Reverse Osmosis Separation of Nickel from Dilute Solutions

Abstract

Cellulose acetate membranes were characterized in terms of the pure water permeability constant, the solute transport parameter, the mass transfer coefficient, and percent solute separation using a reference system of aqueous sodium chloride solution. The membranes were used in the determination of reverse osmosis characteristics such as product rates and solute separation of dilute nickel salt solutions. The effect of the chemical species present in aqueous nickel salt solution on the degree of separation of nickel has been determined. The results of this study can be used in predicting the general reverse osmosis separation behavior of metals such as Zn, Cu, Pb, Mg, and Mn encountered in acid mine-water samples     

Comparative Study of Separation of Acetonitrile from Aqueous Solutions by Pervaporation using Different Membranes

Pervaporation of acetonitrile-water mixtures was carried out using three commercial membranes, viz: polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF). The effects of feed concentration and feed temperature on the pervaporation performance, total and partial permeate fluxes, as well as acetonitrile selectivity, were investigated. It was found that increase in temperature yields higher total fluxes and lower selectivity for acetonitrile-water system. Changing concentration of acetonitrile in the range concerned leads to significant effect on total flux and selectivity. PDMS membrane was found to be most selective for acetonitrile separation. The total flux through the membranes was found to be in the order of PTFE > PVDF > PDMS, and the acetonitrile selectivity was found to be in the order of PDMS > PVDF > PTFE. The activation energies of water and acetonitrile associated with the permeation process for the PDMS, PTFE, and PVDF membranes were calculated to be in the ranges of 0.29–0.99, 0.6–0.87, 0.45–2.73 kJ/mol for acetonitrile and 1.23–1.95, 1.37–1.71, 1.16–3.37 kJ/mol for water at different concentrations, respectively.     

Ultrafiltration of Albumin-Ethanol Solutions on Mineral Membranes

Abstract

This paper investigates the ultrafiltration of albumin-ethanol solutions on ZrO₂ mineral membranes for the preparation of human albumin from plasma. The classical process consists of a preconcentration phase of a 20% ethanol-albumin 7.5 g/L solution to raise albumin concentration to 80 g/L, then a diafiltration to reduce ethanol concentration to less than 0.3 g/L, and a final concentration to adjust albumin concentration to its final value of 210 g/L. The potential advantages of mineral membranes relative to the polysulfone membranes presently used are a longer membrane life and higher permeate fluxes in the presence of ethanol. In addition, they lend themselves to the use of back flushing or pulsatile flows for reducing membrane fouling. Using 2.7 mm i.d. Carbosep membranes with a 10 kd cut-off and velocities of 7 m/s, permeate fluxes of 40 L/hμm² at 4[ddot]C were obtained with 50 g/L albumin, 20% ethanol solutions representative of the preconcentration phase, while 45 to 50 L/hμm² were obtained at albumin concentrations of 100 g/L without ethanol at 8[ddot]C, representative of the final concentration phase. These fluxes compare favorably with fluxes obtained previously in our laboratory with polysulfone membranes which were respectively of 22 and 40 L/hμm² for the same solutions. This study confirms the expectation of a smaller reduction in the presence of ethanol of the permeate flux for the mineral membranes while albumin concentration in the permeate remained generally under 0.4 g/L irrespective of retentate concentration. The superposition of pressure and flow pulsations on the filter inlet by a piston-in-cylinder system decreases concentration polarization and increases permeate flux by 50 to 60% as compared with steady flows under the same conditions.     

Separation and Recovery of Metals from Dilute Solids and Aqueous Phases

Abstract

Present practice for the extraction of metals from low grade dilute ore sources and the recovery of metal values from dilute solutions is reviewed. Special problems associated with extraction from both solid and aqueous phases for copper, gold and silver recovery are considered. Emphasis is directed toward the application of insitu solution mining technology for recovery of metal values in the future.     

Removal of Dyes from Aqueous Solutions by Low Pressure Batch Ultrafiltration

Abstract

The use of a low pressure batch ultrafiltration method to separate dyes from aqueous solutions was investigated at 22°C. Several factors affecting the membrane performance, such as the hydraulic permeability and the rejection coefficient, were examined, including initial dye concentration, the operating pressure, as well as especially the membrane material and the ionic nature of dye molecules.     

