土壤化學(xué)英文

土壤化學(xué)英文課件第1頁，共63頁，2023年，2月20日，星期六SoilpH第2頁，共63頁，2023年，2月20日，星期六ThepHofasoilappliestotheH+ionconcentrationinthesolutionpresentinsoilporeswhichisindynamicequilibriumwiththepredominantlynegativelychargedsurfacesofthesoilparticles.

土壤PH是指土壤孔隙溶液中的氫離子濃度，它與土壤顆粒以負(fù)電荷為主的表面達(dá)到動態(tài)平衡。2.2.1SoilpH土壤PH第3頁，共63頁，2023年，2月20日，星期六Hydrogenionsarestronglyattractedtothesurfacenegativecharges,andtheyhavethepowertoreplacemostothercations.氫離子被吸附在表面負(fù)電荷,能夠置換大多數(shù)陽離子.ThediffuselayerclosetoanegativelychargedsurfacehasahigherconcentrationofH+ionsthanthebulksoilsolution.接近負(fù)電荷層的擴(kuò)散層具有比土壤溶液更高的氫離子濃度.Whenthesoilsolutionisdiluted,thediffuselayerexpands,causingthepHofthebulksolutiontoincrease.

當(dāng)土壤溶液被稀釋時,擴(kuò)散層會擴(kuò)大,導(dǎo)致土壤溶液的PH升高。第4頁，共63頁，2023年，2月20日，星期六ThishasimportantimplicationsforthemeasurementofsoilpHinthelaboratory.Thisnormallyinvolvesmixingdrysoilwith2-2.5timesitsweightofwater,shakingandthenmeasuringthepHinthesupernatantsolutionafter30minutes.

ThepHvalueobtainedisabout1to1.5unitshigherthanthatofthesoilsolutionneartothesolidsurfaceswherethereactionstakeplace.

第5頁，共63頁，2023年，2月20日，星期六ThisdilutioneffectisusuallyovercomebymeasuringthepHinasuspensionofsoilinasolutionofaneutralsalt,suchasCaCl2orKCl.Normally,pHismeasuredinsuspensionsofsoilwithdistilledwaterandwithadilutesalt.ItisusuallyassumedthatthepHvaluegivenisfordistilledwaterunlessotherwisestated.第6頁，共63頁，2023年，2月20日，星期六SoilpHisaffectedbythechangesinredoxpotentialwhichoccurinsoilsthatbecomewaterloggedperiodically.ReducingconditionsgenerallycauseapHincrease,andoxidationbringsaboutadecrease.Variationsofupto2unitscanoccuroverayearingleysoilspronetowaterlogging.Oxidationofpyrite(FeS2)inasoilparentmaterialcancauseamarkeddecreaseinpH.第7頁，共63頁，2023年，2月20日，星期六SoilshaveseveralmechanismswhichservetobufferpHtovaryingextents,includinghydroxyaluminiumions,CO2,carbonates

andcationexchangereactions.However,evenwiththesebufferingmechanisms,soilpHdiffers

