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Removal of organic pollutants in model water andthermal wastewater using clay mineralsEmese Szabó a , Krisztina Vajda a , Gábor Veréb a , András Dombi a , Károly Mogyorósi b ,Imre Ábrahám c & Marcell Májer ca Institute of Material Sciences and Engineering, University of Szeged, Szeged, Hungaryb Research Group of Environmental Chemistry, Department of Inorganic and AnalyticalChemistry, University of Szeged, Szeged, Hungaryc UNICHEM Kft., Kistelek, HungaryPublished online: 20 Sep 2011.

To cite this article: Emese Szabó , Krisztina Vajda , Gábor Veréb , András Dombi , Károly Mogyorósi , Imre Ábrahám &Marcell Májer (2011) Removal of organic pollutants in model water and thermal wastewater using clay minerals, Journal ofEnvironmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering, 46:12, 1346-1356,DOI: 10.1080/10934529.2011.606679

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Journal of Environmental Science and Health, Part A (2011) 46, 1346–1356Copyright C© Taylor & Francis Group, LLCISSN: 1093-4529 (Print); 1532-4117 (Online)DOI: 10.1080/10934529.2011.606679

Removal of organic pollutants in model water and thermalwastewater using clay minerals

EMESE SZABO1, KRISZTINA VAJDA1, GABOR VEREB1, ANDRAS DOMBI1, KAROLY MOGYOROSI2,IMRE ABRAHAM3 and MARCELL MAJER3

1Institute of Material Sciences and Engineering, University of Szeged, Szeged, Hungary2Research Group of Environmental Chemistry, Department of Inorganic and Analytical Chemistry, University of Szeged, Szeged,Hungary3UNICHEM Kft., Kistelek, Hungary

Water treatment method was developed for the removal of different anionic dyes such as methyl orange and indigo carmine, and alsofor thymol applying sodium bentonite and cationic surfactant - hexadecyltrimethylammonium bromide (HTAB) - or polyelectrolytes(polydiallyldimethylammonium chloride, poly-DADMAC and poly-amines). The removal efficiency of these model substrates wasexamined in model water using UV-Vis spectrophotometry, HPLC and TOC analysis. The clay mineral and HTAB were added inone step to the polluted model water in Jar-test experiments. The influence of the cation exchange capacity (CEC) of the appliedclay mineral and the presence of polyaluminium chloride coagulant (BOPAC) were also tested for the water treatment process. Thestructures of the in situ produced and pre-prepared organoclay composites were compared by XRD analysis. The rapid formationof organoclay adsorbents provided very efficient removal of the dyes (65–90 % in 3–10 mg/L TOC0 range) with 200 mg/L sodiumbentonite dose, however thymol was less efficiently separated. Adsorption efficiencies of the composites were compared at differentlevels of ion exchange such as at 40, 60 and 100 %. In the case of thymol, the elimination of inorganic carbon from the model waterbefore the TOC analysis resulted in some loss of the analysed volatile compound therefore the HPLC analysis was found to be themost suitable tool for the evaluation of the process. This one-step adsorption method using in situ formed organoclay was betterperforming than the conventional process in which the montmorillonite-surfactant composite is pre-preapared and subsequentlyadded to the polluted water. The purification performance of this method was also evaluated on raw and artificially polluted thermalwastewater samples containing added thymol.

Keywords: Wastewater purification, thermal water, organic pollutants, montmorillonite, organoclay, cationic polyelectrolytes,adsorption.

Introduction

There is an expanding demand for the development of effi-cient and economic treatment technologies that are capableof dealing with toxic or hazardous organic contaminants inindustrial wastewaters. Some of these organics are not eas-ily removed by microbiological treatments therefore theirremoval by physical or chemical methods has to be carriedout.[1–4] There are many new adsorbent materials that areinexpensive and efficient enough for these target substances.Smectite-type clay minerals such as sodium montmoril-lonite could be efficiently modified by cationic surfactantsin water using ion exchange reactions.[5–11]

