorbing an anionic surfactant, viz., sodium dodecyl sulfate (SDS) at aqueous pH values less than the point of zero charge of 6.8. The hydrophobic titania surface was capable of adsorbing hydrophobic organic compounds, such as 1,2-dichlorobenzene and phenanthrene at dilute concentrations from the aqueous phase. The adsorption partition coefficients for both compounds on SDS hemi-micelles on TiO2 are of magnitudes similar to their octanol–water partition constants, which are indicators of similar hydrophobic environments. The potential uses of SDS-coated TiO2 for simultaneously adsorbing and photo-chemically degrading hydrophobic organic compounds as a means of treating dilute wastewater streams are suggested.
Salts are by-products in the 1,3-propanediol fermentation broth. The separation technique for 1,3-propanediol generally requires desalting before putting into operation. Previous studies on the downstream processing of biologically produced 1,3-propanediol were mainly focused on the removal of these salts, rather than the recovery of these salts. In this paper, a whole recovery process of salts in the actual fermentation broth was discussed. First, batch crystallization was achieved by analyzing the characteristics of this system. Then the process of crystallization was optimized with uniform design. Our studies indicated that batch crystallization can effectively recover sodium succinate from actual 1,3-propanediol fermentation broth. The final purities and overall yield of sodium succinate and sodium sulfate were 98.4%, 99.1% and 64.1%, 72.3% under the optimum conditions, respectively.
The pore dimensions and distribution of carbon membranes can be finely adjusted by various post-treatment methods to meet different separation needs and objectives. In this study, the post-oxidation effect on the gas permeation performance was investigated in the poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) derived carbon membranes with oxidation conditions (oxidation temperature and time). The post-oxidized carbon membranes were prepared by carbonization at 700 °C, followed by the air-oxidation. The permeances of gas species increased with increasing oxidation temperature and time due to increase in pore characteristic properties, such as pore volume, pore size and its distribution. The influence of the post-oxidation on the extent of the gas permeance modification was higher for gas species having a large molecular size. The carbon membranes post-oxidized at a low temperature (e.g., 200 °C) and a short time (e.g., 1 h) showed high permeation performance. The post-oxidation on the permeation results clearly showed that the gas permeation properties could be modified by appropriate oxidation conditions.
Cyphos® IL-101, a tetraalkylphosphonium chloride salt (ionic liquid, IL) has been immobilized in capsules prepared by ionotropic gelation in calcium chloride solutions. The IL content was varied in the resin between 0.29 and 1.28 mmol IL g−1. These resins have been tested for Pt recovery from HCl solutions. The equilibrium was very slightly affected by the concentration of HCl and chloride ions. The sorption isotherms were modeled using the Langmuir equation: the maximum sorption capacity was influenced by the drying of the resin but remained close to 177 mg Pt g−1 for wet resin (i.e. 0.9 mmol Pt g−1, dry weight basis, or 0.7 mol Pt mol−1 Cyphos) and 142 mg Pt g−1 for dry resin (i.e. 0.73 mmol Pt g−1, or 0.57 mol Pt mol−1 Cyphos). The presence of nitrates, nickel or copper ions (added under the form of chloride salts) did not significantly decrease sorption capacity even at concentrations as high as 5 g L−1. Conversely, zinc at the concentration of 5 g L−1, significantly decreased Pt sorption, probably due to the competition effect of chloro-anionic Zn species. This is another evidence of the ion exchange mechanism involved in the binding of hexachloroplatinate species. The kinetics are weakly affected by the agitation speed (in the range 150–350 rpm) indicating that the resistance to film diffusion is not the limiting step. The kinetics are affected by the IL content, metal concentration and more specifically the drying of the resin: intraparticle diffusion sounds to be the controlling kinetic step: the intraparticle diffusion coefficient varied between 2 × 10−12 and 18 × 10−11 m2 min−1, depending on experimental conditions. Platinum can be desorbed from loaded resin using either nitric acid (5 M) or thiourea (0.1 M in 0.1 M HCl acid solution). The resin was efficiently used for three sorption/desorption cycles using nitric acid: a decrease in sorption capacity and desorption efficiency was observed beginning with the third cycle, probably due to a progressive degradation of the resin.
Phosphonium ionic liquid: trihexyl(tetradecyl)phosphonium chloride (Cyphos®IL 101) has been used as a novel reagent in the presence of toluene to extract palladium(II) from hydrochloric acid solutions of various concentrations. Extraction data indicate that Cyphos®IL 101 is a very efficient and fast extractant. The increase in HCl concentration has negative influence on the extraction and about 97 and 54% of palladium(II) can be effectively extracted with Cyphos®IL 101 from 0.1 and 3 M HCl, respectively. The equilibrium of palladium(II) extraction from aqueous 0.1 and 3 M HCl with this phosphonium ionic liquid is achieved after 5 min. Successful stripping of palladium(II) from the loaded organic phase is achieved with 0.5 M ammonia solution. Cyphos®IL 101 can be reused at least in 5 cycles of extraction-stripping process.
The commercial Nafion®117 cation exchange membrane is a good material for high proton conduction. In the present work, we studied transport numbers of monovalent and divalent metal cations (Na+, Zn2+) in competition with the proton through this membrane as well as membrane chemically modified with a conducting polymer by using the electrochemical Hittorf method. The oxidant concentration (FeCl3) used to polymerise the pyrrol inside the membrane matrix influences greatly the modification. The modified membrane has been used in an electrodialysis pilot having three compartments. The electrode compartments contain aqueous sulphuric acid solutions, whereas the central one contains an organic electrolytic solution (sodium iodide + organic solvent). The solvents used are methanol, dioxan, N-methylformamide and acetonitril. Characterisation of ionic transport and permeability of solvent have been investigated. The results obtained are compared to those measured using unmodified membranes. The application of this work could also concern pollutants removal (metal cations) from industrial effluents using electromembrane techniques. Addition of solvent in electrolyte solution could modify the properties of transport and in certain case improve the extraction. The process could be achieved in two stages: firstly, the salt is separated from the organic effluent and secondly, the impurities are removed to obtain the purified solvent. Thus, this research work opens perspectives towards the separation between different constituent solvents.
