Polymer-assisted Ultrafiltration Research Articles

Efficient Removal of Uranyl Ions Using PAMAM Dendrimer: Simulation and Experiment

In this work, using atomistic molecular dynamics (MD) simulations and polymer-assisted ultrafiltration experiments, we explore the adsorption and removal of uranyl ions from aqueous solutions using poly(amidoamine) (PAMAM) dendrimers. The effects of uranyl ion concentration and the pH of the solution were examined for PAMAM dendrimers of generations 3, 4, and 5. Our simulation results show that PAMAM has a high adsorption capacity for the uranyl ions. The adsorption capacity increases with increasing concentration of uranyl ions for all 3 generations of PAMAM in agreement with experimental findings. We find that the number of uranyl ions bound to PAMAM is significantly higher in acidic solutions (pH < 3) as compared to neutral solutions (pH ∼ 7) for all uranyl ion concentrations. Additionally, we find an increase in the number of adsorbed uranyl ions to PAMAM with the increase in the dendrimer generation. This increase is due to the greater number of binding sites present for higher-generation PAMAM dendrimers. Our simulation study shows that nitrate ions form a solvation shell around uranyl ions, which allows them to bind to PAMAM binding sites, including the amide, amine, and carbonyl groups. In polymer-assisted ultrafiltration (PAUF) experiments, the removal percentage of uranyl ions by G3 PAMAM dendrimer increased from 36.3% to 42.6% as the metal ion concentration increased from 2.1 × 10-5 M to 10.5 × 10-5 M at a pH of 2. Our combined experiment and simulation study suggests that PAMAM is an effective adsorbent for removing uranyl ions from aqueous solutions.

Efficient removal of antimony from aqueous solution by sustainable polymer assisted ultrafiltration process

To minimize the health risks from antimony in aqueous environment, a polymer assisted ultrafiltration (PAUF) process with polyethersulfone (PES) membrane was employed to remove antimony for the first time. Effects of polymer, pH value and functional groups/Sb ions quantity ratio on antimony removal were systematically explored. Finally, antimony rejection efficiencies of 85.8 ± 0.9%–94.7 ± 1.9% were obtained with gradually reduced normalized water permeate flux from 1 to 0.61 ± 0.02 in 120 min PAUF process under the optimal conditions of polyethyleneimine (PEI), pH = 3 and functional groups/Sb ions quantity ratio = 8. Relevant mechanism investigations indicated that the macromolecule PEI-Sb complexes were formed mainly due to electrostatic interaction during complexation, and then were rejected in ultrafiltration by pore sieving. Meanwhile, ionic strength experiments indicated that the addition of NaCl resulted in significant decline (4.0 ± 0.8%–49.2 ± 3.2%) in antimony rejection efficiencies due to electric double-layer compressing and competition complexation. Moreover, membrane cleaning of 0.2% NaClO and PEI regeneration under pH value of 8 were performed to achieve sustainable cyclic PAUF with reused membrane and polymer. Simultaneously, antimony also could be recovered for reuse during the regeneration of PEI. Results of steady antimony rejection and water permeation demonstrated that this process is a viable alternative for sustainable antimony removal from aqueous environment.

Municipal Solid Waste as Secondary Resource: Selectively Separating Cu(II) from Highly Saline Fly Ash Extracts by Polymer-Assisted Ultrafiltration

Urban mining from fly ash resulting from municipal solid waste incineration (MSWI) is becoming more and more important due to the increasing scarcity of supply-critical metals. Metal extraction from acid fly ash leaching has already been established. In this context selective Cu recovery is still a challenge. Therefore, our purpose was the separation of Cu(II) from MSWI fly ash extracts by polymer-assisted ultrafiltration (PAUF). We investigated three polyethyleneimines (PEIs) with regard to metal retention, Cu(II) selectivity, Cu(II) loading capacity, and the viscosity of the PEI containing solutions. A demanding challenge was the highly complex matrix of the fly ash extracts, which contain up to 16 interfering metal ions in high concentrations and a chloride content of 60 g L−1. Overcoming that, Cu(II) was selectively enriched and separated from real fly ash extract at pH 3.0. At pH 1.0, a PEI-free Cu(II) concentrate was obtained and PEIs could be regenerated for reuse in further separation cycles. The PAUF conditions developed at laboratory scale were successfully transferred to pilot scale, and hyperbranched PEI (HB-PEI) was found to be the most suitable reagent for PAUF in a technical scale. Moreover, HB-PEI enables photometric control of the Cu(II) enrichment.