Address correspondence to Karoly Mogyorosi, Research Groupof Environmental Chemistry, Department of Inorganic and Ana-lytical Chemistry, University of Szeged, Dom ter 7, Szeged, Hun-gary H-6720; E-mail: k.mogyorosi@chem.u-szeged.huReceived January 7, 2011

Permanent negative charges on the clay mineral sheetscan be compensated by organic cations by replacing thesodium ions. Usually long ion exchange time and someheating are applied to ensure the complete ion exchangebetween these ions. Considering the cationic exchange ca-pacity of the used clay, the inorganic ions can be replacedby a desired percentage. The organic cations change the hy-drophilic nature of montmorillonite for organophilic andthis makes them suitable for adsorbing different type oforganics from water.[6,9,12–15] Organoclays can be used ef-ficiently to remove anionic dyes,[15,16] cationic dyes[17] andnon-polar contaminants, such as hydrocarbons (toluene[3]),pesticides,[12] polycyclic aromatic hydrocarbons,[18] napht-ene[20] and phenols[9,13,14,19] as well.

Although the clay minerals are relatively inexpensive,their use is limited due to the time and energy consumingsynthesis of organoclays. Shen[21] suggested that the for-mation of organoclay and the adsorption could be accom-plished in a one-step process in which the swollen sodium

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Clay mineral removal of organic pollutants from water 1347

montmorillonite is added to the polluted water that is fol-lowed by the addition of the cationic surfactant in a calcu-lated amount based on the cation exchange capacity (CEC)of the clay. It was concluded that the in situ forming organ-oclay aggregates are capable to adsorb organics very ef-ficiently. Phenol for example could be adsorbed within afew minutes. Ma and Zhu also studied the performance ofthis one-step process for the removal of acid dye[16], phenol,p-nitrophenol and β-naphthol.[22]

In our present study, applying this novel one-step pro-cess, the influence of the cation exchange capacity was in-vestigated with three different types of sodium bentonitesamples for the removal of anionic dyes, such as methyl or-ange and indigo carmine. These types of organic pollutantsare representative model compounds for the anionic pol-lutants in industrial wastewaters. Cationic polyelectrolyteswere also tested for the removal of these dyes with the sameapproach. Sodium bentonite with the highest CEC valuewas used to compare the efficiency of the in situ and pre-prepared organoclay adsorbents for the removal of thymolwhich was selected as a representative pollutant for thermalwaters containing phenol derivatives.

Materials and methods

Synthesis of the organoclay composites

Three different type of sodium bentonite samples wereused in this study. Sodium bentonite from Sud-ChemieAG (SBS, CEC = 0.80 mmol/g), SPV 200 Wyoming typesodium bentonite (AMCOL Specialty Minerals, CEC =0.82 mmol/g) and Kunipia-F sodium bentonite (KunimineIndustries, Japan, JCSS-3101, CEC = 1.15 mmol/g) wereused as received from the suppliers. The main clay mineralin these powders is sodium montmorillonite. Two differentmethods were used for the synthesis of the organoclay com-posite adsorbents. In method 1, the organophilic clay wasproduced before its application. Sodium montmorillonitewas allowed to swell in water for minimum 24 h (csusp = 10g/L) at room temperature.

Hexadecyltrimethylammonium bromide (HTAB,Sigma-Aldrich, 95 %) surfactant solution (100 mL) wasadded dropwise to 300 mL of the sodium bentonitesuspension under stirring. The HTAB solution containedthe calculated amount of cationic surfactant that wasenough to exchange the sodium ions on the given claymineral in 40, 60 and 100 % (0.503, 0.754 and 1.257 gHTAB/100 mL). The ion exchange process was carriedout under stirring at 60±1◦C for 5 h and the suspensionwas continuously stirred at room temperature for anadditional 16 h. The dispersion was filtered and washedby approximately 1 L of MilliQ water in order to removethe dissolved impurities from the sample. Organoclay

adsorbents were stored in water as aqueous suspensionre-adjusting its concentration to 10 g/L.

