Ion Rejection Rate Research Articles

Exceptional ion rejection ability of directional solvent for non-membrane desalination

The recently demonstrated directional solvent extraction (DSE) is promising for very low temperature, membrane-free water desalination. In this paper, we combine atomistic simulations and experimental validation to demonstrate that the currently used directional solvent, decanoic acid, can reject all major salt ions in seawater, with very high rejection rates. The salinities of the DSE recovered water show that ion rejection rates are ∼98%–99%—similar to those of the best reverse osmosis membranes. Our test also shows that the DSE process can desalt seawater to produce fresh water that meets drinking water standards.

Layer-by-Layer Assembly of Polyelectrolyte Multilayers in Three-Dimensional Inverse Opal Structured Templates

A novel means of layer-by-layer deposition (LbL) of polyelectrolyte multilayers on three-dimensionally porous inverse opal (3D-IO) structures is presented. The 3D-IO structures comprising UV-curable polymer are highly flexible and can be readily demonstrated as free-standing films with double-sided open porosity over a large scale. A conflict between the intrinsically hydrophobic polymeric structures and waterborne characteristics of the LbL deposition process is overcome by employing a mixed solvent system of water and alcohol. The deposition pH of the LbL assembly can strongly affect the charge density and the degree of entanglement of polyelectrolyte chains, resulting in contrastingly different film deposition and growth behaviors. Since this method utilizes a three-dimensionally structured surface as a deposition substrate, 3D-IO films with a thickness of tens of micrometers can be uniformly and completely deposited with polyelectrolyte multilayers using only several tens of bilayer depositions, which can offer a new pathway of fabricating functionalized polymeric films. Finally, the LbL treated 3D-IO films are applied to nanofiltration membranes for removing multivalent metallic cations. Due to the enhanced Donnan exclusion effect as a result of multiple interfaces formed inside the 3D-IO structures and the relatively large volumetric ratio of water-permeable polyelectrolyte complexes, outstanding membrane performance was observed. Specifically, a good rejection rate of metal ions was achieved even under highly diluted feed conditions without sacrificing the high permeation flux.

Treatment of dye and cadmium solutions using asymmetric kaolin porous tubular support

Kaolin porous support ceramic was prepared from kaolin. The characterization of the porous properties and structure of the support synthesis was carried out by scanning electron microscopy (SEM), absorption rate, shrinkage rate and Hg-porosimetry methods. The pore size distribution showed a unimodal pore size distribution with an average pore size of about 0.9µm. The reliability of support was measured by filtration tests and removal of heavy metals.Filtration studies using porous tubular supports were performed for solutions containing methylene blue and Evans blue. The study of the liquid filtration and flow through these supports showed that the methylene blue rejection rate was 99% while the Evans blue rate reached 90% for a 90minute filtration time under a pressure of 2bar. We beforehand tested the flow rate for each support with distilled water and the results show that the support of kaolin gave a flux for distilled water of 31.0L/h at the pressure of 2bar. At a pressure of 3.5bar an increase in the distilled water flux through the support was observed.The rejection rate of cadmium ions was more significant. A rejection rate of 99.99% using a 10−4mol/L solution of this heavy metal for two-hour treatment time was obtained.

Evaluation of the steric, electric, and dielectric exclusion model on the basis of salt rejection rate and membrane potential measurements

The current work focuses on the application of the steric, electric, and dielectric exclusion (SEDE) model to the study of both the ion rejection rate and the membrane potential of a nanofiltration polyamide membrane. The aim of this study was to evaluate the performance of the SEDE model and to compare it with steric/electric exclusion theory. Experiments were conducted with CaCl 2 solutions at various concentrations. The SEDE model is a four-parameter model because the effective pore size ( r p ), the effective thickness-to-porosity ratio ( Δ x / A k ), the effective volume charge density of the membrane ( X), and the dielectric constant of the solution inside the pores ( ε p ) have to be known to predict the rejection rate and the membrane potential. The first parameter was estimated from membrane potential measurements performed at high salt concentrations and the second from water permeability. In the case of single salt solutions, experimental rejection rates and membrane potentials can be described by a number of couples of values ( X , ε p ) because both electric and dielectric exclusion contribute to reject ions. A set of couples ( X , ε p ) were first estimated by fitting membrane potentials. One of the couples was found to provide a good description of experimental rejection rates as well. Results showed that the polyamide membrane is negatively charged in CaCl 2 solutions at natural pH and that the membrane charge increases with the salt concentration. A decrease in the effective dielectric constant inside the pores with respect to its bulk value was found. This is indirect evidence that dielectric exclusion plays a major role in the transport phenomena of the studied NF membrane. The standard steric/electric theory was also used to fit experimental rejection rates and membrane potentials, the effective volume charge density being the single adjustable parameter in this case. Unlike the SEDE model, the steric/electric exclusion theory was unable to account simultaneously for both rejection rate and membrane potential data by using a unique choice for X and ε p . This highlights the global coherence of the SEDE model and the nonappropriateness of the description of transport in NF membranes by the classical steric/electric exclusion theory.

Characteristics and application of multiple membrane process in plating wastewater reutilization

A multiple membrane process aimed at reutilization of plating combined wastewater after physical and chemical pretreatment in mechanical industry was developed for selective separation to reduce cost and mitigated the increasing heavy metal pollution. The process was divided into three stages: firstly, microfiltration (MF) and ultrafiltration (UF) was used to separate the possible organic and suspended matters, secondly, electrodialysis (ED) was carried out for effective desalination, and thirdly, the concentrate from ED was treated by nanofiltration (NF) and reverse osmosis (RO) separately to increase the recovery rate of water. Results showed that filtration characteristics of UF membrane here was not so good as usually, even if compared with MF membrane. And RO performed better than NF in wastewater separation, especially in anti-compacting ability of membrane. Since the rejection rate of heavy metal ions and COD in ED/RO process is high, all the product water exceeded the related qualification and could be reused as cooling water in industry.