Poly(itaconic acid)-assisted ultrafiltration of heavy metal ions’ removal from wastewater

The complexation–ultrafiltration technique has been introduced as a capable system to remove heavy metals ions from wastewater. This method needs a water-soluble polymer; therefore, in this paper we synthesized super water-soluble poly(itaconic acid) (PITA) and employed it in polymer-assisted ultrafiltration process to remove Pb(II) ions from synthetic wastewater solutions. The itaconic acid can be produced from different agricultural products and is a green and eco-friendly material. Factors influencing the removal of the metals ions including poly(itaconic acid) concentration, pH and permeate flux were investigated. The results showed that the maximum percentage of metal ion removal was obtained in the basic pH (pH > 7). The flux test was performed by 200 mg/L of poly(itaconic acid) and after 60 min, the flux of membrane was 33.4 L/m2h. The simultaneously selective removal ability of the poly(itaconic acid) for adsorption of different metal ions (Pb2+, Sn2+, Cu2+, Zn2+, and Cd2+) was also studied. The trend of rejection was Pb2+ > Cu2+ > Sn2+ > Zn2+ > Cd2+. The highest rejection of Pb(II) ions was achieved as 86%. Generally, the results of this research demonstrated that poly(itaconic acid) (with two carboxyl groups on its repeating unit) is more effective in removing heavy metals ions from wastewater in comparison with customary polymers.

PAMAM dendrimer-enhanced removal of cobalt ions based on multiple-response optimization using response surface methodology

This study introduces poly(amidoamine) PAMAM dendrimers as new macromolecular complexation agents for Co(II) removal in polymer-assisted ultrafiltration (PAUF). A five-level three-factor design of experiments (DOE), central composite design type, and response surface methodology (RSM) were used together to find out the interaction effects and optimize three variables, i.e., initial Co(II) concentration ([Co2+]0), PAMAM dendrimer-to-Co(II) ratio (r), and pH of solution. Multiple-response simultaneous optimization was conducted by using desirability function. The goal of 73.6% overall desirability was attained for the removal efficiency (R) and metal retention capacity (q). The predicted results obtained for the simultaneous optimization are R = 76.78% and q = 392.09 mg/g. The optimum conditions derived via RSM were found to be as follows: [Co2+]0 = 4.14 mg/L, r = 2, and pH = 9.0. Verification experiments (R = 75.73% and q = 387.32 mg/g) confirmed the validity of the predicted model. The DOE–RSM-utilized and desirability function-optimized PAMAM dendrimer-enhanced ultrafiltration (PAMAM-DEUF) process was used for the first time in this study. The results are comparable to those provided by the reference PAUF technique.

Evaluation of Jeffamine® Core PAMAM Dendrimers for Simultaneous Removal of Divalent Heavy Metal Ions from Aqueous Solutions by Polymer Assisted Ultrafiltration

Different generations (G3-G4) of amine-terminated Jeffamine® T-403 core poly(amidoamine) PAMAM dendrimers (JCPDs) were used as new macromolecular heavy metal chelating agent templates in polymer assisted ultrafiltration (PAUF) for the investigation of their removal ability for some of the divalent metal ions: Cu, Co, Ni, Cd, and Zn from aqueous solutions under competitive conditions. The effects of pH and generation size of JCPDs were also investigated. Extent of binding (EOB) data can be appropriately expressed by a tetradentate coordination for JCPDs at pH 9 where the maximum removal of metal ions was observed. At pH 9.0, the affinity of both generations towards heavy metal ions was also observed in the decreasing order of Zn(II) > Co(II) > Ni(II) > Cu(II) > Cd(II). Results revealed that the highest total binding capacity was observed for G3-NH2 (262.79 ± 1.62 mg/g) as a little bit higher than that of G4-NH2 (257.27 ± 2.57 mg/g). EOB studies also proved the active contribution of amide groups to metal binding ability of PAMAMs. Both generations were selective towards Cu(II) ions at lower pH 5 and pH 7. From these results, it was concluded that studied JCPDs have the desired technical properties to be used for the removal of toxic metals from wastewaters.

