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by: Sabina Okuneva


Sabina Okuneva
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This 56 page Class Notes was uploaded by Sabina Okuneva on Saturday September 12, 2015. The Class Notes belongs to GEOL 3020 at University of Georgia taught by Staff in Fall. Since its upload, it has received 55 views. For similar materials see /class/202260/geol-3020-university-of-georgia in Geology at University of Georgia.

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Date Created: 09/12/15
Biogeochemical cycles of carbon sulfur iron and oxygen producing biogeocnemical redox reactions in 01 4239 69 20139 One would think that redox states Fez w39 ea Fel it too would be an important playerig ferric iron being an 39 39 Tmn i imnnnzm 39 39 39 was ea 5139 ro sulfur redox botn involve reaction with diatomic oxygen molecules For example oxidation from Fel to Fez requires l ofau ol molecule wnereas oxidation from 5139 to 55 talres 2 ol molecules Redox oforganic carbon and methane requires one to two 01 molecules eg CquotH10 or CquotIrL to c 0 Ifwe look at the occurrence of elements in the earth39s cmst we seetnat o c Fe and s quot 39 InbiotaN quot 39 in tri a N1 Let39s just rust explore the coupling between Fe 0 and 5 oxidation of FeSz and organic 5 oxidation 502 and H25 Volcanic 02 02 02 and H25 02 C3804 dissolution 02 and H28 from metamorphism deep diagenesls Subducllon cf CaSO4 F652 and organicS Figure ml The langrlerm sulfur ydc Downward pointing arrows associated with 02 signify 0 consumption upward pointing arrow signify 02 production l uw COZarld hydrolnerrnal H28 For 02 Oxford Unlveralty Press loo pp The major reactions involving the long term sulfur cycle include the redox of iron sulfur and oxygen 1502 4Fe82 8H20 ea 2Fe203 ssof 16H This reaction above can be thought of as the sum of several reactions left right left right involving 1 plant photosynthesis respiration or burial weathering of organic matter 2 bacterial sulfate reductionsulfide oxidation 3 sedimentary pyrite formationpyrite reduction and 4 the neutralization of acid and bicarbonatedissociation of carbonic acid The reactions for each are shown below 1 16C02 16H20 ea 16CH20 1602 2 16CH20 ssof ea 8H2s 16HCO3 3 2Fe203 8H2s 02 ea 4Fe82 8H20 4 16H 16HCO3 ea 16C02 16H20 If we include the burial and weathering of carbonates Where Burial left right Weathering left right 5 16Caz 16HCO3 69 16CaCO3 8H20 Weathering 9Burial Then we can combine the reactions of the carbon cycle and sulfur cycle to account for the burial and weathering of pyrite 6 2Fe203 88042 16Ca2 16H 16HCO3 69 16CaCO3 1502 4FeS2 16HZO The balance of oxygen in the atmosphere over long periods of time can be expressed by the balance between the burial of organic matter Fbg and pyrite Fbp and the weathering of organic carbon ng and pyrite Fwy This is expressed by the stoichiometry of the reactions where 158 is the ratio of oxygen to sulfate molecules AOZAt 1bg ng 158 Fbp Fwy Oceanic Carbon and Sulfur Rutk quot Sul de n s gure 5 Hump mm balame made rm mearhun mm mm ydu at my mm atmmphm nxygnn when m mmarsummn lhlncnallslhcnl l mass m um mmmphm bupxmeand ibycumparimunegligiblsl m culfule mm from uxldalwe mamon m pymz mlfme ux fmm vumhen39ng um lemes sulhu degassing ux 10 pymn rm rulcznism mvummr n L rm buns ux am sulfalcs En ssdimam h buual nm of pynln n mumams 5 P39sInsy sJ smml 1 mum a a 503 56 1 2 a a mo Eon 3m mu 5M m zi so 25 20 5 115 m 5 n a mu zon son mu am Sun imemm Mg WWW movthnlwnmmmm mmMmWMWWW mm m Biogeochemical cycles of carbon r e the ecosphere as a senes ofwelledefmed reservoirs From the perspecuve geochemmal cycles Lhasa serv rrsean be eonsrdered boxes de ned by a setof prr a an no ofmodelmg re o boundary conditions Thrs approach to modelmg rs someumes referred to as quotbox modelrngquot oirs umts of mass per umtof me For example rus esumated that srnee 1750 humans have pumped A A The race has 1 r rrrcreased erh ume Currently we are emmmg about7 x 10 gc peryear Global coz Emlsslnns Imm FossIIFuels and cemem Produclion in trillion meIric tons of cannon RUDD mun n metric tons of carbon EEE E E K D Q u li ewrzensmorzozo oao oemw 4 e W W Q x l lr Years major rnreracuonserhrn the reservorrs The mass balance of a system requires that the rate of mass change in a reservoir AM over time At is equal to the input uxes Fi plus any production P minus the output ux F0 and any consumption C This is why we have spent so much time discussing hydrologic models ie uxes and biogeochemical reactions in the subsurface ie P and C AMIAtFiP FoC The pre industrial 1750 concentration of CO2 in the atmosphere was 280 ppmv We can use the ideal gas law 1 mol gas at STP 224 I to calculate the Earth s atmospheric carbon mass given the mass and composition of the atmosphere Mass of atmosphere 5 X 1021 g Fractions of gasses rounded N2 078 02 021 Ar 001 Molar conversions 12 gCmoleCOz 28 gNZmoleNz 32 gOZmoleOZ 40 gArmoleAr ZMNZMOQMN 2 Ma gC 280 ppmv10 312W02 MaSSgC W 5x1021 g 58x1017 gc Earth s atmosphere is nearing 390 ppmv which represents an 40 increase over 250 years This change is AMAt 04 x 58 x 1017 gC250y or on average AMAt 93 x 1014 gCy Note the carbon increase is different than that expected for the anthropogenic carbon produced Can you think why Note that we assumed a linear rate of change The graph above shows that the rate is non linear The inout uxes production and consumption Fi F0 P C terms need to be balanced if equilibrium is expected ie AMAt 0 In addition to the anthropogentic ux of carbon into the atmosphere there are other natural sources and sinks of carbon Perhaps one of the most difficult tasks is identifying the transport paths and measuring the size of the ux For the atmospheric CO2 reservoir these natural processes include photosynthesis by terrestrial plants respiration by terrestrial and surface oceans and Fi ocean CO2 degassing and CO2 dissolution F0 Fa F0 P and C rain CO2 degassing and CO2 dissolution 1 2 3 4 Once the transport paths are identified then they must be quantified If the mass of material M in a reservoir at a given time is known and the instantaneous rate of addition Fi P and subtraction F0 C is known then the residence time RT for that chosen point in time can be determined RT MF Let s use a simplified example of CO2 in the atmosphere where the rate of change is zero This situation is known as an equilibrium condition ie Fi 2 F0 and P C We ll assume the only CO2 source is burning fossil fuels and the only sink is dissolving CO2 into the oceans Mass of carbon dioxide in atmosphere today 2 390 ppmv 812 x1015 gC Flux 7 x1015 gCy 812x1015 gC Residence Time 2 Is g 3 116 y 7x10 Non equilibrium conditions Fi F0 andor P C If the rate of fossil fuel production were to double and the efflux rate remains unchanged then how much carbon would there be in the atmosphere after 1 year 812 x1015 gC 14 x 1015 gCy x 1 y 7 x 1015 gCy x 1 y 819 