The uptake of 85Sr, 134Cs and 57Co on a framework sodium titanosilicate of an ideal formula Na2Ti2O3(SiO4) · 2H2O was investigated. Samples of varying crystallinity were synthesized and this effect on cation affinity was studied. The material exhibited high affinity for cesium in slightly acidic to alkaline solutions, but potassium and the presence of sodium at high pH interfered significantly with selective 134Cs uptake. The weakly acidic exchanger took up 85Sr and 57Co efficiently above neutral pH in 0.1 M NaNO3. The crystallinity of the material proved to be an important factor in efficient removal of 85Sr from calcium bearing effluents. The semi-crystalline titanosilicates had a high affinity for 85Sr over Ca2+ at neutral pH. The affinity for cesium in the presence of potassium was improved as well in samples of lower crystallinity.
Vertical electrokinetic-flushing equipment suitable to the geological characteristics of Korean nuclear facility sites was developed for the decontamination of some real radioactive soil. The optimum reagent and electric current were chosen through vertical electrokinetic-flushing experiments. The effect of the particle size of some soil and the radioactive concentration of some soil on the removal efficiencies of the nuclides from said soil were analyzed. The experimental results are as follows. The removal efficiencies of 60Co and 137Cs by nitric acid were increased by 3.3% and 2.0% more than those by acetic acid. And, moreover, when nitric acid instead of acetic acid was used, it had the advantage of a reduction of the electricity consumption due to its higher electrolytic conductivity. The higher the radioactivity concentration of the soil was, the higher the removal efficiencies of 60Co and 137Cs were. Namely, the removal efficiencies of 60Co and 137Cs from the soil of a high concentration (2850 Bq/kg) were increased by 13.7% and 3.9% more than those from the soil of a low concentration (135 Bq/kg). The larger the particle size of the soil was, the higher the removal efficiency of 137Cs was. Namely, the removal efficiency of 137Cs from the soil of average 1.2 mm particle size was increased by about 2% more than that from the soil of average 0.6 mm particle size. Also, the removal efficiencies of 60Co and 137Cs by the application of an electric current of 20 mA/cm2 were increased by 1.3% and 4.2% more than those by the application of 10 mA/cm2. The removal efficiencies of 60Co and 137Cs from the radioactive soil of 1825 Bq/kg were 99.9% and 94.3% by an electrokinetic-flushing decontamination by the application of an electric current of 20 mA/cm2 for 50 days.
Distribution coefficients of cesium on natural and cation-enriched (Na+, K+, NH4+ and Ca+2) forms of clinoptilolite were measured by batch, radioactive tracer technique. The measurements were carried out for an initial cesium concentration range of 10−6–10−1 mol/dm3 and at temperatures of 25, 40, 60 and 80 °C. Experimental isotherms evaluated from distribution coefficients were fit to Langmuir, Freundlich and Dubinin-Radushkevich (D-R)models. Of the models tested, D-R model was found to represent the isotherms better in a wider range of concentrations than either Langmuir or Freundlich model. Breakthrough behavior of cesium on natural and cation-enriched forms of clinoptilolite for a particular set of conditions were also determined in a small size column. Column parameters were evaluated using mass transfer zone concept.
Adsorption isotherm of ethyl acetate (EA), a toxic volatile organic compound, is studied in E-Merck 13X molecular sieve at three different temperatures 35, 45, and 55 °C. Freundlich, Langmuir, and Langmuir–Freundlich isotherm model parameters and their temperature dependencies, saturation capacity, and heat of adsorption are found out from the experimental data. Isosteric heat of adsorption is determined using Clausius–Clapeyron equation and experimental data. Mass transfer coefficient of ethyl acetate is evaluated using Uptake curve method. Results show that the isotherm is of Brunauer type-I and was well fitted with both Langmuir and Langmuir–Freundlich isotherm models. Heats of adsorption from Langmuir isotherm model and isosteric heat of adsorption are comparable and are in the order of 105 J/kg. Overall mass transfer coefficient values are in the order of 10−4 s−1.
Permeation of 177Lu(III) through supported hexane membrane containing di-(2-ethylhexyl)phosphoric acid (DEHPA) as a carrier has been studied. The donor solution was 0.2 mol dm−3 ammonium acetate buffer, pH 5.0–5.5, that is optimal for peptide labeling, and the acceptor solution was 2 mol dm−3 HCl. A miniaturized supported liquid membrane (SLM) contactor with 10 μl donor and acceptor channel and ultra thin, flat poly(tetrafluoroethene) laminated on polyester fleece (PTFE) was applied in the work reported herein. The donor phase was pumped continuously through the donor channel, while the acceptor was stagnant during the SLM extraction. The influences of carrier concentration and donor flow rate on extraction of 177Lu(III) have been investigated. The results are discussed in the term of mass transfer coefficient, mass transfer resistance and extraction efficiency. Based on the experimental results of SLM extraction of 177Lu(III), this technique has been applied for the separation of free radionuclide from the labeled peptide as a purification procedure within the production of the radiopharmaceutical. An analog of somatostatin, lanreotide, which was conjugated with chelating moiety 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (DOTA) was labeled with 177Lu(III). The characterization of the labeled conjugate as well as the complexation yield and the efficiency of purification by membrane extraction were carried out by HPLC analysis.
The photocatalytic degradation of an azo dye acid red 18 (AR18) using ZnO as a photocatalyst in aqueous solution has been investigated under UV irradiation. The blank experiment for either illuminated AR18 solution or the suspension containing ZnO and AR18 in the dark showed that both illumination and the catalyst were necessary for the destruction of AR18. The effects of operational parameters such as the amount of photocatalyst, dye concentration and initial pH have been examined. The study on the effect of oxidants such as (NH4)2S2O8, KBrO3 and H2O2 on the photooxidation of AR18 reveals that the addition of (NH4)2S2O8 and KBrO3 increases the dye removal whereas the addition of H2O2 decreases the photocatalytic degradation. The unusual decrease by the addition of H2O2 is due to its low adsorption on the ZnO surface.