Efficient Complexation-Ultrafiltration Process for Metal Ions Removal from Aqueous Solutions Using a Novel Carboxylated Polyethylenimine Derivative (PEI-COOH)

The presence of large quantities of toxic heavy metals (i.e. cobalt, chromium, lead, cadmium, zinc, etc.) in the environment may be a serious threat to humans. Hence, the development of novel methods able to eliminate these toxic contaminants from wastewater in efficient and economically viable ways is highly desirable. In this work we assayed the ability of two polymers, polyethylenimine (PEI) and its carboxylated derivative (PEI-COOH), to complex heavy metals and to remove them from contaminated water by polymer-assisted ultrafiltration. PEI is able to complex efficiently Ag, Al, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sn and Zn and reduce their concentration in permeate to values < 4 ppm. Interestingly, PEI is very efficient to remove Cr and Sn down to a concentration less than 0.1 ppm. Moreover, PEI-COOH derivative is more efficient than PEI to remove Ag, Al, Cd, Co, Cu, Ni, Pb, and Zn to a concentration less than 0.4 ppm (ICP-OES analysis). Our preliminary results indicate that PEI-COOH is able to complex those metals that are not complexed by PEI, hypothesising that the combined use of these two polymers may be efficiently employed as a powerful strategy for the complete removal of heavy metals from wastewater. Keywords: Polyethylenimine, Complexation, Ultrafiltration, Wastewater, Metal ions

Response surface modeling and optimization of copper removal from aqua solutions using polymer assisted ultrafiltration

The present paper discusses response surface methodology (RSM) as an efficient approach for predictive model building and optimization of hybrid complexation–ultrafiltration process. In this work the application of RSM is presented for optimization of dead-end and cross-flow polymer assisted ultrafiltration (PAUF) dealing with the removal of Cu(II) ions from aqua solutions using polyacrilic acid (PAA) as chelating agent. All experiments were performed according to statistical designs in order to develop the predictive regression models used for optimization. The optimization of dead-end PAUF was carried out to ensure a high rejection coefficient. While the goal of cross-flow PAUF optimization was to improve hydrodynamic conditions in membrane apparatus, i.e., to minimize the permeate flux decline and to increase the average permeate flux. In the dead-end PAUF experiments a commercial polymeric membrane made of regenerated cellulose was used. The maximum rejection coefficient of 99.9% was obtained for following optimal conditions: C PAA = 0.3 g/L, r (PAA/Cu) = 2.78 (w/w) and pH 5.56. The cross-flow PAUF experiments were carried out using a commercial metallic tubular membrane equipped with rotating shaft inside (helical module). The optimal hydrodynamics conditions determined in this case by RSM were Δ P = 0.19 bar, Q R = 54 L/h and W = 41.33 Hz (2480 rpm). The analysis of variance (ANOVA) was performed to validate the developed regression models. Also, the response surface plots were drawn for spatial representation of the regression equations.

Chemical and operational aspects in running the polymer assisted ultrafiltration for separation of copper(II)–citrate complexes from aqueous media

The polymer assisted ultrafiltration (PAUF) process for treatment of wastewaters containing metal ions chelated with citric acid has been studied giving particular attention to the chemical and operational aspects. The polyethylenimine (PEI) polymer bound quantitatively the copper(II)–citrate chelate at pH 5.5 forming the ternary PEI–Cu–citrate complex as discussed considering the stability constants. The ternary complex was separated by UF membranes producing a permeate with very low metal concentration. Best performance was obtained with the Iris 30 membrane (permeate flux 167.4 L h −1 m −2; rejection 98.8%) by operating at 4 × 10 5 Pa (4 bar). The limiting concentration (maximum retentate concentration for obtaining a copper(II) concentration in the permeate lower than 1.3 mg L −1 corresponding to 2.04 × 10 −5 mol L −1), was 250 mg L −1 (3.93 × 10 −3 mol L −1) for Iris 30 membrane and 400 mg L −1 (6.29 × 10 −3 mol L −1) for Iris 10 membrane by operating with both constant trans-membrane pressure and constant permeate flow rate modes. The polymer regeneration was carried out with good results by operating with the diafiltration method and using both the membranes, but the Iris 30 membrane, operated at 4 × 10 5 Pa (4 bar), performed a little better owing to the higher flux. The copper ion present in the diafiltration permeate was recovered by oxidising the citrate in a membrane photoreactor. The obtained results permitted to draw an integrated membrane process combining complexation–UF–diafiltration–photocatalysis to treat metal containing wastewaters (e.g. washing water from soil remediation) for obtaining water recyclable in the process itself or safely discharged, recycling the polymer and recovering the metals.