x1017 gC Under this non steady state condition the formal definition of residence time becomes relative to the in ux and efflux rates After one year 15 Fi Influx Residence Time M 58 y 14x1015 L y 15 F0 Efflux Residence Time W 116 y 7x1015 g y Residence time is not to be confused with the concept of renewal time or renewal rate Renewal time RnT can be thought of as the time it takes to replace preexisting material with new material Renewal is strongly dependent upon the mixing that takes place in a reservoir If the rate of mixing were rapid as in our steady state atmosphere scenario above ie homogenized within days then how long would it take to make a 5050 mixture in the atmosphere At what point is the system renewed In a well mixed equilibrium system the replenishment of new material or removal of old material will follow logarithmic half life decay It is not difficult to see that in our atmospheric CO2 example after another 116 years the amount of original carbon will be reduced to 14 h the amount at the start A generally accepted dilution value With regard to the remaining fraction of old material is about 164391 or six half lives 12 12 12 x 12 14 12x12x12 18 12 x12 x12 x12 116 12 x12 x12 x12 x12 132 12 x12 x12 x12 x12 x12 x 164 The relations between residence time and mixing time are important If the concentration of carbon is uniformly distributed than the residence time is much longer than its mixing time The distribution of any component in a reservoir Will depend on 1 uxes 2 reservoir size 3 mixing Let s look at a simplified three box model for cycling of carbon on a long term basis These ideas are discussed in more detail in a book by Robert Berner 2004 The Phanerozoic Carbon Cycle CO2 and 02 Oxford University Press 150 pp Initial simplifying assumptions include the following H Consider only one species m the total concentration of carbon ie only grams C not different phases eg CHZO CaCO3 HCO339 CH4 C0 C02 Carbon species are conserved ie no production or consumption P and C 0 Steady state fluxes 3 Conversion 00210 dissolved H003 by Volcanic CaMg sflicale wealhering 02 002 from sedimentary organic C weathering i 0 co Bj al 3 C02 and CH4 from Metamorphism amp Deep Diagenesis Subduction of 03003 amp Organic 0 rigum N 39 m n m h guithg haracle snc of the longrmrm cyde A schematic version of 4 39 4 below uxes are formulated in the following way M1 Mass of Carbonaterc reservoir M Mass of organicrc reservoir M3 Mass of oceanratmosphererbiotzrsoil OABS reservoir Fm Flux from carbonateer OABSVC by weathering of air and Mgrearbonates Fm Flux fmm eanbonaec m OABSVC by volcanism metamorphism and diagenetje degassing WE Flux fmm organierC to OABSVC by weathering of sedimentary organic carbon F Flux from organierCto OABSVC by volcanism metamorphism and diagenetje degassing Fm Flux from OABSVC to carbonaterC by buna1 in sedimean ha Flux from OABSeCto organierC by buna1 in sediments L 39L o b kw 39Ieeun quot as AMEAt Fm FWa Fm Fma e FM 7 Fha Longterm Carbon Cycle Carbonate F Organic C C Carbonate Organic urial Burial Organic Carbonate Weathering Weathering in gt r a Ocean 7 Fi Atmosphere 7 I Volcunism W momsou quotW Voleanis Metamorphian C Memmorpliisni Dingeneue degassing Diugenetie degassing An additional mass balance expression for the stable carbon isotope system 613C is presented in the following useful equation recall the 6 notation from our previous lecture notes A63M3At26wchc 6 F 6 F 6 F 6chbc6bngg wg wg me me mg mg The driving forces ie feed backs behind the uxes are not always well understood The approach to modeling the uxes between two reservoirs i of mass M and M is to empirically scale the models as zeroth and first order equations The expressions for these are Fij constant and Fij kil M respectively The masses of carbon reservoirs involved in the short and long term cycles are in the following table It should be readily noted that all the surface reservoirs can be grouped together and they still collectively pale in size compared to the rock reservoirs 1 metric ton 106 g or 104 kg Reservoir Moles Carbon Metric Tons Carbon Ratio to carbonate Carbonate C rocks 5 00E21 600E 16 100000000 Organic C in rocks 125E21 150E16 025016200 Ocean DIC 280E18 336E13 000056000 Soil organic matter 3 00E 17 360E 12 0 00006000 Atmosphere 600E16 720E11 000001200 Terrestrial biota 500E 16 6 00E11 0 00001000 Marine biota 500E 13 600E08 000000001 Flux Moles Cy Metric Tons Cy Ratio to fossil fuel Photosynthesis land 525E15 630E10 1000 Respiration land 512E15 614E10 975 Respiration ocean 377E15 4 52E10 717 Photosynthesis ocean 375E15 4 50E10 714 Fossil Fuel 525E14 630E09 100 Forest fires 133E 14 160E09 025 Rivers 333E 13 4 00E08 006 Burial 333E13 400E08 006 Weathering 183E 13 220E08 003 Metamorphism 100E 13 120E08 002 If you consider the flux of carbon from weathering and metamorphism over millions of years then the amount stored in the surficial system is relatively small ie the amount of carbon coming from degassing in much larger than what can be stored in the surface reservoirs Most of the world s carbon is stored as limestone Weathering of limestone and Ca feldspars is an important step in returning carbon from the atmosphere to the oceans The chemical reactions can be represented as Fm Caco3 1C02 H20 9 Ca2 2HCO3 and CaAlZSiZO8 2C02 3H20 9 Ca2 AlZSiZOSOH4 2HCO3 The Ca2 and bicarbonate HCO3 travel via the rivers to the oceans and are precipitated as calcium carbonate Fm Ca2 2HC03 a Caco3 C02 H20 If the above precipitation reactions are added then the following overall reaction is obtained 2H20 CaAIZSiZO8 CO2 CaCO3 AIZSi205OH4 This reaction is a key reaction in the longterm carbon cycle because it represents a means to extract carbon dioxide from the atmosphere and store it in the rock reservoir It is the combination of the 1 weathering carbonates and Ca and Mg silicates and 2 marine carbonate formation that makes a long term sink for carbon Note that the weathering of N a and Ksilicates do not create the same effect as Ca and Mg because Na and K carbonate minerals do not form in massive deposits The longterm feedback to keep the atmosphere carbon levels from dropping is the degassing process In effect it is the reverse of the above reaction during burial metamorphism and volcanism Caco3 AIZSiZOSOH4 a CaAIZSiZOS C02 2H20 Inspection of the above weathering reactions allows one to assess the relative importance of carbonate versus silicate weathering cycles It can be argued that on million year time scales the effect of carbonate weathering is small The long term weathering and subsequent precipitation of carbonate in the oceans results in no net change in the amount of atmospheric CO2 the residence time of dissolved carbon in the oceans is about 100000 years Note that in reaction of atmospheric CO2 with carbonate there is only one mole of carbon consumed and two moles of bicarbonate produced ie one of the carbons come from the