The clay composites are named by indicating the nameof the method and the sodium bentonite used and alsothe degree of cation exchange accomplished by hexade-cyltrimethylammonium (HTA) cations based on the CECvalue, for example M1-Kunipia-F-100. Organophilic clayadsorbents were also prepared in situ in the contaminatedmodel waters in method 2 that involves the addition ofsodium bentonite aqueous suspension and subsequent ad-dition of the appropriate amount of HTAB solution to thesolution of the selected substrates. Samples from both syn-thesis methods were dried before XRD analysis at 50◦C inair.

Evaluation of the removal efficiency

Two different anionic dyes, methyl orange (MeO,Spektrum-3D) and indigo carmine (InC, Sigma-Aldrich)and also thymol (T, Sigma-Aldrich, 99 %) were used in thebatch adsorption tests. Figure 1 represents the structureof the selected organic substrates. Dyes were applied atfour different initial total organic carbon (TOC) contents,such as 3, 5, 10 and 25 mg/L. In a typical test, tap waterwith the substrate (TOC0 = 3 mg/L) was stirred in Jar-testequipment (Velp JLT6) with the stirring rate of 180 rpmwhile the sodium bentonite suspension was added (from10 g/L stock dispersion providing 200 mg/L final sodiumbentonite concentration) and subsequently the surfactantsolution (cHTAB = 7 g/L) in the calculated volume to pro-vide the desired level of ion exchange (the total volume ofthe treated system is always 500 mL).

Then the stirring was slowed down to 40 rpm and con-tinued for 20 minutes and finally stopped. The formedorganophilic aggregates were then separated by simple sed-imentation in the subsequent 40 minutes of settling time.Aliquots were taken from the supernatant of the treatedmodel water for analysis by UV-Vis spectrophotometry,HPLC and TOC analysis. The total treatment time in theJar-test experiments was always kept to be 1 hour. The in-fluence of polyaluminium chloride (BOPAC, Unichem Kft)

Fig. 1. Chemical structure of methyl orange, indigo carmine andthymol.

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Table 1. Properties of the applied cationic polyelectrolytes.

Polyelectrolyte Type of flocculant Relative molecular weight Total solids (%)U.S. ANSI/NSF

Standard 60∗(mg/L)

Superfloc C573 Polyamine Low 49.0–52.0 20.0Superfloc C577 Polyamine Medium 49.0–52.0 20.0Superfloc C591 Poly-DADMAC High 19.0–21.0 50.0Superfloc C592 Poly-DADMAC Medium 39.0–41.0 25.0

∗Standard for drinking water chemicals.

with high basicity on the sedimentation was also investi-gated applying it in the dose of ∼40 mg/L (added fromstock solution cBOPAC = 10 g/L). BOPAC is an aluminiumcontaining coagulant (cAl3+ = 10.25 %, with the basicity of83 ± 2 %, general formula Al2(OH)5Cl; pH = 3.8).

Four different types of cationic polyelectrolytes (CytecIndustries Inc., Superfloc series) with polyamine and polydi-allyldimethylammonium chloride (poly-DADMAC) struc-ture were also tested in the adsorption experiments (seedetails of the polyelectrolytes in Table 1). Polyelectrolyteswere applied in the concentration range that is allowed bythe U.S. ANSI/NSF Standard 60 for drinking water treat-ments (see also Table 1). Concentration of PE used in ourexperiments is expressed in the mass of PE product pervolume unit (mg/L).

Thermal wastewater originated from a southern Hun-garian thermal spa (Kistelek, Hungary) was also used forthe purification experiments both with and without addedthymol (the composition of the original thermal water isdescribed in Table 2). For these experiments, Kunipia-Fsodium bentonite was applied in two different concentra-tions (200 and 2000 mg/L) in the M2 method with HTABin 60 % and 100 % of the CEC value. The efficiency ofC577 cationic polyelectrolyte (cPE = 200 mg/L, cclay = 2000mg/L) was compared with the results obtained with HTABcationic surfactant.

