removal of

Rev Chem Eng 2014; aop

Carmen Teodosiu, Rodica Wenkert, Lavinia Tofan* and Carmen Paduraru

Advances in preconcentration/removal of environmentally relevant heavy metal ions from water and wastewater by sorbents based on polyurethane foam Abstract: An increased interest in the removal of heavy metal ions from aqueous media is encountered due to their toxicity and negative impacts on ecosystems, human health and economic activities. A variety of processes may be used for the removal of heavy metal ions from water and wastewater, such as chemical precipitation, ion exchange, adsorption, membrane processes, etc. However, the removal efficiencies of heavy metals by adsorption depend on several factors such as initial loads of heavy metals in the influent, purpose of treatment (drinking/industrial water production, wastewater treatment for disposal or recycling), costs of the overall process, and properties and conditions for regeneration of the sorbent materials. In this context, the use of polyurethane foams as heavy metal ion sorbents is of a special interest because they provide versatile applications in heavy metal effluent management. This study reviews relevant published researches that are concerned with new sorbents based on polyurethane foams applied in batch and dynamic systems for separation and/or preconcentration of heavy metal ions in environmental aqueous media. This review is divided into the following sections: synthesis of polyurethane foams; physical and chemical properties of polyurethane foams; preconcentration of pollutant metal ions from environmental aqueous media by different types of polyurethane foam (untreated, loaded, reacted and composite polyurethane foams); the applicability of sorbents based on polyurethane foams for water and wastewater treatment; comparison of sorbents based on polyurethane foam with other sorbents for heavy metal ion removal. *Corresponding author: Lavinia Tofan, Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, “Gheorghe Asachi” Technical University of Iasi, 73 Prof. Dr. D. Mangeron Street, 700050 Iasi, Romania, e-mail: [email protected] Carmen Teodosiu and Carmen Paduraru: Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, “Gheorghe Asachi” Technical University of Iasi, 73 Prof. Dr. D. Mangeron Street, 700050 Iasi, Romania Rodica Wenkert: Soroka University Medical Center, Rager Boulevard, P.O.B. 151, Beer Sheva 85025, Israel

Keywords: heavy metals; polyurethane foam; sorbents; wastewater; water. DOI 10.1515/revce-2013-0036 Received November 13, 2013; accepted April 8, 2014

1 Introduction Heavy meals are continuously released into the environment from natural processes like volcanic activity and weathering of rocks. The population dynamics, rapid urbanization and nonuniform distribution of urban areas, the economy development associated with energy use and waste generation from domestic and industrial sources have considerably enhanced the release of heavy metals. The impacts of these metals on the ecosystems and on humans are relevant from the economic, environmental and public health point of view. Some metals are essential minerals for aerobic/anaerobic organisms. However, numerous studies have shown that many heavy metals such as copper, zinc, lead, cadmium or mercury seriously affect the environment and health due to their toxicity and bioaccumulation tendency. Furthermore, unlike the majority of organic pollutants that are susceptible to biological degradation, heavy metal ions do not biodegrade into harmless end products and normally present acute and chronic toxicity (Gavrilescu 2004). In this context, the need to efficiently remove and/or recover these heavy metals is one of the most important environmental issue. From all the water consumers, industry is producing the most severe environmental impacts due to the variety, volume and toxicity of pollutants and, in many cases, due to the lack of appropriate treatment before disposal. Moreover, insufficiently treated effluents can affect water resources and their treatment (downstream) for drinking and industrial purposes. Sustainable solutions for the usage of water resources can be found only by considering both management and technological practices in the context of well-defined national and international associated environmental policies. As water pollution is

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2 C. Teodosiu et al.: Removal of heavy metal ions by polyurethane foam

and Farag 1975, 1978). These features allowed their utilization in separation and preconcentration procedures with relatively high flow rates in batch and dynamic systems. These initial studies have resulted in others by using unloaded and physically or chemically modified PUFs for environmental applications (Tofan et al. 1994, 1995, 1996, Bîlbă et al. 1998a,b, Braun et al. 2000, Lemos et al. 2007, Türker 2012). This review presents a literature survey for the years 2001–2013 and offers an overview of new sorbents based on PUF available for use in preconcentration and removal of heavy metal ions from natural waters and wastewaters. This study considers an integrated approach over the synthesis, characterization and applicability of different types of PUFs for the removal of heavy metals as well as the comparison of these sorbents with other sorbents effective for such processes.

affecting large areas and different countries, apart from the technical improvements of water and wastewater treatment facilities, control and monitoring of industrial activities, institutional development and adoption of pollution prevention programs, there is still a strong need to improve environmental awareness, public information and participation in environmental policy making (Teodosiu 2002, Teodosiu et al. 2013). Several processes were developed for the removal and recovery of toxic and/or valuable heavy metals from water or municipal/industrial wastewater, i.e., reverse osmosis, electrodialysis, ion exchange, coagulation/flocculation, phytoremediation, chemical precipitation/neutralization and sorption on various media (Qdais and Moussa 2004, Hui et al. 2005, Ahluwalia and Goyal 2007, Tofan et al. 2008, Wan Ngah and Hanafiah 2008, Wang and Chen 2009, Abdel Salam et al. 2011, Barakat 2011, Fu and Wang 2011, Katsou et al. 2011, Wan Ngah et al. 2011). Sorption has evolved into one of the most effective processes of heavy metal removal/recovery due to its advantages such as high removal efficiencies, applicability for various concentrations, lack of sludge production, sorbent versatility, etc. (Wan Ngah and Hanafiah 2008, Wang and Chen 2009, Barakat 2011, Fu and Wang 2011). A wide range of solid materials that are suitable as sorbents for heavy metal ions is available. Among them, activated carbon, cross-linked polystyrenes, polyurethane foam (PUF), silica gel and inorganic oxides are of special importance. In the past years, PUF has attained considerably attention due to its efficiency, low cost and easily handling and storage, which is convenient for different water and wastewater applications. The potential possibilities of PUF as a suitable sorbent for wastewater treatment have been pointed out in 1970 (Bowen 1970). Braun and Farag verified that open-cell-type resilient PUFs have remarkable mass transfer properties and rapid sorption owing to their quasi-geometric membrane (Braun

2 Synthesis, physical and chemical properties of the PUFs PUFs can be defined as plastic materials in which a proportion of the solid phase is replaced by gas in the form of numerous small bubbles (Braun and Farag 1978). From the geometrical point of view, if the gas bubbles occupy a volume larger than 76%, those will be distorted into a quasi-spherical polyhedral (Braun and Farag 1978). PUFs can be prepared in soft, flexible and rigid form using a variety of polyethers and polyesters. The two most important reactions in the preparation of urethane foams are those between hydroxyl compounds (polyester or polyether polyols) and isocyanate and those between isocyanate and water. The second reaction is responsible for the foaming process due to the liberation of carbon dioxide (Tofan et al. 1994): O

H H

+

+

CH2

CH

CH3

HO

CH2

O

C

n CH2

+

CH

CH3

CH3 H

H

O CH2 CH

+

O CH2

C

n

HO

polyether

CH3

CH3 HO ~ ~ OH + 2 OCN R

HOH

NCO

NH

+

(1)

O

O OCN R

H

OH +

CO

~~

NH

OC

R NCO

(2)

prepolymer

HOH + OCN R

NH

CO

O C NH R NCO + HOH + OCN R

O ......