carbonate itself For the reaction of atmospheric CO2 with Casilicate there are two moles of carbon consumed and two moles of bicarbonate produced In this regard Ca and Mg silicate weathering is a more effective carbon sequestering mechanism on longer time scales Fossil fuels Longtum burial ofoI ganic rmttex represents a form of net photosynLhesxsquot 1n the organro suboyole carbon and oxygen undergo redox reaouons cq HZO 9 CHZO q ZCHZO gt cq c1 1 c1bol gt cq ZHZO M b o 1 r reservorr The currentme of extinction 1 about 100 times the present day natural rate Thu 1 at reservorr to carbon m the aLrnosphere Maumn Loz Blon ll Mann when Dioxide Meawremenrs by 7 Sm vs Instmtute nszEantrEuhy Netmnal Oneamz and Almbsphenz Assmuun coz CONCENTRATION ppm 385 0 a O m 1 01 RECENT MONTHLY MEAN CO2 AT MAUNA LOA oquot Nmmwm 2005 2006 2007 Biogeochenristry The lirnits oflife as we know it are de ned as the Earth39s ecospheie Ecosphere atmosphere lithosphere hydrospheie biota Limits of life 6 yeim in space Emlllm wlmlir 5 MRqu nr 500m hillkllb mum Dmmmnm llvdmdmnm T 113 Temperature C 15 0 E 5 5 3 Q l2lx almnwhznt praisur I plam t 39 I solar A M p39 cycles an e uy eg impacts Biochernistry b 39 39 39 39 p in irruall all connining CrH bonds The 3D geomeuy including symmetry determines their chemical behavior The many types o 39 39 quot 39 property on 39 L39 bond and share electmns from single bonds to triple bonds ie 2 e to 5 e organic cornpounds are generally grouped by those that bond H hydrocarbons o N s P and halides Benzene Organic matter is comprised of biomolecules or polymers With molecular masses RMM that range up to the millions These include Carbohydrates small sugars to large celluloses generalized by the formula CHZO Proteins large N bearing amino acids linked in long chains and include carboxylic groups COZH and amino groups NH2 Lipids small extractable fats and oils Nu c Acids e g Peoxymnugciacid DNA angbonucleigacid RNA 1 Fl 3 D 40 llllllllllltl 2 1 I y y rllll DNA Red Oxygen Blue Nitrogen Gray Carbon Yellow Phosphorous Hydrogen not shown Scale in angstroms A Phosphatesugar spiral backbone N bearing base pairs held by H bonding A C G T adenine cytosine guanine and thymine respectively The pattern of base pairs contains genetic information Breaking of the H bonds allows the transmittal of genetic coding that is held in RNA RNA is most often used as a template to generate new proteins The collective information ie pattern of base pairs is contained in a DNA segment that is called a gene Change in the pattern of base pairs caused by radiation and or the presence of other chemicals leads to mutation Biological weathering Surficial processes that involve chemical reactions include activities in the Earth s hydrosphere biosphere atmosphere and lithosphere Our recognition of the range of temperature pressure and chemical Jquot that the L39 F has increased 1 greatly in the past few decades and that range will likely continue to broaden Perhaps the most important agents of weathering are microbe scale biological activities In the subsurface and oceans these include the by products of viruses bacteria lichens algae fungi and plant roots Also important is the decaying organic matter which includes all the above as well as detritus that comes from the all parts of the five kingdoms of life Viruses Consist of protein and genetic material DNA and RNA Size range 002 to 025 Mm We really don t know much about their role in biological weathering Even though we don t know much about them it is likely that they are important Viruses are the most abundant biological entity on earth total 1030 to 1032 viruses Kutter and Sulakelidze 2005 with current estimates suggesting at least one type of virus for every living organism Flint et al 2000 Currently little is known about what effect phage activity attachment infection and lysis has on bacterial mineralization In the search for signs of life on early Earth and on other planets many scientists have focused on bacterial mineralization and preservation in the rock record However lacking from the literature is the potential role of bacteriophages in bacterial mineralization Phages attach to bacterial surfaces infect bacterial cells and cause lysis thus releasing progeny into the environment This relationship has the potential to effect bacterial mineralization as 1 phages attach to the same components in bacterial cell walls that attract metal cations and anions in the surrounding environment 2 long term viral infection of a bacterial cell causes conformational and structural changes of the cell surface where phages and ions bind possibly altering the reactivity of the site and 3 lysis of a bacterial cell expels intracellular material into the immediate surroundings and creates cell fragments exposing previously unexposed potential reactive nucleation sites The above notes were abstracted from Jennifer Kyle Prokaryotes Contain a cell wall and nucleiod In the 1980 s and 1990 s our ability to rapidly replicate DNA sequences led to a revolutionary ability to examine larger molecular make up of different life forms In essence the similarity of genetic coding as recorded in the sequence of base pairs has provided a means to compare evolutionary relationships between different organisms This has led to the development of a phylogenetic tree of life For the most part only a portion of the genetic sequence has been employed to date Most chose to employ the ribosomal ribonucleic acid 16s rRNA part of the entire gene sequence The reason for using this part is based on a compromise of haVing enough genetic information base pairs for good statistical correlation but not too many because that experimental and computational time needed to look for similarity becomes excessive Also the thermal stability range of the 16s rRNA molecule is sufficiently large to allow for Polymerase Chain Reactions PCR to amplify the genetic material On this basis the Prokaryotes have been diVided into two groups These two groups are the Archaebacteria and the Eubacteria The phyla of life on Earth based on our modification of the Whittaker five kingdom system and the symbiotic theory of the origin of eukaryotic celis PLANTAE ANIMALIA FUNGI haplodiploids v diploids haploids CRANiATA CEPHALOCHORDATA UROCHORDATA ECHINODERMATA HEMICHORDATA CHAETOGNATHA ANTHOPHYTA GINKGOPHYTA GNETOPHYTA 3 CYCADOPHYTA CH ELiCERATA Chromosomal gt Histogenesis PRIAPULIDA Embryogenesis FILICINOPHYi A KINORHYNCHA SPHENOPHYTA CTENOPHORA PSILOPHWA CNiDARIA PLAOOZOA PROTOCTISTA RHODOPHYTA Dikaryosis PHAEOPHYTA Meiosis g m OOMYCOTA iii GAMOPHYTA Gamemge es39s 39 CHYTRIDIOMYCOTA I CHLOROPHYTA ZOOMASTIGOTA GRANULOREF39CULOSA PLASMODIOPHORA II DISCOMITOCHONDRIA XENOPHYOPHORA HYPHOCHYTRIOMYCOTA I MitOsns I CRYPTOMONADA MYXOSPORA DIATOMS Myceila XANTHOPHYTA LABYRINTHULATA Steroidogenesis CHRYSOMONADA MYXOMYCOTA Aerobiosis HAPTOMONADA EUSTiGMATOPHYTA ACTINOPODA Photosynthesis