Hexathia-18-crown-6 (HT18C6) was used as a specific ion carrier for the transport of silver ion through a chloroform bulk liquid membrane. In the presence of thiosulfate ion as a suitable stripping agent in the receiving phase, the amount of silver transported across the liquid membrane after 60 min is 99.5±1.0%. The selectivity of Ag+ transport from the aqueous solutions containing other Mn+ cations such as Tl+, Mg2+, Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Pb2+, Hg2+, and Cr3+ ions was investigated. Except with Hg2+ ion, non of the cations used interfere the silver transport, even at a Mn+/Ag+ molar ratio of 500. The interfering effect of Hg2+ ion was successfully eliminated in the presence of EDTA at pH 5.
Mineralization of an anthraquinone dye, C.I. Reactive Blue 19 (RB19), by single ozonation, single sonolysis, and ozonation combined with sonolysis (O3/US) was carried out in a laboratory-scale experiment. O3/US treatment rendered a more effective result than the other two methods. The effect of several operational parameters, including initial dye concentration, pH, ozone dose, and ultrasonic energy density, on the reduction of total organic carbon (TOC) was also investigated. The concentrations of related anions (maleic acid, oxalic acid, acetic acid, formic acid, nitrite ion, nitrate ion and sulfate ion) and the ammonium ion during mineralization were detected by ion chromatography (IC) and the ammonia–Nessler's reagent colormetric method, respectively. Other carbon based intermediates (3,6-dinitrosocyclohexa-1,4-diene, aniline, phenol, benzo-1,4-quinoe, phthalic acid, butene diacid, oxalic acid, and acetic acid) were detected by gas chromatography/mass spectrometry (GC/MS). Based on the results of these analyses, we propose a possible degradation pathway of RB19 during the O3/US process.
To increase the activity of immobilized catalyst by synergetic effect of adsorption and to extend the activity of Fe0, a composite membrane with Fe0, activated carbon fiber (ACF) and TiO2 was prepared, using dip-coating, impregnation and chemical reduction methods. The activity of the prepared membrane was evaluated for mineralizing 2,4-dichlorophenol (2,4DCP) in water under UV illumination. The co-presence of Fe0 and TiO2 enhanced 2,4DCP degradation. ACF addition and its adsorption effect were shown in promoting 2,4DCP mineralization and TOC removal by comparing activities of composite membranes with Fe0/TiO2/ACF or Fe0/TiO2. Effects of pH and iron loading ratio to TiO2 on degradation rate of 2,4DCP using the composite membrane were investigated and optimized. The optimal pH was 6 and the optimal loading of Fe0 was 1 wt% to TiO2. The repeated test results and XRD patterns of catalysts before and after reaction proved that the Fe0/TiO2/ACF membrane was durable and stable in its photocatalytic activity.
The heterogeneous photocatalysts of the ruthenium(II)-tris-bipyridine/titanium dioxide/zeolite Y ([Ru(bpy)3]2+/TiO2/zeolite Y) family perform in a manner very similar to a “Fenton-catalyst” in the oxidative degradation of the model pollutant 2,4-xylidine (1-amino-2,4-dimethyl-benzene). Upon photoexcitation using visible light, an electron-transfer reaction to hydrogen peroxide is observed. The oxidation rate of 2,4-xylidine follows a distinct percolation behavior, which is dependent on the amount of titanium dioxide incorporated as nanoparticles into the zeolite Y's framework. The maximum of the photocatalytic degradation of 2,4-xylidine at pH 3.0 was found to be at 34.5 ± 0.5% TiO2 per weight. The optimization of the performance parameters of this particular [Ru(bpy)3]2+/TiO2/zeolite Y photocatalyst was undertaken in a pilot reactor (V = 3.25 L), equipped with a medium pressure mercury lamp (TQ 718). Important factors in the apparent photocatalytic efficiency have been determined: (a) the availability of dissolved oxygen, (b) the substrate concentration and (c) the concentration of the dispersed photocatalyst. At higher starting concentrations of 2,4-xylidine (>200 mg C L−1), the photocatalytic oxidation process is hampered by parasitic light absorption by an azo-dye formed and, especially, by competitive adsorption of hydrogen peroxide and 2,4-xylidine at the nanoscopic TiO2-centers. It is noteworthy that 2,4-dimethylphenol and oxalic acid were the main reaction products, when 200 mg C L−1 of 2,4-xylidine were oxidatively degraded, whereas a multitude of reaction intermediates were detected when the starting concentration of 2,4-xylidine was 500 mg C L−1. Evidence is given that hydroxylamine is formed during the oxidation of 2,4-xylidine, which subsequently is either reduced to ammonium or generated from the disproportionation of hydroxylamine to ammonium and nitrogen. In the discussion section of this report, the observed reaction behavior is rationalized, based on the elementary chemical reactions occurring in the irradiated heterogeneous reaction mixture.
The degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) under UV light was studied under various conditions. A photoreactor was used for the photochemical reaction. Calibration curves for 2,4-D were generated at two different absorption maxima (230 and 283 nm). The effects of various parameters such as light intensity, exposure time, various solvents (10% methanol and 10% acetonitrile) and micellar media (cationic and anionic) and the effects of some other parameters such as O2, wavelength of light, pH, other commonly occurring ions (e.g. Cl−, SO42−, Ca2+/Mg2+, Fe3+, NO3−) were studied. The percentage of degradation of 2,4-D was achieved up to 81% in simple aqueous medium. But in cetyltrimethylammonium chloride (CTAC, a cationic micelle) the percent degradation can even be further increased. The percent degradation of 2,4-D using solar irradiation under similar conditions as that applied for the photoreaction using the photoreactor was compared. Using the solar light the degradation was very negligible. The reaction in general follows zero-order kinetics. But in CTAC micelle the reaction follows first-order kinetics.