R NH C

NH R

NH CO O

O

~ ~ O NH C O

NH R

NH

O

NH C

CO

-CO 2

O OC O

NH

R

NH C

NH

R

O

........

O

R = aromatic group. Authenticated | [email protected] author's copy Download Date | 5/23/14 5:53 PM

NH C O

(3)

C. Teodosiu et al.: Removal of heavy metal ions by polyurethane foam 3

The use of catalysts (tertiary amines or organometallic compounds) allows the increase of the rate of reaction (2) and the settling of a proper ratio between chain expansion and foaming rate. The flexible PUF of polyether type has the most significant environmental applications. To prepare this type of PUF, propylene oxide adduct (average molecular mass of 3000 and 90% content in terminal secondary hydroxyl groups) and 2,4 and 2,6-isomers of toluene diisocyanate in 80:20 and 65:35 molar ratios are frequently used. The majority of feedstock for PUFs is still based on crude oil, but in recent years, alternatives based on renewable resources have been developed, like polyols based on vegetable oils (Tanaka et al. 2008, Campanella et al. 2009, Zou et al. 2012). The properties of these vegetable oil-based PUFs are often comparable to or even better than those prepared from petroleum (Pfister et al. 2011). The properties of PUFs depend on various structural factors (crystallinity, cross-linking degree, chain rigidity, constraints to its rotation, intermolecular bonds) and can be changed in wide range by a proper selection of raw materials (Tofan et al. 1994). Thus, the flexible foams are prepared from polyols with average molecular mass and low degree of cross-linking, whereas the rigid foams are obtained from resins with low molecular mass and highly cross-linked structure. The main physical and chemical features of the PUFs with application in separation/preconcentration of heavy metals from wastewaters can be systematized as follows: – hydrophobic character; – large porosity; bulk density of 10–35 kg/m3; surface area of 7.6–92.5 m2/kg; – reversible swelling in water, HCl until 8 m, H2SO4 until 4 m, HNO3 until 2 m, glacial CH3COOH, NH4OH 2 m, NaOH 2 m, organic solvents (benzene, carbon tetrachloride, chloroform, acetone, alcohols); – dissolution in concentrated H2SO4 and concentrated HNO3; – degradation by heating to 180–220°C and UV exposure; – low anionic exchange capacity; relatively fast sorption rate of chemical species (Braun and Farag 1978). These properties make the open-cell PUF an ideal inert support for immobilization by physical adsorption of different modifying agents (organic extractants, ion exchangers, precipitates). In addition, the components are retained on PUFs due to both absorption and adsorption, which results in the uniform distribution of sorbates in the whole volume of the sorbent. Thus, a dual mode

of sorption mechanism involving absorption related to “solvent extraction” or “weak base anion ion exchange” and an added component for “surface adsorption” has been proposed (Farag et al. 2007, El-Shahawi et al. 2008, 2011a,b,c, Bashammakh 2010).

3 Preconcentration of pollutant metal ions from environmental aqueous media by different types of PUFs PUF can be used in batch or dynamic systems with large applicability for environmental applications, without any treatment (unloaded PUF) or after reagent loading. The reagent-loaded PUF can be prepared either physically (known as loaded, impregnated or immobilized PUF) or chemically (reacted PUF).

3.1 Sorbents based on unloaded PUFs Unloaded PUF retains heavy metal ions after complex formation (thiocyanate, chloride, iodide complexes). Generally, unloaded PUF functions according to the succession of steps shown in Figure 1. Table 1 summarizes some recent applications of unloaded PUF in separation/preconcentration and determination of heavy metals [Ag(I), Au(III), Co(II), Cr(VI), Cu(II) and Pb(II)] from natural waters and wastewaters.

Figure 1 The successive steps involved in the sorption of heavy metal ions by unloaded PUF.


4 C. Teodosiu et al.: Removal of heavy metal ions by polyurethane foam Table 1 Separation/preconcentration of heavy metal ions from natural water and wastewaters by using unloaded PUFs. Heavy metal ions

Sample

Uranyl

Cd(II)

Fe(III)

Sorption medium

Remarks

References

Tap and industrial waste waters

Thiocyanate

El-Shahawi et al. 2005

Spiked waters

Ammonium diethyl dithiophosphate

The sorption of uranyl ions involved in the formation of a ternary complex ion associate of uranyl ions, thiocyanate and PUF is highly dependent on pH, shaking time, surfactant type, extraction media, temperature and analyte concentration The elution step is performed with ethanol

Tarley and Arruda 2004

Thiocyanate and HCl

Cd(II)

Iodide

Au(I)

Cyanide

Se(IV)

Spiked to fresh waters

Bromide

Cu(II)

Tap water Mineral water Seawater

Eriochrome Black T (EBT)

Very dilute aqueous solutions Aqueous solutions Spiked deionized water

The achieved limit of detection was 0.12 μg/l Maximum sorption capacity was found to be 2.06 × 10-4 mol/g. It is possible to remove around 95% of the Fe(III) in solution through five consecutive cycles The monolayer coverage constant was found to be 23.7 ± 0.4 mg/g The capacity of PUF toward gold(I) sorption was found to be 5.29 ± 0.9 mg/g. The retained gold(I) species were recovered quantitatively (95.4 ± 3.4%) from PUF packed columns using perchloric acid The critical capacity of Se(IV) onto unloaded foam column was found to be equal to 0.3 mg/g. The value of the breakthrough capacity of selenium uptake was calculated as 0.65 mg/g The quantitative extraction of Cu(II) was achieved in a medium containing 60 mg/l of EBT and pH 1.5. The minimum time required to obtain total extraction of Cu(II) from solution was 30 min, when 200 mg of PUF was stirred with 100 ml of the samples