significantlyduetolocalizedvariationswithinthesoil.Diurnalfluctuations（日變化）ofmorethan1unitmayoccur,aswellasvariationsindifferentpartsofafield.第8頁，共63頁，2023年，2月20日，星期六SoilpHusuallyincreaseswithdepthinhumidregionswherebasesareleacheddowntheprofile,andcandecreasewithdepthinaridenvironmentswhereevaporationcausessaltstoaccumulateinthesurfacehorizon.Asaresultofthevariationswhichcanoccur,itisnotpracticabletoexpresssoilpHmeasurementsmoreaccuratelythantothenearest0.2divisionofaunit.第9頁，共63頁，2023年，2月20日，星期六Ingeneral,heavymetalcationsaremostmobileunderacidconditions,andincreasingthepHbylimingusuallyreducestheirbio-availability.However,molybdateanionsbecomemoreavailablewithincreasingpH.SoilsgenerallyhavepHvalueswithintherange4-8.5,owingtothebufferingbyAlatthelowerendandbyCaCO3attheupperendoftherange.第10頁，共63頁，2023年，2月20日，星期六BradystatesthatthenormalpHis5-7insoilsofhumidregions,andpH7-9inthesoilsofaridregions.However,themaximumrangeofpHconditionsfoundinsoilsis2-10.5.Inatypicaltemperateenvironment,suchastheUK,soilsnormallyhaveapHintherange4-8.TheoptimumpHformostarablecropsis6.5onmineralsoilsand5.5onpeatysoils.SoilpHcanberaisedbyliming.第11頁，共63頁，2023年，2月20日，星期六2Soilorganicmatter第12頁，共63頁，2023年，2月20日，星期六Themainfeaturewhichdistinguishessoilfromregolith(decomposedrock風(fēng)化層,土被)isthepresenceoflivingorganisms,organicdebrisandhumus.Allsoilscontainorganicmatter,althoughtheamountandtypemayvaryconsiderably.Colloidalsoilorganicmatterhasamajorinfluenceonthechemicalpropertiesofsoils,andcanbedividedinto'non-humic'and'humic'substances.Thenon-humicsubstancescompriseunalteredbiochemicalssuchasaminoacids,carbohydrates,organicacids,fatsandwaxesthathavenotchangedfromtheforminwhichtheyweresynthesisedbylivingorganisms.第13頁，共63頁，2023年，2月20日，星期六Humicsubstancesareaseriesofacidic,yellowtoblackcolouredpolyelectrolytes（高分子電解質(zhì)）ofmoderatelyhighmolecularweight.Theyareformedbysecondarysynthesisreactionsinvolvingmicroorganismsandhavecharacteristicswhicharedissimilartoanycompoundsinlivingorganisms.Theyhaveawidevarietyoffunctionalgroups,includingcarboxyl(羧基),phenolichydroxyl(酚式羥基),carbonyl(羰基),esterandpossiblyquinone(醌)andmethoxygroups(甲氧基

)[5,6].Whilepredominantlycomposedofhumicsubstances,soilhumusalsocontainssomebiochemicalsboundtothehumicpolymers.Theelementalcompositionofhumusistypically(onanash-freebasis):44-53%C,3.6-5.4%H,1.8-3.6%Nand40.2-47%O[7].第14頁，共63頁，2023年，2月20日，星期六Traditionally,humushasbeenseparatedinthelaboratoryintothreefractions:humin,whichisinsolubleinalkali,humicacid,whichissolubleinalkaliandinsolubleinacidandfulvicacid,whichissolubleinbothacidandalkali.Thesesubstancescannotberegardedasdistinctlydifferent,butmerelyaspartofacontinuumofcompoundsvaryinginmolecularweight,Ccontent,Ocontent,acidityandcationexchangecapacity(CEC)intheorder:humin>humicacid>fulvicacid,withNcontentdecreasingthroughthesamesequence[6].第15頁，共63頁，2023年，2月20日，星期六LessthanhalftheCinhumicacidsisaromatic;muchoftheremainderoccursasunsaturatedaliphaticchainscontainingcarboxylgroupswhichalsocontributemostofthetitratableacidity.Humicacidshavemolecularweightsintherange20000-100000,andthefulvicacidfractiongenerallyconsistsoflower-molecular-weightcompounds.

Apartfromcontainingupto10%polysaccharides,thegeneralcompositionoffulvicacidissimilartothatofhumicacid.

Thefulvicacidfractionmaycontainprecursorsanddegradationproductsofthehumicacidfraction.

Huminsareconsideredtobehumicacid-typecompoundsadsorbedontominerals[7].第16頁，共63頁，2023年，2月20日，星期六Methodsusedtodeterminetheorganicmattercontentofsoilsinclude（1）eitherthepercentagelossinweightafterignitioninafurnaceat375oCfor16h.(2)ortheoxidationofCbyaciddichromatefollowedbythetitrationofexcessdichromate[8].Organicmattercontainsabout58-60%organicC(%orgCx1.67=%OM).Withinthesoilprofile,theorganicmattercontentisalwayshighestinthesurfacehorizon,butpodzols(灰化土)andvertisols(變性土)mayhavesometrans-locatedhumicmateriallowerdowntheprofile.2008.10-9第17頁，共63頁，2023年，2月20日，星期六3Clayminerals第18頁，共63頁，2023年，2月20日，星期六2.2.3ClaymineralsClaymineralsareproductsofrockweatheringandhavemarkedeffectsonboththephysicalandchemicalpropertiesofthesoils.

