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Journal of the Chilean Chemical Society

versión On-line ISSN 0717-9707

J. Chil. Chem. Soc. vol.61 no.1 Concepción mar. 2016

http://dx.doi.org/10.4067/S0717-97072016000100001 

ARSENIC SORPTION USING MIXTURES OF ION EXCHANGE RESINS CONTAINING N-METHYL-D-GLUCAMINE AND QUATERNARY AMMONIUM GROUPS

GULSAH OZKULAb, BRUNO F URBANOa, BERNABÉ L. RIVASa* NALAN KABAYC, MAREK BRYJAKd

a University of Concepción, Polymer Department, Faculty of Chemistry, Concepción, Chile.
b
Ege University, Faculty of Sciences, Department of Chemistry, Izmir, Turkey.
c Ege University, Faculty of Engineering, Department of Chemical Engineering, Izmir, Turkey.
d Wroclaw University of Technology, Faculty of Chemistry, Wroclaw, Poland
.

e-mail: brivas@udec.cl


ABSTRACT

The method of synthesis and the arsenie removal properties of ion-exehange resins based on N-methyl-D-glueamine and trimethylammonium groups are presented. The N-methyl-D-glueamine based monomer was synthesized by the reaetion of 4-vinyl benzyl ehloride with N-methyl-D-glueamine, along with theuse of N,N-methylene-bis-aerylamide as a erosslinker reagent for polymerization. In addition, poly(4-vinylbenzyl)trimethylammonium was synthesized. Arsenatesorption studies were conducted and the pH effect, kinetics, sorption capacity, and elution performance were studied. The experimental data were fitted to kineticmodels, such as the pseudo-first order and pseudo-second order models. The pseudo-second order model exhibited the best correlation with the experimental data.The Langmuir and Freundlich isotherms were fitted to the experimental data, and the Freundlich isotherm exhibited the best fit.

Keywords: Arsenie, N-methyl-D-glueamine, ion exehange, ion exehange resin mixture.


INTRODUCTION

The removal of metal ions and oxyanions from dilute or eoneentrated solutions has reeeived a great deal of attention in the last 40 years, to reeoverhigh-cost metals or to decontamínate effluents1.

A number of these studies have developed sorption proeesses ineluding adsorption and ion-exehange meehanisms, preeipitation, solvent extraetion,eonjunetion of membranes and polymers using simple materiais sueh asaetivated earbon or more sophistieated materials sueh as espeeially tailoredpolymers as well as biosorbents, sueh as fungal or baeterial biomass, andmateriais of biologieal origin, ineluding alginate and ehitosan2'14.

One of the more harder pollutant is arsenie whieh is found in various forms in all segments of the environment, and its eompounds are eonsidered ashighly toxie substanees; these arsenie eompounds are generated from naturaloeeurrenee and antropogenie sueh as: pestieides, dyes and drugs, etc15. Thepresenee of arsenie in natural waters is a worldwide problem. The major naturalsouree of arsenie in groundwater is leaehing from geologieal formations.Drinking arsenie-eontaminated water for long periods of time eauses eaneersin the skin, lung, urinary bladder, and kidney16, 17. Arsenie pollution has beenreporte d reeently in the USA, China, Chile, Bangladesh, Taiwan, Mexieo,Argentina, Poland, Canada, Hungary, New Zealand, Japan, and India18. TheWorld Health Organization (WHO) and the Environmental Proteetion Ageney(EPA) have strietly redueed the máximum eontaminant levei reeommended forarsenic from 50 µg L-1 to 10 µg L-1 to minimize the risk to humans19.

Arsenie ean exist in many oxidation states in the natural environment, ineluding the -3, 0, +1, +3, and +5 valenees. Two forms of arsenie are eommonin natural waters: arsenite (AsO33-) and arsenate (AsO43-), referred to as arsenie(III) and arsenie (V), respeetively17, 20, 21.

Several methods, sueh as oxidation, preeipitation, eoagulation, adsorption, ion-exchange, and the use of membranes filtration, have been developed forarsenie removal from water22-24. The adsorption proeess, whieh ean reduee the arsenie eoneentration to the minimum level, appears to be the most promisingapproaeh amongst the available methods and has been widely used for arsenieremoval because of its low cost and high efficiency25,26. Strong base anion-exehange resins that eontain quaternary ammonium groups attaehed to apolymerie matrix have been extensively studied for their ability to removearsenic and have been found to exhibit a higher affinity for divalent species(HAsO42-)24. Therefore, for these resins, the optimum pH for sorption isbetween 7 and 9, where the eoneentration of HAsO42- speeies is high27.