CiLiOPHORA DiNOMASTIGOTA AICROSPORA s ores 39 CYANOBACTERIA p n W RH39ZOPODA ARCHAEPROTiSTA Phomms AlNBAC39i39FFii 7 CHLOROFLEXA Cquot 39LOROB39A Chemoautotrophic bacteria I k I EURYARCHAEOTA Motlilty DEINOOOCGI SPiROCHAEI AE Methanogens and halophiis quotSEAS3 SAPROSPiRAE z j PIRELLULAE g L Q 6 TH ERMOTOGAE CRENARCHAEOTA PROTEOBACTERIA APHRAGMABACTERIA Thermoacrdophils 49 Fermentation EUBACTERIA ARCHAEA ARCHAEBACTERIA Reproduction last common ancestor 39 I BSi r 83 87 8 1 2 B13 B lO B11 Aerobes Facultative anaerobes Microaerophils Pseudomonas reen nonsulfurs Nitrosomonas Purple sulfurs Thiobaclus nonsulfurs Methanogens and halophils EURYARCHAEOTA The biochemical pathways for metabolism in prokaryotes are numerous and depend upon the sources and sinks of protons electrons and the relative ease of energy in the systems recall the electron tower and free energy of reactions Energy can come from photosynthesis and or chemosynthesis Some of the pathways used include Autotrophy Where inorganic carbon is used to make organic matter Photolithoautotrophs Electron sources H2 H28 H20 SO Fe 2n HZX nCO2 light9 nHZO nCHZO ZnX Chemolithoautotrophs Electron sources H2 H28 H20 SO Fe Heterotrophy where organic molecules are used to make organic matter Chemorganotrophs Hetrotrophs You me and others Eukaroyotes Membrane bound nucleus and organelles Includes Protoctista Fungi Plants and Animals Bacteria Prokaryotes in figure above and Eukaryotes are widely distributed throughout the weathering environment All gain their energy through some type of redox reaction As a natural by product of their metabolic activity these organism exude organic acids Organic acids can be simple in structure or they can be very complex Commonly they contain a carboxylic group COZH which when ionizes produces acid COZH 9 C02 H Here are some simple acids CH3C02H bacteria C02H2 COHC02HCH2COZH2 Clutamlz and 5 Data Bank v 394 A 39 quot F nlvir acid 39 Hum ic acid The piedictive capability ofthe ionic potentialquot concept breaks down when ions inteiact with organic acids 39 39 39 39 39 39 to claw A complex is n 39 39 39 b b an 4 L r move through the subsurface they can he used by bacteria which will then cause the Fe and Al to precipitate out as biologically induced mineials Example of chelaliou of ferrous iron by oxalic acid 2 H20 Fe QHZO 9 2H QHZO Fe 2 H20 Energetics source amount and ow of energy Chemical energy is derived from the energy stored in chemical bonds When bonds are made or broken there is a quantifiable amount of energy expended This statement holds for both biological and non biological mediated reactions Electrons are transferred by oxidation reduction reactions redox Remember OIL RIG Oxidation Is Loss of electron Reduction Is Gain of electron Oxidant e 9 reduced form Reductant e 9 oxidized form Electron acceptor gains electrons Electron donor gives up electrons All redox reactions are coupled half reactions No free electrons are present The reactions must be added to make a complete reaction The generally accepted convention is keep the electrons on the left side of the reaction Oxidant reductant 9 reduced oxidant oxidized reductant Major elements that are redox sensitive under earth surface conditions include H O C S N Fe and Mn Minor elements that are redox sensitive under earth surface conditions include V AS Se and Hg Example of overall redox reaction H2 1202 9 H20 H is oxidized zero state to 1 H is the electron donor reducing agent or reductant O is the reduced 0 to 2 O is the electron acceptor oxidizing agent or oxidant The above reaction is the sum of the following half reactions H2 2e 9 2H Oxidation of H2 12 O2 2e 9 02 Reduction of O2 12 O2 2e 2H 9 H20 Reduction of O2 coupled with H 12 O2 H2 9 H20 Overall reaction Compounds that serve as either electron acceptor or donors are often expressed as couples with the convention of putting the oxidized form on the left and reduced form on the right eg 2HH2 12 02 H20 oxidantreductant acceptor donor Example of breakdown of ilmenite in soil to pseudorutile 07502 3FeTiO3 15H20 9 FeZTi3O9 FeOH3 The above reaction is the sum of the following half reactions 313e2Tio3 3e 9 Fe32Ti3o9 Fe3 Oxidation of Fe2 07502 15H20 3e 9 3OH Reduction of 02 The electron acceptor or donor couples are 02 OH Fe2Tio3 Fe32Ti309 The more stable end product of ilmenite weathering is hematite and anataserutile This is not a redox reaction It s a dissolution precipitation reaction FezTi3O9 9 FeZO3 3TiO2 The transfer of energy during bond breaking redox reactions is often part of biological processes Surficial processes are often controlled by microbial and plant mediated reactions reactions that occur both inside the cell walls and outside the cell walls Microbes that gain energy from breaking organic chemical bonds are called organtrophs Microbes that gain energy from breaking inorganic chemical bonds are called lithotrophs Microbes that gain energy from sunlight are called phototrophs The energy ie the work needed to transport ions against a concentration gradient comes from the internal energy that is released during the reaction The energy available to do work is the free energy ie the AG of reaction Standard reduction potential Electrons are transferred in a redox reaction The transfer occurs from the oxidant to the reductant As a consequence an electron potential exists between the redox pair Recall the change in free energy of a reaction at equilibrium is related to temperature and R the gas constant AG RTaneq By definition the electron potential is related to the free energy of reaction AG nFAE RTaneq where n number of electrons F Faraday constant 96484 kJvolt g equivalents and AE is the difference in standard reduction potential between the oxidant and reductant E the reduction potential is also sometimes called the standard electrode potential Many standard electron potentials are tabulated in the literature Using the examples from above H2 2e 9 H Oxidation of H2 12 02 2e 2 H1 9 H20 Reduction of O2 2HH2 E 042 V 12 02 H20 E 082 V In essence this is telling us that 02 has a high tendency to accept electrons high reduction potential and H1 has a tendency to donate electrons low reduction potential In this case the electrons flow from the H2 to 02 The overall reaction 12 02 H2 9 H20 has a total potential of 124 V which equals 23734 kJmol The possible combinations of redox pairs give rise to the concept of the electron tower The reduced substance in the couple with the lower reduction potential will donate electrons to the oxidized substance with the higher reduction potential ie electrons fall down the tower The flow of energy if it is to be used for biosynthesis must therefore go from oxidant to reductant Examples with H2 as the electron donor H2 SO 9 H28 AE 042 028 014 V 4H2 8042 9 H28 H20 2OH AE 042 022 020 V H2 Fe 2OH 9 Fe2 2H20 AE 042 020 2 062 V pH 7 H2 Fe 2OH 9 Fe2 2H20 AE 042 076 2 118 V pH 2 H2 12 02 AE 042 