Concepts in Soil Science: Sorption, Ion Exchange, and Redox Processes, Quizzes of Environmental Science

Download Concepts in Soil Science: Sorption, Ion Exchange, and Redox Processes and more Quizzes Environmental Science in PDF only on Docsity! TERM 1 sorption DEFINITION 1 broadly defined as the transfer of ions from the solution to the solid phasegeneral term used when mechanism at surface is unknown TERM 2 specific adsorption DEFINITION 2 ions displace OH-, H+, H2O from surface and form covalent bondslose waters of hydration (inner-sphere) TERM 3 non-specific adsorption DEFINITION 3 ions held in DDL by weak electrostatic bondsretain waters of hydration (outer-sphere) TERM 4 adsorbate DEFINITION 4 material that accumulates at an interface TERM 5 adsorptive DEFINITION 5 molecule or ion in solution that has the potential to be adsorbed TERM 6 adsorbent DEFINITION 6 the solid surface on which the adsorbate accumulates TERM 7 monodentate DEFINITION 7 adsorbed ion forms single covalent bond with a surface TERM 8 bidentate DEFINITION 8 adsorbed ion forms two covalent bonds with a surface TERM 9 mononuclear DEFINITION 9 bidentate surface complex forms 2 bonds with a single metal center TERM 10 binuclear DEFINITION 10 bidentate surface complex forms one bond each with 2 different metal centers TERM 21 sorption of anions reactivity of mineral surfaces DEFINITION 21 similar to cation sorptionterminal OH more reactive than bridging TERM 22 selectivity of anions DEFINITION 22 not well understoodsolution analogyfollows tendency to form insoluble precipsExample: Fe-phosphate, sulfate, nitrate TERM 23 shared charge DEFINITION 23 + charge central atom shares formally with each oxygenZ/# bonded oxygenssmaller shared charge stronger metal- oxygen bondsmaller the shared charge the greater the effective charge residing on each oxygen, the stronger the metal-oxyanion ionic bond TERM 24 oxyanions of weak acids chemisorb optimally at ________ pH DEFINITION 24 moderate to high TERM 25 oxyanions of strong acids chemisorb optimally at ____ pH DEFINITION 25 low TERM 26 oxyanion sorption maximizes near pKa value _____ DEFINITION 26 pKa value of the protonated form of the anion TERM 27 anion sorption disfavored at ____ pH DEFINITION 27 highOH- and carbonatesurface charge TERM 28 desorption of anions DEFINITION 28 orders of magnitude slower than sorption (hysteresis) surface complex (bi vs. mononuclear) more reversible than cations sorption (ligand exchange reaction) TERM 29 Chemical nature of OM DEFINITION 29 Lewis base functional groupsHardness O>N>SCa(hard) vs Cd (soft)Degree of preference reduces with increased adsorption of preferred metalsAffinity sequence:Cu>Ni>Pb>Co>Ca+>Zn>Mn>Mg TERM 30 sorption as a continuous process DEFINITION 30 chemisorption at low end of solubility to precipitation at high end TERM 31 hetergogeneous vs homogeneous nucleation DEFINITION 31 homogeneous:-formation of crystal nuclei pure solutions supersaturated with respect to a solid phase-precipitation begins when solutions are supersaturated by large marginheterogeneous:-solid surface catalyze precipitation reactioncrystallographic similarities-formation of crystal nuclei at surfaces of a diff solid that is present before the initiation of precipitationreduces extent of supersaturation TERM 32 precipitation/co-precipitation DEFINITION 32 can control solubility of abundant elements in soilstrace metals--> chemisorption is dominant TERM 33 coprecipitation DEFINITION 33 mineral must readily dissolve (high Ksp) and recrystallizesimilar ionic radiikinetics not thermodynamicsimportant with redox active elements (Fe, Mn)Mn2+, Cd2+, Fe2+ in calciteCr3+, Mn3+, and V3+ in Fe3+ and Al3+ oxidesCu2+, Zn2+, Ni2+, Co2+ in magnetite TERM 34 adsorption isotherms DEFINITION 34 most common way to represent adsorption dataplot of quantity of adsorbate retained by the solid as function of the equilibrium concentration of the adsorptivesuggests but does not confirm adsorption mechanism TERM 35 L-type DEFINITION 35 langmuirhigh affinity, chemisorption TERM 46 Analytical Methods for Characterizing Metal Attenuation DEFINITION 46 Two approaches used to infer (bio) availability and/or characterize attenuation mechanisms:chemical extraction vs. spectroscopic/microscopic techniquesbioavailability may be more directly evaluated using organisms TERM 47 analytical challenges for metal attenuation DEFINITION 47 contaminant characterization within heterogeneous media hydrated samples discriminating between surface and bulk species defining relative components (and end-products) TERM 48 Simple Soluble Metal Extraction Techniques DEFINITION 48 Toxicity Characteristic Leaching Procedure (TCLP) Synthetic