Separation of Dissolved Phenolics from Aqueous Waste Stream using Micellar Enhanced Ultrafiltration

The micellar enhanced ultrafiltration (MEUF) process has been used for the separation of phenol and o-cresol from aqueous solutions at room temperature (30 + 2°C) using a cationic surfactant, cetyltrimethylammonium bromide (CTAB), and polyethersulfone membrane of molecular weight cut-off 10 kDa. The effect of the cross-flow rate, the surfactant to pollutants (S/P) concentration ratio in feed, the variation of pollutants concentration in the feed keeping S/P constant, the presence of Na₂SO₄ and NaCl salts and mixed surfactants on the rejection of each solute and permeate flux have been studied in detail. The % rejection of phenol and o-cresol without using the surfactant observed was 24% and 41% respectively, which was increased to 60% for phenol and 80% for o-cresol at S/P ratio of 8. The effect of salts was also investigated. There was no significant effect of the cross-flow rate on the % rejection of the solutes. The effect of the membrane pore size was also investigated using 1 KDa and 30 KDa PES membranes. Characteristic parameters of MEUF such as the distribution coefficient, micelle loading, and the micelle binding were also estimated.     

Multistage Decomposition Kinetics of Ozone In Dilute Aqueous Solutions

AbstractDecomposition of ozone in dilute aqueous solutions was found to be a complex process kinetically. Initial ozone dose-time had a significant impact on reaction order. Solutions dosed initially for less than one minute displayed uniform second-order kinetics. For doses applied over 5 and 15 min periods at a pH -2, reaction order changed from 2 to 1 to 0 as ozone decomposition progressed. At a pH of 6.65, the transition was from a reaction order of 2.5-3 to 2. This behavior has been ascribed to the effect of accumulated ozone decomposition products on the decomposition process.     

Separation of Some Dyes from Aqueous Solutions by Flotation

Abstract

Separation of the dyes brilliant green, neutral red, eriochrome black T, and eosin from aqueous solutions by flotation was studied using oleic acid surfactant. Nearly 100% of the investigated dyes could be floated under the optimum conditions. The effect of pH on the flotation efficiency was studied in particular. At pH ≤ 2, 7.5, ≤ 5, and ≤ 6, the maximum flotation was achieved for brilliant green, neutral red, eriochrome black T, and eosin, respectively. The effects of oleic acid and dye concentrations, some ions, and temperature on the floatability were examined. Moreover, the selective separation of some dyes was attempted.     

Mass Transfer in Molybdenum Extraction from Aqueous Solutions Using Nanoporous Membranes

Modeling of non‐disperse solvent extraction of molybdenum(VI) with PC‐88A as extractant and a nanoporous hollow‐fiber membrane contactor as extractor was performed. Computational fluid dynamics was applied for modeling and simulation of molybdenum extraction. Concentration, pressure, and velocity distributions for molybdenum were determined. The extraction of Mo⁶⁺ was greatly influenced by the flow rate of feed solution. The extraction efficiency was reduced with higher feed flow rate and increased with the molybdenum content in the feed. The pressure drop along the shell side of the membrane extractor was found to be not significant, being one of the advantages of membrane extractors which assist in reducing the operational costs. The proposed simulation method is capable to prognosticate the performance of solvent extraction of molybdenum in membrane extractors.     