Immobilization of N-methyl-D-glueamine (NMDG) on poly(vinyl benzyl ehloride) beads yields an effeetive and highly seleetive sorbent for arsenateions. Only a few studies on arsenie removal have used NMDG as the ligand (attaehed to new supports)28, 29. It has been demonstrated that ion exehangeresins eontaining NMDG ligands improve the retention of arsenate as H2AsO4-and that the sorption is efficient in acidic conditions (in the pH range of 3 to6)28.

In this way, it is expeeted to aehieve a high arsenie sorption in a wide range of pH by means of ion exehange resins mixture (ammonium and glueamine-based polymers) in the same bateh.

In this study, the resins were eharaeterized with FT IR speetroseopy and batch studies were performed to evaluate the efficiency of arsenic removalusing mixtures of synthetie ion exehange resins that eontain N-methyl-D-glueamine and quaternary ammonium groups. The sorption performanees of these resins were investigated by ehanging the polymer:polymer ratio in mol.Moreover, the kinetie and equilibrium data were also evaluated by means ofkinetie and isotherms models.

EXPERIMENTAL

Materials

The monomer N-(4-vinylbenzyl)-N-methyl-D-glueamine (VBNMDG) was synthesized using the preeursors 4-vinylbenzyl ehloride (VBC, Aldrieh) and N-methyl-D-glueamine (NMDG, Aldrieh) as reeeived. The reagent N,N-methylene-bis-aerylamide (MBA, 98% Aldrieh) and ammonium persulphate(Aldrieh) were used as erosslinker and initiator reagents, respeetively. Forthe synthesis of poly [(4-vinylbenzyl)trimethylammonium ehloride] resin(PClVBTA), (4-vinylbenzyl) trimethylammonium ehloride (Aldrieh) wasemployed. Hydroehlorie aeid, nitrie aeid, and perehlorie aeid were used asstripping agents.

Synthesis

Synthesis of poly[N-(4-vinyl benzyl)-N-methyl-D-glucamine] resin

The reaetion of N-methyl-D-glueamine and 4-vinyl benzyl ehloride was performed in a three-neck round-bottom flask using a mole ratio of 1:1.Reagent grade N-methyl-D-glueamine (44 mmol) was dissolved in 150 mL of a 2:1 volume solvent mixture of dioxane and deionized water. The solution wasadded to the reaetor and heated for 20 min until the NMDG was eompletelydissolved. Subsequently, 44 mmol of 4-vinyl benzyl ehloride was dissolved in20 mL of dioxane, and then was added slowly to the reaetor. The reaetion wasmaintained under reflux with constant stirring for 5 h, and a yellowish solutionwas obtained. To remove unreacted VBC, the final solution was washed withethyl ether twiee. The VBNMDG monomer, whieh was dissolved in a dioxane/water solvent, was transferred to the reaetor, and then N,N-methylene-bis-aerylamide (15 mol-% based on monomer) was added. After the erosslinkingreagent was dissolved, ammonium persulfate (1 mol-%) was added. Themixture was degassed with a nitrogen gas for 10 min, and then the reaetion wasstirred overnight under nitrogen atmosphere at 70°C. The resin was extraetedand washed with dioxane and distilled water and subsequently dried in an ovenat 50 °C. Finally, dry resin was sieved, and a partiele-size fraetion in the rangeof 180 to 250 pm was chosen for all of the sorption experiments (see Fig. 1).

Synthesis of poly[(4-vinylbenzyl)trimethylammonium chloride] resin

The reaetion was performed using 37.7 mmol of (4-vinylbenzyl) trimethylammonium ehloride and N,N-methylene-bis-aerylamide (15 mol-% based to monomer) dissolved in water. After the erosslinking reagentwas dissolved, potassium persulfate (1 mol-%) was added. The mixture wasdegassed using nitrogen gas for 10 min. The reaetion was stirred ovemightunder nitrogen atmosphere at 70 °C. The resin was washed with distilled waterand subsequently dried in an oven at 50°C. Finally, dry resin was sieved, anda particle-size fraction in the range of 180 to 250 pm was chosen for all of thesorption experiments (see Fig. 1).


Fig. 1. Synthetic resin structures

Physicochemical characterization

The morphology and structure of the resin was evaluated by infrared spectroscopy (Perkin Elmer 1760-X spectrometer using a range of 4000 to 400cm-1 and KBr pellets). The arsenic concentrations were determined by atomicabsorption spectroscopy (FIAS-100 flow injection atomic spectrometry); forthese measurements, As(V) was reduced to As(III) using HCl (50%), KI (20%) and ascorbic acid (10%).

