Adsorption of phenthoate and acetochlor from water by clays and organoclays

ISN 1001-0742Journal of Enironmental Sciences Vol. 16,No.5 ,p.738- -741 ,2004CNI1- -26291XArticle ID: 1001-0742(2004)05-0738-04CLC number: X131.2Documeat code: AAdsorption of phenthoate and acetochlor from water by clays and organoclaysLIAO Min, XIE Xiao-mei(College of Enironmental and Resource Sciences , Depertment of Resources Seience, Zhejiang University, Hanghou 310029, China. E-mail: liaomin@zju.edu.cn)Abstract: Adsorption of phenthoate and acetochlor onto kaolin, montmorillonite, bentonite clays and respectiveorganoclays prepared by the exchange of quaternary ammonium as tetradecyltrimethy| ammonium bromide(TTAB)，dodecytrimethylammonium bromide ( DTAB)，and cetyloyidinium chloride (CPC) were studied. The adsorptionequilibrium data points were ftted to Freundlich isotherm equations. The adsorption of phenthoate and acetochlorwere signiticantly enhanced by surtactant treatment of the clays. The amount of both pesticides adsorbed per unitmass of organoclay fllwed the order of TTA-kaolin < TTA-montooilonite < TTA bentonite, which is inconsistentwith the organic carbon content of the clays . The removal eficiency of organomontmorillonite to treat acetochlor is inthe order of CP(Ci6 )-montmorillonite > TTA( C,a )-montilonite > DTA(C2 )-montillonite. Phenthoate isadsorbed to greater extent than acetochlor by each adsorbent, which may be due to the higher hydrophobicity ofphenthoate, indicating considerable hydrophobic interaction between adsorbent/ adsorbate systems.Keywords: adsorption; clays; organoclays; phenthoate; acetochlorcations to hydrate and to their inherent organophilic natureIntroduction(Sheng，1996). These organoclays have generally beenImmobilization or separation of contamninants containedconsidered as good adsorbents of non-ionic organicin polluted water is an objective of increasing importance in acontaminants from industrial wastes, such as a-naphthylaminevariety of environmental sttings. The extent of pesticide( Zhu，1997 ) or pentachlorophenols ( Boyd，1988c ).contamination of the water environment has recently raisedHowever, very few works have been reported on adsorption ofmuch concern because of the potential health hazardsagricultural chemicals by organoclay ( Zhu，1997; Sanchez-associated with the entry of these compounds into the foodMarin，1991; 1984).chain of humans and animals( Pimentel, 1993; Jin, 2001).The objective of the present study is to evaluate theThe pollution of the water environment with pesticides iseffectiveness of organoclays in removing the pesticides fromaffected through their use in the control of weeds and insects,water and how the alkyl chain length of quaterary ammoniumleaching run-off from agricultural and forest lands, depositioncation exchanged onto clays affect the magnitude of solutefrom aerial applications and discharge of industrial wastewatersorption. We investigated the adsorption of phenthoate [ 0,0-(Thompson，1992; Huang, 2002).dimethy- s-( a-ethoxycarbonylbenzyl ) phosphorodithioate ]The wide range of pesticides used makes it extremelyand acetochlor [ 2 '-ethyl-6 '- methyl-N-( ethoxymethyl )-2-difficult to produce a single method for pesticide disposal thachloro- acetanilide] from water by kaolin， tetradecyl-applies widely. Therefore, several methods for removal andtrimethylammonium ( TTA )-kaolin，montmoillonite， TTA-disposal of these chemicals may be required to solve thismontmorillonite，bentonite and TTA-bentonite .Whileproblem. Adsorption on solid substrates, such as clay oradsorption of acetochlor was also made on dodecyltr-activated carbon, is one of the methods, which have beeimethylammonium ( DTA )-rmontmorillonite and cetylused for removing organic pollutants from water( W eissmnahr,pyridinium( CP )- montmorillonite to study the effect of alkyI1997; Martin, 1997; Jaynes, 1991).chain length of surfactant exchanged .In an attempt to design new adsorbents to remove non-1 Experimental procedureionic organic contaminants from waste water， severalresearchers have replaced the inorganie cations of clays by1.1 Materialslarge alkyl ammonium cations in order to change th1.1.1Adsorbentshydrophilic surface of clay into hydrophobic ( Sheng, 