Theircontributiontosoilchemicalpropertiesresultsfromtheircomparatively

largesurfacearea

andpermanent

surfacenegativecharge.Thesoiltexturalclassisdependentonthepercentagesofclay,siltandsand-sizedparticles.第19頁，共63頁，2023年，2月20日，星期六Theclayfractioncomprisesthedispersedmineralsofdiameterlessthan2um(0.002mm).Inmostcases,thisspecifically

appliestothemineralogicallydistinctgroupofclayminerals,althoughitcanalsoincludefinelygroundparticlesofotherminerals.Claymineralsaresheetsilicate硅酸鹽(orphyllosilicate頁硅酸鹽)structuresformedmostcommonlyfromcombinationsofAl-OHoctahedra八面體(gibbsitesheet水鋁片)andSi-Otetrahedra四面體(silicasheet硅片);第20頁，共63頁，2023年，2月20日，星期六inaddition,abrucitesheet(鎂片),comprisingMgandFepartiallysubstitutedforAlinthegibbsitesheet,isfoundinalotofminerals.Themostcommontypesofclaymineralsinclude:thekaolinites(高嶺石)comprisingonesilicasheetandonegibbsitesheet(水鋁片)withaSi:Alratioof1:1;theillites(伊利石)comprisingtwosilicasheetsandonegibbsitesheetwithaSi:Alratioof2:1;andthesmectites(alsocalledmontmorillonites；蒙脫石)withtwosilicasheetsandonegibbsitesheet,andanSi:Alratioof2:1.第21頁，共63頁，2023年，2月20日，星期六Inallthemineralsexceptkaolinites,isomorphoussubstitutionwithintheminerallattice（晶格）givesrisetoanetnegativechargeonthesurfaceofthemineral.ThisiscausedbytrivalentAlsubstitutingfortetravalentSianddivalentMgsubstitutingforAl.Inkaolinitethe1:1unitsaretightlybondedtogetherbyhydrogenbondsbetweenhydrogenandoxygenatomsofadjacentlamellae(薄片).第22頁，共63頁，2023年，2月20日，星期六Smectites(蒙脫石)havethelargestspecificsurfaces(700-800m2/g)owingtorelativelyweakinterlayer(夾層)bondingallowingsoilsolutiontopenetratebetweentheunits.TheCECisalsoquitehigh(80-120cmol/kg)asaresultofthislargespecificsurface.Vermiculites(蛭石)haveanintermediatespecificsurface(300-500m2/g)andahighCEC(100-150cmol/kg)[7].第23頁，共63頁，2023年，2月20日，星期六Thespecificsurfaceofthesemineralsisrelativelysmall(5-100m2/g)incomparisonwiththeotherclayminerals,andtheircationexchangecapacityislow(3-20cmol/kg)becauseverylittleisomorphoussubstitutionhasoccurred.Illitemineralshavethe2:1unitsbondedbyKions,andthespecificsurfaceandCECarelargerthanthoseofkaoliniteminerals(100200m2/gand10-40cmol/kg).第24頁，共63頁，2023年，2月20日，星期六

Claysrarelyexistinpureforminsoils;theyusuallyhavehumiccolloidsandhydrousoxide

precipitate（沉淀物）

linkedtothem.Thecombinedorgano-mineral

colloidalcomplex

playsaveryimportantroleincontrollingtheconcentrationsofionsinthesoilsolution.第25頁，共63頁，2023年，2月20日，星期六4Oxidationandreductioninsoils

第26頁，共63頁，2023年，2月20日，星期六2.2.4Oxidationandreductioninsoils

Soilsaresubjectto

variationsinoxidationreduction(redox)statusandthismainlyaffectstheelementsC,N,O,S,FeandMn,althoughAg,As,Cr,Cu,HgandPbcanalsobeaffected[13].

Redoxequilibriaarecontrolledbytheaqueousfree-electronactivity,whichcanbeexpressedaseitherthe

pEvalue(thenegativelogoftheelectronactivity)orEh(themillivoltdifferenceinpotentialbetweenaPtelectrodeandthestandardHelectrode)[14].