In order to remove micro-pollutant 2,4-DCP (dichlorophenol, 1–50 mg/L) from aqueous solution using low pressure membrane separation process, and to study photocatalytic/oxidative cleaning of membrane fouled by adsorption, a new organic/inorganic hybrid composite membrane with adsorption, filtration and photocatalysis property was studied which contains coated chitosan (CS), activated carbon fiber (ACF) adsorbent and titanium dioxide on terylene fabrics. The scanning electron microscopy (SEM) of the membrane showed TiO2 as the top layer, while CS and ACF were under TiO2. FTIR spectrum analysis reflected the feature of CS, ACF and TiO2, and water flux measurements indicated that the composite membrane with coating layer still possessed high filtration property. The adsorptive removal of 2,4-DCP using both static and dynamic modes (25–100 L m−2 h−1) was highly efficient. The CS/ACF/TiO2 membrane adsorption capacity can be regenerated by oxidizing adsorbed 2,4-DCP via in situ or off-site photocatalysis and/or Fenton oxidation, and both off-site oxidation methods are more efficient than in situ oxidation.
The photoelectrochemical degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) at a Pt doped TiO2/Ti electrode was investigated. The electrode was prepared by first oxidizing the surface of a titanium sheet to form TiO2 and then doping platinum in H2PtCl6 solution. The degradation efficiency of 2,4-D in the solution with 51 mg/l concentration was, respectively, 16% for electrochemical process and 27% for photochemical process after 5 h reaction. It became 53% when photo- and electrochemical processes were integrated. The 10% higher 2,4-D degradation efficiency by the integrated method than the sum of the two individual processes demonstrates an obvious synergetic effect between the photo- and electrochemical catalysis. Besides, a decrease in current density was observed with reaction time. The degradation efficiency increased with the increase of potential bias. The degradation of 2,4-D was also dependent on pH and concentration of sodium sulfate acting as a supporting electrolyte.
An airlift inner-loop bioreactor packed with honeycomb-like ceramic as the carrier was developed and its capacity to immobilize microorganism was studied through adding bacteria, Achromobacter sp., capable of degrading 2,4-dichlorophenol (2,4-DCP), directly to the reactor under continuous operation. Effects of phenol in the feed with 2,4-DCP on 2,4-DCP removal were investigated under fed-batch and continuous operations. The results showed that the pure strain could be easily immobilized on the carrier and proliferated using 2,4-DCP as the sole carbon source. In the process of fed-batch operation, removal rate of 2,4-DCP decreased with the increase in run number, while that of phenol was just to the contrary. In the continuous operation, 2,4-DCP loading rate was kept at 29.72–32.23 mg/(l day), but phenol loading rate was increased stepwise from 325.56 to 602.79 mg/(l day). The results showed that with the increase of phenol loading rates, the removal efficiency of 2,4-DCP declined from 100 to 87.9%, while that of phenol remained at about 99.6%. Presence of phenol in feed inhibited the biodegradation of 2,4-DCP and caused the major carbon source shift from 2,4-DCP to phenol.
This paper reports on the preliminary results of an experimental study to compare two methods for extracting energetic compounds from soils. A number of military industrial sites have soils contaminated with energetic compounds (explosives, propellants and pyrotechnics). One decontamination method being considered is solvent extraction using acetone as the solvent liquid.Bench scale experimental results are reported on removing 2,4 dinitrotoluene (DNT) from sand and clay samples via packed bed or stirred tank methods of extraction. The experiments show that either approach is effective in removing the energetics. However, the stirred tank method appears to require a shorter contact time and less acetone per mass of treated soil than the packed bed method.The experiments also consider the effects of aging on spiked samples and the effects of conditioning the samples as dry, wetted in water, or wetted in acetone on the effectiveness of the extraction. The results here are preliminary but may be used to guide future studies.
Liquid–liquid extraction (LLE) of platinum(IV) from acidic solutions such as chloride, sulphate and nitrate has been investigated using bis(2,4,4-trimethylpentyl) monothiophosphinic acid (Cyanex 302) in kerosene. Increase in acid concentration increases the percentage extraction of metal up to 3 mol L−1 for chloride and sulphate solutions whereas up to 1.0 mol L−1 for nitrate solutions thereafter it decreases. The extraction of platinum(IV) content increases with increase in the extractant concentration in the ascending order of sulphate > chloride > nitrate. Detailed comparative studies were conducted by varying the diluents, alkaline metal salts, temperature, loading capacity of the extractant, recycling of extractant and stripping of metal with three mineral acids and thiourea. The present investigations focused on the mixture of extractants such as Cyanex 302 with organophosphorous extractants such as Cyanex 272, PC 88A, D2EHPA and TBP. The extraction behavior of other associated elements like iron, copper, silver, palladium, aluminum, magnesium and calcium was also studied.
Solvent extraction separation of antimony(III) and bismuth(III) was carried out from aqueous acidic solutions with Cyanex 302 in toluene. Quantitative extraction of antimony(III) was observed in the acidic range of 0.1–1.0 M H2SO4 and 0.1–2.0 M HCl with 8.5×10−2 M Cyanex 302 in toluene, whereas that of bismuth(III) was observed in the acidic range of 0.01–0.1 M HNO3 and 0.01–0.1 M HCl with 1×10−2 M Cyanex 302 in toluene. Antimony(III) from the organic phase was stripped with 8.5 M H2SO4 and determined spectrophotometrically by the iodide method at 425 nm. Bismuth(III) from the organic phase was stripped with 2 M HNO3 and determined spectrophotometrically by the thiourea method at 470 nm. The optimum extraction conditions were evaluated by a critical study of acidity, extractant concentration, period of equilibrium and effect of diluents. Separation of bismuth(III) and antimony(III) from one another in varying ratios of 1:1, 1:2, 1:4, 2:1 and 5:1 and multicomponent mixtures of commonly associated metals was found to be possible by this method. It was successfully applied for analysis of antimony and bismuth in real samples.
This paper aimed to reveal the removal effectiveness and the mechanism of catalytic ozonation in the presence of aluminum oxides (γ-AlOOH, γ-Al2O3, and α-Al2O3) for the degradation of a taste and odor compound. Results showed that catalytic ozonation in the presence of aluminum oxides can substantially enhance 2,4,6-trichloroanisole (TCA) removal compared with the sole ozonation. However, three kinds of aluminum oxides exhibited different catalytic activity in catalytic ozonation for the degradation of TCA remarkably. Scavenging experiments of hydroxyl radicals revealed that the improving removal effectiveness of TCA was due to the enhancing generation of hydroxyl radicals. The catalytic activity of the aluminum oxides was related to highly hydroxylated surface. The surface hydroxyl groups on the aluminum oxides were active sites in catalytic ozonation. The density of surface hydroxyl groups and the surface Brønsted acidity determined the difference of the catalytic activity of aluminum oxides. The higher density of surface hydroxyl groups and the stronger Brønsted acidity of the surface can remarkably enhance the catalytic activity.
