Removal of Fe(III) ions from dilute aqueous solutions by alginic acid‐enhanced ultrafiltration

The removal of Fe(III) ions from aqueous solutions was studied using membrane filtration. A water‐soluble polymer alginic acid (AA) was used to bind the metal ions, which was followed by batch ultrafiltration using poly(methyl methacrylate‐methacrylic acid) membranes modified with poly(ethylene glycol) (PMMA‐MA‐PEG). The complexation behavior of AA and the effect pH on the rejection of iron were investigated. Maximum recovery of 87.13% was obtained when the filtration was carried out in the presence of AA at pH 3.1. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1096–1101, 2000     

Removal of ammonium ions from aqueous solutions with coal-based activated carbons modified by oxidation

The main purpose of this work is to study the possibilities for removal of ammonium ions from aqueous solutions by the two coal-based activated carbons (one obtained from Bulgarian lignite from the Chukurovo deposit, and the second, available as commercial product) and their oxidized modifications. The porous texture and surface chemistry of the adsorbents were characterized. Adsorption of ions was investigated using solutions with different concentrations in the range 35-280 mg l⁻¹ in a static mode. Equilibrium modeling data were fitted to linear Langmuir’s and Freundlich’s equations and maximum adsorption capacities were calculated.     

Removal of cadmium from wastewater by enhanced ultrafiltration using surfactants

In order to recover cadmium ion from wastewater, a process based on enhanced ultrafiltration was finalised. The originality of the solution here proposed lies on the coupled use of ceramic membranes and of a surfactant added to the water to be treated. This paper deals with the study of the influence of experimental conditions upon permeation flux and selectivity of the separation. The process is efficient and flexible since a single stage treatment allows to reduce the concentration of cadmium in the effluent by a factor of about 750; this high performance in selectivity is on a par with high fluxes of permeate (roughly 170 L.h.^?1.m^?2 at 25°C and 3 × 10⁵ Pa).     

Removal of chromium (III) and cadmium (II) from aqueous solutions

Chromium and cadmium are toxic heavy metals present in wastewaters from a variety of industries. A strong cationexchange resin, Amberlite IR 120, was used for the removal of chromium and cadmium. The resin was prepared in two different cationic forms, as Na⁺ and H⁺. The optimum conditions were concentration, pH, stirring time and resin amount. The concentration range was between 2–50 mg/L, pH range between 2–10, stirring time between 5–60 min, and the amount of resin was from 50–1000 mg. Exchange capacities, moisture content and optimum conditions of this resin were determined in a batch system. The stirring speed was 2000 rpm during all of the batch experiments. The initial and final chromium and cadmium amounts were determined by atomic absorption spectrophotometry. The optimum conditions were found to be a concentration of 20 mg/L, pH of 5.5, stirring time of 20 min and 100 mg of resin. The results obtained show that the Amberlite IR 120 strong cation-exchange resin performed well for the removal and recovery of chromium and cadmium.     

Preparation of poly (isophthalamide-graft-methacrylamide) and its utilization in the modification of cellulose acetate ultrafiltration membranes

Methacrylamide was grafted on to poly (isophthalamide) (PIPA-g-MAA) to improve its solubility and hydrophilicity. Then, PIPA-g-MAA incorporated high performance cellulose acetate ultrafiltration (CA) membranes were prepared by phase inversion technique and physical properties of the membranes were studied by various analytical methods. The efficiency of these membranes in the removal of arsenic from aqueous stream was studied and an effort has been taken to correlate the separation efficiency with morphology. Overall results suggest that membrane hydrophilicity, structure and performance were improved significantly by the addition of PIPA-g-MAA. Thus PIPA-g-MAA can be considered as an effective modification agent for CA membranes.     

Preparation of poly(acrylic acid)/starch hydrogel and its application for cadmium ion removal from aqueous solutions

In this paper, potassium bromate/thiourea dioxide redox system was used to initiate the graft copolymerization reaction of acrylic acid onto maize starch. The so obtained polyacrylic acid/starch graft copolymer was crosslinked by further treatment with alkaline epichlorohydrin to get three dimensional hydrogel. This crosslinked hydrogel was used for the removal of the heavy element, Cd²⁺ from its aqueous solution by adsorption. All factors which are expected to affect the adsorption process, like adsorbent concentration, immersion time, graft yield of the adsorbent, Cd²⁺ concentration and adsorption temperature were extensively studied and reported in the text. The study and investigations demonstrated that the adsorption efficiency is affected by the adsorbent graft yield and the adsorption medium temperature. In addition, on fitting the data obtained from the adsorption process, it was found that the adsorption obeys both Langmuir and Freundlich adsorption isotherms but the Langmuir isotherm shows better mathematical fitting for the equilibrium data than does Freundlich model, based on the higher R² value for the Langmuir isotherm.     