Analytical and material characterization methods

Two different anionic dyes, methyl orange and indigocarmine were spectrophotometrically (Agilent 8453) mea-sured at 463 nm and 610 nm, respectively. The measuredchanges in the absorbance at 274 nm were used to esti-mate the removal efficiency of organic compounds in realwastewater samples since thymol has an absorption max-imum at this wavelength. The spectrophotometric mea-surements were all carried out in a 10 mm quartz cell.Background measurements were taken in the matrix ofthe samples except in the case of real wastewater at whichMilliQ water was used as blank.

The concentration decrease of thymol was followed us-ing an Agilent 1100 series HPLC system. This consists of abinary pump; a micro vacuum degasser; a diode array de-tector (λd = 274 nm); a thermostated column compartmentand ChemStation data managing software. The chromato-

graphic system was equipped with Rheodyne Model 7725injector with a 20 µL loop and a Licrospher RP-18 column.The eluent consisted of a 65:35 methanol: water (v/v) mix-ture and the flow rate was 0.8 mL min−1.

TOC measurements of the catalysts were performed witha Euroglas 1200 TOC instrument. Supernatant samples inthe volume of 100 µL were analysed. The TOC calibrationcurve was determined using aqueous solutions of oxalicacid. For the experiments with thymol, model water wasused (membrane filtered water with added salts, such asCaCl2×2 H2O, 1.1 mmol/L; MgSO4×7 H2O, 0.8 mmol/L;KCl, 0.03 mmol/L and NaHCO3, 3.6 mmol/L). The inor-ganic carbon content was removed from the sample byacidifying it with HCl solution (37 wt %, 100 µl/10 mLsample) and purging with nitrogen for 10 min. For com-parison, some experiments were also carried out in real

Table 2. Composition and characteristics of the thermalwater.

Cations c (mg/L)

Sodium 362Potassium 9.1Lithium 0.07Ammonium 8.4Calcium 7.2Magnesium 2.3Iron 0.046Manganese 0.014

Anions c (mg/L)Nitrite <0.02Nitrate <1Chloride 37Bromide 0.2Iodide 0.02Fluoride 1.3Sulfate 14Sulfide <0.1Phosphate 0.02Carbonate <15Hydrocarbonate 982pH 7.59Specific conductance (µScm−1) 1594CODMn (mg/L) 7TOC (mg/L) 5

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Clay mineral removal of organic pollutants from water 1349

thermal wastewater samples with added thymol followedby HPLC.

X-ray diffraction patterns were collected on a Bruker D8Advance diffractometer, using Cu Kα radiation (λ = 0.1542nm). The basal spacing (dL) of the layered structures wascalculated from the (001) reflection via the Bragg equation.

Results and discussion

Structural changes in the motmorillonite structure duringthe formation of the organoclay

Sodium cations are replaced on the surface of clay min-eral sheets in both above described methods. The efficiention exchange process requires that the montmorillonite beapplied when it is swollen in water. In aqueous suspensionthe aggregates of individual sheets can be disaggregated re-sulting in better contact with the cationic surfactant (Fig.2a). In method 1 the organoclay composite is formed at60◦C for 5 h and results in a well-ordered layered structurein which the alkyl chains are aligned in a certain patterndepending on the degree of ion exchange.

It should be noted that as the ion exchange level increasesup to 100 % the organoclay becomes hydrophobic. There-fore this adsorbent is not very easily redispersed in water,which makes its application in powder form less convenientfor water purification purposes. Obviously, the adsorbentcould also be stored in water, and used in concentratedsuspension; however, its strong aggregation still limits thetransfer of substrates into the interlamellar space inside theaggregates.

In the presence of the pollutant, especially at higher con-centrations, the interlamellar distance is further increas-ing due to the adsorption.[4] In the case of method 2, theswollen clay mineral sheets are taken apart in the treatedwater providing a better availability for both the cationicsurfactant and the pollutants (Fig. 2a). Based on the mea-surements in the literature[13,22] the ion exchange with theorganic cations and the parallel adsorption of the pollu-tant approaches its equilibrium in a relatively short time(in about 1 hour). Kunipia-F, M1-Kunipia-F-100 and M2-Kunipia-F-100 samples were studied with XRD method asdry powders (Fig. 2b).

