Soil CEE 5680
Utah State University
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This 2 page Class Notes was uploaded by Damien Rutherford on Wednesday October 28, 2015. The Class Notes belongs to CEE 5680 at Utah State University taught by Judith Sims in Fall. Since its upload, it has received 15 views. For similar materials see /class/230459/cee-5680-utah-state-university in Civil and Environmental Engineering (CEE) at Utah State University.
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Date Created: 10/28/15
COURSE NOTES CHAPTER 4 Adsorption and Reactions of selected organic molecules on clay mineral surfaces 1 P 81 Introduction 1 quotIt is generally agreed that the clay fraction of soil is the most important in in uencing the reactivity of organic moleculesquot quotAn understanding of the reactivity of even simple organics on clay mineral surfaces whether pristine or chemically modi ed can aid in the prediction and perhaps prevention of groundwater contaminationquot 2 p 82 41 Factors affecting clay surface reactivity Figure 41 p 82 surface functional groups in smectite clay 2 De nitions Lewis Acid An electron pair acceptor AM B gt AlzB eq 1 Lewis Base 2 An electron pair donor Bronsted Acid 2 A proton donor In aqueous solutions all acids transfer proton to water molecule to give hydronium ion H30 AlOHSi gtO H eq 2 0 M 0M 6q 3 Bronsted Base A proton acceptor In aqueous solutions a base accepts a proton from a water molecule forming the hydroxide ion OH 3 In presence of liquid water edge positions OH groups and Lewis acid sites eg A13 Aquated sites may be source of Bronsted acidity Al0H2 gt O H cq4 4 Terminal OH groups engage in coupling reactions with organic containing functional groups Si OHMge ROH gt SiORedge H20 eq 6 5 Most impgrtant property of smectit clays ability to swell in presence of water and thereby provide access to large internal surface area interlamellar adsorption and reactivity hydrolysis of exchange ions of gallery exchange cations Hydrolysis Splitting by water MH20nXga11ery gt MH20n10Hx391gt 1 H cq 7 6 Fig 41 illustrates ability of smectite clays to shuttle electrons between structural redox centers Fe2 3 and organic molecules adsorbed on the external or internal gallery surfaces Mnlayer RH quot39gt Mn391layer R39 H eq 8 Mn1ayr An mgt Nun1layer AW C10 3 Skip 42 pp 8485 4 p 85 4 3 Adsorption of phenolic compounds 1 haracteristics Bronsted acids tendenCy to ionize oxidation to humic and fulvic acids polymerization reactions 2 Oxidation and oxidative polymerization processes facilitated by clays and other mineral surfaces containing redoxactive metal ions eg CuIl FeIII MnIV 5 p 85 Sec 431 Organo Clays 1 Tendency for smectite clay to adsorb organic guest molecules can be facilitated by ionexchange reactions involving organo cations I 2 p 86 quot Designer Claysquot replace exchangeable Na with alkylammonium cations Implications for engineering quotorgano clays may have utility as selective adsorbents as liners in waste ponds and burial sites p 86 6 Skip 4 32 pp 8688 7 Sec 44 Selected Organic Reactions Sec 4 41 Bronsted amp Lewis Acid Catalysis 1 quotOrganic reactions on clay minerals can be selective amp ef cientquot 2 Example terminal alkene to 2239dialky1ether RCHCH2 H20 gt RCH O CHR where RC3H7 to C14H29 eq 10 I CH3 CH3 This reactions occurs on AlIII CrlII FeIII and CuIIexchanged smectites with speci city 3 Skip the remainder of section to p 93 chemistry not needed 8 Sec 442 Electron Transfer Reactions 1 For an e from Ar ring to metal ion center metal ions must be partially dehydrated to allow for close approach of the two species and for binding of Ar ring to metal center via pi electron donation 2 Example CuII with benzene CuII C6H6 gt CuI C6H6 eq 25 cation benzene radical cation The radical cation reacts further with neutral benzene to initiate further quotOxidationpolymerizationquot reactions leading to formation of p polyphenyl C5H6 C5H6 CuII gt ppolyphenyl CuI Il eq 26 Implications 1 The CuI formed in these reactions can be reoxidized by air thus making the oxidative polymerization reaction catalyticll 2 p 94 Dibenzop dioxin dioxin reacts with CuII smectite to form radical cations Radical cations react to form oxidative polymerization products mainly dimers Suggestions to Oxidative polymerization reaction to convert dioxins to less mobile and perhaps less toxic products 3 p 94 PCP formed 2356 TeCP upon reaction with CuII smectite End Chapter 4