The temperature and concentration dependent effects of CO and CO2 on the performance of a ∼3 μm thick Pd/Ag 23 wt% membrane, employed in a microchannel configuration, were investigated. The microchannel system consisted of six parallel channels, 13 mm long, 1 mm wide and 1 mm deep. The membrane permeance was determined to 5.1 × 10−3 mol m−2 s−1 Pa−0.5 at 300 °C under pure hydrogen. After the last experiment, a small leakage occurred, that reduced the H2/N2 separation factor to ∼3300 at 200 kPa absolute pressure difference.Both CO and CO2 showed an inhibitive effect on hydrogen permeation. The CO effect was strongly dependent on both temperature (275–350 °C) and CO concentration/partial pressure (0–5 mol%). The CO inhibition occurred rapidly upon exposure, with a sharp drop in flux between 0 and 0.25 mol% CO. The time required to restore the initial flux value after CO exposure became longer when the exposure temperature was lowered. CO desorption hence was the main mechanism for flux restoration at the higher temperatures, while it was controlled by other, slower processes at the lower temperatures.The effect of CO2 was slower, and long time exposure was necessary to reach apparently stable values. Only a weak effect was observed at 350 °C, while at 300 °C, a nearly linear decrease was observed over several days. We suggest that the main inhibition mechanism was not CO2 (or CO from reverse WGS) competitive adsorption, but rather a slow formation and removal of strongly adsorbed species.
Separation of copper, zinc, cobalt and nickel ions from synthetic leach liquor using supported liquid membrane was studied. LIX 84I, TOPS-99 and Cyanex 272 were used as the mobile carrier for the supported liquid membrane. From the synthetic leach liquor containing 8.97 mole/m3 copper, 40.83 mole/m3 zinc, 27.49 mole/m3 cobalt, 420.51 mole/m3 nickel and 75.677 mole/m3 ammonium sulphate, copper was first separated using LIX 84I followed by zinc using TOPS-99 and cobalt using Cyanex 272. The solution was made copper free using 10% LIX 84I in the membrane phase and 900 mole/m3 H2SO4 in the strip solution at pH 4.5. After copper was separated, the leach liquor was made zinc free at pH 3.65 using 0.15 M TOPS-99 in the membrane phase and 900 mole/m3 H2SO4 in the strip solution followed by separation of cobalt using Cyanex 272. It was observed that co-permeations of zinc, cobalt and nickel with copper using LIX 84I were 0.076, 0.085 and 0.10 mole/m3, respectively. Co-permeations of cobalt and nickel with zinc using TOPS-99 were 0.187 and 0.323 mole/m3 and co-permeation of nickel with cobalt using Cyanex 272 was 3.407 mole/m3, respectively. Separation factors for metal ions with different extractants were calculated and reported.
Thin a-SiOxCyHz membranes were deposited from two different organosilicon precursors, a linear one the octamethyltrisiloxane (MDM) and a cyclic one the hexamethylcyclotrisiloxane (D3), in a low-frequency plasma polymerization process. The chemical structure of polysiloxane plasma materials was characterized using two different spectroscopic analyses: the X-ray Photoelectron Spectroscopy (XPS) and the 29Si solid-state Nuclear Magnetic Resonance (NMR). Both techniques show that it is possible to synthesize a wide range of materials, more or less organic and close to silicone-type conventional polymers, depending on whether the energetic character of the plasma is low or high. The structural differences between plasma films synthesized from MDM (PP-MDM films) and plasma materials deposited from D3 (PP-D3 films) are all the more pronounced that the plasma conditions are soft due to the better preservation of the monomer chemical structure. The NMR analysis allows to display the presence of cyclic siloxane chains in PP-D3 layers whereas PP-MDM materials are exclusively composed of linear siloxane chains.
The paper presents a new complex chiral selector of di(2-ethylhexyl)phosphoric acid (D2EHPA) and O,O′-dibenzoyl-(2R,3R)-tartaric acid ((−)-DBTA) and its enantioselectivity on d,l-tryptophan (Trp). The influence of the initial concentration of d,l-Trp, (−)-DBTA, D2EHPA were studied. Both the distribution ratio and enantioselectivity of d,l-Trp are greatly improved with the complex extractant instead of (−)-DBTA individually. It was also found that the enantioselectivity of the complex extractant was changed by the D2EHPA content, although pure D2EHPA has no chiral separation ability. By adjusting the equilibrium pH in the aqueous phase, a high chiral separation efficiency with a maximum enantioselectivity of 5.3 and an enantiomeric excess (e.e.) of up to 57% in aqueous phase were reached at PI point. Finally, the most reasonable extraction mechanisms of the complex to Trp enantiomers have been suggested.
This study individually investigated organic solvents and supercritical carbon dioxide (SC-CO2) extractions to recover 3,5-diprenyl-4-hydroxycinnamic acid (DHCA) from Brazilian propolis. An experimental design was applied to show the effect of two independent operational parameters on the recovery and purity of DHCA for these SC-CO2 extractions. Our experimental results indicated that temperature and addition ratio of ethyl-acetate are two major factors to influence the recovery and purity of DHCA in the extracts. A design point at 50 °C (323 K) and 4 wt.% ethyl-acetate addition ratio subsequently responded that DHCA recoveries were substantially enhanced from 3.7 wt.% (no adding) to 13.9 wt.% (6 wt.% adding) and DHCA purities in the SC-CO2 extracts were all over 40 wt.%, much better than that of Soxhlet ethyl-acetate extraction (16.9 wt.%). A further purification of the SC-CO2 extract using a normal phase Silica-gel 60 resin column chromatography without two solvent partitions could yield a purified product containing 95 wt.% DHCA. The total DHCA recovery was twice higher than that when the solvent partition was used. Finally, the inhibition of human serum low density lipid revealed a positive relationship between the DHCA purity in the SC-CO2 extracts and the anti-oxidative ability.