Adsorption characteristics of zinc ions on sodium dodecyl sulfate in process of micellar-enhanced ultrafiltration

To separate zinc ions from aqueous solution efficiently, micellar-enhanced ultrafiltration(MEUF) of hollow ultrafiltration membrane was used with sodium dodecyl sulfate(SDS) as surfactant. The formation of micellar and the adsorption mechanism were investigated including the influence of the ratio of SDS to zinc ions on the micelle quantity, the micelle ratio, the gross adsorptive capacity, the rejection of zinc ions and the adsorption isotherm law. The results show that the rejection rate of zinc ions reaches 97% and the adsorption of zinc ions on SDS conforms to the Langmuir adsorption isotherm and the adsorption is a chemical adsorption process.

Transport of water and alkali metal ions through MFI zeolite membranes during reverse osmosis

Molecular sieve zeolite membranes have recently been shown to be potentially useful for treating saline wastewater by reverse osmosis. In this paper, reverse osmosis of 0.1 M solutions of alkali metal chlorides, including LiCl, NaCl, KCl, RbCl, and CsCl, has been investigated on MFI-type zeolite membranes synthesized from an aluminum-free precursor. The MFI zeolite membrane exhibited high rejection rates ( r i > 95%) for all alkali metal ions at an applied pressure of 2.75 MPa. The rejection rates of Li + and Na + declined slightly while the ion flux increased more dramatically than did the water flux with moderately raising the temperature. Increasing the hydraulic pressure difference across the membrane resulted in significant enhancements in both the water flux and the ion rejection rates but with much less influence on the ion flux. The ion flux increased monotonically with the crystallographic ion size from Li + to Cs + while the dependence of the corresponding water flux on ion size exhibited a maximum for the 0.1 M KCl solution. The ion separation by reverse osmosis on the MFI zeolite membranes was found to rely on the restricted access of hydrated ions to the zeolitic pores and the competitive diffusion of water and ions in the zeolite channels.

Transport Properties and Electrokinetic Characterization of an Amphoteric Nanofilter

Transport properties of a tubular nanofilter with amphoteric properties have been investigated by means of the SEDE (steric, electric, and dielectric exclusion) homogeneous model. Within the scope of this 1D model, the separation of solutes results from transport effects (described by means of extended Nernst-Planck equations) and interfacial phenomena including steric hindrance, the Donnan effect, and dielectric exclusion (expressed in terms of (i) the Born dielectric effect, which is connected to the lowering of the dielectric constant of a solution inside nanodimensional pores, and (ii) the interaction between ions and the polarization charges induced at the dielectric boundary between the pore walls and the pore-filling solution). The effective volume charge density of the membrane has been determined from tangential streaming potential experiments coupled with conductance experiments in a potassium chloride solution at various pH values ranging from 2 to 11. The inferred values have been used in the SEDE model to compute the ion rejection rates with the dielectric constant of the solution inside the pores as a single adjustable parameter. The model provides a relatively good description of experimental data even at extreme pH values for which a ternary system has been considered (K+, Cl-, and H+ or OH- depending on the pH). The fit to experimental data at the membrane isoelectric point indicates that the confinement effect decreases the dielectric constant inside the pores only slightly (with respect to its bulk value). However, the (pH-dependent) ionization of surface sites has been found to lead to a substantial lowering of the dielectric constant inside the pores.

EFFECT OF OPERATING CONDITIONS ON THE SEPARATION OF AMMONIUM AND NITRATE IONS WITH NANOFILTRATION AND REVERSE OSMOSIS MEMBRANES

ABSTRACT This paper presents the pilot scale membrane separation studies on the Elmali Lake raw water in Istanbul, which is highly polluted by discharging of sewage waters. Low pressure nanofiltration (NF) and reverse osmosis (LPRO) membranes having the surface area of 2 m2 have been used during the experimental runs. Experiments were conducted at different pressures, temperature and pH ranges. Feed flow rate was about 300 L/h. As a result, flux values increased linearly with increasing pressure. Ammonia and nitrate ion rejections also increased with increasing pressure and characteristics of rejection were similar for the both types of membranes. Permeate flux value increased proportionally with the temperature. The temperature changing has also influenced the rejection rate of ammonia and nitrate ions. Both ammonia and nitrate ion rejections at neutral pH values were very high. Therefore, neutral pH value is suitable for TFC-S and TFC-HR membranes to remove ammonia and nitrate ions.

Abatement of heavy metals and softening of hard water by the CoAlPO4‐5/polysulfone membrane

AbstractTo improve the membrane, if CoAlPO4‐5 was appropriately added, it could increase the rejection rate of metal ions compared with the PSf membrane. Besides, penetration rate would also increase, and the pressure applied could be lowered when the improved membrane was used. The optimum amount of CoAlPO4‐5 added for Co : Al : P = 0.1 : 0.92 : 1.0 is about 5 wt %, while for the Co : Al : P = 0.08 : 0.93 : 1.0, this optimum value would shift toward a higher wt % because the latter has less active sites per unit weight of CoAlPO4‐5. The hydrated radius of metal ion had great influence on the rejection rate. The larger the radius, for example, that of the +3 valence cations, the higher the rejection rate would exhibit, and the rate for Cd2+was much lower because its radius was the smallest one. Moreover, although incompatibility existed in the improved membrane and the variation of applied pressure was limited, durability of this membrane under the operating conditions was good. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2768–2773, 2001