Aquatic Redox Chemistry PDF
Preview Aquatic Redox Chemistry
g Aquatic Redox Chemistry s.or001 cw 1 | http://pubs.ak-2011-1071.f 1b mber 24, 20oi: 10.1021/ ed ept1 | S1 N on 2, 20 Aer Gb HIem Cpt MISe OF b): V We NIe ( Uat y D d bon Downloade Publicati In Aquatic Redox Chemistry; Tratnyek, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011. g s.or001 cw 1 | http://pubs.ak-2011-1071.f 1b mber 24, 20oi: 10.1021/ ed ept1 | S1 N on 2, 20 Aer Gb HIem Cpt MISe OF b): V We NIe ( Uat y D d bon Downloade Publicati In Aquatic Redox Chemistry; Tratnyek, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011. 1071 ACS SYMPOSIUM SERIES Aquatic Redox Chemistry Paul G. Tratnyek, Editor Oregon Health & Science University g s.or001 Timothy J. Grundl, Editor cw 1 | http://pubs.ak-2011-1071.f ESUbtneerivhfeaarrnsdi-tByKao.rfHlWsaUisdcnoievnresrliseni–itänMt,iTlEwübadiuinktgoeeern 1b mber 24, 20oi: 10.1021/ ed ept1 | S1 N on 2, 20 Aer Gb HIem Cpt MISe OF b): V We NIe ( y UDat Sponsored by the d bon ACSDivisionofEnvironmentalChemistry Downloade Publicati ACS Division of Geochemistry AmericanChemicalSociety,Washington,DC DistributedinprintbyOxfordUniversityPress,Inc. In Aquatic Redox Chemistry; Tratnyek, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011. LibraryofCongressCataloging-in-PublicationData Aquaticredoxchemistry/PaulG.Tratnyek,TimothyJ.Grundl,StefanB. g Haderlein,editor[s];sponsoredbytheACSDivisionofEnvironmentalChemistryandACS s.or001 DivisionofGeochemistry. cw 1 | http://pubs.ak-2011-1071.f G1IIr.SnocBGuplunNr.ddoc9ewums7na.8dbt-e-wi-0br-a-l-(8itCAoe4rgaC1rrr2aeSb-pco2shhn6yai5cmcrag2ople-no4r-te-seCfinueotrm-ne-Cngscroeeernssigseaersnes;.sds12ei0.ns7d.O1eI)xx.i.Tdaratitonny-erke,dPuacutiloGn.reIIa.cGtiorunn--dCl,oTnigmreostsheys.J3.,. mber 24, 201oi: 10.1021/b 1C9G5h55eB31m1-.41iIs99ItI-r7.-y.dH.7cV7a2..dA3Ae6rml7eei2nr0i,c1Sa1tnefCanheBm.iIcVa.lASmoceireitcya.nDCivhiesimonicaolfSGoecoiecthye.mDiisvtirsyi.onofEnvironmental ed 2011031438 ept1 | S1 N on 2, 20 Aer Gb HIem ThepaperusedinthispublicationmeetstheminimumrequirementsofAmericanNational Cpt Standard for Information Sciences—Permanence of Paper for Printed Library Materials, MISe ANSIZ39.48n1984. OF b): V We Copyright©2011AmericanChemicalSociety NIe ( y UDat DistributedinprintbyOxfordUniversityPress,Inc. d bon Downloade Publicati Ao$Df4lrl0tihv.R2eei5,UgDhp.Stlasun.sRCv$eeo0rspse.y,7rr5vMiegpAdhe.tr0RAp1eac9pgt2rie3osi,gasrUllapoSpawhiAdie.cdtRocfoeothppreuyinbiCntleigocrpanbytaeirloyigunohsnoetdrCotrnhleelapyatr,rpoapednrroucmevctiiCidtoteeendndtftebohryra,tsISanaelcpce.te,ioro2-fn2cps2haa1Rgp0eot7essreoifnwre1oeth0ooi8dsf bookispermittedonlyunderlicensefromACS.Directtheseandotherpermissionrequests toACSCopyrightOffice,PublicationsDivision,115516thStreet,N.W.,Washington,DC 20036. Thecitationoftradenamesand/ornamesofmanufacturersinthispublicationisnottobe construedasanendorsementorasapprovalbyACSofthecommercialproductsorservices referenced herein; nor should the mere reference herein to any drawing, specification, chemicalprocess, orotherdataberegardedasalicenseorasaconveyanceofanyright or permission to the holder, reader, or any other person or corporation, to manufacture, reproduce,use,orsellanypatentedinventionorcopyrightedworkthatmayinanywaybe relatedthereto. Registerednames,trademarks,etc.,usedinthispublication,evenwithout specificindicationthereof,arenottobeconsideredunprotectedbylaw. PRINTEDINTHEUNITEDSTATESOFAMERICA In Aquatic Redox