The saturation sorption capacity of unloaded PUF varies in wide range from about 0.04 mmol/g to over 1.5 mmol/g of unloaded foam, depending on the nature of the cation under study (Tofan et al. 1994). The retention of the anionic complexes of metal ions on unloaded PUF was explained in the literature by a mechanism of “cation chelation” (Dmitrienko and Zolotov 2002). Recently, a weak base “anion exchanger” and a “solvent extraction” of the [AuCl4]- on unloaded PUF in acidic media has been proposed (Moawed 2008, Bashammakh et al. 2009). Thus, at pH < 4, the protonation of the ether oxygen (-CH2-+OH-CH2-) and/or urethane nitrogen (-+NH2-COO-) of the unloaded PUFs results in the formation of complex ion associate between the anionic complex [AuCl4]- and the protonated unloaded PUF sorbent (Bashammakh et al. 2009): Ether group, PUF: (-CH 2 -O-CH 2 -) foam + H + ( -CH 2 -+OH-CH 2 -) foam

(4)

(-CH 2 -+OH-CH 2 -) foam + [ AuCl4 ]aq [ -CH 2 -+OH-CH 2 -][ AuCl4 ] -foam

(5)

Nunes de Almeida et al. 2007

Saeed and Ahmed 2004 Farag et al. 2007

Bashammakh 2010

Soriano and Cassella 2013

Urethane group, PUF: (-NH-COO-) foam + H + ( - + NH 2 -COO-) foam

(6)

(- + NH 2 -COO-) foam + [ AuCl4 ]aq [ - + NH 2 -COO-][ AuCl4 ] -foam

(7) At pH values > 4, the effect of the deprotonation of the ether oxygen and/or urethane nitrogen of the unloaded PUFs minimizes the formation of complex ion associate and the diffusion of gold(III) as [AuCl4]- through a thin polyurethane film is most likely consistent with its solubility in the PUFs (Bashammakh et al. 2009). This mechanism is in good agreement with that previously reported for the retention of cadmium from iodide media by unloaded PUF (Saeed and Ahmed 2004). Future research is focused on testing the ability of unloaded PUF and its performances for online preconcentration, separation and determination of heavy metal ions. Thus, a simple and accurate online procedure for preconcentration and determination of dissolved iron



in natural waters using unloaded polyether-type PUF as solid extractor has been developed (Cassella 2002). In the flow injection system developed by Cassella, the analyte was preconcentrated from acidic aqueous medium as iron-thiocyanate complex with post-elution with ascorbic acid solution and spectrophotometric measurement with 1,10-phenanthroline as colorimetric reagent. Another proposed method could be applied on column packed unloaded PUF for simple, reliable and low cost procedure for quantitative and chemical speciation of Au(I) and Au(III) on-site analysis (Bashammakh et al. 2009).

3.2 Sorbents based on loaded PUFs Flexible open-cell PUFs can be physically modified with various organic extracting and chelating reagents. The loading process (Figure 2) offers a wider range of applications that improve the selectivity and the capacity of the sorbents. By swelling into organic extractants, PUF can be loaded with large amounts of tri-n-butyl-phosphate (TBP), methyl isobutyl ketone and diethyl ether. A detailed study revealed that the flexible open-cell PUFs retained TBP much more efficiently than other known bead supports.

Moreover, the PUFs of polyether type have an increased capacity of TBP retention than the polyester foam (Tofan et al. 1995). By impregnation of solid foams, the selectivity of the hydrophobic organic extraction agents and the fastness of the kinetics of the sorption process between the metal ions in aqueous solution and the loaded PUFs are combined. Special attention should be given to the TBP-loaded PUF due to the double function of TBP: (a) plasticizer, which significantly increased the foam permeability, and (b) extracting agent with high solvation power in ionic association systems. Thus, the excellent properties of the flexible open-cell PUF of polyether type impregnated with TBP allowed quantitative separation of silver, gold, bismuth, cadmium, cobalt, chrome, copper, mercury, nickel, lead, palladium, tin, tantalum, thorium (Tofan et al. 1995) and calcium (Mondall and Kundu 2005) and the concentration of iron (Bîlbă et al. 1998a,b) and gallium from chloride media (Tofan et al. 2007). Thus, the experiments carried out on a column filled with PUF loaded with TBP indicated the quantitative retention of Fe(III) (99.3–99.9%) from hydrochloric solutions (4 m) with an initial concentration of 5.6–39.2 mg Fe(III)/l. In order to estimate the efficiency of the chromatographic column used, the number of theoretical plates, N, and the height

Figure 2 Schematic representation of the loading process.



Tofan et al. 1996 log q = log KF+(1/n)log C, where q is 1.820 (278 K) the amount of metal ion taken up per 3.88 (295 K) gram of loaded foam (mg/g), C is the 6.76 (313 K) cation concentration left in solution at 1.886 (278 K) equilibrium (mg/ml), KF is the Freundlich 2.430 (295 K) constant related to the sorption capacity, 3.10 (313 K) and n is the Freundlich constant related to the energy of sorption 5.3665 Tofan (295 K) et al. 2007 4.762 (295 K) 1262.87 (278 K) 2216.2 (295 K) 3424 (313 K) 0.5301 (278 K) 0.5535 (295 K) 0.5835 (313 K) q = KLCq0/(1+KLC), where q is the amount of metal ion sorbed on solid phase (mmol/g of foam), C is the equilibrium concentration of the metal ion in solution (mmol/ml), KL is the Langmuir constant related to the sorption capacity (l/mol), and q0 is the maximum capacity of sorption (mmol/g)

Ga(III) Pd(II) Ni(II) Ga(III)

PUF loaded with Reference Freundlich isotherm (Freundlich 1906) dimethylglyoxime (6.3866 mg DMG/g foam) Polyurethane foam impregnated with tri–n–butyl–phosphate (5.1714 TBP/g foam) Langmuir isotherm (Langmuir 1916)

Some chelating reagents [dithizon, diethylammonium diethyldihiocarbamate, 1-(2-pyridylazo)-2-naphtol] dissolve in different plasticizers (TBP, α-di-n-nonylphatalate, α-noctyl-phatalate) and the PUF matrix swells in their solutions. The plasticized chelating PUFs are characterized by superior permeabilities, ensuring increased mobilities of the metallic ions. In this context, the possibilities of cation-complexing agent interaction are more varied, the plasticized PUFs having an increased sorption efficiency as compared to the unloaded foams (Tofan et al. 1995). The sorption process of heavy metal ions on loaded PUFs is evaluated and characterized by Langmuir and Freundlich isotherms (Saeed 2008). A comparison between Langmuir and Freundlich isotherm models for the sorption of some metal ions on two kinds of loaded PUF is presented in Table 2. The applicability of the Langmuir isotherm for the batch sorption systems as presented in Table 2 suggests the formation of a monolayer covering on the surface of the loaded PUFs. Also, it can be seen from Table 2 that the values of the n Freudlich constant are above unit, indicating favorable sorption of gallium(III) by PUF impregnated with TBP at all working temperatures (Tofan et al. 2007).