The extent of phenol degradation by the advanced oxidation process in the presence of zero valent iron (ZVI) and zero valent copper (ZVC) was studied using 20, 300 and 520 kHz ultrasonic (US) reactors. Quantification of hydrogen peroxide has also been performed with an aim of investigating the efficacy of different sonochemical reactors for hydroxyl radical production. It has been observed that the 300 kHz sonochemical reactor has the maximum efficacy for hydroxyl radical production. Phenol degradation studies clearly indicate that degradation of phenol is intensified in the presence of the catalyst and hydrogen peroxide, which can be attributed to enhanced production of hydroxyl radicals in the system. Experimental data shows that with ZVI, when the reaction was subjected to 300 kHz, complete phenol removal and 37% TOC mineralization was achieved within 25 min, whereas, in the case of 20 kHz US treatment no phenol was detected after 45 min and 39% TOC mineralization was observed. This novel study also investigated the use of zero valent copper (ZVC) and results showed that with 20, 300 and 520 kHz ultrasonic rectors, phenol removal was 10–98%, however, the maximum TOC mineralization achieved was only 26%. A comparative study between hydrogen peroxide and ozone as a suitable oxidant for Fenton-like reactions in conjunction with zero valent catalysts showed that an integrated approach of US/Air/ZVC/H2O2 system works better than US/ZVC/O3 (the ZOO process).
Oily wastewater cleanup can be carried out by gas flotation. When properly operated gas flotation units can reduce oil concentrations of wastewater effluents to well below 40 mg/l. Gas flotation is particularly valuable for heavy oils (oils having a density close to that of water). The flotation process relies on the attachment of gas bubbles to the dispersed oil droplets. This attachment is heavily dependent on the complex processes involving the surface characteristics of the oil droplets and their interaction with gas, and can only be optimally achieved if the surface science conditions are properly understood. The attachment mechanisms include the oil/bubble contact, the interactions of chemical additives (usually surfactants) in aiding this contact and the spreading of the oil around the gas bubble. Additionally, initial agglomeration of the oil emulsion droplets is needed to increase the droplet size to within the range needed for effective flotation, ∼60 μm. This paper examines the essential surface science of the gas flotation process, particularly the gas attachment to oil droplets and the use of surfactants. We discuss the stages of attachment of the gas bubble to the oil droplet, and provide further photographic evidence concerning the importance of the spreading of the oil around the gas bubble for gas flotation.
The zinc plant purification cake (CINKUR Co., Turkiye) was leached with sulphuric acid. The transport of cadmium from this leach solution-containing zinc, iron, copper, aluminum, cadmium, nickel and cobalt through emulsion liquid membrane (ELM) using amine extractant dissolved in kerosene as a mobile carrier was studied. The ELM consists of Aliquat 336 as a carrier, Span 80 as a surfactant, commercial kerosene as organic solvent and 6 M ammonia solution as stripping solution. The study has highlighted the importance and influence of membrane composition for maximizing the extraction of cadmium. The influence of acid and cadmium concentrations of feed solution, type and concentration of stripping solution, mixing speed, potassium iodide (KI) concentration, carrier concentration, surfactant concentration and the effect of volume ratio of the stripping phase to the membrane phase was investigated. The optimal conditions for the transport of cadmium ions have been found. The results showed that it is possible to extract 90–99% of cadmium after 10 min contact time by using ELM from the acidic leach solutions, containing Fe, Al, Cu, Zn, Pb, Co and Ni ions, at the optimum operating conditions.
Transport of uranyl ion across a supported liquid membrane made from Aliquat 336 in CHCl3 as the carrier was investigated from an aqueous feed containing hydrochloric acid. The transport rates were correlated with the pore size, carrier concentration, nature of organic carrier and the feed acidity. Maximum transport was observed for a carrier concentration of 30% (v/v) and a feed acidity of 6 M HCl. Significant transport of the feed acid was observed when Aliquat 336 was used as the carrier. Species of the type [R3R′N+]·[UO2HCl4−] appears to be transported along with the ion-pairs [R3R′N+]2·[UO2Cl42−] and [R3R′N+]·[UO2Cl3−] which is responsible for the acid transport. The transport behaviour of several fission products obtained from an irradiated target of natural U was also investigated. Selective separation of U was possible from most of the radionuclides with the exception of Mo, Tc and I, whose permeation was <10%. A separation method for trace amount of 233U from bulk thorium matrix was also developed which could find application in the processing THOREX feed solutions.
Aliquat 336/PVC-based polymer liquid membranes were used to extract Cd(II) and Cu(II) from aqueous solutions. The membranes demonstrated different extraction rate, capacity and chemical and morphological stabilities in the extraction of Cd(II) and Cu(II). Although the membrane showed good extraction rate and capacity to Cd(II), its chemical and morphological properties deteriorated badly after extraction. On the other hand, although the membrane showed a somewhat lower extraction capacity to Cu(II), it showed a much higher chemical and morphological stability. In this study, X-ray photoelectron microscopy (XPS) and lateral force atomic force microscopy (AFM) were used to characterize the chemical and morphological changes of the membrane before and after the extraction. The data in this work show that, XPS and AFM are good tools for membrane surface characterization. The sources of bleeding of the extractant (Aliquat 336) on membrane surface can be clearly identified. Although that actual cause of the membrane deterioration is not yet clear, the results from this work suggest that it could be related to the redistribution of the Aliquat 336 from the membrane bulk to the membrane surface. Information from this study is therefore useful to the future work on improving the membrane stability.