Separation and Fractionation of Macromolecular Solutions by Ultrafiltration

Abstract

The present state-of-the-art of membrane ultrafiltration with reference to macromolecular fractionations is reviewed. Ultrafiltration is now a widely used technique, both in the laboratory and industrial applications, which stems from the development of asymmetric membranes followed by the recognition of the importance of fluid mechanical and mass transfer processes and their management through equipment design and fluid-flow practices. However, large-scale fractionation of macromolecular mixtures or solutions such as proteins has not yet been feasible. This inability is attributable to a number of factors, viz., concentration polarization and fouling processes which may also be coupled with limitations imposed by nonuniform pore size as well as protein–protein (solute) interactions, the latter being determined by the solution chemistry. It is now well recognized that boundary-layer and interfacial effects, in general, are extremely important in membrane applications, as evidenced by a number of manifestations. Several models have been put forward to explain the effects of concentration polarization, whereas membrane-fouling owing to solute-membrane interactions and membrane pore-obstruction or secondary membrane formation via macrosolute deposition, thus causing major changes in effective pore size distribution and therefore effecting inevitable changes in membrane characteristics, have hardly been considered in detail in ultrafiltration transport modeling. Nevertheless, the recognition of the importance of surface and colloid chemical phenomena in governing membrane performance has focused attention upon techniques of membrane modification and feed solution properties control as the key to ultrafiltration applications. These are particularly important for macro-molecular fractionations which depend upon a reasonably clear understanding of the mechanisms of the various processes and which emerge from a good deal of basic or fundamental research.     

Treatment of Aqueous Ionic Surfactant Solutions by Dynamic Ultrafiltration

Abstract

This paper investigates the reduction of concentration of an ionic surfactant (sodium dodecyl benzene sulfonate) present in an aqueous solution by ultrafiltration. A dynamic filtration system consisting of a metal disk rotating near a flat circular organic membrane was used in this study. Membranes cut off tested were 10, 20, and 50 kDa. The maximum rejection rate was 92% at 10 kDa. Permeate fluxes kept increasing with transmembrane pressure until at least 1400 kPa, reaching 400 Lh^?1m^?2 at 10 kDa and 950 at 50 kDa for a rotation speed of 1000 rpm. However, raising the rotation speed above 500 rpm at 900 kPa had only a moderate effect on performance, indicating probably strong interactions between surfactant molecules and the membrane and that the permeate flux was mostly limited by pressure.     

Application of Polyelectrolyte‐Enhanced Ultrafiltration for Rhenium Recovery from Aqueous Solutions

Polyelectrolyte‐enhanced ultrafiltration was investigated for rhenium(VII) recovery from aqueous solutions by using polyquaternium‐6 (PQ6) as a complexing agent. The effects of the operating parameters on the permeate flux (J) and the rhenium rejection coefficient (R) were studied. In the process of concentration, J declines slowly and R is about 1. The concentrated solution was used for the decomplexation. It takes 10 min to achieve the decomplexation equilibrium at a chloride ion concentration of 100 mg L^–1. The decomplexation percentage reaches 45.6 %. In the diafiltration process, rhenium is extracted effectively, and the purification of the regenerated PQ6 is satisfactory. The regenerated PQ6 was used to bind rhenium(VII). The binding capacity of the regenerated PQ6 is close to that of fresh PQ6.     

Aqueous Membranes for the Separation of Gaseous Mixtures

Abstract

Gas mixture separation characteristics of aqueous surfactant films were studied. Permeation constants of carbon dioxide, oxygen, nitrogen, helium, and propane through aqueous films of 2 wt% Ivory Liquid and of 2 wt% Duponol WN were determined. Binary gas mixtures of carbon dioxide-nitrogen and carbon dioxide-propane were enriched in one of the components using a thermally induced driving force.     

Studies on Permeation,Rejection, and Transport of Aqueous Poly(ethylene Glycol) Solutions using Ultrafiltration Membranes

Abstract

The permeate flux and retention of aqueous solutions of poly(ethylene glycols) (PEG) with different molecular weights ranging from 4000 to 35,000 Da have been investigated using various compositions such as 100/0, 90/10, 80/20, and 70/30 wt% of cellulose acetate (CA)/sulfonated poly(etheretherketone) (SPEEK) ultrafiltration blend membranes. The factors affecting the rejection rate and permeate flux such as molecular weight of PEGs, concentration of the solute, composition of the membranes, and transmembrane pressures have been studied. It is seen that the increase in the concentration of PEG results in the decreased permeate flux and increased rejection for increasing CA content in the membranes. A similar observation in the flux and rejection was made for increasing the molecular weight of PEGs. Further, the mass transfer, diffusion, and true retention coefficients of the solute have been studied with different operating variables like molecular weight and concentration of PEGs. An increase in the molecular weight of PEGs results in the decrease of mass transfer and diffusion coefficients and increase of the true retention coefficient. A reverse trend is observed with increasing concentrations of PEG.     