Chemistry; Tratnyek, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011. Foreword The ACS Symposium Series was first published in 1974 to provide a mechanism for publishing symposia quickly in book form. The purpose of the series is to publish timely, comprehensive books developed from the ACS g sponsoredsymposiabasedoncurrentscientificresearch. Occasionally,booksare s.or001 developed from symposia sponsored by other organizations when the topic is of cw 1 | http://pubs.ak-2011-1071.f fpkoaerpeanepBrispnermftoeoparreeyrsiaatbtgeteoreeatexnhicdnelcgucodhtmeoedmpptruioesbhtblreiyesnthstaeiauvrdebfiooecocnoukcvse,e.trthahegeepbaroonopdkof;sooerdtihnteatrebsrlemesotatfyocbtoheneateadnudtdesideisntocreepv.riSoeovwmieddee 1b mber 24, 20oi: 10.1021/ caaodnmddempdr.aenDhuersnacsfrtisivpeotnsfecashrsea.pptrWeerpshaearnreedappienpercro-aprmervieairteaew-,reeodavdpeyrrvifoioerrwmtoaofitr.nainltarcocdeupcttaonrcyecohrarpetjeercstioarne, ed ept1 | As a rule, only original research papers and original review papers are S1 N on 2, 20 included in the volumes. Verbatim reproductions of previous published papers Aer arenotaccepted. Gb HIem Cpt MISe OF b): ACSBooksDepartment V We NIe ( Uat y D d bon Downloade Publicati In Aquatic Redox Chemistry; Tratnyek, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011. Chapter 1 Introduction to Aquatic Redox Chemistry Timothy J. Grundl,1,* Stefan Haderlein,2 James T. Nurmi,3 and Paul G. Tratnyek3 g s.or001 1GeosciencesDepartmentandSchoolofFreshwaterSciences,Universityof mber 24, 2011 | http://pubs.acoi: 10.1021/bk-2011-1071.ch 32DCievnistieornfoorfEAnWpvpSiilsricceoiodennnmGscieeennoU-tsMancliDi*ievlagwn-enr7craud2esun0isBtkd,7yielE6,o@e,Bbm,TueeMorüwalhvibemlacewinrur.eadtglodau-enKrukn,eSaOery,lsRsWteU9mI7n5s0i,v30eO26r0rs1eitgäotnTHübeainltghen&, ed Sept11 | n 20 Oxidation-reduction (redox) reactions are among the most AN oer 2, important and interesting chemical reactions that occur in Gb aquatic environmental systems, including soils, sediments, CHIptem aquifers, rivers, lakes, and water treatment systems. Redox MISe reactionsarecentraltomajorelementcycling,tomanysorption OF eb): processes, to trace element mobility and toxicity, to most V W NIe ( remediationschemes,andtolifeitself. Overthepast20years,a Uat greatdealofresearchhasbeendoneinpursuitofprocess-level y D d bon understanding aquatic redox chemistry, but the field is only deati beginning to converge around a unified body of knowledge. ac wnloPubli Thischapterprovidesaverybroadoverviewofthestateofthis Do convergence, including clarification of key terminology, some relatively novel examples of core thermodynamic concepts (involving redox ladders and Eh-pH diagrams), and some historical perspective on the persistent challenges of how to characterize redox intensity and capacity of real, complex, environmental materials. Finally, the chapter attempts to encourage further convergence among the many facets of aquatic redox chemistry by briefly reviewing major themes in thisvolumeandseveralpastvolumesthatoverlappartiallywith this scope. ©2011AmericanChemicalSociety In Aquatic Redox Chemistry; Tratnyek, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011. Definitions and Scope Historically, the terms oxidation and reduction arose from experimental observations: oxidationreactionsconsumedO byincorporatingOintoproducts 2 and reduction reactions reduced the mass or volume of products by expelling O (1). Chlorinesubstitutionisequivalenttooxygeninthiscontext,sochlorination is oxidation and dechlorination is reduction. A similarly empirical definition of reduction is that it usually involves incorporation of hydrogen, and, therefore, oxidation can be regarded as dehydrogenation (e.g., dehydrogenase enzymes catalyzeoxidation). More rigorously, oxidation-reduction (redox) reactions are commonly understood to occur by the exchange of electrons between reacting chemical g species. Electronsarelost(ordonated)inoxidation,andgained(oraccepted)in s.or001 reduction. Oxidation of a species is caused by an oxidizing agent (or oxidant), mber 24, 2011 | http://pubs.acoi: 10.1021/bk-2011-1071.ch ifwbgeesrllaeoheesnomccieexcttTrrrhicaoordheolnniaeazndcscdetcecertdeeafiien)opdnpn.sntestisisffittwieynoheriinaolttsehvsifpocec(eatnerhcspo.riegefirnamo.dsc,rtueiotcd(hcnaaaeien-nldfisLdgsenppqeieaiteuwcsigcoaieiifittnsenhecssmteftr((doooe(oer2bdrmfi)yem,rnloea)iorrd,tneseiurodtdecgnupdtrescaeuonenfrx(eedpttr)r)hcoa,e.eoslnwendcBSshcee,ieirsfimcöpbnhcntuisiilstttdateicroenodaldnonyntat,shmtbatereheelorslade.deetiuxenlJacelt)u)ertc.iesntoaTrtdbnnohaeadnesdrsseemlafs(adrcuatooitnoldmretdnes-r ed Sept11 | allowsforredoxreactionsthatoccurbyatom-transferaswellaselectrontransfer n 20 mechanisms. While often ignored, the role of atom-transfer mechanisms can be AN oer 2, important,particularlyinredoxreactionsinvolvingorganiccompounds. HIGemb Redoxreactions,definedinclusiv,arecentraltomanypriorityandemerging Cpt areas of research in the aquatic sciences. This scope includes all aspects OF MIeb): Se aoqfutahteica(qi.uea.,ticaqsuceioeunsc)esa:spneocttsjuosftetnhvoisreonimnvenotlavlinpgrotcheessheysdirnostphheeraet,mbouspthaelrseo, V W NIe ( lithosphere, biosphere, etc. (3). As a field of study, aquatic redox chemistry y UDat also has multidisciplinary roots (spanning mineralogy to microbiology) and d bon interdisciplinary applications (e.g., in removal of contaminants from water, adecati sediment,orsoil). Despiteitscross-cuttingappeal,however,verylittlepriorwork wnloPubli hasusedaquaticredoxchemistryasaniche-definingtheme. Themainexception Do tothisappearstobeseveralpublicationsbyDonaldMacalady(e.g,(4)),whichis convenient and appropriate—and not entirely coincidental—given the origins of thisvolume(seePreface). Core Concepts Any redox reaction can be formulated as the sum of half-reactions for oxidation of the reductant and reduction of the oxidant. The overall free energy ofaredoxreactionisdeterminedbythecontributinghalf-reactions,andthefree energy of each half-reaction depends on the reactants, products, and solution conditions. At a common set of standard conditions, the free energies—or correspondingredoxpotentials—canbeusedtocomparetherelativestrengthof oxidantsandreductantsandtherebydeterminethethermodynamicfavorabilityof 2 In Aquatic Redox Chemistry; Tratnyek, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011. the overall reaction between any particular combination of half-reactions. This type of analysis is well suited for a variety of graphical representations, the two most common of which are redox ladders and Eh-pH (or Pourbaix) diagrams. Thefundamentalsofconstructingthesediagramsarepresentedinnumeroustexts on aquatic chemistry (3, 5, 6), geochemistry (7, 8), and other fields (9). Some newdatathatcouldbeusedinconstructingsuchdiagramsaregiveninChapters 2, 3and4ofthisvolume. Figure1isaredoxladderthatsummarizesadiverserangeofredoxcouples