Ultrafiltration of Polymer‐Metal Complexes for Metal Ion Removal from Wastewaters

AbstractSummary: A case‐study using macromolecular metal complexes is described. The results of a process named Polymer Assisted Ultrafiltration (PAUF) for ion removal from various types of waters is reported. The water soluble polymers such as polyetilenimine (PEI), polyacrylic acid (PAA), polyacrylic acid sodium salt (PAASS) and poly(dimethylamine–co–epichlorohydrin–co–ethylenediamine) (PDEHED) as chelating agents, the Cu2+ as model ion and five ultrafiltration membranes have been used. The complexing agents were previously tested to establish the binding capacity and the best operating conditions for the process. Among the tested polymers the PEI appeared the most interesting one because its binding mechanism does not involve a counter ion release. It was tested in the simulation of wastewaters treatment containing the Cu2+ ion chelated with citric acid; this is a problem of interest in the recycling of water from soil washing operations. The polyethylenimine quantitatively bound the copper‐citrate chelate at pH 5.5 and the three component complex was separated by UF membranes producing a permeate with very low metal concentration. The polymer regeneration was carried out with good results by operating with the diafiltration method. The copper ion present in the diafiltration permeate in a form chelated with citric acid was recovered by oxidising the citrate in a membrane photoreactor. The positive results of the described case‐study show that Macromolecule‐Metal Complexes play a key role for running effectively and selectively the PAUF process for removing metal ions from various type of waters.

Polymer assisted ultrafiltration for copper?citric acid chelate removal from wash solutions of contaminated soil

The removal of heavy metals from aqueous systems such as wash-solutions of contaminated soil by using Polymer-Assisted Ultrafiltration (PAUF) has been studied. For the extraction of metal ions from contaminated soil citric acid is used as a chelating agent. Cu2+ as metal ion and the polymer polyethylenimine (PEI) as ligand were used in the various experiments. Optimal chemical conditions for copper complexation by citric acid were determined by means of complexation tests. The results showed that citric acid is able to chelate copper ions at pH 5.5, while decomplexation occurs at pH ≤ 2. Maximum bonding capacity (saturation condition) was 0.625 mg Cu2+ per mg citric acid, meaning 2 mol Cu2+ per mol citric acid. Complexation tests in the system polyethylenimine–citric acid–copper showed that the polymer is able to complex the copper–citric acid chelate at pH = 6 while release occurs at pH < 3. The saturation condition was 0.333 mg Cu2+ per mg PEI. The ultrafiltration tests, carried out at three trans-membrane pressures (2, 3 and 4 bar), showed the possibility of using the PAUF technique for copper ion removal from aqueous solutions.

Comparison of polyethylenimine, polyacrylic acid and poly(dimethylamine-co-epichlorohydrin-co-ethylenediamme) in Cu2+ removal from wastewaters by polymer-assisted ultrafiltration

Some results on metal ions removal from wastewaters using water-soluble polymers such as polyethylenimine (PEI), polyacrylic acid (PAA), polyacrylic acid sodium salt (PAASS) and poly(dimethylamine-co-epichlorohydrin-co-ethylene-diamine) (PDEHED) as chelating agents and the Cu2+ ion as the model in combination with a polymer-assisted ultrafiltration process (PAUF) are reported. In particular, the performances of these polymers in Cu2+ removal from wastewaters were compared. Tests of bonding capacity and best operating conditions of the process showed that complexation conditions depend on pH; indeed, copper ions are complexed by PEI, PAA, PAASS and PDEHED at pHs higher than 6, 4.6, 4.6 and 8, respectively. The decomplexation reactions took place at pH < 3. Bonding capacity was 0.333 mg Cu2+/mg polymer, meaning a ratio of polymer/Cu2+ = 3 (ww) for PEI, PAA and PAASS. For the chelating agent PDEHED, a ratio of PDEHED/Cu2+ = 0.5 (ww) was determined. UF tests, realized at two trans-membrane pressures (2 and 4 bar) by using five different flat-sheet membranes, showed that the PAA polymer and the PAN GKSS HV2/T membrane can be used when the objective of the purification process is to decrease metal concentration not lower than a certain value. The PDEHED polymer is useful if the objective of wastewater treatment is to obtain complete copper removal. Simple washings with tap water were enough for regeneration and reuse of the membranes.

Metal ions removal from wastewater or washing water from contaminated soil by ultrafiltration–complexation

In the present paper a process for removal of ions from wastewater or from washing water of contaminated soil by using the weakly basic water-soluble polymer polyethylenimine (PEI) as chelating agent and the Cu 2+ ion as model in combination with an ultrafiltration process was investigated. The complexing agent was preliminarily tested to establish the best operative conditions of the process. Next, ultrafiltration tests by using five different membranes were realised to check membrane performance like flux and rejection. Finally, the possibility for recovering and recycling the polymer was tested in order to obtain an economically sustainable process. Obtained results showed that complexation conditions depends on pH: indeed, at a pH>6 PEI–Cu 2+ complexes are formed, while at pH<3 the decomplexation reaction takes place. Saturation condition is 0.333 mg Cu 2+/mg PEI, meaning a ratio PEI/Cu 2+=3 (w/w). UF tests showed good results using the PAN 40 kDa membrane reaching an average copper concentration in the permeate of 2 mg/l and a flux of 135.4 and 156.5 l/h.m 2 at 2 and 4 bar, respectively. Metal rejection, permeate flow rate, and possibility to regenerating and recycling the polymer makes the polymer-assisted ultrafiltration process (PAUF) very interesting for metal ion removal from waters.