Table 2 Quantitative description of some metal ion-loaded PUF batch sorption systems on the basis of the Langmuir and Freundlich models.

equivalent to a theoretical plate, H, have been calculated. The average values were found to be N = 59.07 and H = 0.846; these values point out the feasibility and efficient use of the column packed with TBP loaded foam for Fe(III) retention from hydrochloric solutions (4–6 m). The properties of the packed column did not change significantly with time, the sorption capacity of Fe(III) being almost constant over 10 repeated cycles of sorption-desorption (Bîlbă et al. 1998a,b). The chelating agent-loaded PUF can be prepared in two ways (Tofan et al. 1995): – By the direct contact between a certain amount of spongious material and a solution of the organic reagent in a volatile solvent. The efficiency of these polyurethane sorbents in selective and quantitative separation of metal ions from very dilute aqueous solutions is mainly due to the feasibility of the PUF to act as “solvent” for the formed complexes, for instance, the colloidal particles of nickel and palladium dimethylglyoximates (Tofan et al. 1996). Thus, the PUF loaded with dimethylglyoxime (6.3866 mg dimethylglyoxime/g foam) could be efficiently used for concentration of Ni(II) and Pd(II) ions and their separation from each other and from Cu(II), Cd(II), Zn(II) and Co(II) ions (Tofan et al. 1996). – Through the plasticizers (dissolution of a chelating reagent into a plasticizer followed by the swelling of the PUF in the obtained solution).

PUF impregnated Reference with TBP (5.1714 TBP/g foam)



Despite the fact that these materials can suffer from poor selectivity and leaching out the reagents, physically modified PUFs are extensively used, as presented in Table 3. Current and future studies consider the development of new strategies and the improvement of the analytical performances of the previously reported methods for fast and selective removal of heavy metal ions onto loaded PUFs. Thus, recently, a procedure based on the formation of tetraiodobismuthate [BiI4]-aq in the test aqueous solution in the presence of KI-H2SO4 followed by subsequent extraction of [BiI4]-aq by procaine hydrochloride (PQ+Cl-)-immobilized PUFs has been proposed (El-Shahawi et al. 2011a,b,c). The developed PQ+Cl-treated PUF sorbent could be packed in columns for the removal of bismuth(III) species from industrial wastewater. A recent study has revealed that the uptake of Cr(VI) from HCl (3.0 mol/l) medium by tetraphenylarsonium chloride (TPAs+Cl-)- and tetraphenylphosphonium bromide (TPP+Br-)-loaded PUFs proceeded most likely as follows (El-Shahawi et al. 2011a,b,c): + HCrO4aq + H aq +Claq [ CrO3Cl- ]aq + H 2O

+ [CrO3Cl- ]aq +TPX foam [ CrO3Cl- iTPX + ] foam

( where X = As or P ).

(9)

(10)

Another method based on the use of the ion-pairing reagent tetraheptylammonium bromide (THA+.Br-) immobilized PUF sorbent in packed columns for the retention of ultra trace concentrations of gold(III) from aqueous chloride medium of pH 3–4 at 5 ml/min flow rate has been developed (El-Shahawi et al. 2011a,b,c). The capacity data (17 ± 0.7 and 19.5 ± 0.65 mg/g) of the developed sorbent are better than the data (11. 21 ± 1.8 and 5.29 ± 0.9 mg/g) previously reported. The method was applied satisfactorily ( > 95%) for the analysis of total inorganic gold(I) and/or gold(III) ions in wastewater samples and anodic slime (El-Shahawi et al. 2011a,b,c). A novel sorbent based on chitosan-impregnated PUF [maximum sorption capacity of 76.6 and 96.01 mg/g for copper(II) and nickel(II), respectively] has been successfully used for the removal of heavy metal ions from wastewaters (Prakash et al. 2011). One of the most important results of this study was the fact that the PUF provided enough sorption sites to overcome mass transfer limitations; thus, the process of Cu(II) and Ni(II) sorption on chitosan-impregnated PUF could provide extra value for practical applications (Prakash et al. 2011).

3.3 Chemically modified (reacted) PUFs The reacted PUFs are characterized by the fact that the chelating reagent is bonded to the backbone of the polymer via chemical bonds. The synthesis method differentiates between two types of reacted PUFs (Dmitrienko and Zolotov 2002). The first type is represented by the functionalized PUFs. They are obtained by covalently linking chemical reagent to the side group in the prepared PUF material (Dmitrienko and Zolotov 2002). There are some functional groups (terminal amino, isocyanate in the toluene diisocyanate moiety, carbonyl and imino of the urethane groups, hydroxyl groups in the polyol residues) in the polymer chain that can be used for this purpose. However, the only way known so far is performed by using the terminal amino groups. The modification by azo coupling of the terminal amino groups to different organic compounds results in selective polyurethane sorbents with improved sorption capacity (Table 4). The second type corresponds to the grafted PUFs as presented in Table 4. In this case, the reagent, carefully selected, is added during the manufacturing process of the PUF and acts as a monomer that participates in the polymerization reaction. Thus, the reagent should contain side groups necessary for polymerization and chelation and must be soluble in the mixture of the polymerization reaction (Dmitrienko and Zolotov 2002). There is a continuous and increased interest in the synthesis of new sorbents based on chemically modified PUFs and their use as solid-phase extractor of heavy metal ions in water and wastewater samples. In this context, the novel resins of PUF linked with aminophenol or o-hydroxyphenylazonaphtol can be mentioned. These resins have been recently synthesized and used for preconcentration of nickel, cadmium and zinc ions from natural water samples prior to their atomic absorption spectrometric determination (Burham et al. 2011). The lead content in well water and drinking water samples was determined after its separation and preconcentration on a new sorbent based on PUF functionalized with 4,5-dihydroxy-1,3-benzenedisulphonic acid (Lemos et al. 2012). Under optimum conditions, the proposed system presented enrichment factors of 38 (50 ml) and 114 (500 ml) (Lemos et al. 2012).