Nonionic organic contaminants (NOCs) such as benzene, toluene, and phenol from contaminated wastewater can be effectively adsorbed by organo-zeolites. Organo-zeolites were prepared from synthetic ZSM-5 and natural zeolites, by exchanging the quaternary amines, i.e. hexadecyltrimethylammonium (HDTMA) bromide and n-cetylpyridinium bromide (CPB). The maximum adsorption of CPB onto these zeolites is in the order of clinoptilolite>ZSM-5-88 (SiO2/Al2O3=88)>ZSM-5-31 (SiO2/Al2O3=31) which is mainly dependent on the external cation exchange capacity (ECEC) of each zeolite. Batch adsorption experiment was carried out to remove benzene, toluene, and phenol from aqueous solution using the above-mentioned organo-zeolites. In addition, as-synthesized MCM-41 molecular sieve was employed for removal of organic contaminants from aqueous solution. The experimental results were fitted to the Langmuir, Freundlich, Redlich–Peterson and linear equation isotherms to obtain the characteristic parameters of each model. Our resultant data showed that nonlinear form of Langmuir, the Freundlich and Redlich–Peterson could be fitted well with sorption data in most cases. According to the evaluation using the Langmuir equation, the maximum organics adsorption by synthesized MCM-41 was much greater than that of the natural clinoptilolite and ZSM-5 zeolites.
Synthetic and natural zeolites, modified by the quaternary amines, i.e. hexadecyltrimethylammonium (HDTMA) bromide and n-cetylpyridinium bromide (CPB) as well as MCM-41 molecular sieve were employed for removal of chromate from aqueous solution. Obtained data from chromate adsorption experiments over the mentioned materials were compared. It was shown that adsorption data for modified zeolite using the amine was consistent with Langmuir isotherm equation. The maximum chromate adsorption over as synthesized MCM-41 was much greater than that of the natural clinoptilolite and ZSM-5 zeolites.
This study compares the surface properties and the acetone adsorption potentials of mesoporous silica particles (MSPs) and Si-MCM-41. The Si-MCM-41 and MSPs are synthesized, respectively by hydrothermal method and evaporation-induced self-assembly (EISA) method. The results show that the surface area and pore diameter of MSPs are similar to those of Si-MCM-41. But the synthesis of Si-MCM-41 frequently requires longer time and tedious procedure as compared to that of MSPs. The bulk density of MSPs is 3.0–5.0 times higher than that of Si-MCM-41. The mass-based acetone adsorption capacities of these two materials are almost similar. This implies that MSPs have a higher volume-based acetone adsorption capacity than Si-MCM-41 so that less space is required for volatile organic compounds (VOCs) adsorption using MSPs as the adsorbent. The pressure drops of both powder and pellet forms of MSPs are also smaller than those of Si-MCM-41 for adsorbing the same amount of acetone. In addition, as compared to commercial H-ZSM-5 zeolite, both MSPs and Si-MCM-41 reveal better performances on the regeneration ability. As a result, both MSPs and Si-MCM-41 show high adsorption/desorption potential but the MSPs are better as novel adsorbents in terms of overall engineering consideration.
Studies on solvent extraction and selective recovery of Cd and Ni from sulphate solutions using TOPS 99 (Talcher organophosphorus solvent, an equivalent of di-2-ethylhexyl phosphoric acid) as extractant alone and in combination with Cyanex 471 X (triisobutyl phosphine sulphide) as synergist were carried out from an aqueous feed containing 0.541 g/L Cd and 1.182 g/L Ni. Variation of equilibrium pH of aqueous phase from 1 to 6 increased the percentage extraction of metals. Cd/Ni separation factor of 369 was obtained at an equilibrium pH of 4.5 with 0.05 M TOPS 99 and separation factor of 485 was obtained at an equilibrium pH of 4.0 with 0.1 M TOPS 99. Studies on extraction of Cd from Ni using mixed extractant systems containing 0.025, 0.05 and 0.075 M extractant and varying synergist concentrations at a total concentration of 0.1 M indicated that a combination of 0.05 M TOPS 99 and 0.05 M Cyanex 471 X concentrations is optimum to achieve ∼97% Cd extraction and 2.7% Ni co-extraction in single stage at an equilibrium pH of 4.2 with high separation factor (β) of 1085. McCabe–Thiele diagram for Cd extraction at different phase ratios with 0.05 M extractants each, indicated the necessity of two theoretical stages for >99% Cd extraction at an aqueous to organic phase ratio of 1.5. Accordingly, a two stage counter-current extraction simulation test was conducted at pH 4.2 with 0.05 M TOPS 99 and Cyanex 471 X each at an aqueous to organic (A/O) phase ratio of 1.5, which confirmed Cd extraction of 99.4% with co-extraction of 2.03% Ni. Under similar conditions of extraction at lower A/O phase ratio of 1.4 increased Cd extraction to 99.9% and decreased Ni co-extraction to 0.28%, which improved the Cd–Ni selectivity.
Simultaneous degradation of 4-chlorophenol (4CP) and Ethylenediaminetetraacetic acid (EDTA) was investigated in a heterogeneous Ultrasound/Fenton like system. In this system, zero valent iron (ZVI) was adopted and H2O2 was self-produced through oxygen activation catalyzed by iron/EDTA ligand reactions. It was found that pseudo first-order degradation kinetic was well applied for both 4CP and EDTA. The role of reaction components was discussed respectively and the effects of initial operating parameters on the degradation rate of 4CP and EDTA were investigated. The results showed that the competitive degradation relationship between 4CP and EDTA is weak. ZVI and EDTA are the essential components and they have important effect on the degradation of both compounds. Ultrasound (US) presented synergistic improvement on the degradation rate through overcome kinetic barrier of OO band by ultrasonic cavitation effect. A non-radical degradation pathway seems credible and ferryl-EDTA complex ([FeIV O]EDTA) instead of OH is identified as the principal oxidant.
Dissolved zinc is present in natural waters and process streams generated by the mining and metallurgical industry. These streams usually have a low pH. By using sulfate reducing bacteria, sulfide can be produced that precipitates with zinc as zinc sulfide (sphalerite), which can be easily separated from the wastewater and even reused as zinc concentrate. In this study, a sulfate reducing gas-lift bioreactor was operated at pH 5.5 using hydrogen as electron donor for sulfate reduction. We demonstrate effective zinc removal (7.2 mmol L−1 d−1) with low zinc effluent concentrations (0.65–8.8 μM) in a system combining sulfide generation by sulfate reducing bacteria (7.2–10.6 mmol SO42− L−1 d−1) at low pH (5.5) with the bio-precipitation of crystalline sphalerite. To investigate the effect of the sulfide excess on the settling properties of the sphalerite precipitates, the sulfide excess concentration was varied about two orders of magnitude (0.008–2.2 mM). The results show that crystalline sphalerite was formed in all cases, but larger particles with better settling properties were formed at lower sulfide concentrations.