082 2 124 V Activity of electrons Let s consider the redox of ferrous and ferric iron and half cell reaction Fe e 69 Fe2 An equilibrium relation can be established where aFe2 661 aFe3 ae or a a6 F62 K 6 gal F63 We must define the hydrogen redox potential with the standard hydrogen electrode SHE whereby a platinum wire in a H solution at 25 C and 1 atmosphere of hydrogen gas and by convention the activity of an electron 1 Other conventions are discussed in Drever s 1997 book on The geochemistry of natural waters 3quoti edition Prentice Hall Fe e gt Fe 12H2 e gt H aH 1 We can define the activity of electrons in log form similar to pH where pa log10ae Now let s consider the redox of hydrogen and half cell reaction H e 69 12 H2 a 05 i ClHCle The overall reaction for iron redox in the electrode system is therefore Fe 05 H2 gas 69 Fe2 H The activity of electrons can be given in units of volts Eh or pe Where F Faraday s constant 96484 kJ per volt grarn equivalents R 2 gas constant 8314 X 10 3 kJ per Kmol 36 At 25 C Eh 0059 pe FIGURE 713 Stability relations in the system Fe O HZO S CO2 at 25 C assuming ES 10 6 ECO2 100 after Garrels and Christ 1965 Solid solution boundaries are drawn for an activity of dissolved Fe species of 106 Eh V 15 5 Fe2 aq Hematite Fe 03 05 o Eh V Locus of measured Eh values After L G M BaasBecking et al Limits of the natural environment in terms of pH and oxidationreduction potentials J Geo 682243 84 Copy right 1960 by The University of Chicago Press Stable nxygen isntnpes and the temperaturejice balance nf the Earth nceans Stable Isotopes of Oxygen Relative percenmges O 9976 quot0 0004 0 0020 Measurement m r mtln m W Oxygenis combined with carbon to form C0 The CO2 gas is ionized in avacuum and sent through a strong magnaic field The de ection ofthe ion path is related to its mass By putting detectors at dlfft 39 39 u 39 fthe magnetic f quot39 4 quot different mass can be detected and measured Notation The inevimlale differences amongst rnassrspectrometers necessitate the use of a smndard r r 1 5180 M4 11000 Rstd 18 Where wimpy and Rm 3 We a expressed in units or per mil 39 kl Ttnmh ar reported relative to Standard Mean Ocean Water SMOW The bommrllne When 5 30 is positive the iatio is large and the sample is heavy or enriched When 5 30 is negative the iatio is small and the sample is light or depleted Rayleigh distillation vi eamerm isotopes preferentially precipitate l H nl n M nZ Kn The lower the temperature or evaporation the greater the fmcuonauon 1000 s or years by how much ice is stored in the caps The more iee stored in the caps the heaVier the oceans fmclionation 39 39 39 39 39 umumui mic To put this into numbeis Ifthe 3 of the oceans 0 7 men during wann penods the a 39 n 25 WW 39 39 o of the water that makes it to the poles may be 40 0 39 39 H and 1H TL 39 39 39 theisotopes H and 1H is therefore more exmme than 50 and O Vostok Ice Con Data depth m H mm 650 600 550 500 450 Biological fractionation which live in the oceans As they make their hard pans the oxygen isotopes in the Caco is enved from the oxyg 39n the oceans Fish tank experiment If the sanie ini a1 isotopic connposiiion then each foram population will have a different rate at which an organism metabolizes 61806 algow A T C As temperature goes up A becomes less Each tank has water with the same oxygen isotopic composition Only the water temperature at which the each shell grows is varied Experiments show the isotopic composition of the shells fractionate the oxygen such that the cooler tanks produce shells that are isotopically heaVier Likewise the warmest tank produces the lightest shells The result for that particular species is a fractionation curve that describes the temperature effect on the difference between the shell39s isotopic composition and the water isotopic composition 513011 3 DD D39iiuj 51531 3 DD D39iiuj 5130 w 3 DD Elfin J75JTW39quot39 Jirwquoth in r 25w 513 I Cl CI 39 231 SE 311 E 539 1 I 39 39 1 III quot j E 39 393 s 1 3 1 3 4 61 80 difference b etveen cal 05 te and vate r Paleothermometer 5 u x 5quot QALCABEOUS N u A l G 1 I f W 39 E F NNOEOSSILS sgALE 5 er mm an mm msz mm sum with imam mm s m mmpuamle at m acean cm assumponm Na because we stung changes Emma m a o Campansanafplankmnlc 5m dwe mg mama hamm dwe mg imam Assumz 1 pm imam mummsme wamxmmpenmn 2 mum imam mummmm wamxmmpenmn thauemams mm we Ifcaemnngplankmnlc mama imam pnsemdmacan 12 mm hecamz hzavlzx may plankmnlc imam mngsuaemngmnmm imam hecamz hzavlzx u m Bump signalafthz henthnnlcs dues nmchange mum 51w anaceansn ace caalmg unthnm an we wlnmz mamas A masnle at we stab axygen mm a o pnsemd m cannmntzl we mus at mm age hzlps 2mm changes In a o Ebhmwan changes m nygen smnpes m panmmc and bammc mm hgm n an heavy a ncvased 5 m2 vumme 0 D a 2y wean sunace panmmc bammc mo w PDE 4L u a 5 a ao Va SMOW L a quotPnu A9490 we 397 vs PDE 5D A Emauowg l THE mvw39quot PULSE OF THE PLEISTOCENE 5a Ltmmmmmmmn um mar414 1m awn 5 7 mm m5 Hinhev SM Laval Low Gre nland glacial ice 7 RIP 39 lawman am 99 Cnl ur Wanner is Ho Fracture ling calcite Devi le N vada Mimdxad u an Im 39 i 39 7 Pollen In Iraluan take sediments AIM um um I 200000 Hubcaua memo mow Lana saw Lmo Early Eu unlmwrms Walchsnl welcmo EM 535 Sasle quotWMquot Enammmm I Tia I Inc Hod Wlwons nan g llmcmm Kansan l quotirww z A warm 5 Riss gt Mmdul W39 139 gym1 WW P emocena Pnkslacano Plsismns Pnlsoacnna Flamesquot Plnlslmane mm mm aummm wmw nmmruwummMnwm ls Imamma Chen carbonme rr Atm 20 02 1 F39ehhc and clasuc 1 Warm m Metamorpmc vocks L Sedimentary rocks amph39mmes g Oceanwaie remperature Q3 oi formanon Tropwca Temperate Prempuauon Archc WOW y 7 Permanent we uelds Lecture notes for GEOL3020 Mineral Thermodynamics This is a prelude to mineral associations In your studies of systematic mineralogy you have been noting the occurrence of minerals Rock defined as an aggregate of one or more mineral The study of rocks is known as petrology Petrology includes the identification of minerals and their associated textures size and shapes and abundance The information derived from petrology is used to understand the origin and formation of the rock So not only does a geologist need to be a mineralogist for identification purposes but she he must also be a physical chemist and bio geochemist to know something about conditions under which near surface minerals undergo reaction or change Minerals form and disappear in response to changes in specific physical and chemical conditions The role of the geochemist is to determine the history of those changes in conditions Biogeochemistry entails the study of a wide range of ecologic environments where minerals form One must understand phase relations in waters of lakes and oceans metals in hydrothermal ore deposits gases in volcanoes uid phases and solid phases in magma soils mineral solids liquids gases and organics in the regolith organic matter in sedimentary rocks With basic