Feasibility study on the recovery of chromium (III) by polymer enhanced ultrafiltration

The viability of recovering chromium (III) was studied by polymer enhanced ultrafiltration (PEUF) and its application to tannery wastewater treatment. Four polymers with different functional group, molecular weight and acid-basic equilibrium were tested at 40 and 60 °C in order to investigate the complexation and decomplexation of chromium (III) ions on the polymer chains: polyvinyl alcohol (PVA), polyacrylic acid-co-maleic acid (PACM), polyethylenimine (PEI) and ethoxylated polyethylenimine (EPEI). The reversibility of the polymer metal binding was studied by operating in a dead-end PEUF system. The best chromium (III) rejections for both reactions were obtained by EPEI. The feasibility of recovering chromium (III) with EPEI was also studied in a cross-flow PEUF system. Chromium ions were complexed by EPEI chains at pH = 5 and decomplexed at pH = 1. Membrane fouling due to conformational variations of EPEI was observed at high ionic strengths.     

用DIOSO从水溶液中萃取镉的研究

为探究亚砜类化合物对水中重金属镉的萃取效率和萃取机理，报道了利用二异辛基亚砜(DIOSO)萃取水溶液中镉的情况，实验制备了DIOSO，以其为萃取剂探索其对水溶液中镉的萃取情况，得出最佳萃取条件，在此条件下最高萃取率为99.7%。为达到萃取剂的回收循环利用，实验研究了不同反萃剂对Cd(Ⅱ)的反萃情况，得出利用0.2 mol/L NaOH为反萃剂时能把有机相中的Cd(Ⅱ)全部洗脱出来，反萃率达99.86%。在此基础上，结合光谱和热力学分析，DIOSO对Cd(Ⅱ)的萃取过程可能是离子间发生了缔合作用。DIOSO对水中Cd(Ⅱ)的成功萃取，可以为工业废水污染中Cd(Ⅱ)的处理提供重要理论研究基础。     

Biosorption of cadmium(II) and lead(II) from aqueous solutions using Pleurotus ostreatus immobilized on bentonite

The purpose of this work was to evaluate the potential of a white rot fungi (P. ostreatus) immobilized on bentonite, in a continuous flow removal of trace heavy metals. The procedure is based on the biosorption of Cd(II) and Pb(II) ions on a column of bentonite loaded with dried, dead fungi components prior to their determination by atomic absorption spectroscopy (AAS). Cd(II) and Pb(II) were determined with a relative error of less than 5%. Various parameters such as “pH, amount of adsorbent, eluent type and volume, flow rate of the solution and matrix interference effect” on the retention of the metal ions were investigated. This procedure was applied to Cd(II) and Pb(II) determination in aqueous solutions, including tap water system. The optimum experimental parameters were determined to be pH 5, concentration of 10 mg/L, contact time of 30 min and 0.2 g of adsorbent for a quantitative adsorption of the metals. The optimum flow rate was found to be 2.5 mL/min for all metal ions. Each column can be used up to 20 successive analyses without considerable change in recoveries of metal ions.

The proposed method is excellent as regards simplicity, sensitivity, selectivity, precision, accuracy and column stability.     

Polarographic studies of cadmium(II) ions binding in aqueous polyelectrolyte solutions

Polarographic behaviour of cadmium(II) ions in aqueous solutions of polyacrylic acid with and without indifferent electrolyte (potassium chloride) has been examined. Data for polyacrylic acid were compared with those for the monomer. The diffusion current of polarographic reduction of cadmium(II) ions in the range 0 ? [KCl] < 0.2 N in the presence of polyelectrolytes depends upon the concentration and degree of polymer neutralization and also upon the nature of cation (Na⁺, K⁺) in the polyacrylate salt.     

Adsorption of cadmium from aqueous solution by phosphogypsum

In the present study, the adsorption of cadmium on phosphogypsum, a waste material from the manufacture of phosphoric acid by wet process, was studied. Before batch adsorption study, phosphogypsum was pre-conditioned by milk of lime. Effect of initial pH on cadmium adsorption was investigated. It was found that cadmium adsorption was dependent on solution pH and maximum cadmium removal was observed in the pH range of 9.5 and 11.5. The Langmuir and Freundlich theories were used to describe the cadmium adsorption process, and the Freundlich isotherm showed the best fit to the process. Maximum adsorption capacity of lime-preconditioned phosphogypsum was found to be 131.58 mg/g.     