3.4 Sorbents based on enzymes and cells immobilized in PUFs PUF is a suitable support material for the immobilization of enzymes and whole cells (Romaskevic et al. 2006).


8 C. Teodosiu et al.: Removal of heavy metal ions by polyurethane foam Table 3 Sorbents based on chelating agent-loaded PUF with applicability in preconcentration and removal of heavy metal ions from aqueous media. Retained heavy metal ion

Chelating agent loaded PUF

Sample

Remarks

Zn(II), Cd(II), Hg(II)

Nile Blue A

Wastewaters

El-Shahat et al. 2003

Pb(II)

2-(2-Thiazolylazo)-p- cresol (TAC)

Saline samples

Hg(II)

2-(2-Pyridylazo)resorcinol (PAR)

Natural waters

Cd(II)

2-(2-Pyridylazo)resorcinol (PAR)

Drinking waters

Zn(II)

Natural waters from Salvador (Brazil)

Cd(II) Pb(II)

2-[2′-(6-Methyl benzothiazolylazo)]4-bromophenol (Me-BTABr) 2-(6″-Methyl-2′ benzothiazolylazo) chromotropic acid (Me-BTANC)

Zn(II)

Aqueous solutions

Hg(II)

N-Benzoyl-N phenylhydroxylamine (BPHA) Crystal violet and some onium cations

Water

Hg(II) Cd(II) Pb(II)

Ammonium pyrrolidine dithiocarbamate (APDC)

Hg(II)

1-(2-Thiazolylazo)-2- naphtol (TAN)

Industrial wastes from a common effluent treatment, chloralkali industry and municipal sewage Natural waters

The extraction was accomplished in 15–20 min. Zn was separated from 3 to 5 m HCl, Cd from 4 to 6 m as thiocyanate complexes and Hg was separated from 1 to 2 m HCl as chloride The sorption process occurred at pH 10, after 40 min of agitation between the phases. The detection limit was 0.25 μg/l Optimum sorption was observed from acetate medium at pH 6 with the maximum equilibration time being 30 min The experimental optimum conditions are pH 8.2, flow rate of 8.5 ml/min and elution concentration of 1 mol/l The detection limit was 0.37 μg/l. An enrichment factor of 23 and a sampling rate of 48 samples per hour were achieved The enrichment factor obtained was 137 for 180 s of preconcentration time. The proposed procedure allowed determination of metals with detection limits of 0.80 and 3.75 μg/l (0.10 and 0.47 μg/g of solid sample) for Cd and Pb, respectively Maximum sorption (∼98% of 8.9 × 10-6 m) is achieved from a buffer solution of pH 8 using 75 mg/ml BPHA-loaded PUF Quantitative retention and recovery (99.5 ± 2.1%) of Hg(II) ions at ≤ 5 ppb level by the foam column were achieved In fixed bed downflow column studies, a quantitative uptake of Hg(II) (400 mg/l), Cd(II) and Pb(II) (60 mg/l) was attained at flow rates of 3.68 l/m2·s

Saeed et al. 2005

Pb(II) Cd(II) U(VI)

2-Aminoacetyl thiophenol (AATP) 1-(2-Pyridylazo)-2naphtol (PAN)

The kinetic studies indicate that the sorption occurs through intraparticle diffusion process. Sorption of Hg(II) ions is endothermic, spontaneous and entropy driven The preconcentration factors are 167 and 250 for Pb and Cd, respectively Quantitative sorption of U(VI) was achieved after 30 min equilibration time from pH 7 buffer

Natural and tap waters

Aqueous solutions from natural samples Aqueous media

The resulting sorbents open a new area of applications for heavy metal effluent management (Alhakawati and Banks 2004, Zhang and Banks 2006). Thus, mycella of Aspergillus niger B-77 immobilized on PUF showed a

References

Sant’Ana et al. 2004

Saeed et al. 2003

Dos Santos et al. 2006

Lemos et al. 2003

Garna et al. 2006

Rashid and Munir 2008

El-Shahawi and Nassif 2003 Anjaneyulu and Rao 2009

Burham 2009 Saeed and Ahmed 2005

three-fold increase in uptake of copper(II) from aqueous solutions compared to free cells (Tsekova and Llieva 2001). Mycella of Rhizopus delemar immobilized on PUF cells can be used repeatedly for the removal of more than


By coupling polyether polyol, rosaniline and toluene diisocyanate

Hydroxylphenol azo derivatives were built in the backbone of untreated PUF by coupling of o-aminophenol to the diazotized foam. The amino group o-aminophenol was then diazotized and coupled to pyrazolone By the covalent condensation of alizarin complexone to PUF through -N = Cgroups

Rosaniline-grafted PUF (Ros- PUF)

Acetylacetone bonded PUF (AA-BPUF) PUF functionalized with resorcinol (Res-PUF)

PUF functionalized with pyrazolone

Alizarin complexone functionalized PUF (ALC)

By covalent coupling through the -N = N- group Covalent linking of resorcinol with PUF through a -N = N- group

PUF functionalized with β-naphtol (β-Nap PUF)

Based on covalent linking of 4-hydroxytoluene and 4-hydroxylacetophenone with PUF through a -N = N- group By covalently linking the reagent with PUF matrix through a -N = N- group

By covalently linking Alizarin red S with PUF, through a -N = N- group

PUF functionalized with 4-hydroxytoluene and 4-hydroxyl acetophenone

Alizarin red S bonded PUF (Al-PUF)

By coupling the PUF matrix with oxine through a -N = N- group

PUF functionalized with quinolin-8-ol (Ox-PUF)

Synthesis method

Type of reacted PUF

Table 4 Sorbents based on chemically modified PUF.