1996;中国煤化工，，montoilonite andZhu, 1997; Boyd, 1988a) . The resulting organoclay surfaceKaolin was procured fromsorbs effectively a wide variety of organic compounds fronZh:*YHC NMH Gted Company ( China ). .water and air. This is due to lesser tendency of organicMontmorillonite and bentonite were obtained from ZhejiangFoundation item: The National Key Busic Rescarch Support Foundation of China( No.2002CB410804) and the National Natural Science Foundation of China ( No.39970146)No.5Adsorption of phenthoate and acetochlor from water by clays and organoclays39Yuhong Clay Chemical Limited Company( China) . Bentonitekaolin,TTA-kaolin,montmorilloniteand TTA-s composed of montmorillonite. The three clays havemontmorillonite, bentonite and TTA-bentonite were fitted todifferent cation exchange capacity ( CEC) and CEC wasFreundlich equation with r > 0. 98. The Freundlich isothermsdetermined by 0.1 mol/L NH AC exchanging method < Bao,for adsorption of pestieides are shown in Figs. 1-3. The2000). The CEC of kaolin, montmoillonite and bentoniteFreundlich models for liquid phase adsorption can be wittenare 10.0, 44.0, and 102.0 meq 100 g', respectively .as follows :1.1.2 Organic cationInq. = lnKr+()nc..The quatemary ammonium cations( surfactants) used forpreparingorganoclayswere 95%tetradecyltrimethylwhere, C. is the equilibrium concentration, q。 is the amountammonium bromide ( TTAB )，99% dodecylrime-adsorbed at equilibrium ( mg/g) and n，Kp constants for athylammonium bromide (DTAB) and 98 % cetylpyridiniumgiven adsorbate- adsorbent system .chloride (CPC). All of them were procured from Sigma3.5 rChemical Company ..0 F1.1.3 Adsorbates.5 tThe adsorbales used in this study are technical grade.ot(99%) phenthoale and acetochlor and were supplied by.5 FBayer Chemical Company .1.2 Preparation of organoclayhe orgaroclays were prepared by the similar way asdescrbed by G. Sheng et al. ( Sheng，1996). Theorganoclays have relatively high surface area compared withInC。clay. The surface area of clays and organoclays are listed inTable 1 as determined by BET N2 adsorption method .Fig.1 Freundlich plor for adsorpion of pesticides on kaolin and TA-kadin◆phenthoate on TTA-kaolin;■ phenthoate on kaolin; ▲acetochlor on 'ITA-Table 1 Surface area of days and organoclayskaolin; x actclor on kaolinMaterilSurface area, m'/gKaolin13.10Both K, and n are constant being indicative of theTTA. kalin23.45extent of adsorption and degree of non-linearity betweenMontinoilorite83.00solution concentration and adsorption， respectively. TheTA-otnprilonite103.30different parameters of Freundlich model are shown inBentonite148.50Table 2.TTA-bentonite191.04Table 2 Freundich parameters for adsorption of pesticides on clays and1.3 Adsorption equilibrium experimentIn adsorption experiments fixed amount (50 mg) ofAdsorbate AdsorbentKpCorrelation coefficient, Padsorbent and 50 ml of an aqueous solution of pesticide ofAcetochlor Kaolin.1.02 3.210.9870varied concentration were placed in 250 ml Erlenmeyer flask0.9975and shaken on shaker bath at constant temperature(25土1C)Motoilonite 0.49 1.010.9946for 24 h to ensure the equilibrium. All the adsorptionTTA-M1.34 1.180.9927experiments of pesticides were caried out at their natural pH0.9999TTA-B2.53 0.8260.9901(6.0--6.5 ). After equilibrium the suspension wasPhenthoate Kaolin1.06 1.190.9974centrifuged and concentration of solutes determined by a high-TTA-ksolin6.53 3.30. 9805pressure liquid chromatograph ( HPLC) equipped with UVMortmoillonite 2.38 1 . 720. 9939detector and Cg reversed-phase column. Separation of5.57 1.20.9893phenthoate was performned by a mixed solution as mobile1.15 1.3SC0.9988phase ( mixed with ( v/v) 100% n-hexane， 0.1% 2-3.25 0. 7690.9996propanol) and detected at 230 nm. While separation ofThe calculated K; value indicated the high adsorptionacetochlor was performed by a mixed solution as mobile phaseaffinity of organoclay for pesticides than their respective clay.