Preparation of starch/poly(N,N-Diethylaminoethyl methacrylate) hydrogel and its use in dye removal from aqueous solutions

Starch/poly(N,N-Diethylaminoethyl methacrylate) graft copolymer was synthesized by graft polymerizing N,N-Diethylaminoethyl methacrylate monomers onto cooked starch using ceric ammonium nitrate/nitric acid mixture as an initiator. After extracting the graft copolymer from the homopolymer and evaluating the graft yield, the graft copolymer was subjected to crosslinking treatment using epichlorohydrin in alkaline medium to convert it to hydrogel. The so prepared hydrogel was evaluated for its swelling ratio which was found to be 100. The hydrogel with its cationic functionality was tried for removing the anionic dye Direct Red 81 from its aqueous solution and all factors affecting the hydrogel adsorption capacity towards the anionic dye, like the hydrogel graft yield, the adsorbate pH, the immersion time and the hydrogel dose were studied. The data obtained from the adsorption results were found to fit well to the Langmuir adsorption model.     

Removal of hexavalent chromium anions via polymer enhanced ultrafiltration using a fully ionized polyelectrolyte

A fully ionized polyelectrolyte was synthesized for Cr(VI) removal from aqueous solutions by continuous polymer enhanced ultrafiltration (PEUF). Effect of operating parameters such as pH, loading, polymer, and competing ion concentrations were examined. Highest Cr(VI) retention was obtained at a loading of 0.01 at pH 4. Increasing both polymer and chromate concentrations at a fixed loading of 0.01 decreased the retention which demonstrated the effect of crowding. In the presence of competing anions such as chloride and sulfate, Cr(VI) retention decreased for all of the pH values studied. Even at high competing anion concentrations, significant retentions of Cr (VI) were obtained.     

Water-soluble functional polymers in conjunction with membranes to remove pollutant ions from aqueous solutions

Water-soluble functional polymers have attracted a lot of attention due to their potential applications in different research fields. In environmental sciences, they can be used to remove pollutants. Since properly modified polymer materials can be used to avoid the growth of bacteria, fungi, and algae, they also attract interest from diverse biomedical fields.This review places special emphasis on the study of water-soluble polymers that contain one or more amine, amide, carboxylic acid, hydroxyl, phosphonic acid, quaternary ammonium salts, and sulfonic acid groups at the backbone or side chain and their ability to remove ion pollutants from aqueous solutions. In additional, this review differentiates between different experimental procedures, including the liquid-phase polymer based retention (LPR) technique that combines the use of water-soluble polymers and ultrafiltration membranes, as well as arsenic removal by combining LPR and electrocatalytical oxidation (EO) techniques. EO and LPR can also be coupled off-line to remove arsenic inorganic species from aqueous solutions. A variety of studies show that the functional groups on the polymer and the solution pH have a marked effect on ion removal.     

Shear thickening behavior of dilute poly(diallyl dimethyl ammonium chloride) aqueous solutions

Using dynamic light scattering (DLS) and capillary dynamic viscoelasticity (DVE) analyzer, we investigated dilute (0.5 mg/ml) poly(diallyl dimethyl ammonium chloride) (PDADMAC) aqueous solution properties for three different molecular weights of PDADMACs mixed with various concentrations of NaCl. The dependence of PDADMAC molecular chain conformations in aqueous solutions on polymer molecular weight and NaCl concentration were studied. By analyzing dynamic shear viscosity η′(ω), viscoelastic relaxation times t_r, and shear rate at tube wall ?_a(ω) of PDADMAC aqueous solutions in oscillatory flows, we proposed that polymer chain conformations varied with increasing shear frequency ω via the following steps: intra-polymer associations, dissociation of intra-polymer associations, stretching of polymer chains, inter-polymer aggregations, and dissociations of inter-polymer aggregations. The intra-polymer associations lowered the n′ exponent of storage modulus G′(ω) (G′(ω) ∼ ω^n′) with n′ < 2, and the polymer chain stretching and inter-polymer aggregations caused shear thickening (i.e. upturn of η′(ω)) of PDADMAC aqueous solutions. The behaviors of the lowering of n′ exponent with n′ < 2 and the shear thickening were favored by increasing ionic strength of solutions. By comparing η′(ω) data with DLS hydrodynamic radii (R_h) data, we also confirmed the possibility of inter-polymer aggregations in dilute solutions when polymer chains were stretched in oscillatory flows.     