Authenticated | [email protected] author's copy Download Date | 5/23/14 5:53 PM Separation/preconcentration of Cu(II), Zn(II) and Cd(II) from tap water

Removal of Pb(II) and Cd(II) from tap and lake waters

Selective separation and determination of Ag(I) and Hg(II) in tap water and industrial wastewater Preconcentration of Pb(II) and Cd(II) from tap water Quantitative separation and determination of Ag(I) and Hg(II) in traces from natural and wastewaters Preconcentration and determination of Cd(II) and Hg(II) from tap water

Separation and determination of Zn(II), Cd(II) and Hg(II) in tap and lake waters

Separation and preconcentration of Zn(II), Cd(II), and Hg(II) ions in traces from wastewaters Separation and preconcentration of Ag(I), Hg(II), and Pb(II) ions from wastewaters

Preconcentration and/or removal of Ag(I) and Pb(II) from wastewaters

Environmental applications

The procedure provides concentration factor of 100

The capacities of β-Nap PUF were 0.1 and 0.07 mmol/g for Ag(I) and Hg(II), respectively. Enrichment factors > 50 were achieved The capacity sorbent has been found to be 4.5 and 6.9 μmol/g for Pb and Cd, respectively The capacities of the foam material were 0.15 and 0.07 mmol/g for Ag(I) and Hg(II), respectively The sorption capacities of Ros-PUF were 0.12 and 0.08 mmol/g for Cd(II) and Hg(II), respectively. Preconcentration factors were ∼100 The detection limits were 0.072 and 0.016 μg/l for lead and cadmium, respectively. Enrichment factors were 250 and 312 for Pb(II) and Cd(II), respectively

The sorption capacities of the Ox-PUF were 0.16 and 0.07 mmol/g for Ag(I) and Pb(II), respectively The capacities of the foam material were 0.27, 0.16 and 0.09 mmol/g for Zn(II), Cd(II), and Hg(II), respectively The capacities of the Al-PUF were 4.2, 2.5 and 2.4 mmol/g for Ag(I), Hg(II), and Pb(II), respectively. Preconcentration factors of 50 were achieved The functionalized foam shows excellent stability toward various solvents. The detection limit was 0.46 μg/l

Features

Azeem et al. 2010

Burham et al. 2009

Moawed 2004a,b

Moawed et al. 2004

Burham et al. 2008

Moawed et al. 2005

Burham et al. 2006

Moawed et al. 2004

El-Shahat et al. 2004

Moawed et al. 2006

References


By azo coupling of the toluidine-NH2 in PUF to active -CH2- in acetylacetone and further reaction By replacing the primary amine with hydroxyl group

Acetylacetone phenylhydrazone functionalized PUF Polyhydroxy PUF (PPF)

By chemical treatment of PUF with carbon disulfide

By using water hydrolysis of polyurethane diazonium chloride salt

Low density polyhydroxy PUF (LPPF)

Dithiocarbamate modified PUF

PUF grafted with 2-[2′-(6-methylbenzotiazolilazo)-4aminophenol (Me-BTAP)

By coupling polyethylene glycol, 2-[2′-(6-methyl-benzotiazolilazo)-4aminophenol and toluene diisocyanate

Synthesis method

The incorporation of rhodamine B into PUF was prepared by mixing rhodamine B with polyol(polyether) prior to the addition of diisocyanate reagent to form the PUF material

Rhodamine B (Rod.B) grafted PUF

Type of reacted PUF

(Table 4 Continued)

Separation, preconcentration and determination of Mn(II) and Fe(III) in water samples

Preconcentration and determination of Fe(II), Mn(II) and Cu(II) in tap and lake waters Separation and preconcentration of Au(III) ions from spring, sea and wastewaters Preconcentration and determination of Cu(II), Zn(II) and Mn(II) in tap waters

Preconcentration of Cd(II) and Pb(II) from water samples

Separation and determination of Bi(III), Sb(III) and Fe(III)

Environmental applications

Grafted Rod.B-PUF is more stable than loaded Rod.B-PUF, which has been recycled many times without decreasing its capacity significantly. More or less complete recoveries (96–100%) of the tested elements was obtained. The preconcentration factor was 40 The sorbent showed remarkable characteristics, such as resistance to swelling and changes in pH, low resistance to flow passage and simplicity in preparation. The preconcentration factor was 30 and 35 for cadmium and lead, respectively The capacity of the sorbent was 149.2⫿0.5, 237.5⫿0.2 and 200.2⫿0.1 μg/g for Fe(II), Mn(II) and Cu(II), respectively The maximum sorption capacity of LPPF for gold(III) was 70.5 mg/g. The recovery of Au(III) was 99–100% A preconcentration factor of 100 has been achieved for all metal ions. The obtained recovery varied between 90.8% and 96.8% The sorption capacity of PPF was 8.7 μmol/g. A recovery of 99–100% of the tested ions was achieved

Features

Moawed et al. 2013a,b

Abdel-Azeem et al. 2013

Moawed and El-Shahat 2013

Burham et al. 2013

Oliveira and Lemos 2012

Moawed et al. 2011

References




composite PUF with 50% Hap could be used for wastewater treatment ( Jang et al. 2008). Another type of composite PUFs was made via the polymerization of toluene diisocyanate and polyether polyol with activated carbon fiber and immobilized microorganisms and used for the removal of Cu(II) ions from aqueous solutions; for synthetic wastewaters, the removal of Cu(II) after 4-h treatment was 85% (Zhou et al. 2009). A special study was devoted to the selective removal of lead(II) ions by alginate/PUFs, generated by the reaction of sodium alginate with NB-9000B, a polyisocyanate type of prepolymer of polyurethane; the adsorbent was a hydrophilic and flexible alginate/polyurethane composite foam (ALG/PUCF) with the alginate chemically immobilized in the cell walls of the foam (Sone et al. 2009). Due to its high stability, flexibility and ease of use and reuse after regeneration with ethylenediamine-N,N,N′,N′-tetraacetic acid, disodium salt (EDTA-2Na), the ALG/PUCF may be successfully applied for elimination of Pb(II) ions from contaminated water.

92% of copper(II) and cobalt(II) ions from aqueous solutions (Tsekova and Petrov 2002). The dynamic removal of some heavy metal ions in a single-component system by packed columns consisting of biomass of Phanerochaete chrysosporium immobilized on PUF cubes has been reported; the maximum capacities for lead, copper and cadmium were 70.7, 43.7 and 70.8 mg/g, respectively, and their yields were 39.2%, 40.6% and 41%, respectively (Pakshirayan and Swaminathan 2006). Online determination of Sb(III) and total Sb from river water and effluent samples using yeast Saccharomyces cerevisiae immobilized on PUF and hydride generation inductively coupled plasma optical emission spectrometry has been proposed (Menegário et al. 2006). The detection limits of the developed procedure were 0.8 and 0.15 μg/l for total Sb and Sb(III), respectively.