Polymer/salt aqueous two phase systems (ATPS) based on polyethylene glycol (PEG) 600, sodium citrate and ammonium sulfate were used to partially purify plasmid DNA (pDNA) from Escherichia coli alkaline lysates. The effect of pH and lysate load on the binodal curve was analyzed and tie-lines were determined in order to establish the optimal conditions for ATPS formation. A series of extraction experiments were performed at pH 6.9 using a 20% (w/w) lysate load and systems with 16.5% (w/w) salt, 19.0% (w/w) PEG 600, and a tie-line length of 37.1% (w/w). Under these conditions, plasmid DNA was recovered in the salt-rich bottom phase. However, whereas with sodium citrate-based systems recovery yields closer to 100% were obtained, the use of ammonium sulfate enabled higher purification although with lower recoveries. Thus, the performance of ATPS prepared by combining sodium citrate and ammonium sulfate was also evaluated. A mixture of 25% (w/w) ammonium sulfate and 75% (w/w) sodium citrate offered a good compromise between plasmid recovery (91.1%) and purity (17.2%). Multi-step extraction procedures were evaluated in order to improve the process performance. Although the majority of the impurities were removed in the first step, incremental increases in the purity were obtained with the inclusion of extra steps. The top to bottom phase volume ratio was increased in order to increase plasmid concentration in the bottom phase. Although this was achieved using a phase ratio of 4, it was not possible to concentrate plasmid relatively to the starting lysate. Overall, the results show that ammonium sulfate, a salt which has a high environmental impact, can be partially replaced in ATPS by sodium citrate, without significant decrease in the performance of plasmid purification.
A mathematical model based on filtration theory, coupled with resistance in series model and gel polarization/film model has been developed in the present study. Unlike the cake filtration equipment where cake deposition continues until the wash cycle comes, in case of continuous stirred ultrafiltration the deposited solutes are allowed to build up over the membrane indefinitely, along with continuous back transport of deposited solutes into bulk by the turbulence created by stirring action. To account for this back transport, a coefficient called back transport coefficient has been defined which is found to be independent of any operating variables. Variation of polarized layer resistance was also studied with different operating variables like bulk concentration, stirrer speed and pressure differential. A correlation was also developed relating polarized layer resistance with those operating variables. A comparative study has been made between experimentally found polarized layer resistance value, using ultrafiltration data of Bhattacharjee and Bhattacharya, with those found from correlation and this developed model based on filtration theory. The model has been found to predict the polarized layer resistance reasonably well once the three parameters describing the model viz. permeability coefficient, back transport coefficient and membrane hydraulic resistance are known along with the operating condition. Using the above-mentioned parameters, it is also possible to predict flux and/or total permeate volume at any time under a given operating condition.
Development of a solvent extraction flow sheet for the separation and recovery of Cu(II), Ni(II) and Zn(II) using LIX 84 I as an extractant from sulphate solutions was investigated. Extraction of the metals depends on the equilibrium pH of the aqueous phase and increases with rise in equilibrium pH. Based on the difference in their extraction behavior as a function of equilibrium pH of the aqueous phase, it was possible to separate and recover these metals. Their extraction behavior clearly demonstrates the application of LIX 84 I as the extractant for the selective separation of Cu(II), Ni(II) and Zn(II) in pure form. The copper extraction isotherm was obtained by contacting the metal solution and 0.05 M LIX 84 I at different aqueous to organic (A:O) phase ratios at an equilibrium pH of 4.0. The McCabe–Thiele plot suggested that quantitative copper extraction is achievable in two counter-current stages (C–C) at A:O phase ratio of five, which gave 99.4% copper extraction efficiency. The results of two-stage stripping simulation for 0.745 gpl of Cu-loaded organic (LO) carried out at O:A ratio of 1.5:1 with 2 M H2SO4 gave copper stripping efficiency of 99.94%. Copper in the strip solution was enriched by more than seven times. The extraction of nickel with the same concentration of LIX 84 I at an equilibrium pH of 7.50 at A:O phase ratio of 1:1.1 in two stages gave nickel extraction efficiency of 99.4%. A two-stage counter-current stripping simulation (CCSS) for nickel LO at A:O phase ratio at 1:1 gave nickel stripping efficiency of 99.93%. Further extraction of zinc with the same concentration of LIX 84 I at an equilibrium pH of 9.0 at A:O phase ratio of unity for two stages gave zinc extraction efficiency of 99.81%. A two-stage counter-current stripping simulation for zinc LO at A:O phase ratio of unity with 3 M H2SO4 gave zinc stripping efficiency of 99.7%. Based on the results, a complete solvent extraction flow sheet of the process was developed with extraction and stripping efficiencies >99.5%.
The reversed micellar solution formed by Sorbitan trioleate (Span 85) coupled with Cibacron Blue F3G-A (CB) as an affinity ligand show good potential for use in reversed micellar protein extraction operations. In this work, the extraction behavior of lysozyme and ovalbumin with the reversed micellar phase has been investigated at extensive pH values and CB concentrations. The partitioning isotherms of lysozyme and ovalbumin were expressed by the Langmuir equation. By addition of 3 vol.% hexanol to the reversed micellar phase, the extraction capacity of lysozyme reached 6.38 mg/mL, over seven times higher than that of ovalbumin (0.83 mg/mL). Thus, lysozyme was separated from crude chicken ovalbumin solutions with a purification factor over 20. Moreover, the reversed micellar solution was recycled three times for the separation, and the purification factor was kept nearly 20 in the recycling. Incomplete back extraction of lysozyme to the stripping solution compromised the total recovery yields in the following recycles, so more effective back extraction method needs to be developed to make the extraction system more attractive. In general, the present results have shown the potential of the affinity-based reversed micellar system for application in protein separations.