(mixed with (v/v) 75% methyl alcohol， 25% water) andThis is中国煤化工1ase on organoclaysdetected at 220 nm. The flow rate was 1 ml/ min and injectionpreparedyl chain quatemaryvolume was 10 μ.ammoniuMYHC N M H Ghobicity. Non-ionic2 Results and discussionorganic compounds are easy to be adsorbed on alkyl organicphase, in which adsorption mechanism is governed by one2.1 Equilibrium isotherms studypartitioning process ( Boyd，1988b; Lee， 1989; Jaynes,Adsorption isotherms of phenthoate and acetochlor on.740LIAO Min et al.Vol.164.0rwith acetochlor ( solubility = 235 mg/L)， and hence hashigher adsorption afinity due to bhydrophobic interactions(Sheng，1996).3.Table 3 Adsorption eMcieAdsorbatleAdorhentRemoval, %Amount adsorbed, mg/g1.5-Acetochlor Kaolin13.211.3211.TTA-K27.322.732Motrurillonite37.233.7230.DTA-M52.335.23323一TTA-M63.146.314ImC。CP-M78.817.881Bentonite3.350Fig.2Freundlich plot for adsorption of pesticides on mntoilonite andTTA-B89.158.915TTA-montmilonitePhenthoaleKaolin46.364.636◆phenthoate on T-montmoillonite;■ phenthoate on montnorilonite; ▲72.507.250acetochlor on TTA- mnmoilonitn; x acetochlor o momtmoiloniteMomtoillonite48.314.83190.579.057s.05. 3604.5-99.359.9354.0Noles: *Acetochlor Co = 10 mg/L; phenthoate Co = 10 mg/L; weight of adsorbent3.5=50 mg3.0i2.52.3 Comparison of sorption using different organoclays2.The adsorption of organic， non-ionic and sparingly1.5soluble contaminants by soils in aqueous media is essntiallygoverned by the organic matter content in the soil. Thepositive correlation between the organic matter content and05the adsorption of non-ionic organic contarminants, such aC。pesticides，is well documented in the literature ( Sanchez-Fig.3 Freundlich plot for adoption of pesticides on bentonite and TTA-Camazano, 1994). The removal percentage of organoclaysbentonite( TTA-kaolin，TTA-montmorillonite and TTA-bentonite) to◆phenthoate on TTA- bentonite; Iphenthoate on bentonite; ▲acetochlor onremove phenthoate and acetochlor was positive relative to theTTA-bentonite; x acetochlor on bentoniteamount of cationic surfactant exchanged. As move from kaolin1991; Wang, 1997). This fact suggested that adsorption ofto bentonite, the cation exchange capacity increases in thenon- ionic pesticides phenthoate and acetochlor by organoclayorder of bentonite > montmorillonite > kaolin. The higher theis govemed mainly by hydrophobic interaction betweencation exchange capacity of clay the more will be theexchange of surfactant and resulting clay surface will be morepesticide molecules and hydrophobic surface of clay .hydrophobic. Adsorption capacities of organoclays inereased.2 Comparison of adsorbatesThe hydrophobic sorption characteristics of organicin the order of TT- Abentonite > TTA- montnorillonite > TTA-kaolin. To assess hydrophobicity of organoclay surface Pccompounds from water on organoclays are closely related totheir solute properties such as water solubility and octanol-( organic carbon content) is an important parameter. Po canwater partition coeffcient ( Zhu， 1997 ). To comparebe obtained from the following equation:adsorptive capacity of organoclay removal eficiency(R) isP2(%) = fa x 100,calculated by using the following equation:where, foe is the organic carbon mass fraction( carbon amountin TTA-bromide adsorbed on clay )/weight of clays( mg). TheR=(C。二Cx 100.Cmagnitude of P。 for different organoclays namely TTA-Where, Co is the initial concentration of pesticide and C。 iskaolin，TTA-montmoillonite and TTA-bentonite are 1.87,he equilibrium solution concentration. R is expressed i8.14 and 19.86, respectively. From Po data it is clear thatterms of percentage .higher adsorption of pesticides on TTA-bentonite is due to itsAs can be seen from Table 3, adsorption of phenthoatehighe中国煤化工is greater than acetochlor. The higher adsorption of2.4D.C N M H Gfactantsphenthoate by clay and organoclay compared with that ofLIeCt or cnain lengun o1 exchanged surfactant onacetochlor is probably due to the low water solubility( greateradsorption of pesticides on montmorillonite system is shown inhydrophobicity) of phenthoate. Phenthoate is less waterFig.4, Table 3 and Table 4, respectively. It can be seensoluble, more hydrophobic ( solubility = 10 mg/L) comparedfrom Fig. 4, Table 3 and Table 4 that as the chain length ofNo.5Adsorption of phenthoate and acetochlor from water by clays and organoclayscationic surfactant increases from ddecyltrimethyl ammoniumReferences:(C2) exchanged montmorillonite to cetyl pyridinium( C16 )exchanged montmorillonite adsorption of acetochlor increases.BaoS