ThepEunithastheadvantageofallowingelectronstobetreatedlikeotherreactantsorproducts,allowingbothchemicalandelectrochemicalequilibriatobeexpressedwiththesingleequilibriumconstant.TheconversionfactorfortheunitsisEh(mV)=59.2pE[14].第27頁，共63頁，2023年，2月20日，星期六LargepositivevaluesofpE(orEh)favortheexistenceofoxidisedspecies,andlowornegativevaluesofpE(orEh)areassociatedwithreducedspecies[15].Redoxpotential(Eh)ismeasuredusingaPtelectrodeandacalomelelectrode（甘汞）connectedtoamillivoltmeter,butitisdifficulttogetaccuratereadings.However,oxydicsoilconditionsusuallygivevaluesintherange+300~+800mV(pE5.1-13.5)butmostlyfrom+400~+600mv(pE6.8-10.1).Anaerobic(厭氧的)soilshavevaluesfrom+118~-414mv(pE+2--7)[15,16].第28頁，共63頁，2023年，2月20日，星期六MeasurementsofEhcanbeusedtodeterminewhetheroxidisingorreducingconditionsexist,butfrequentlysoilcoloursprovideagoodindicationofredoxstatus.Redandbrowncoloursindicateoxicconditions,andblue-greenandgreycoloursindicategleyedsoils（潛育土）.However,strong-colouredparentmaterialsmaymaskthesecolourchangesinsomesoils.RedoxreactionsinsoilsarefrequentlyslowbutarecatalysedbysoilmicroorganismswhichareabletoliveoverthefullrangeofpHandpEconditionsnormallyfoundinsoils(pE+12.7to-6.0andpH3-10)[15].

08/04/1第29頁，共63頁，2023年，2月20日，星期六Respirationbymicroorganisms,mesofauna（土棲中型動物區(qū)系100um~2mm）andplantrootsconsumesarelativelylargeamountofoxygen.Iftheoxygeninazoneofsoilbecomesexhausted,ashappenswithwaterlogging（漬水）orcompaction（壓實）,microorganismswithanaerobicrespirationpredominateandsusceptible（活性的）elements(Mn,Cr,Hg,Fe,CuandMo)aregraduallyreduced[15,16].第30頁，共63頁，2023年，2月20日，星期六WhenFe(III)isreducedtoFe(Il)thereisaslightpHincreaseinacidsoilsandaslightdecreaseinalkalinesoils.MostwaterloggedsoilshaveapHof6.7-7.2[16].WhenthepEbeginstorise,Fe(II)isoxidisedinpreferencetoMn(II).OxidesofbothFeandMncanbedissolvedbyeitherdecreasingpHorEh,butMnoxidesaremoreeasilydissolvedthanFeoxides.WithincreasingEhandpH,FeoxidesprecipitatebeforethoseofMn.SmallchangesinEhorpHcangiverisetoeitherextensivedissolutionorprecipitationofFeoxides[18].

第31頁，共63頁，2023年，2月20日，星期六

FeandMnoxidesoccuras

(i)coatingsonsoilparticleswheretheyareintimatelymixedwithclays,(ii)fillingsinvoids(空隙)and(iii)concentricnodules.PrecipitationofFeisinitiallyintheformofgelatinous（凝膠狀的）hydratedFeoxide(Ferrihydrite,Fe5(O4H3)3水鐵礦)whichgraduallydehydrateswithageingtomorestableforms,suchasgoethite針鐵礦[2,18].Ferrihydriteco-precipitatesotherions,includingCu,Mn,Mo,Ni,V(釩)