The XRD pattern of the original Kunipia-F shows adistinct peak at 7.30◦ (2�), from which a 1.21 nm basaldistance (dL) can be calculated. This is a typical valuefor air dry sodium montmorillonite samples. For the M1-Kunipia-F-100 sample a significant shift of the peak (4.34◦,2�) was noticed. The calculated dL = 2.04 nm value ofthis sample is referred to the intercalation of HTA cations.These ions not only modify the nature of the surface butalso behave like pillars in the interlamellar space.[7,9,20,23]

Sanchez-Martin and co-workers[7] measured dL = 2.11 nmfor an octadecytrimethylammonium-modified montmoril-lonite sample.

Liu and co-workers[9] observed a gradual increase in thebasal distance varying the degree of organophilization be-tween 0.5 and 2.5 CEC with HTA cations (dL = 1.47–1.91nm). Lagaly and Dekany[24] summarized in their reviewstudy that the arrangement of alkyl chains in the interlamel-lar structure depends mostly on the length of the alkyl chainand its surface density. Four different types of alkyl chainarrangement can be distinguished, such as (i) monolayers,(ii) bilayers of flat lying chains, (iii) pseudotrimolecular lay-ers and (iv) paraffin-type monolayers (this type is drawn onFig. 2a). It should be noted that the diffraction peak ofthe M2-Kunipia-F-100 sample was located at about thesame position (4.48◦, 2�; dL = 1.97 nm) as the peak deter-mined for the sample synthesized in method 1. Althoughthe gallery height is very similar in this case, its XRD inten-sity is much lower which indicates the random orientationof the modified lamellae in this sample. This further con-firms the picture presented in Figure 2a.

Adsorption experiments with indigo carmine and methylorange

Indigo carmine (InC) was applied in 3, 5 and 10 mg/L(TOC) concentration in tap water. Three parallel experi-ments were carried out: one experiment using HTAB sur-factant alone, one using clay mineral and surfactant (SBS,cclay = 200 mg/L, 100 % of CEC) and one using SBS,surfactant, and BOPAC coagulants added subsequently tothe InC solution (Fig. 3a). The cationic surfactant and theanionic dye forms a precipitate that can also be removedfrom the solution since its low solubility in water (removalefficiency was about 60–70 %). However in the presence ofSBS, it reaches 85–90 % at a 3–5 mg/L initial TOC concen-tration.

Applying BOPAC, the efficiency slightly decreases, mostlikely due to the competitive adsorption of surfactantcations and the positively charged very small aluminiumhydroxide particles formed under the coagulation process.The sedimentation is sufficiently rapid in the absence ofcoagulant therefore its use is simply disadvantageous. Sim-ilar observations were found with methyl orange (MeO,Fig. 3b). It can be removed by the HTAB surfactantalone in 62–70 %, and in 80–84 % using sodium bentonite(SBS).

Polyelectrolytes can also be efficiently adsorbed on thesurface of clay minerals[25–27] and therefore could modifythe surface for better adsorption performance. Churchmanfound that pre-prepared cationic surfactant-clay compos-ites can be efficiently used as adsorbents for toluene.[28] Inour experiments, four different types of cationic polyelec-trolytes were tested (see details in Table 1). The appliedconcentration of polyelectrolytes was selected in the rangethat can be used for drinking water purification techniques(concentration of PE used is expressed in the mass of PEproduct per volume unit, mg/L).

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Fig. 2a. Scheme of adsorption of organic pollutant in method 1 and 2.

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Clay mineral removal of organic pollutants from water 1351

Fig. 2b. XRD patterns of Kunipia-F montmorillonite, and theorganocomplexes made with HTAB (100 % of CEC) in method1 (M1-Kunipia-F-100) and in method 2 (M2-Kunipia-F-100)(color figure available online).

Sodium bentonite (SBS) concentration was the same asin the experiments described above (200 mg/L) and theinitial concentration of dyes was 3 mg/L (TOC0). It canbe seen from Figures 4 and 5 that indigo carmine can bevery efficiently removed by these cationic polyelectrolytes,except with C573 that is a polyamine-type cationic poly-electrolyte with low relative molecular weight. The removalefficiency was found to be about 90 %. This is slightly betterthan that obtained with HTAB cationic surfactant (85 %).However, significantly lower efficiency was found for methylorange for all tested cationic polyelectrolytes (12–16 %only).