Viability of the Use of Polymer-Assisted Ultrafiltration for Continuous Water Softening

We examined the viability of a continuous metal-removing process using polymer-assisted ultrafiltration. The proposed system has two connected sections at different pH. Each section has an ultrafiltration membrane that filters the aqueous solution and retains the polymer. In the first section, the metal is attached to the polymer. In the second section, the metal is detached. The polymer is recycled, and then recovered, by pumping from the second section into the first section. Preliminary experiments provided sufficient information for simulations of the continuous removal of Ca2+ from water. A poly(acrylic acid–maleic anhydride) sodium salt was selected as the polymer. Ceramic membranes of 5 kDa cut-off were used to filtrate the aqueous solutions. We show that the proposed system continuously removes Ca2+ from water in a satisfactory way.

Feasibility of the use of polymer-assisted membrane filtration for brackish water softening

The feasibility of using polymer-assisted ultrafiltration for brackish water softening, i.e. the removal of Na +, K +, Ca 2+, Mg 2+, Cl −, NO 3 −, and SO 4 2− from water, was studied. Three weakly basic, cationic water-soluble polymers chitosan, poly(ethylenimine), and poly(diallyl dimethylammonium chloride) were selected. The membranes Amicon YM10, YM30 (regenerated cellulose), and PM10 (polysulfone) were used. Experiments were performed as a function of solution pH. It was shown that the removal of divalent Ca 2+ and Mg 2+ was more efficient than that of univalent Na + and K +. In addition, the rejection of anions decreased in the order NO 3 −>Cl −>SO 4 2−. Finally, the fouling of membranes during filtration was analyzed by conventional cake filtration theory taking into account incompressible or compressible nature of the deposited cake.

Ultrafiltration rejection of dissolved ions using various weakly basic water-soluble polymers

The rejection of divalent metal ions including Cu 2+ and Zn 2+ from water in polymer-assisted ultrafiltration was studied. Three weakly basic water-soluble polymers: chitosan, poly(ethylenimine), and poly(diallyl dimethylammonium chloride) were selected, and the hydrophilic membrane Amicon YM10 (regenerated cellulose) was used. Experiments were performed as a function of solution pH. It was shown that a higher rejection of Cu 2+ was obtained compared to Zn 2+ as long as the pH was not far less than 7. The effect of added alkaline earth cation Mg 2+ on metal rejection and filtration flux was examined. The regeneration of the three polymers from a retentate by electrolysis and acidification was finally evaluated.

Hyperbranched Chelating Polymers for the Polymer-Assisted Ultrafiltration of Boric Acid

Two hyperbranched chelating polymers, glucoheptonamide derivatives of dendrimeric poly(amido amine) and poly(ethylene imine), were employed in polymer-assisted ultrafiltration and concentration of boron from aqueous feed streams. For feeds containing approximately 1 mM B (10 ppm), volume reduction factors of 20 were observed in cyclic adsorption–desorption. The concentrations of both polymers declined due to permeation through an ultrafiltration membrane with pore sizes which should have retained them. Acid-catalyzed hydrolysis of the amide linkages between the polymer backbone and the chelating side groups is implicated in this loss of polymer mass and effectiveness.

Boron Removal by Polymer-Assisted Ultrafiltration

Abstract Boron contamination of natural waters is a widespread environmental problem which lacks a cost-effective solution. Polymer-assisted ultrafiltration is a method of boron removal that is compatible with other water-treatment processes. This boron removal technique exploits the pH-dependent complexation between boric acid and a macromolecule containing vicinal diol groups to prevent boric acid from passing through an ultrafiltration membrane. The concentration of boron in treated water was reduced from 10.5 ppm to less than 2 ppm through ultrafiltration of an aqueous solution containing boric acid and a polymer synthesized by grafting N-methyl-D-glucamine (NMG) onto poly(epichlorohydrin). The NMG groups, when tethered to the polymer, exhibited stronger affinity for boron than expected from equilibria between NMG and boric acid.