Sorption studies

Batch sorption experiments were performed to evaluate the arsenate retention by PVBNMDG and PClVBTA resins. The effect of pH on retentionwas studied to obtain a correlation between arsenic speciation and the sorptionperformance of the resins PVBNMDG and PClVBTA at a particle size rangeof 180 to 250 pm. The arsenic aqueous solutions were adjusted to a pH of 3-9using dilute HNÜ3 and NaOH solutions. In these studies, various amounts of PVBNMDG (10, 20, 30, 40, and 50 mg) and PClVBTA (1, 2, 3, 4, 5, and 10mg) were contacted with 10 mL As(V) solution (10 mg/L) in a shaker at 30 °Cunder a stirring rate of 140 rpm for 24 hours. The sorption performances of these resins were investigated by changing the polymer:polymer ratio in mol.The different PVBNMDG:PClVBTA molar ratios, such as 1:3, 1:1, and 3:1,were prepared, resulting in a total amount of 50 mg of resin per ratio. Theseexperiments were performed by contacting 50 mg resin with 10 mL As(V)solution (10 mg L-1) at 30 °C under a stirring rate of 140 rpm for 24 hours. Toevaluate the effect of time on sorption, kinetic experiments were performedusing 10 mL of As (V) solution (10 mg L-1) at 3-9 pH and with the sorbentsof molar ratio of PVBNMDG: PClVBTA as 25:75 (50 mg). The experimentswere performed at 30 °C and under a stirring rate of 140 rpm. The samples werewithdrawn from the shaker at different time intervals (0, 1, 3, 5, 10, 15, 30, 60,120, and 1440 min). The experimental data were evaluated using conventional and diffusion'reaction kinetic models. The equilibrium experiments (isotherms) were performed using a range of arsenic concentrations (5'650 mg L-1) and a1:3 molar ratio of PVBNMDG:PClVBTA. These experiments were performedat 30 °C for 24 hours at pH 3.0, 6.0, and 9.0. The experimental data wereevaluated using Langmuir and Freundlich isotherm models to evaluate thesorption process. To study the arsenate elution process, different acid solutionswere used. In the sorption step, a 1:3 molar ratio of PVBNMDG:PClVBTA wascontacted with 10 mL of As(V) solution 10 mg L-1 in a shaker at 30 °C undera stirring rate of 140 rpm for 24 hours. After the sorption step, the resin wascontacted with 4 M HCl, HNO3 and HClO4 in a shaker for 4 hours at 30 °C toevaluate the elution performance.

RESULTS AND DISCUSSION

Infrared spectroscopy

Figure 2 shows the infrared spectra of the synthetic resins. The PVBNMDG resin exhibited the characteristic absorption bands at 1080 cm-1 v(C-O), 1455cm-1 v(CH2), 1653 cm-1 v(C=C), and 2956 v(C-H). The signals in the regionof 1000 cm-1 and 1150 cm-1 are characteristic of the glucamine group attributedto the C-O and C-N vibrational bands, respectively. Meanwhile, the PClVBTAresin exhibited the characteristic absorption bands at 1120 cm-1 v(C-N), 1482cm-1 v (N+-(CH3)3), and 1644 cm-1 v (C=C). The presence of these bandsconfirms the structure of the resins.30


Fig. 2. Infrared spectra of the PVBNMDG and PClVBTA resins.

Arsenic sorption

For all adsorbents, pH is a key factor determining the performance of the sorption processes. Hydronium in water can change the structural properties of the ligands of the resins and also the speciation of the metal ions in aqueoussolution, thereby affecting the sorption. Figure 3 shows the effect of pHand the adsorbent amount on the arsenate sorption determined by the batchequilibrium procedure. The curves indicate that removal of arsenic for bothresins increases as the amount of resin increases due the higher of numberof exchange sites. However, the pH significantly affects the sorption. ForPClVBTA resin, máximum retention was observed at pH 9, where arsenic isfound primarily as HAsO42-. This result is consistent with strong basic anionexchange resins with ammonium groups, which interact better with the divalentspecies of arsenic in the pH range of 8 to 10.27 The arsenic removal decreasedat pH 6 because HAsO42- and H2AsO4- ions exist in equilibrium, and at pH3.0, the removal exhibits its lowest value. By contrast, PVBNMDG resinexhibits maximum retention at pH 6.0, where arsenic is found primarily as H2AsO4-. The main characteristic of V-methyl-D-glucamine as a ligand wasthe interaction of monovalent arsenate species with the protonated tertiaryamine.28, 29, 31 However, the efficiency of the PVBNMDG resin was lower thanthat of the PClVBTA resin.