Adsorption experiments with thymol

Phenolic compounds with good solubility in water areless efficiently removable by organoclay adsorbents thandyes;[22,26] therefore, researchers used a significantly higherconcentration of sodium montmorillonite for phenol re-moval (2000–10,000 mg/L) to lower its concentration tothe desired level. For that reason, the influence of the CECvalue of the clay minerals was investigated for InC removalin a broader concentration range (TOC0 = 3–25 mg/L)with SPV 200 and Kunipia-F sodium montmorillonite sam-ples (Fig. 6).

For both clay minerals the removal efficiency was 100 %up to the TOC0 = 10 mg/L concentration (for SBS sampleit was only 67 % at 10 mg/L TOC0). As it was expected, theKunipia-F sample with a higher CEC value (1.15 mmol/g)showed better removal performance (90 %) at 25 mg/LTOC0 concentration for InC compared to the efficiency ofSPV 200 (CEC = 0.82 mmol/g; 63 % removal efficiency).Thus for the adsorption experiments with thymol, Kunipia-F clay mineral was selected.

The removal of thymol was studied applying the claymineral (200 mg/L) and HTAB cationic surfactant simul-taneously in the model polluted water. The efficiency wasdetermined at three different level of ion exchange, such as40, 60 and 100 %. The supernatant was centrifuged andfiltered for HPLC analysis. The determined concentrationof thymol was then expressed in total organic carbon con-tent (TOCT in mg/L) and the results are shown in Figure7. Increasing the coverage of the clay mineral sheets byHTA cations, the efficiency increased from 13 to 36 % inthe case of M2-Kunipia-F samples and from 13 to 24 % inthe case of M2-SPV 200-type adsorbents. TOC values werealso determined from the supernatant of these purified wa-ter samples (without any filtration or centrifugation), seeFigure 8.

Fig. 3. Removal efficiency of (a) methyl orange (b) indigo carmine using HTAB cationic surfactant, clay mineral (SBS) and BOPACcoagulant (TOC0 = 3, 5, 10 mg/L) (color figure available online).

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Fig. 4. Determination of removal efficiency with indigo carmine in Velp JLT6 Jar-Test equipment (TOCInC,0 = 3 mg/L, cclay =200 mg/L, cC592 = 0-25 mg/L, in last beaker cBOPAC ∼ 40 mg/L) (color figure available online).

Comparing the results shown in Figures 7 and 8, it wasconcluded that during the removal of inorganic carbonsome of the remaining thymol was very likely also purgedout from the samples. TOC measurements could determinethe remaining organic carbon content from both thymoland the non-adsorbed cationic surfactant. Therefore theseTOC values should have been found to be higher thanthat obtained from the HPLC analysis for thymol alone.Results obtained from the HPLC analysis are thereforemore reliable. The developed one-step adsorption processwas compared with the conventional method using pre-adsorbed organoclay for thymol removal (Table 3).

In these experiments the same amount of montmoril-lonite (200 mg/L) and surfactant (calculated for the samedegree of ion exchange, 40–60–100 %) were used in bothmethods. There were no significant differences between the

Fig. 5. Removal efficiency of methyl orange and indigo carminewith different cationic polyelectrolytes using SBS clay mineral(TOCdye,0 = 3 mg/L, cSBS = 200 mg/L) (color figure availableonline).

two methods at 40 and 60 % of ion exchange. However,as it was expected, at complete ion exchange, significantlylarger percentage of thymol was removed by method 2 (36%) compared to the performance with method 1 (25 %).Thus, it can be concluded that these materials can be moreefficiently used when the in situ mixing is applied.

Adsorption experiments with thermal wastewater

Thermal wastewater sample was collected from a Hun-garian thermal spa (see the composition of the originalthermal water in Table 2) to investigate the efficiency ofthe M2 method in real wastewater. Figure 9a shows the ab-sorption spectrum of the raw thermal wastewater (TWW)and the spectra of the purified wastewater samples treated

Fig. 6. Removal efficiency of indigo carmine with different clayminerals (color figure available online).