Adsorption of cadmium ions from aqueous solutions by activated carbon with oxygen-containing functional groups

The adsorption of aqueous cadmium ions (Cd(II)) have been investigated for modified activated carbon (AC-T) with oxygen-containing functional groups. The oxygen-containing groups of AC-T play an important role in Cd(II) ion adsorption onto AC-T. The modified activated carbon is characterized by scanning electron microscopy, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The results of batch experiments indicate that the maximal adsorption could be achieved over the broad pH range of 4.5 to 6.5. Adsorption isotherms and kinetic study suggest that the sorption of Cd(II) onto AC-T produces monolayer coverage and that adsorption is controlled by chemical adsorption. And the adsorbent has a good reusability. According to the FT-IR and XPS analyses, electrostatic attraction and cation exchange between Cd(II) and oxygen-containing functional groups on AC-T are dominant mechanisms for Cd(II) adsorption.     

Treatment of phenol-containing aqueous solutions by membrane-based solvent extraction in coupled ultrafiltration modules

Extractive treatment of phenol-containing aqueous streams by two coupled hollow fiber modules (for simultaneous extraction and stripping) is experimentally and theoretically studied. The effects of hydrodynamic conditions (linear velocities of all three liquids) and concentrations (initial phenol concentrations) are explored and an optimal combination of these process parameters is found for maximisation of the phenol fluxes in both modules. The extraction/stripping performance of the coupled HF modules was compared when using different organic solvent (alcohols and alkanes). Analysis of the mass-transfer resistances of the different liquid layers in both modules is presented based on mathematical model and experimental data from equilibrium measurements and kinetic experiments. It is found that an important part of the overall resistance is located in the aqueous phase’s boundary layers. A substantial improvement of the stripping yield is reached by using a series of stripping modules.     

Removal of nitrite ions from aqueous solutions by poly(N,N‐dimethylamino ethylmethacrylate) hydrogels

Removal of nitrite ions from aqueous solutions by protonated poly(N,N‐dimethylamino ethylmethacrylate) hydrogels (P(DMAEMA)) was investigated. We have shown that polycationic and pendant secondary amine group containing P(DMAEMA) hydogels is very efficient and highly selective for the removal of nitrite ions from aqueous solutions at even in very high concentrations. Adsorption studies have shown that pH of the nitrite solution has influence on the nitrite ion uptake capacity of P(DMAEMA) hydrogels. The adsorption capacity of hydrogels had been increased up to 3100 mg NO/g dry gel, by changing pH of the solution. The results of the adsorption studies showed that the interaction between nitrite ions and quaternized amine groups agree with the Langmuir‐type isotherm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 6023–6027, 2006     

Removal of chromium (VI) from aqueous solutions using poly(4‐vinyl pyridine) beads

Sorption of hexavalent chromium ions from aqueous solution by poly 4‐vinyl pyridine [Poly(4‐VP)] was studied. The batch method was applied for adsorption processes. The effects of initial ion concentration, time, pH and temperature on adsorption were investigated. A treatment time of 60 min was found to be sufficient to reach equilibrium. pH 3.0 was found as the optimum pH value for the process. The maximum adsorption performance was achieved at 86.7 mg g^?1 using 500 mg L^?1 Cr (VI) solutions. The process of adsorption of Cr (VI) was explained by Langmuir isotherm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2865–2870, 2006     

New polymeric structures designed for the removal of Cu(II) ions from aqueous solutions

New polymeric structures obtained by chemical transformations of maleic anhydride/dicyclopentadiene copolymer with triethylenetetraamine, p‐aminobenzoic acid, and p‐aminophenylacetic acid were used for the removal Cu(II) ions from aqueous solutions. The experimental values prove the importance of the chelator nature and of the macromolecular chain geometry for the retention efficiency. The retention efficiency (η_r), the retention capacity (Q _e ), and the distribution coefficient of the metal ion into the polymer matrix (K _d ) are realized by evaluation of residual Cu(II) ions in the effluent waters, by atomic adsorption. Also are discussed the influence of pH, the thermal stability of the polymer, and their polymer–metal complex, as well as the particular aspects regarding the contact procedure and the batch time. Based on the polymers and polymer–metal complexes characterization a potential retention mechanism is proposed. All polymer supports as well theirs metal–complexes are characterized by ATD and FTIR measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1397–1405, 2007