Fig 3. Curves of As(V) removal using a) PClVBTA, b) PVBNMDG for different pH.

Figure 4 shows the effect of pH on arsenate sorption using different resin molar ratios. At pH 3.0, the mixtures of resins exhibited the lowest sorption,reaching only a removal of 33% (1.0 mg g-1), whereas at pH 6.0 and pH 9.0,the uptake efficiency increases; the 1:3 molar ratio presented the best sorption(70.3 % (2.2 mg g-1) and 75.0 % (2.4 mg g-1) for pH 6.0 and 9.0, respectively).

The decrease in sorption as the mole content of PVBNMDG decreases reveals the contribution of glucamine'based resin on arsenic sorption.
Because the 1:3 mixture exhibited the best sorption, this mole ratio was selected for further experiments.


Fig 4. Removal of arsenic for different PClVBTA:PVbNMDG molar ratios at a) pH 3.0, b) pH 6.0, and c) pH 9.0.

Kinetic studies

The kinetic behavior of the resin mixture at the 1:3 molar ratio (PClVBTA:PVb NMDG) was examined for an arsenic concentration of 10 mgL-1 at pH 3.0, 6.0 and 9.0. Figure 5 shows the change of arsenic concentrationsas a function of time. The curves reveal a rapid uptake of arsenic oxyanions,with the maximum sorption achieved after only 2 h of contact, whereas the pHeffect exhibits the same trend observed in the previous experiments (highestsorption at pH 6.0 and pH 9.0).


Fig 5. Change of arsenic concentrations as a function of time using a 1:3 molar ratio of PClVBTA: PVbNMDG polymer. ([As]= 14.3 mg L-1;
resindosage: 5 mg L-1]

The kinetic data were evaluated using the conventional kinetic models of the pseudo-first-order and pseudo-second-order kinetics models, 32,33 and thediffusional/reaction models of the infinite solution model and the unreactedcore model.34

Lagergren proposed the pseudo-first order model for describing the adsorption process of solid-liquid systems, and its linear form is formulated below35:

where qe (mg g-1 resin) and qt are the amount of arsenic adsorbed at equilibrium and at time t, respectively. The slope from a plot of log(qe — qtt) vs.t allows the determination of the rate constant kl (min-1).

The pseudo-second order equation has been widely used due the excellent fit of the experimental data for the entire sorption period of many systems.36The kinetic model can be expressed as below:

Integrating and assuming boundary conditions, the rearranged linear form of the pseudo-second order model is obtained:

where qe and qt are the arsenic amount adsorbed and at time t, respectively, h=kqe2 is the initial sorption of arsenic (mg g-1 min-1), and k2 is the rate constant of sorption (g mg-1 min-1). The sorption kineticdata were adjusted to the models described above, and the parameters obtainedare presented in table 1. Clearly, the pseudo-second order model exhibited the best fit, with a correlation coefficient above 0.999. The rate constant increaseswith the pH, which can be explained by the speciation of arsenic. As statedbefore ammonium-based resin exhibits greater affinity towards divalent arsenicoxyanions, which its maximum concentration occurs at the pH 9.0. In this way, the mixture contains a major proportion of ammonium'based resin favoring the sorption at pH 9.0.


Table 1. Kinetic parameters for the pseudo-first order and pseudo-second order models


The models for process dynamies inelude both the diffusional steps (bulk solution, a film layer at the externai surface of the particle, pores) and the exchange reaction on the active sites. Because the resistance in the bulksolution is easily controlled and negligible, three resistances, i.e., film diffusion,particle diffusion, and chemical reaction, usually determine the overall rate of the ion-exchange process.37 The kinetic study data were evaluated by usingtwo approaches. The first approach is based on Fick's first law of integrationof material balance for infinite solution volume (ISV). The second methoduses the unreacted core model (UCM), in which ion exchange is treated as aheterogeneous reaction. According to the UCM, the metal ions are exchangedon the outermost layer of the particle, and as time passed, the reaction sites aregradually moved toward the core of the particle. The diffusional and reactionmodels summary is shown in table 2.


Table 2. Diffusional and reaction models 34

a X = q/qt and qe and qt are the amounts of As(V) adsorbed at equilibrium and at time t, respectively.

Table 3 presents the correlation coefficients (r2) resulting from the fit of kinetic data to diffusional and reaction models. The maximum correlationcoefficients for the linear models indicate that the rate is particle-diffusioncontrolled according to the ISV models, and the reacted layer is controlledaccording to the UCM models for all pH.