3.5 Sorbents based on composite PUFs An emerging field of interest is represented by the composite PUF/sorbent materials synthesized with various adsorbents: activated carbons, zeolites, clays, etc., these composite materials possess better sorption properties and are very promising sorbents for heavy metal ions in aqueous solutions (Pinto et al. 2006, Liu and Li 2012). Hydroxyapatite/polyurethane (Hap/PU) composite foams synthesized with two different Hap contents of 20% and 50% exhibited well-open structure ( Jang et al. 2008). These composite PUFs were investigated for their ability to remove Pb(II) ions from aqueous solutions. With a maximum Pb(II) sorption capacity of 150 mg/g, the

4 The applicability of sorbents based on PUFs in water and wastewater treatment The open-cell PUFs (plastic materials in which a proportion of the solid phase is replaced by gas in a continuous phase) have been successfully used in column studies regarding the treatment of large volumes of effluents containing heavy metals, as presented in Table 5. These materials

Table 5 Practical uses of PUFs in water and wastewater treatment. Type of polyurethane

Wastewater

Collected metal ions

Immobilized ion exchange polyurethanes Synthetic primary coolant of a nuclear power plant 2-Aminophenol-bonded PUF, Cooling water of a hydroxyphenylazoacetylacetone-bonded sulfuric acid unit PUF and hydroxyphenylazonaphtolbonded PUF 3-Sulfonamoyl-phenyl-spiro-[4-oxo Industrial wastewater of thiazolidin-2,2′-steroid] physically electroplating industry immobilized onto PUF (samples of 0.5 l) Tetraphenyl phosphonium bromide Industrial wastewater physically immobilized PUF from electroplating industry Ammonium pyrrolidine dithiocarbamate Municipal sewage loaded PUFs Chloro-alkali industrial wastes

Removal efficiency References

Co(II)

Cu(II), Ni(II), Pb(II), Mn(II), Zn(II), Fe(III)

Cd(II) (5.10 μg/ml)

Cr(VI) ( < 0.01 μg/ml)

Pb(II), Hg(II), Cd(II), Ni(II), Cu(II) and Cr(VI), Hg(II)


98% Yeon et al. 2004

89.3–106.66 El-Shahat et al. 2008

∼100% Tawfiqmakki et al. 2011 ∼98.6 ± 2% El-Shahawi et al. 2011a,b,c 70–82% Murthy and Marayya 95–98% 2011


can be efficiently applied over a wide range of metal ion concentrations and do not lose their efficiency even with repeated cycles of sorption-desorption. Furthermore, the sorbed metal can be almost quantitatively recovered by a relatively easy desorption (Table 6). Regarding the economical feasibility, it was found that the operational costs for the removal of 1 kg of mercury ions from 20 kl of the effluent using one-time ammonium pyrrolidine dithiocarbamate-loaded PUF as sorbing medium were US$5000 and can be significantly reduced by increasing the number of recycles (Murthy and Marayya 2011).

5 Comparison of sorbents based on PUF with other sorbents for heavy metal ion removal It is very well known that a direct comparison between performances of different sorbents from data coming from different sources is difficult because the test solutions and process conditions differ significantly from one setting to the other. This is probably the reason why there are few publications containing detailed studies of comparisons between sorbents. From our literature survey, it is evident that the cellular structure of the PUF sorbents offer unique advantages over conventional sorbents, low-cost sorbents and nanosorbents in rapid, versatile effective

separation and/or preconcentration of heavy metal ions from aqueous solutions, as presented in Table 7. For a better argumentation, Figure 3 is shown based on data from literature studies and our previous studies: PUF (Tofan et al. 1996, Reddy and Reddy 2003, Alhakawati and Banks 2004, Moawed 2004a,b, Saeed et al. 2007, El-Shahawi et al. 2008, Abdel Salam et al. 2011), chelating resins (Bîlbă et al. 1998a,b, Asouhidou et al. 2004, Pandey and Thakkar 2004, Ngeontae et al. 2007, Rengaraj et al. 2007, Shah et al. 2011), hemp (Tofan et al. 2001, 2009a,b, 2010, Paduraru and Tofan 2008), pine bark (Acemioglu et al. 2004, Mohan et al. 2007, Vijayakumaran et al. 2009, Amalinei et al. 2012, Gonçalves et al. 2012, Tofan et al. 2012), fly ash (Gupta et al. 2003, Tofan et al. 2008, 2009a,b, 2011, Özkök et al. 2013), zeolites (O’Connell et al. 2008), cellulose powder (O’Connell et al. 2008, Wan Ngah and Hanafiah 2008). It can be observed from Figure 3 that sorbents based on PUF are competitive against conventional sorbents and low-cost sorbents, being very suitable for the removal and recovery of heavy metal ions from large volumes of industrial wastes.

6 Conclusions This review presents a literature survey of new sorbents based on PUF available for use in preconcentration and removal of heavy metal ions from natural waters and

Table 6 Desorption and multiple sorption/regeneration cycles for heavy metal ions removal by sorbents based on PUFs. Sorbent

Retained metal ions

Desorbing solution

Metal recovery (%)

Number of sorption/ desorption cycles

1-(2-Thiazolylazo)-2-naphtol imbedded PUF Tetraphenylarsonium chloride and tetraphenylphosphonium bromideloaded PUFs Alginate/polyurethane composite foams

Pb(II)

0.03 N Perchloric acid

96–99.7

Saeed et al. 2007

Cr(VI)

2 m Sodium hydroxide

97.5 ± 2.6

5

El-Shahawi et al. 2008

Pb(II)

∼100

4

Sone et al. 2009

Alizarin complexone functionalized PUF

Cu(II) Zn(II) Cd(II) Bi(III) Sb(III) Fe(III) Cu(II) Mn(II) Zn(II)

Disodium salt of ethylenediaminetetraacetic acid 0.1 m Nitric acid

∼100

Azeem et al. 2010

2 m Sodium hydroxide

96–100

Moawed et al. 2011

0.4 m Hydrochloric acid

93.6 97.2 93.5

70

Rhodamine B grafted PUF

Acetylacetone chemically anchored to PUF


References

Abdel-Azeem et al. 2012


Table 7 Assessment of sorbents with large applicability in heavy metal ions removal from wastewaters. Sorbent

Advantages

Activated carbons

Excellent sorption performances that allow a high quality of the treated effluents Large surface area Strong interaction with a wide range of trace elements ions High sorption capacity High rate of sorption

Silica gel

Good mechanical strength Possibility to undergo heat treatment Resistance to swelling caused by solvent change High sorption capacity Chelating agents can be easily loaded or bound chemically Wide range of structure and physicochemical characteristics High capacity of sorption High rate of sorption Important selectivity for different concentrations Able to be regenerated and used in many cycles of sorption-desorption Tolerant for a wide range of wastewater parameters Very low cost Simplicity of preparation Easy to purchase Resistance to changes in pH Provides high preconcentration factors Versatile applicability in multielement preconcentration procedures or in specific procedure Easy use in automatic and online preconcentration systems Low cost Local availability Good cost-effectiveness ratio Renewability Unique structure Special structure characteristics High sorption capacity High selectivity Infinite recyclability