D, 2000. Soil and griculural chemistry analysis[ M]. Beijing: ChinaAgrcultural Press .The calculated K; value also increased with the chain lengthBoydS A. LeeI F, Morland M M, 1988a. Ateruting organie cntarinantof cationic surfactant increasing, which is atibuted to longermobility by soil mdification[J]. Nature, 333: 345- -347 .chain alkyl having higher hydrophobicity( Wang, 1997). ThisBoyd S A, Mortland M M, Chiou C T, 1988b. Sorption characteristics of organicalso indicated that hydrophobic interactions are playing ancompounds on hexadecyltimethylamumounium smetite[J]. Soil Sci Soe Am J,52: 652- -657.important role in adsorption.BoydS A, Mortland M M, Sun s et al., 1988e. Pentachlorphenol sopion by4.0 rorganoclays[J]. Clays Clay Miner, 36: 125- -130..5-HuangGQ, LiL, LiX G, 2002. Transference and tasformation of pesticide insoil: A review of mechanism and models[J]. Agro- Envinonental Protection,.021(4): 375-377..5Jaynes w F, Boyd s A, 1991. Clay mineral type and organice compound sorption旨2.0by hexadecyltrimethylammonium-exchanged clays[J]. Soil Sci Soc AmJ, 55:43- 48.1.5-Jin X, 2001. Adsorption or degradation of pesticides in soil and ecotoxicity toecosystem[J]. J Zunyi Normnal Cllege, 3(2): 89 -90.LeeJF, Crum J R, Boyed s A.1989. Enhanced retention of organic contaminantby soils exchanged with organie cations[J]. Environ Sei Technol, 23:一231365-1372.InCeMartin RJ, NG w J, 1997. The repealed exhaustion and chenical regneration ofactivated carbon[J]. Water Res, 21: 961- -965.Fig.4 Freundlich plot for adsorption of acetochlor on DTA- montnmilonite,Pimentel D, 1993. Environmental and economic efeee of reducing pesticide inTAnontoillonite and CP- monoiloniteagriculture[J]. Ecosystems and Environment, 46: 273- 288.◆CP-mnotillonite;■TTA- montilonite;▲DTAnontmoilloniteSancher-Camgzano M. Sanchez-Martion M J, 1994. Organo elays a adorbentsfor aziphosmethyl and dichlorvos in aqueous[J]. Water Air and SoilTable 4 Freundlich parauneters for ndsorption of acetochlor on organoclaysPlluion, 74: 19- -28.Adsorbate AdsorbentKp n Crrelation cofftcient,r Sancher Marin M J. Sanchex-Camazano M，1984. Aspects of asopion ofAcetochlor CP-motnmoillonite 2.78 1.230.9971azinphos -methyl by smectites[J]. J Agrie Food Chem, 32: 720- -72TTA- montmoilonite 1.34 1.180.9927Sanchea Martin M J, Sanche-Camozano M，1991 。Relationship between theDTA-nomtmoilonite_ 1.12 1.260.9977structure of organiphosphorus pesticides and adsorpion by soil cornponents[J]. SoilSei, 152: 283- -288ShengC Y, XuSH, BoydS A, 1996.3 Conclusionswater by hexadecytrimethylammonium- exchanged clays[J]. Water Res, 30:1483- -1489.The adsorption of phenthoate and acetochlor on claysThompson D C, MacDonald L M, Staznik B, 1992. Persistence of hexazinone andand organoclays has been studied. The cationic surfactantsmetsulfuron methyl in a mixed- wood/boreal foret lake[J]. J Agnic Foodwere exchanged onto the clay surface by ion- exchange,Chem, 40: 1444- -1449 .whereby the hydrophilic surface of claywas renderedWangX R，Wu s N, Li W S et al., 1997. Contaminated environmentremediation with orgaocay mineruls[J]. Environ Chem, 16(1): 1-14.hydrophobic and enhanced the adsorption capacity ofWeissmahr K w, Haderlein S B, Schwarzenbach R P, 1997. In siu inveligationorganoclays for pesticides compared with clays. Freundlichof 1 ,2-dibromethane sorption/desorption processes on clay mineral surface byequation gives the best fit to adsorption of phenthoate anddifuse relelctance infrared spectrocopy[J]. Environ Sei Technol, 26(2):acetochlor by clays and their organoclays over the entire329- 335.concentration range studied. Higher adsorption of phenthoateZhu L Z, li Y M, ZhangJ Y, 1997. Sorption of organobentonites lo some organicpllutants in water[J]. Environ Sei Technol, 31: 1407- - 1410.by clay and organoclay may be attributed to its low watersolubility compared with acetochlor. Among all the organoclay(Received for review September 28, 2003. Acceped October 20, 2003)studied TTA-bentonite has high adsorption capacity due to itshigher P。。 value. As the chain length of exchangedquantemary ammonium cations increases ，adsorptionincreases indicating that adsorptionf pesticides byorganoclay is predominantly governed by hydrophobicity of中国煤化工MYHCNMHG