Table 3. The correlation coefficients (r2) according to diffusion and reaction models.

Adsorption isotherms

Equilibrium sorption isotherms are one of the most important tools used to design adsorption processes. Moreover, isotherms provide useful informationabout the interaction between the adsorbate and the adsorbent. The experimentaldata were fitted to the isotherm models of Langmuir and Freundlich. The curvesindicates that for a concentration as high as 600 mg L-1 of As (V), the resins donot saturate (Fig. 6a). Unusual for this type of experiment is the shape of the curve for experiments at pH 3.0, which exhibits a concave shape, indicatingan initial stage of low sorption and then increasing from Ce = 110 mg L-1. Theexplanation of these results can be ascribed to the low affinity of monovalentarsenic species with the mixture, whereas the increase of sorption can beattributed to the increment of the gradient concentration. The isotherms at pH 6.0 and pH 9.0 were adjusted to isotherm models (Langmuir and Freundlich)by means of a non-linear regression fit (see Figure 6b). Both of the isothermmodels describe well the experimental data, with correlation coefficients above0.98. The maximum uptakes of resins from the Langmuir fit were 237 mg g-1 and 392 mg g-1 for pH 6.0 and pH 9.0, respectively. Different studies haveinvestigated the efficiency of arsenic sorption using commercial ion exchangeresins, such as Amberlite IRA-400, Purolite A-505, Relite A-490, and DiaionWA20/30 38-40. Anion exchange resins have a higher affinity towards divalentanions than towards monovalent anions, and the maximum sorption is reachedbetween pH 6.0 and 9.0, where the concentration of divalent anions is maximal.For instance, Awual et al.40 studied the arsenic sorption using commercialweak-base anion exchange resins and found that as the pH increases the arsenicsorption decreases, which was attributed to the diminishing of protonated amineform. On the other hand, Donia et al.41 prepared a synthetic ion exchangerstarting from a glycidyl methacrylate/methylene-bis-acrylamide resin withimmobilized tetraethylenepentamine, and subsequently modified with glycidyltrimethylammonium chloride. The sorbent displayed the highest sorption at pH 6.0 and a equilibrium capacity (Langmuir) of 1.8 mmol g-1.

Elution studies

Metal ion elution and sorbent regeneration is a critical consideration in the analysis of the process costs and the metal recovery in a concentrated formor further disposal. For effective reuse, a successful desorption process mustrestore the sorbent such that it exhibits properties that are close to its initialproperties. This process must be performed when the sorbent is exhaustedby the use of a suitable eluent. Arsenic acid (H3AsO4) is a weak acid withthree pKa values: 2.2, 6.9, and 11.5. Therefore, when acid reagents are usedas eluents, the arsenic monovalent and divalent anions attached to the resin (H2 AsO 4- and HAsO2-) are transformed into the acid H3AsO4 , which is a noncharged molecule and later leached.38 The elution study was performed with different 4 M acid solutions (HCl, HNO3 and HCIO4). Figure 6 shows the elution efficiency of HCl, HNO3 and HCIO4 solutions reaching 96.0%, 96.1% and 92.3% elution, respectively. These results demonstrate that acid solutionsare good stripping reagents for arsenic.


Fig 6. Arsenic sorption isotherms for mixture 1:3 at different pH values.

 

Fig 7. Elution profile of arsenic using HCl, HNO3 and HC104.

CONCLUSIONS

Ion exchange resins poly[(4-vinylbenzyl)trimethylammonium chloride] and poly [A-(4-vinyl benzyl)-A-methyl-D-glucamine] were successfullysynthesized. The evaluation of the arsenic uptake revealed that ammonium-based resins possess the highest sorption. Ion exchange resins mixtures of 0.25 mole fraction of PCIVBTA exhibited the best performance reachingapproximately 80% of removal. Kinetic and equilibrium studies showed that the sorption process is well described by the pseudo-second order modeland the Langmuir isotherm. Regarding the elution performance, the acidicconditions by means of HCl and HN03 exhibited the best results.

ACKNOWLEDGEMENTS

The authors thank the 7FP-MC Actions Grant CHILTURPOL2 (PIRSES-GA-2009 Project, grant number: 269153), FONDECYT (Grant No 1110079), PIA (Anillo ACT 130), Grant C0NICYT-CNRS, and REDOC (MINEDUC Project UCO1202 at U. de Concepción). B.F. Urbano thanks FONDECYT Initiation 11121291 and CIPA CONICYT Regional Project R08C1002.

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