Polymeric (ion-exchange and chelating) resins (typically based on cross-linked polymers having polystyrene, phenolformaldehyde or acrylate matrices)

PUFs

Unconventional low-cost sorbents (waste, by-products, raw materials) Nanosorbents

wastewaters by considering an integrated approach over the synthesis, characterization and applicability of different types of PUFs for the removal of heavy metals as well as the comparison of these sorbents with other sorbents effective for such processes. Sorbents based on unloaded PUF generally work in batch conditions according to the following succession

Disadvantages

References

Low reproductibility Non-selectivity High reactivity Ability to act as catalyst of undesirable chemical reactions Drastic conditions for analyte elution Difficulty in removal of heavy metals at ppb levels Low selectivity Hydrolysis at basic pH

Zhao et al. 2011, Fu and Wang 2011

Zougagh et al. 2005, Lemos et al. 2007

High operational costs Limited use in specialized environmental applications such as treatments of industrial wastewaters to the parts per billion levels Non-environmentally friendly

Asouhidou et al. 2004, Crini 2005, Pan et al. 2009

Unable to retain metal ions without prior complexation Relatively low sorption capacity

Lemos et al. 2007, 2012

Low sorption capacity Difficult to recover Mechanisms of sorption are not fully understood Expensive Non-environmentally friendly

Wang et al. 2012

of steps: the reaction between the metal ion and a complexing agent→addition of unloaded PUF→retention of the formed complex on PUF. The extraction or chelating reagent-loaded PUFs were developed so as to increase the sensitivity and specificity of the foams for the removal of heavy metal ions. The resistance of the loaded foams toward reagent leaching out limits their applicability. This



30

25

Cu(II)

Zn(II)

Cd(II)

Cr(III)

Pb(II)

Ni(II)

q (mg/g)

20

15

10

5

0 PUF

Chelating resins

Hemp

Fly ash

Pine bark

Zeolites

Cellulose powder

Figure 3 Comparison of sorbents based on PUF with other sorbents for heavy metal ion removal.

observation has led to the synthesis of new PUF sorbents that are prepared by building up chelating groups on the terminal amino groups in the PUF. Sorbents based on enzymes and whole cells immobilized on PUF could open a new area for environmental applications. The composite PUF/sorbent materials posses better sorption properties and are considered as very promising sorbents for heavy metal ions in aqueous solutions. The open-cell PUFs can be efficiently applied in the treatment of large volumes of effluents containing a wide range of heavy metal ion concentrations and do not lose their efficiency even for repeated cycles of sorption-desorption. Compared to conventional and low-cost sorbents for pollutant ion removal from aqueous solutions, the sorption using PUF offers the opportunity to preconcentrate and separate heavy metal ions with higher selectivity and sensitivity. Acknowledgments: This study was realized with the support of the WATUSER Project (Integrated System for Reducing Environmental and Human Related Impacts and Risks in the Water Use Cycle, PN-II contract no. 60/2012) financed by the Romanian government.

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Carmen Teodosiu is a professor in the Department of Environmental Engineering and Management at the “Gheorghe Asachi” Technical University of Iasi (TUIASI), Romania. She obtained her chemical engineering degree at TUIASI (1981), her postgraduate diploma with distinction (1995) and Master of Science in Environmental Science and Technology with distinction (1996) at the International Institute of Hydraulics and Environmental Engineering, UNESCO-IHE Delft, the Netherlands, and her PhD in Chemistry at TUIASI in 1998. Prof. Teodosiu’s research and teaching experience is in the fields of water and wastewater treatment processes, environmental management/integrated water resources management. Prof. Teodosiu has published more than 140 scientific papers in international peer-reviewed journals and conference proceedings and has been involved as director/researcher in 23 international grants and 37 national grants.

Lavinia Tofan is an associate professor in the Department of Environmental Engineering and Management at the “Gheorghe Asachi” Technical University of Iasi (TUIASI), Romania. She obtained her chemical engineering degree at TUIASI (1984) and her PhD in analytical chemistry at TUIASI in 1998. Prof. Tofan’s research and teaching experience is in the fields of analytical chemistry, environmental analytical chemistry, separation and concentration of elements by sorption and biosorption, adaptation and development of analytical methods for the determination of elements in low concentrations. Prof. Tofan has published more than 70 scientific papers in international peer-reviewed journals and conference proceedings, and has been involved as director/researcher in 25 national grants.

Rodica Wenkert is head of the laboratory, Department of Microbiology, Soroka University Medical Center Beer-Sheva, Israel. She obtained her chemistry degree at “Gheorghe Asachi” Technical University of Iasi (TUIASI), Romania (1984), and her PhD in analytical chemistry at TUIASI in 2007. Dr. Wenkert’s research experience is in the field of separation and concentration of elements by sorption. She has published more than 25 scientific papers in international peer-reviewed journals and conference proceedings. She was a scientific committee member of several international conferences.

Carmen Paduraru is lecturer in the Department of Environmental Engineering and Management at the “Gheorghe Asachi” Technical University of Iasi (TUIASI), Romania. She obtained her chemical engineering degree at TUIASI (1980) and her PhD in analytical chemistry at TUIASI in 2005. Dr. Paduraru’s research and teaching experience is in the fields of recovery of platinic metals using complex-forming polymeric sorbents, separation and concentration of polluting metallic ions by sorption on nonconventional materials, and adaptation and development of analytical methods for the determination of elements in low concentrations. Dr. Paduraru has published more than 50 scientific papers in international peer-reviewed journals and conference proceedings, and has been involved as director/researcher in 15 national grants.


Rev Chem Eng 2014 | Volume xx | Issue x

Graphical abstract Carmen Teodosiu, Rodica Wenkert, Lavinia Tofan and Carmen Paduraru Advances in preconcentration/ removal of environmentally relevant heavy metal ions from water and wastewater by sorbents based on polyurethane foam

Review: The article discusses important research dealing with new sorbents based on polyurethane foams applied in batch and dynamic systems for separation and/or preconcentration of heavy metal ions in environmental aqueous media.

DOI 10.1515/revce-2013-0036 Rev Chem Eng 2014; xx(x): xxx–xxx

Keywords: heavy metals; polyurethane foam; sorbents; wastewater; water.