andZn,andactsasascavenger（凈化劑）adsorbingbothheavymetalcationsandanions,suchasHPO42+andAsO43-[18].第32頁，共63頁，2023年，2月20日，星期六Theseandotherheavymetalsareaffectedbytheindirecteffectsofreducingconditions.Sulphate（硫酸鹽）ionsarereducedtosulphide（硫化物）belowpE-2.0,whichcanleadtotheprecipitationofmetalsulphides,suchasFeS2,HgS,CdS,CuS,MnSandZnS[15].WhenreducingconditionscausethedissolutionofhydrousMnandFeoxides,theirco-precipitatedmetalsarereleasedintothesoilsolution[13].Specialisedbacteria,suchasThiobacillusferrooxidansandMetallo-geniumspp.arealsoinvolvedintheprecipitationofFeandMnhydrousoxides,respectively[16].April8,2008第33頁，共63頁，2023年，2月20日，星期六Apartfromferrihydrite,themorestablemineralformsofFeoxideinsoilsinclude:goethite(a-FeOOH，針鐵礦)whichisthemostcommonFeoxideintemperate,subtropicalandtropicalsoils,haematite(a-Fe2O3，赤鐵礦)whichisfoundmainlyintropicalsoils第34頁，共63頁，2023年，2月20日，星期六ThemineralformsofhydrousMnoxidesinsoilsare:birnessite水鈉錳礦,hollandite錳鋇礦,lithiophorite鋰硬錳礦[19].第35頁，共63頁，2023年，2月20日，星期六2.3TheadsorptionofmetalionsbysoilsandtheirconstituentsThemostimportantchemicalprocessesaffectingthebehaviourandbio-availabilityofmetalsinsoilsarethoseconcernedwiththeadsorptionofmetalsfromtheliquidphaseontothesolidphase.第36頁，共63頁，2023年，2月20日，星期六Theseprocessescontroltheconcentrationsofmetalionsandcomplexesinthesoilsolutionandthusexertamajorinfluenceontheiruptakebyplantroots.Severaldifferentmechanismscanbeinvolvedintheadsorptionofmetalions,includingcationexchange(ornon-specificadsorption),specificadsorption,organiccomplexationandco-precipitation.第37頁，共63頁，2023年，2月20日，星期六However,althoughtheextentofadsorptioncanbemeasuredandisotherms（等溫線）calculateditisfrequentlydifficulttobepreciseaboutwhichparticularprocessisresponsiblefortheretention（保持力）ofmetalsinanyparticularsoil.Inordertoprovideanintroductiontotheadsorptionmechanismsreferredtointhefollowingchapters,thedifferentadsorptionmechanismswillbediscussedbriefly.第38頁，共63頁，2023年，2月20日，星期六2.3.1CationexchangeMostheavymetals(withcertainexceptions,includingthemetalloidsAs,Sb銻andSeandthemetalsMoandV釩)existmainlyascationsinthesoilsolution,andtheiradsorptionthereforedependsonthedensityofnegativechargesonthesurfacesofthesoilcolloids.Inordertomaintainelectroneutrality,thesurfacenegativechargeisbalancedbyanequalquantityofoppositelychargedcounter-ions（抗衡離子）.Ionexchangereferstotheexchangebetweenthecounter-ionsbalancingthesurfacechargeonthecolloidsandtheionsinthesoilsolution[19].第39頁，共63頁，2023年，2月20日，星期六Ithasthefollowingcharacteristics:itisreversible（可逆性）,diffusioncontrolled（質(zhì)量作用定律）,stoichiometric（等價離子交換）and,inmostcases,thereissomeselectivityorpreferenceforoneionoveranotherbytheadsorbent[20].Thisselectivitygivesrisetoareplacingorderamongstthecations,determinedbytheirvalency（化合價）anddegreeofhydration.Thehigherthevalencyofanion,thegreateritsreplacingpower(H+ionsbehavelikepolyvalentions)andthegreaterthedegreeofhydration,theloweritsreplacingpower,otherthingsbeingequal.

第40頁，共63頁，2023年，2月20日，星期六Adsorptionbycationexchangecanalsobedescribedastheformationofouter-spherecomplexeswiththesurfacefunctionalgroupstowhichtheyareboundelectrostatically[15].TheCECofmineralsoilscanrangefromafewto60meq/100g,butinorganicsoilsitmayexceed200meq/100g[21].TheCECofsoilsisfarlargerthantheiranionexchangecapacity,owingtothegreaternumberofnegativechargesonthecolloidsurfaces.Thesenegativechargesareoftwotypes:(i)permanentcharges(independentofpH)duetoisomorphoussubstitution（同晶形取代）ofmajorelementionswithin2:1claymineralsandedgeeffectsonclayminerals;(ii)pH-dependentchargesonhumuspolymersandhydrousoxides.第41頁，共63頁，2023年，2月20日，星期六Thelatterareduetothedissociationofprotonsfromcarboxyl（羧基）andphenolichydroxylgroups（酚式羥基）onhumicpolymersandOandOHgroupsonthesurfaceofhydrousoxidesandtheedgesofkaolinite（高嶺石）crystals.