thataresignificantinaquaticredoxchemistry. Thetopofthefigureisboundedby severalstrongoxidants(e.g.,hypochlorite,monochloramine,andozone)thatare capable of oxidizing essentially any compound found in aquatic environments. Similarly, the bottom of the figure is bounded by strong reductants (zerovalent g mber 24, 2011 | http://pubs.acs.oroi: 10.1021/bk-2011-1071.ch001 mewomesTunnxhaeacvgiettjdhieiaornaoTrlroa,snevhsn)ettseeesmroirtrerhaamfioedtlarhnlrnetiwsetrntsdaaeyaa.rndictlseaedoocerTrxlcuezluthaesricmnpnceesooetsaacnnredttbomdalponiroieneteefxianrooCidFsctdfniichissassgreyatcne.eoppsutdnftsttsueiet1smnmcarengsinoidanssd2s.tpgiutdrnHarraoeeneayqCscvddlspueohuessoa1tacpnste1cptieetdhacitcsoanelisfotlrte(yolsrtTys1ihs,tEftt8ieaehabs.AnmlaeuvlynPtorodasteclruh)uodoetemtoomsyhuifxedelpot,mreoicfamsuotinttecnuhardnrodtpeoenzlfblefsegoyoistrraacuodmlbthnvehilmdatlaoteihltrteeriyeimntnfnaobtefibiarnam-oqembsellueiaddisaststamtbehooildycesff. ed theseTEAPs. TheTEAPthatprovidesthemostenergyrecovery(thoseatthetop Sept11 | oftheredoxladder)favorsthetypesofmicroorganismsthatutilizethatprocess. AN on er 2, 20 Alasddtherebmeocostmfeasvomraobsltefaevleocrtarbolne.aTccheipstporroicsedssepclaenterde,stuhletinnesxetqTuEenAtiPalopnrothgerersesdioonx Gb HIem (in space or time) from TEAPs higher on the redox ladder to those below. This MICSept basicunderstandingofTEAPsandtheireffectonaquaticredoxchemistryiswell OF eb): established, but a detailed understanding of the fundamental controls on these V W processesisstillemerging,asdiscussedinChapter4ofthisvolume. NIe ( Once environmental conditions are established, however, many important Uat y D redoxreactionsproceedwithoutfurthermediationbyorganisms. Thesereactions ded bation are considered to be abiotic when it is no longer practical (or possible) to wnloaPublic hlianlkf-rtehaecmtiotnos arnepyrepsaerntitceudlairnbtihoelo2gnidc-a6lthacctoilvuimtyns(4,in1F0)ig.. T1hucsa,nmbaenymoorfethoer Do less a/biotic—depending on conditions—and the overall favorability of these processesisnotnecessarilyaffectedbymicrobiologicalmediation(i.e.,theredox ladder applies either way). However, systems where biotic and abiotic controls on contaminant fate are closely coupled currently are frontier areas of research (e.g., Chapters19-24). The 2nd-6th columns in Fig. 1 arranged so they represent families of major redoxactivespeciesinorderfromrelativelyoxidized(andoxidizing)torelatively reduced (and reducing). Thus, the second column includes the reactive oxygen species that arise mostly by photochemical processes in natural waters. The chemistry of some of these processes is described in Chapters 8 and 9. Other oxidants that arise mainly in water treatment processes are not shown because they plot above the scale used in the figure, but two are discussed in later: 3 In Aquatic Redox Chemistry; Tratnyek, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011. g s.or001 mber 24, 2011 | http://pubs.acoi: 10.1021/bk-2011-1071.ch schaFotwieggnuorareriee1s.fooRrfeesdpnoevxcirioleasndmtdheeanrttsaaulrmeaqmimuaaprtoiizcritnacgonntrdeinpitriaeoqsnuesna(ttpaicHticv7he,ermmediosostxtryoc.tohTuehprelseposolfutoetrenstsiiaaxtls1 n Septe2011 | d mmiMcr)o.bTiaElAmPestaabreoltiesrmm.iFnaolretlheectorrognaanciccecpotnintagmpirnoacnetscseastetghoartyd,ethfieneuprepgeirmgersooufp GAN ober 2, ofthpeotleonwteiarlsse(tre(gdrseyemnbsoylms)boshlso)wasremrueldtiu-eclteiocntropnotceonutipallessftoorstthaebfilersstpeelceicetsroannd HIem