POMS Membrane for Selective Separation of Ethanol from Dilute Alcohol-Aqueous Solutions by Pervaporation

Lignocellulosic biomass has potential as an alternative to corn as starting material for the production of ethanol for the development of non-fossil fuel energy sources. In this case, low concentration bioethanol is gained by yeast fermentation and it has to be efficiently recovered and concentrated. For this purpose pervaporation separation of dilute alcohol-aqueous solutions was carried out using a poly(octhylmethyl siloxane) [POMS] membrane. The effect of different process parameters (feed composition, feed temperature, feed flow rate, permeate pressure) on pervaporation performance were investigated and discussed in terms of the separation factor and the total flux. The membrane studied was ethanol to water selective at ethanol feed concentrations lower than 2.5% w/w, while the highest permeability was achieved at feed temperature of 95°C.     

Centrifugal Polyelectrolyte Enhanced Ultrafiltration for Removal of Copper‐Citrate Complexes from Aqueous Solutions

Abstract

To replace the conventional dead‐end polyelectrolyte enhanced filtration (PEUF), which is a time consuming process in the optimization of process variables, centrifugal polyelectrolyte enhanced ultrafiltration was investigated to remove copper‐citrate complex in aqueous phase with a cationic polyelectrolyte, poly(diallydimethylammonium chloride) (PDADMAC). Effects of concentration ratios between polyelectrolyte, copper, and citrate and pH were observed. Below pH 3, copper was not removed by centrifugal PEUF. At the same concentration (1 mM) of citrate and copper, removal of copper at pH 5 was the highest value of 54%, 90%, and 98% with 5, 10, and 20 mM PDADMAC, respectively. Removal of copper decreased with the logarithmic ionic strength. Since the centrifugal PEUF is very economical in time compared with conventional dead‐end PEUF, the present method should be a valuable tool in the optimization of process variables.     

Ultrafiltration Carbon Membranes from Organic Sol-Gel Process

We present a simple approach for preparing mesoporous carbon membranes on macroporous fly-ash-based ceramic supports via sol-gel polymerization of resorcinol with formaldehyde. The support was dip-coated and dried at 45°C under ambient pressure without a special drying process. The mesoporous carbon membrane was obtained after carbonization under a nitrogen atmosphere. The coating–pyrolysis process only required one cycle. The graphitization degree increased with carbonization temperature, as shown by X-ray diffraction. However, Raman spectroscopy revealed that defects emerged at high carbonization temperature. Scanning electron microscopy clearly showed the mesoporous carbon layer and macroporous support, a uniform carbon layer with thickness less than 1 µm forming on the support. The obtained carbon membrane shows uniform pores and high mesopore volume. The flux of pure water through the mesoporous carbon membrane was as high as 167 L · m^?2 · h^?1 · bar^?1. The molecular weight cutoff of this membrane was found to be about 20,000 Da.     

Influence of Membrane Solvent on Strontium Transport from Reprocessing Concentrate Solutions through Flat-Sheet-Supported Liquid Membranes

Abstract

The influence of membrane solvents on strontium transport from nuclear fuel reprocessing concentrate solutions to demineralized water through a flat-sheet-supported liquid membrane has been studied using dicyclohexano-18-crown-6 as the extractant and Celgard 2500 as the solid support. Even though the highest values of the distribution coefficients of strontium were obtained with nitrated compounds as membrane solvents, strontium permeabilities were determined only when a membrane solvent was used for which stable SLMs were obtained. Among the latter, the use of 4-nonylphenol as a phase modifier is not satisfactory for long-term strontium transport experiments due to its reactivity with the nitric acid of the aqueous feed solution. We achieved a good correlation between strontium permeability and two parameters of the membrane diffusion coefficient (molecular weight and viscosity of the membrane solvent) for aromatic solvents modified with isotridecanol or 1-decanol. The best results were obtained with n-hexylbenzene (0.7 mol·L^?1 isotridecanol) which should lead to a high strontium decontamination by hollow-fiber-supported liquid membranes. The transport of nitric acid and nonradioactive cations through the membrane was not greatly influenced by the membrane solvent used.