第42頁，共63頁，2023年，2月20日，星期六ThereisapHatwhichthesematerialshaveasurfacechargeofzero,referredtoasthePZC(pointofzerocharge電荷零點：膠體表面凈電荷為零時溶液的pH值。電荷零點可因?qū)Ｐ晕降鹊挠绊懚史枪潭ㄖ怠?.ThePZCforfreshlydepositedferrihydriteisaroundpH8.5,andthatoffreshlydepositedAloxidesispH8.3[12].Consequently,thesehydrousoxidescontributelittletotheCECofsoilsbelowpH8.第43頁，共63頁，2023年，2月20日，星期六Inhumicpolymers,carboxylgroupshavepK(dissociationconstant解離常數(shù)/不穩(wěn)定常數(shù))valuesof3-5,whereasphenolicgroups(苯酚的)havevaluesover7.SomebasicNH3groupsexistatpHvaluesbelow3.AlloftheadsorptivesitesonthehumiccolloidsarethuspHdependent,withCECvaluesofbetween150and300meq/100g.Althoughtheorganicmattercontentofasoilisusuallymuchlessthanthatofclay,itneverthelessmakesamajorcontributiontotheCECofasoilbecauseofitshighadsorptivecapacityatpHsabove5。第44頁，共63頁，2023年，2月20日，星期六2.3.2SpecificadsorptionSpecificadsorptioninvolvestheexchangeofheavymetalcationsandmostanionswithsurfaceligands(配位體：配位化合物中與另一化學(xué)個體連接的離子、分子或分子團(tuán))toformpartlycovalentbonds(共價鍵)withlatticeions(晶格離子)[23].ItresultsinmetalionsbeingadsorbedtoafargreaterextentthanwouldbeexpectedfromtheCECofasoil.第45頁，共63頁，2023年，2月20日，星期六Forexample,Brummer[24]showedthattheadsorptivecapacitiesofamorphous（無定型）FeandAloxidesforZnwere7and26timesgreater,respectively,thantheirCECsatpH7.6.SpecificadsorptionisstronglypHdependentandisrelatedtothehydrolysisoftheheavymetalions[24].Themetalsmostabletoformhydroxycomplexes（氫氧化物）arespecificallyadsorbedtothegreatestextent.Therefore,thepK(equilibriumconstant)valuesofthereactionM2++H2O=MOH++H+determinetheadsorptionbehaviourofthedifferentmetals.SpecificadsorptionincreaseswithdecreasingpKvaluesbut,inthecaseofCuandPbwhichhavethesamepKvalue,Pbwiththegreaterionicsizeismorestronglyadsorbed.第46頁，共63頁，2023年，2月20日，星期六Brummer[24]givestheorderforincreasingspecificadsorptionas:Cd(pK=10.1)<Ni(pK=9.9)<Co(pK=9.7)<Zn(pK=9.0)<<Cu(pK=7.7)<Pb(pK=7.7)<Hg(pK=3.4).ThehydrousoxidesofAl,FeandMnarethoughttobethemainsoilconstituentsinvolvedinthespecificadsorptionreaction.第47頁，共63頁，2023年，2月20日，星期六Inadditiontobeingadsorbedonmineralsurfaces,heavymetalionscanalsodiffuseintomineralssuchasgoethite,Mnoxides,illites,smectites(蒙脫石)andsomeotherminerals[24].TherelativerateofdiffusionofthemetalionsintomineralsincreaseswithpHuptoamaximumwhichisequaltothepKvalueforthesituationwhenM2+=MOH+onthemineralsurface.AbovethispHtheMOH+>M2+andtherelativediffusionratedecreases.Forexample,themaximumrelativediffusionratesforCo,NiandZndecreaseintheorderNi>Zn>Cdandcanberelatedtotheirionicdiameters(Ni=0.69A),Zn=0.74AandCd=0.97A).第48頁，共63頁，2023年，2月20日，星期六Adsorptionofmetalsbygoethitethereforecomprisesthreedifferentsteps:first,surfaceadsorption;second,diffusionintogoethiteparticlesandthird,adsorptionandfixationatpositionswithinthemineralparticles[24].08/04/15第49頁，共63頁，2023年，2月20日，星期六2.3.3Co-precipitationCo-precipitationisdefinedasthesimultaneous（同時）precipitationofachemicalagent（載體）inconjunctionwithotherelementsbyanymechanismandatanyrate.