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Clay mineral removal of organic pollutants from water 1353

Fig. 7. Remaining total organic carbon content in the supernatantof thymol solutions calculated from its concentrations determinedby HPLC (different percentage of CEC of used sodium bentoniteswas exchanged by HTA cations) (color figure available online).

with Kunipia-F sodium bentonite (cclay = 2000 mg/L) andHTAB used in 60 % and 100 % of the CEC of the claymineral.

It can be seen from the spectra that significantly lower ab-sorbances were recorded in the spectral range of 230–400nm. The original raw TWW was slightly yellow and thetreated water samples were completely colorless and trans-parent. However the treated samples showed significantlyhigher light absorption below 220 nm. This is most likelycaused by the presence of bromide anions which remain inthe solution phase during this method. For comparison, theabsorption spectrum of KBr solution in MilliQ water (cKBr

Fig. 8. Remaining total organic carbon content in the supernatantof thymol solutions measured by TOC analysis (different percent-age of CEC of used sodium bentonites was exchanged by HTAcations) (color figure available online).

Fig. 9a. Absorption spectra of raw and treated thermal wastewater(TWW) samples using Kunipia-F sodium bentonite and HTABcationic surfactant or C577 polyelectrolyte in M2 method. Thespectrum of KBr solution in MilliQ water is given for reference(color figure available online).

= 2.3 mmol/L; equal to the applied molar concentration ofHTAB at 100 % of CEC for 2000 mg/L Kunipia-F sodiumbentonite) is also indicated in Figure 9a. This means thatthe organic pollutants were removed very efficiently underthese conditions.

The absorption spectrum of the purified water treatedwith C577 cationic polyelectrolyte (cPE = 200 mg/L,cclay = 2000 mg/L) is also shown. At this concentrationthe treated water was also colorless and transparent, show-

Fig. 9b. Absorption spectra of raw, artificially polluted and treatedthermal wastewater (TWW) samples containing added thymol(TOCT,0 = 10 mg/L) using Kunipia-F sodium bentonite andHTAB cationic surfactant in M2 method. The spectrum of KBrsolution in MilliQ water is given for reference (color figure avail-able online).

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Table 3. Removal efficiency of thymol measured by HPLC (M1and M2 method).

Treatment

TOCT#

calculated fromHPLC (mg/L)

�TOCTcalculated from

HPLC (%)

Thymol solution 10.0 0.0M1-Kunipia-F-40 8.6 14.3M1-Kunipia-F-60 7.7 22.7M1-Kunipia-F-100 7.5 25.2M2-Kunipia-F-40 8.7 13.4M2-Kunipia-F-60 7.6 24.4M2-Kunipia-F-100 6.4 36.1

#TOCT: total organic carbon content of thymol.

ing significant decrease in the light absorption in the UVrange as well (64 % at 274 nm).

The removal efficiency for thymol was also evaluated inartificially polluted used thermal water with added thymol(TOCT,0 = 10 mg/L) applying Kunipia-F sodium bentoniteand HTAB used in 60 % and 100 % of the CEC of the claymineral. The absorption spectra of the raw and pollutedwastewater are indicated in Figure 9b. It is obvious fromthis figure that thymol can be very efficiently removed fromreal wastewater samples along with other naturally occur-ring organic substances.

The removal efficiency values determined by spectropho-tometry at 274 nm are summarized in Figure 10 at twodifferent clay mineral concentrations (cclay = 200 and 2000mg/L) exchanging the cations in 60 % and 100 % of theadded clay mineral. The removal efficiency of UV light ab-sorbing species could reach about 94–97 % at the higherclay mineral concentration when complete ion exchange isapplied.