transfer. Thechlorinatedaliphaticorganiccontaminantsaregivenbytheirusual Cpt MISe abbreviations;nitroaromaticsincludenitrobenzene(NB),4-chloro-nitrobenzene OF eb): (4ClNB),and2,4,6-trinitrotoluene(TNT).AzBisazobenzeneandANisaniline. V W Theelectronshuttlecategoryincludesmodelquinones(onlyoxidizedforms UNIate ( listed),anthraquinonedisulfonate(AQDS)andanthraquinonecarboxylicacid d by on D (AQCA).Thetwovaluesfornaturalorganicmatter(NOM)aredescribedin deati Chapter7. Inthelastcolumn,GR-1referstocarbonatesubstitutedgreenrust. ac Downlo Publi Datafortheatnhdisafigvuarreiewtyeorefootbhtearinseodurfrcoems,Ceshpaepctiearllsy2(,73,,9a,n1d1,2122i)n. thisvolume hydroxylradical(fromphotoactivationwithTiO ,Chapter10)andsulfateradical 2 (frompersulfate,Chapter12). The 3rd and 4th columns of Fig. 1 are major classes of redox-active contaminants: the metal oxyanions, chlorinated aliphatic hydrocarbons (CACs), and nitro aromatic compounds (NACs). For the metal oxyanions, the oxidized form is the most mobile and toxic, and reduction results in sequestration of insoluble products and lower risk (see Chapters 21, 22); for CACs and NACs, reduction of these compounds may produce more or less toxic end products depending on the latter steps of reaction (see Chapters 19, 20, 23, 24). In the column for organic contaminants, another important distinction is illustrated between the overall reduction potentials (upper, red symbols) and first electron potentials (lower, green symbols). The overall reduction potentials are always 4 In Aquatic Redox Chemistry; Tratnyek, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011. highlyfavorable,butthefirstelectrontransferismuchlessfavorableandthisstep isusuallyratedetermining. The last two columns in Fig. 1 show organic electron transfer mediators (shuttles), especially those that might be associated with natural organic matter (NOM), and some of the many redox couples involving species of iron. These two groups can be regarded as bulk electron donors, or as mediators of electron transferfromotherbulkdonors. Theroleofelectronshuttlesisdiscussedfurther below,andinseveralotherchaptersinthisvolume,especiallyChapter6. A major limitation of redox ladders such as the one shown in Fig. 1 is that all the potentials are shown for a common set of conditions, usually “standard” environmental conditions. The most important of these conditions is pH, which stronglyeffectstheredoxreactionsofsomespecies. Theseeffectsarerepresented g mber 24, 2011 | http://pubs.acs.oroi: 10.1021/bk-2011-1071.ch001 wOprfTbeaayhhndmrieEtustiircoalhecielp-aaoldpyrsmo—Hbjdfbuye(stigohptnalareranoboptynfiitelaoeoFi-mnntpieysaHiIsItlfisheis,ateodpaorlwbedrhsclssyPteiadefotbiohrsunioralraqittbabthuyatnoehiivnxfieopeo)rerognedlpxdaesiHinased(gniQf5icrczo,aHeecrwmdo2oi−mirsffto),hopFnosrotu,evmhuIcFeIesnhriagmdottah.:fsopee2jsHtuh.rtgasgecb.hnl,oeeoogmmlxnweoaemowosmdf(otQep5hmnll.eHeoqp—ssuraohtipnndroedeouwrlncheQnetva−,bipa)njensuwitFgnnpiiloggloHlt.tn’hbs2esoee;.. ed Sept11 | n 20 AN oer 2, Gb HIem Cpt MISe OF eb): V W NIe ( Uat y D d bon deati ac wnloPubli Do Figure2. ComparisonoftheEh-pHstabilitydiagramsforjuglone(amodel quinoneandorganicelectronshuttle,QH)vs. iron(asabulkelectrondonor). Thermodynamic data for juglone obtained from (1). Total aqueous iron concentrationassumedtobe10-6M. 5 In Aquatic Redox Chemistry; Tratnyek, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
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