（定義）Thetypesofagentcommonlyformedincludeclayminerals,hydrousFeandMnoxidesandcalcite（方解石）inwhichisomorphoussubstitution（同晶替代）hasoccurred.Inadditiontoco-precipitation,replacementofCa2+cationsbyCd2+canalsooccurinthesurfacelayerofcalcitewhenitcomesintocontactwithsolutionscontainingCd.Whenallthecalcitesurfacehasreactedinthesolidsolutionway,theremainingCd2+insolutionprecipitatesoutasCdCO3.第50頁，共63頁，2023年，2月20日，星期六2.3.4Organiccomplexationsolid-phasehumicsubstances（腐質(zhì)物質(zhì)）suchashumicacidsalsoadsorbmetalsbyformingchelatecomplexes（螯合作用）.Low-molecular-weight（低分子量）organicligands（配合體）,canformsoluble(可溶的)complexeswithmetalsandpreventthemfrombeingadsorbedorprecipitated.Humiccompoundswithsuitablereactivegroups（官能團(tuán)）,suchashydroxyl（羥基）,phenoxyl（苯氧基）andcarboxyl(羧基)formcoordinationcomplexeswithmetallicions.第51頁，共63頁，2023年，2月20日，星期六Thestabilityconstantsofchelates（螯合）withmetalstendtobeinthefollowingdecreasingorder:Cu>Fe=Al>Mn=Co>Zn.Carboxyl（羧基）groupsplayapredominantroleinmetalbindinginbothhumic（胡敏酸）andfulvicacids（富啡酸）.Themaximumamount（最大量）ofanygivenmetalthatcanbeboundisfoundtobeapproximatelyequaltothenumberofcarboxylgroups.第52頁，共63頁，2023年，2月20日，星期六2.3.5SelectivityofadsorbentsfordifferentmetalsAdsorbentamountofmetalsvaryintheextenttowhichtheyareadsorbedbythemechanismsdescribedandtheadsorbents（吸附劑）.第53頁，共63頁，2023年，2月20日，星期六TherelativeselectivityformetalcationscanbelargelyexplainedintermsoftheLewishardsoftacidbase(HSAB)principle軟硬酸堿規(guī)則：凡是可以接受電子對的物質(zhì)稱為酸，凡是可以給出電子對的稱之為堿。即根據(jù)酸、堿對外層電子控制的程度，應(yīng)用了“軟”和“硬”兩字進(jìn)行分類，把接受孤對電子能力強(qiáng)、對外層電子吸引得緊、沒有易極化的電子軌道、電荷半徑比較大的金屬離子叫“硬酸”；把接受電子能力弱、對外層電子抓得松、易極化、電荷半徑比較小的叫“軟酸”，介乎二者之間的金屬離子叫“交界酸”。第54頁，共63頁，2023年，2月20日，星期六HardLewisacidsprefertoreactorcomplexwithhardLewisbases,andsoftacidsprefersoftbases（硬親硬，軟親軟）.Theterm‘hard’indicatesahighelectronegativity（電負(fù)性）,lowpolarisability（低極化率）andsmallionicradius（離子半徑）,and'soft'impliestheoppositeofthese.HardLewisacidsincludethefollowingcations:Li+,Na+,K+,Rb+,Cs+,Be+,Mg2+,Ca2+,Sr2+,Ti4+Cr3+,Mn2+,Fe3+,Co3+.SoftLewisacidsincludeCu+,Ag+,As+,Cd2+,Tl+,Pd2+,Pt2+.Borderline（交界）metalswhichdonotfitsowellintotheclassificationincludeFe2+,Co2+,Ni2+,Zn2+,Sb3+andPb3+[34].第55頁，共63頁，2023年，2月20日，星期六2.3.6QuantitativedescriptionofmetalionadsorptionTraditionally,theadsorptionofionsbysoilshasbeenquantitativelydescribedbyeithertheLangmuir（郎謬爾）ortheFreundlich（弗羅因德利希）adsorptionisotherms（吸附等溫線：恒溫反映吸附量與平衡壓力之間關(guān)系的曲線,稱吸附等溫線.）.TheLangmuirequationhastheformamountofionsthatwillbeadsorbedbyagivenabsorbate：式中a為在氣體平衡壓力為p

時的吸附量；am為單分子層飽和吸附量；b

為與溫度和吸附熱有關(guān)的常數(shù).第56頁，共63頁，2023年，2月20日，星期六Thisequationisconvenienttouseforsoilsbecausebothamandbcanbeeasilydeterminedbyexperimentandthustheamountadsorbedatanyinputcanthenbeestimated.它指出：在很低的壓力下吸附量與氣體平衡壓力成正比；在壓力