It is important to note, that even at one magnitude lowerconcentration of clay mineral (cclay = 200 mg/L), signif-icant removal of organics was achieved both in the pres-ence and absence of added thymol (66–84 %). Table 4summarizes the purification efficiency values in thermalwastewater in the presence of added thymol determined by

Fig. 10. Removal efficiency values determined by spectrophotom-etry without and with added thymol (TOCT,0 = 10 mg/L) deter-mined at two different clay mineral concentrations (200 and 2000mg/L) and cation exchange capacity (60 % and 100 %) coveredby HTA on Kunipia-F sodium bentonite (color figure availableonline).

spectrophotometry and the HPLC analysis. As it can beconcluded from both measurements, the removal of thymoland other organic substances in the wastewater were veryefficient at higher clay mineral concentration (89–94 %). Itis interesting to note that the removal efficiency determinedby HPLC for thymol in real thermal wastewater (55.3 %)was significantly better than that measured in model water(36.1 %, see Table 3) using the same amount of clay min-eral and HTAB. This better performance might be causedby the higher ionic strength and the beneficial presence ofother organic substances in the real wastewater.

Conclusions

Three different types of clay minerals were found to beefficient for the removal of indigo carmine and methyl

Table 4. Purification efficiency values in thermal wastewater in the presence of added thymol (TOCT,0 = 10 mg/L) measured byspectrophotometry and HPLC analysis determined for thymol (M2 method, Kunipia-F clay mineral).

cclay (mg/L)CEC1 exchanged by

HTA (%) cHTAB2 (mg/L) �A at 274 nm (%)

TOCT3 calculated

from HPLC (mg/L)

�TOCTcalculated from

HPLC (%)

0 0 0 0.0 10.0 0.0200 60 50.3 38.7 5.4 45.7200 100 83.8 65.7 4.5 55.32000 60 502.9 72.9 2.4 76.02000 100 838.2 93.9 1.1 89.1

1CEC: cation exchange capacity.2HTAB: hexadecyltrimethylammonium bromide.3TOCT: total organic carbon content of thymol.

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Clay mineral removal of organic pollutants from water 1355

orange dyes when the organoclay adsorbent compositeswere formed at room temperature after the addition ofhexadecyltrimethylammonium bromide cationic surfac-tant. The newly formed pillared structure of organoclaywas confirmed by XRD analysis in both in situ andconventional pre-synthesis methods. It was concludedthat the higher cationic exchange capacity provided moreefficient removal for indigo carmine. Cationic surfactantswere also efficient for the removal of indigo carmine.

The method was significantly less efficient however inthe case of methyl orange. Kunipia-F sodium montmo-rillonite was used for the removal of thymol. At 100 %of ion exchange with HTA cations, the in situ applica-tion of montmorillonite was more efficient than the con-ventional method using the pre-prepared adsorbent. TheHPLC analysis was found to be a more reliable tool formonitoring the removal of volatile thymol compared tothe TOC analysis due to some loss during purging thesample when inorganic carbon was removed before TOCmeasurements.

It was also concluded that this novel purification methodcan be efficiently used also in real thermal wastewater toremove natural organic compounds including some phenolderivatives as well. This method applied with relatively lowconcentration of clay mineral (200 mg/L) and cationic sur-factant (CHTAB = 84 mg/L) resulted in about 66–84 % ofabsorbance decrease at 274 nm in a real thermal wastewa-ter with and without added model pollutant. Therefore aneconomic water purification technology could apply thismethod with an additional application of advanced oxida-tion processes if necessary. Promising results with cationicpolyelectrolytes also encourage further studies on this novelwater purification method.

Acknowledgments

This work was financially supported by grants fromthe Hungarian Research Foundation (OTKA CK80193and PD78378) and by the Hungarian National Of-fice of Research and Technology (NKFP DA THERMTECH 08 A4). KM also thanks the support of the Hungar-ian Academy of Sciences (Bolyai Janos Research Fellow-ship). AMCOL Specialty Minerals is thanked for providingfree SPV 200 sodium bentonite sample. Kunipia-F sodiumbentonite as a free gift of Kunimine Industries Co., Ltd.is also highly appreciated. Authors would like to acknowl-edge the sodium bentonite (SBS) provided by the researchgroup of the Department of Physical Chemistry and Ma-terial Science at the University of Szeged, led by ProfessorImre Dekany.

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