knowledge from our studies of physical chemistry it is possible to describe the nature of a mineral phase under certain physical and chemical conditions The sub disciplines that provide us with the tools to reconstruct the physical and chemical origins of geological systems include the fields of thermodynamics kinetics and quantum mechanics Thermodynamics is the study of energy and its transformations Kinetics is the study of rates of reactions Quantum mechanics helps us study the mechanisms of chemical reactions ie reaction pathways Classical thermodynamics is based upon the equilibrium state It is based upon the macroscopic ie little underlying knowledge of the crystal structure is required measure of the intensive and extensive properties of phases in the system Intensive properties can be specified at a particular point in the system These properties are not additive in the sense that they do not require a specific quantity of sample for the property to Which they refer Included are temperature density pressure solubility heat capacity viscosity meltingboiling point color resistivity Extensive properties are additive by virtue of the fact that their values constitute a property of the Whole system body Included are volume mass enthalpy heat energy calories joules Using empirically derived parameters that describe the chemical and physical state of matter thermodynamics predicts the energy changes for any given transformation In essence it tells us the most stable state or set of phases that should be present given certain pressure P temperature T and chemical conditions X PIX Thermodynamics predicts What mineral assemblages should occur in a given environment assuming they are in chemical equilibrium The term phase is part of the system that is spatially uniform We can use the term phase synonymously With mineral if it is homogeneous at the atomic scale A phase can be considered a solid liquid or gas With each having its own stability region or field in terms of chemical pressure and temperature conditions Phase Physically distinct mechanically separable homogeneous Phases are described by independent chemical species known as components eg Quartz SiO2 or Kyanite AlZSiO5 Components are the smallest number of chemical entities to define the composition of all phases in the a system eg Si and 02 are components of quartz or A1203 and SiO2 are components of Kyanite System a quantity of material defined by weights or numbers of molecules contained Within a set of boundaries ie imagine a container around the system but the container is not part of the system We generally classify systems into three conditions Isolated systems This is an ideal situation Where there is absolutely no transfer of energy or matter across the boundaries of the system Closed systems In this case there are possibilities for energy transfer but not matter The matter can change in composition due to chemical reaction We sometime assume this in certain geologic environments Open systems Exchange of both energy and matter This most often the rule in geologic environments Example of phase equilibria H20 Although thermodynamics tell us What reactions should take place it does not tell us how fast a reaction Will go Unary systems Examples given are H20 SiOz and AIZSiO5 Where each can be considered a single component system with multiple phases at different temperature and pressure conditions Anatomy of a phase or stability diagram Li uid water 0 m an increasing pressure atm 1 3323 i esven lt34 Gas 4 water vapor u IUD Freezing Boiling Increasmg temperature is 4 Divariant area region Where both T and P can be varied independently Without changing the number of the phases present Univariant curve loci of points curve Where two phases coexist Only T or P can be varied independently Without changing the number of the phase present Triple point The location Where three phases can coexist It is an invariant point Where neither T P nor any other intrinsic parameter can be changed Without causing one phase to disappear The liquidvapor curve extends to a point Where the pressure is so great that the phase remains a liquid So great that the fluid is often referred to as a supercritical uid The point in T P space is termed the Critical Point Metastability At each invariant point there is region Where the univariant curve extends beyond slightly into a third phase region The reason for this condition is attributed to the additional energy that is required to nucleate a new phase In the absence of nucleation energy a metastable phase can persist into another stability region A common example is supericooled wa er achieved by placing a bubble free container of distilled water in the freezer When carefully remoVed from the freezer a tap with a knife will cause instantaneous crystallization This is referred to as the latent heat of crystallization and in the case of solidigas transformation the latent heat of vaporization sun 12m mm mm zonn zann aznn Heat absorbed thj Latent heat of vaporization for water Gibbs phase rule p f c 2 where P number of phases the variance or number of degrees of freedom m the system number of components Example with the Iggy we Illlmznll andalusite series Polymorphs of AleiOS Pressure KHobars m mu an H mm Tmpevamve c f is the number of variables that must be fixed to define a particular set of conditions in the system In the case of the kyanite sillimanite andalusite series like the H20 system there is a triple point or invariant point in T and P space It is the unique set of T and P conditions under which all three phases can coeXist This can be expressed by rearranging the Gibbs phase rule f c p 2 In this case c 1 the component is AlZSiOS p 3 there are three phases at this point Therefore f 1 3 2 0 zero degrees of freedom Along the curve or univariant line there is not one unique set of P and T conditions under which two phases can coeXist In this case c 1 the component is AlZSiOS p 2 there are two phases at this point Therefore f 1 2 2 1 one degree of freedom In the divariant or phase regions only one phase can coeXist No unique set of P and T conditions can be defined by the presence of one mineral phase In this case c 1 the component is AlZSiOS p 1 there is one phase at this point Therefore f 1 1 2 2 two degrees of freedom Binary Systems are cases with two components in the system meaning the system can be described by two chemical entities Binary systems are usually discussed in terms of temperature and the percentages of the components present rather than grams of material at a constant pressure T X diagrams Examples of binary systems Water and powdered glass two components H20 SiOZ two phases liquid and solid Ice and powdered glass two components H20 SiOZ two phases both solid Water and oil two components H20 HC two phases both liquids but are considered immiscible no mixing at the molecular level Water and alcohol two components H20 CH3OH one phase a miscible solution Water 10 g and Salt 1g two components H20 NaCl one phase a solution Water 10 g and Salt 10g two components H20 NaCl two phases a saturated solution and excess solid Olivine FosteriteFayalite series one phase miscible solid solution forsterite can occur with a small fayalite content or fayalite with a small forsterite content Plagioclase AlbiteAnorthite series a partial solid solution with a miscibility gap between the end member ie homogeneous plagioclase Albite Silica Two immiscible solids Mineral Assemblages The study of mineral assemblages allows us to understand the conditions of rock formation Which in turn gives rise to insights to geologic process What is the first step in the study of a rock One usually begins by simply compiling a list the mineral assemblage and noting the textural relationships and relative abundances of each phase Example 1 Igneous mineral assemblage rock type Granite Quartz Orthoclase Albite Biotite The chemical system can be described by SiO2 A1203 K20 NaZO FeO MgO H20 Quartz SiO2 Orthoclase ZKAlSi3O8 K20 6SiO2 A1203 Albite 2NaAlSi3O8 NaZO 6SiO2 A1203 Biotite ZKMgZFe Si3A1 010OH2 K20 6s1o2 A1203 4MgO 2FeO 2H20 gtknote There are likely many other trace elements in a granite We Will only consider the major elements for now Relative to the Wide range of chemical X temperature T and pressure P conditions that exist in the earth if these minerals are texturally uniform equal granular then they can be considered to have formed under very similar conditions ie all around the same time Within a small range of P T X conditions The sequence of events that lead to the formation of a mineral assemblage is termed paragenesis It is assumed that the minerals present formed at or near the conditions of equilibrium ie in its stability field for a given set of P T X conditions In short an assemblage consists of minerals that form under similar P T X conditions Recall Bowen39s Reaction series from your introductory geology class Considered for a closed system case under isobaric conditions in a cooling magma Recall also that the melting and crystallization of a phase is related to 1 Polymerization of Si O tetrahedra 2 Substitution of Al for Si in the tetrahedra 3 Nature of the metal cation compensating charge deficiency ie bond type Phase relations are further modified by composition of the system Geometry Class SiO Example Isolated tetrahedra Nesosilicates 14 Olivines Two tetrahedra Sorosilicates 27 Hemimorphite Ringed tetrahedra C yclosilicates 13 Beryl Single chain Inosilicate 13 Pyroxenes Double Chain Inosilicate 4 11 Amphiboles Sheet Phyllosilcates 25 Elcas Clay 1nerals Quartz Feldspars Framework Tectosilicates 1 2 Feldspathoids Zeolites Example 2 Igneous mineral assemblage rock type Basalt Plagioclase Clinopyroxene Orthopyroxene The chemical system can be described by SiO2 A1203 NaZO FeO MgO CaO Plagioclase Na05 CaO5 AIL5 Si25 O8 14 NaZO 12 Ca0 34 A1203 2SSiO2 Orthopyroxene Hyperstene MgFeSiZO6 MgO FeO ZSiO2 Clinopyroxene Diopside CaMgSiZO6 Ca0 MgO ZSiO2 This mineral assemblage forms under high temperature 1000 to 1200 C and low pressure 1 2 kilobars conditions Eclogite The same chemicals system SiO2 A1203 NaZO FeO MgO CaO can be metamorphosed to a neW assemblage under lower temperature 400 to 800 C and higher pressure 12 to 30 kilobars conditions Kyanite AlZSiO5 Pyrope Mg3AIZSi3O12 Grossular Ca3AIZSi3O12 Omphacite Na pyroxene or diopside With J adeite component Ca Mg Fe SiZO6 augite NaAlSiZO6 jadeite Mineral Assemblages low temperature Let39s reconsider the mineral assemblage found in a granitic rock Quartz Orthoclase Albite Biotite The chemical system can be described by SiO2 A1203 K20 NaZO FeO MgO H20 O2 CO2 Quartz SiO2 Orthoclase ZKAlSi3O8 K20 6SiO2 A1203 Albite 2NaAlSi3O8 NaZO 6SiO2 A1203 Biotite ZKMgZFe Si3Al 010OH2 K20 6s1o2 A1203 4MgO 2FeO 2H20 Upon close inspection one might note that granites are often coated With other mineral products such as Kaolinite AlZSi205OH4 Gibbsite AlOH3 Goethite FeOOH Hematite Fe203 Smectite K025 Na025 Mg2A105 Si4010OH2 nHZO Minerals formed under high PT conditions are not stable near the earth39s surface conditions in the presence of water carbonic acid and oxygen How do primary silicates weather and Why how is this important to pollution problems or global climate change This Will be the subject of later discussions Ionic Potential Mineral behaVior near the earth39s surface may be approached from the standpoint of the geochemical behaVior of their constituent ions in dilute water solutions Behavior of an ion can be characterized by their ionic potential Chargew Ionic potential gt 3 tend to be soluble in water Ionic potential 3 to 12 tend to be insoluble in water Ionic potential gt 12 tend to form soluble hydroxyl complexes ongrue versus rnoongruent disolution Analogy r bumlng of a hydrocarbon that can be represented by the reacuon below CH q quot77gt coz H20 The gases co2 and H20 are colorless and odorless But look at the namel Combustlon ls neyer complete 7 Ones see soot smoke and can smell methane The reason ls that there are partlal reactlons granlte Reactions at surface conditions ie weathering of minerals can be either congruent or incongruent Attacking agents in mineral weathering l acids organic and inorganic 2 dissolved oxygen 3 water Because this is a water dominated system the components in the system are defined by the solid phases the liquid phase water and the dissolved species in the water Congruent Reactions Calcite dissolutionppt CaCO3 gt Ca2 CO3 239 The calcite reaction is pH dependent ie other components are in solution H20 gt H OH39 CO2 H20 gt HZCO3 HZCO3 gt H HCO3 HCO339 gt H CO3 239 Incongruent Reactions Gibbsite formation AlOH3 HZCO3O 7 H20 NaAlSi3O8 gt Na AlOH3 3 H48iO4O HCO3 Kaolinite formation AlZSi205OH4 2H2CO3 9H20 2NaAlSi308 gt 2Na A12s1205OH4 4H4SiO4 2 HCO3 Smectite formation Na025 Al2 A1025 Si375010OH2 nHZO 2 HZCO3 6 H20 225 NaAlSi308 gt 2 Na Nam A12 A1025 Si375010OH2 nHZO 3 H4SiO4 2 HCO3 Stability fields of alteration products assuming equilibrium conditions Paragenesis is related to such factors as 1 Initial composition abundance and texture of primary silicates 2 Generation of acids decomposition of organic matter by microbial activity 3 Rainfall ie flux of water 4 Temperature of reaction Balancing chemical reactions 1 Conserve charge and mass 2 Assume species in reaction 3 Balance cations 4 Balance charge 5 Balance H 6 Check oxygen Example Suppose you want to react carbonic acid and albite in an aqueous system and have gibbsite as the solid reaction product H2co3 NaAlSi308 gt AlOH3 Clearly the above reaction is not mass balanced So you must decide What aqueous species Will be involved Assume bicarbonate sodium and silicon Will be produced The most common species under earth surface conditions are Na H4SiO40 and HCO339 H2co3 NaAlSi308 gt Na AlOH3 3H4SiO4 HCO3 The above reaction is written to balance cations and anions Note also hydrogen in the form of water is needed Below is the final balanced reaction HZCO3 7 H20 NaAlSi308 gt Na AlOH3 3 H4SiO4 HCO3 Chemical weathering and secondary mineral formation Construction of stability diagrams Procedure for constructing activity diagrams This example is simplified for the purpose of demonstration The Athens Gneiss can be represented by mineral assemblage Quartz Muscovite Albite Microcline Kaolinite and Gibbsite Simplifying assumptions Aqueous solution is always present Al is always in a solid phase Si concentrations is fixed by quartz saturation P and T are constant I Write reactions for mineral pairs using ions you wish to plot Kaolinite 5 H20 2 Gibbsite 2 H48i04 Qtz 2 H20 HASin 2 Microcline 9 H20 2H 2K HASiOAO Kaolinite 2 Albite 9 H20 2H 2Na H48i04 Kaolinite Muscovite 9 H20 H 3 Gibbsite 3 H48i04 K 2 Muscovite 3 H20 2 H 3 Kaolinite 2 K Microcline 7 H20 H Gibbsite 3 HASiOAO K 3 Microcline 12 HZO 2 H Muscovite 2 K 6 HASiOAO Albite 7 H20 H Gibbsite 3 H48i04 Na 3Albite K 3H 12 HZO Muscovite 3Na H 6H48i04 Albite K H Microcline Na H ll determine the AG of reaction and solve for K at equilibrium Recall If AG 0 then the reaction will not proceed in either direction at equilibrium state In this case AG 7RTan To calculate the AGWW the AG formzmon must be obtain from a data table such as Robie R A Hemingway B S and Fisher J R 1984 Thermodynamic properties of minerals and related substances at 29815 K and 1 bar 1 0 e5 pascals pressure and higher temperature Bulletin 1452 US Geological Survey Washington DC For the reaction Kaolinite 5 H20 2 Gibbsite 2H48i04 AG f Gibbsite 71155 kJmol AG f Kaolinite 73799 kJmol AGquotf H20 7237 kJmol AGquotf H4810 71308 kJmol AGmwon the products 7 reactants AGmmn 2 x 71155 2 X71308 7 73799 7 5 x 7237 759 kJmol therefore solve for K K 42 x1011 K dH iO Z or log K 7104 log K 2 log aH48104 7104 111 Determine the coordinate system Because the silica activity is fixed by quartz saturation we Wish to display the stability relations for all of the above reactions in terms of K Na and H activities The coordinate system is therefore define by the ratios aK a IN MI IV Determine the relative stability of the none alkaliibearing phases Because kaolinite and gibbsite and quartz do not contain sodium or potassium their stability39s are govern by the silica activity and temperature If quartz saturation is always maintained at an activity of ClHASiOAO 10393 95 the direction of reactions can be assessed For example in step 11 above it was shown that for the reaction of kaolinite mgt gibbsite 2 log aHASin 7104 Therefore under these conditions the equilibrium activity of silica is 10395 4 The reaction will be driven to the left and kaolinite is more stable than gibbsite under these conditions V Assess all the reaction pairs b zero intercept Mineral pairs to be considered Halloysite Kaolinite Muscovite Microcline Albite Gibbsite X X X X X Halloysite X X X X Kaolinite X X X Muscovite X X Microcline X Recall AG rRT aneq Simplifying assumptions 1 solution always present 2 Al always in solid phase 3 Silica is fiXed by quartz saturation 4 P and T are constant at 1 bar and 25 C and 5 Activities of solids and water are unity Kaolinite Gibbsite AlZSi205OH4 SHZO ltmgt 2AlOH3 2H48i04 Keq Zrmsiozto 10gKeq 210 H4SIO4O 104 10 H4SIO4O 520 Note The activity of dissolved silica at quartz saturation see below is greater than the activity of silica with kaolinite and gibbsite in equilibrium Le V395gt 7520 Therefore the above reaction proceeds from right to left Quartz Silica SiOZ ZHZO ltmgt HASiOAo Keq H4SIO4O 10gKeq 10 aH4SIO4O 10 H4SIO4O 395 Halloysite Gibbsite AlZSiZOjOH4 SHZO ltm gt 2A1OH3 2H4SiOA Keq aZH4SIO4O 10gKeq 210 aH4SIO4O 711 10 aH4SIO4O 356 Note The activity of dissolved silica at quartz saturation is less than the activity of silica with halloysite and gibbsite in equilibrium Le V395lt 7356 Therefore the above reaction proceeds from left to right Further note that all gibbsite goes to kaolinite from the kaoliniteigibbsite reaction above Microcline Kaolinite ZKAlSi308 9HZO 2H ltmgt 2K 4HASiOA AlZSiZOjOH4 Keq aZK 4 H4SIOAO Zr1 logKeq 2 log aKJ am 410g ammj 7396 log aKJ am 2 log amsof 7198 Recall that at quartz saturation log a mgof 7395 therefore by substitution log aKJ am 592 Microcline Halloysite ZKAISi3O8 9HZO 2H ltmgt 2K 4HASiOA AlZSiZOjOH4 Keq aZK 4 H4SIOAO Zr1 logKeq 2 log aKJ am 410g awe 7722 10 KM HQ 210 aH4SIO4O 361 Recall that at quartz saturation log a mgof 7395 therefore by substitution log aKJ am 429 Albite Kaolinite 2NaAISi308 9HZO 2H4r lt7gt 2Na 4H48104 AIZSiZOjOH4 K511 01err 4 H4SIO4O Zr1 logKeq 2 log am am 410g amso 044 log aNa am 2 log amsof 7022 Recall that at quartz saturation log a mgof 7395 therefore by substitution 10 N24r HQ 768 Albite Halloysite 2NaAISi308 9HZO 2Hltmgt 2Na 4H48i04 AlZSiZOjOH4 Keq aszr a4H431040 Zr1 logKeq 2 log am am 4 log ammquot 7371 log aNa am 2 log ammf 7185 Recall that at quartz saturation log a mgof 7395 therefore by substitution 10 N24r HQ 605 Muscovite Gibbsite KA13i3010OHZ 9HZO H ltmgt K 3H48i04 3A1OH3 Keq arer 3 Hasiozzo i1 10gKeq 10gaK aH 3 10 msiozzo 1116 logaK am 3 log aHmof 71116 Recall that at quartz saturation logaH4Sio4 7395 therefore by substitution logaK am 069 Muscovite Kaolinite 2KA13i3010OHZ 3HZO 2H ltmgt 2K 3 AlZSiZOjOH4 Keq 10gaZK Zr1 logKeq 2 logaK am 881 logaK am 440 Muscovite Halloysite 2KA138i3010OHZ 3HZO 2H ltmgt 2K 3 AlZSiZOjOH4 Ksq logaZK azm logKeq 2 logaK am 7099 logaK am 7049 Microcline Gibbsite ZKAISi308 7HZO H ltm gt K 3H48104 A1OH3 Keq arer 3 Hasiozzo i1 10gKeQ 10gaK HQ 3 10 H4SIO4O 717 log aKJ am 3 11430 7717 Recall that at quartz saturation logaH4Sio4 7395 therefore by substitution logaK am 468 Microcline Muscovite 3KAISi308 12HZO 2H ltmgt 2K 6H48i04 KAI3 13010OHZ K511 2K4r 6 H4SIO4O ZHQ logKeq 2 logaK am 6 log ammf 71034 logaK am 3 log amof 7517 Recall that at quartz saturation log a mgof 7395 therefore by substitution logaK am 668 Albite Gibbsite 2NaAISi308 7HZO H lt mgt Na 3HASiO4 A1OH3 Keq N34 3 H4SIO4O HQ logKeq logaN3 am 3 log amof 7541 logaNH am 3 log ammf 7541 Recall that at quartz saturation logaH4Sio4 7395 therefore by substitution 10gaNa HQ 644 Albite Muscovite 3NaAISi308 12HZO 2H K ltmgt 3Na 6H48i04 KA13i3OmOHZ Keq 31wr 6 H4SIO4O ZH KQ K511 31wr 6 H4SIO4O HQ 3m KQ 10gKeq 310gaNa HQ 10g H KQ 610 aH4SIO4O 507 3 10 N24r HQ 10g K HQ 610 aH4SIO4O 507 Recall that at quartz saturation logaH4Sio4 7395 therefore by substitution 3 logaNB am VlogaK am 1863 logaN3 aH13logaK am 621 Albite Microcline NaAlSi308 K H ltmgt Na H KaAlSi3O8 Keq Na HQ aK HQ 10gKeq 10gaNa am 10 KM HQ 176 10gaNa HQ 10gaK HQ 176 10gaNa HQ 10gaK aH176 Kaolinite Halloysite AlZSiZOjOH4 ltmgt AlZSiZOjOH4 logKeq 7327 VI Plot lines on coordinates and determine stable forIns Form of equations is y IIIX b Where y 10gaNa am X 10gaK HQ In is the log coefficient


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