Precipitation Leaching Procedure (SPLP) Deionized Water Extraction (DI Water) Limitations unsophisticated measurement of immobilization does not identify attenuation mechanisms TERM 49 Sequential Extraction Procedure DEFINITION 49 series of chemical leaches to determine the various metal binding phases provides semi-quantitative assessment of metal attenuation mechanisms aids in determining mass of metal in each fraction provides means of assessing long-term stability of natural attenuation TERM 50 documented SEP uses DEFINITION 50 site investigationsminingmineralogical evaluationrisk assessment TERM 51 Remedial Technology Screening and Performance Demonstration DEFINITION 51 natural attenuation soil flushing surfactants (Bio) phytoremediation stabilization - lime, fly ash, bentonite, steel powder, calcium oxyphosphate, zeolite, hydroxyapatite, iron-oxide waste product, ferrous-iron TERM 52 Spectroscopic/Microscopic Limitations and Attributes DEFINITION 52 Attributes: specificity for target direct information on bonding spatial and structural information Limitations: relevance to reactivity (surface or bulk information) detection limits access and interpretation TERM 53 Spectroscopic Methods DEFINITION 53 Elemental: energy dispersive and x-ray fluorescenceMolecular Phase: vibrational: infrared (FTIR) and Raman optical: UV-Visible thermal and diffraction: TGA, XRD Atomic: Magnetic: NMR, EPR X-Ray: X-Ray photoelectron and Auger spectroscopy (XPS), X-Ray absorption spectroscopy (XAS) TERM 54 Ideal Qualities of the Method DEFINITION 54 no sample distortion (analysis of hydrated sample)low detection limitsability to deal with heterogeneityelemental specificityease of access TERM 55 General Approach - MNA DEFINITION 55 Screen Metals and Site (MNAtoolbox) Evaluate Data Needs (REgulatory) Demonstrate MNA Present findings and Closure Plan TERM 56 Preliminary Screening DEFINITION 56 evaluate COCs to determine attenuation mechanisms determine MNA mitigators review RODs evaluate receptor status screen site (scorecard) develop conceptual MNA model preliminary evaluation of data needs TERM 57 Evaluate Data Needs (regulatory Interactions) DEFINITION 57 Ascertain data regulators will need determine what data regulator will require explain proposed characterization activities characterize regulators requirements for closure finalize data needs and develop work plan TERM 58 Characterize Attenuation Mechanism(s) DEFINITION 58 differentiate between total and soluble levels (SPLP, TCLP, DIWET, others) analyze for metal fractions (SEP, SEM/AVS) characterize stability of complexes analyze for potential MNA mitigators TERM 59 Present Findings and Closure Plan DEFINITION 59 Present Findings: provide a clear picture of contaminant behavior supported by mathematical and statistical tools a defensable plan based on a clear understanding of attenuation mechanisms Closure Plan: model to determine best siting for proposed down gradient, or vertical assessment points develop a contingency plan determine performance goals and system evaluation criteria TERM 60 Case Study DEFINITION 60 SEP- performed to characterize metal sinks provides qualitative assessment of metal attenuation mechanisms aids in mass balance calculations provides means of assessing long-term stability of natural attenuation TERM 71 Redox RXN DEFINITION 71 involves transfer of electrons between chemical species in a rxn TERM 72 Reducing Agent DEFINITION 72 substance losing electrons and being oxidized TERM 73 oxidizing agent DEFINITION 73 substance gaining electrons and being reduced TERM 74 electromotive force DEFINITION 74 EMFthe voltage generated by electrons following from anode (Zn bar) to cathode (Cu bar)related to the free energy of a redox reaction TERM 75 Free Energy of the rxn DEFINITION 75 deltaG(r) = -nFEhdeltaG(r)= free energy of the rxn in any stateE=EMFn= # of electrons transferredF=Faradays(96.42 kJ/(volt x gram equivalent) TERM 76 nernst equation DEFINITION 76 Eh=Eh^o - 0.059/n log (reduced molecule)/[(oxidized molecule)(H+)^m]Ox. Species +mH+ + ne- = reduced molecule TERM 77 deltaG allows us to predict whether a rxn is spontaneous as written DEFINITION 77 deltaG= -RTlnKdeltaG= (-) is spontaneous (+) is non- spontaneousso for deltaG(r) = -nFE:a deltaG= (-) rxn means E must be positive TERM 78 Eh increases DEFINITION 78 increase in activity of oxidized speciesincrease in proton activity TERM 79 Eh decreases DEFINITION 79 increase in activity of reduced species TERM 80 Eh values range DEFINITION 80 0.500 volts (strongly oxidized) to -0.300 volts (strongly oxidized) TERM 81 ____ not easily transported DEFINITION 81 H electrodecalomel commonly used:Hg2Cl2 + 2e- = 2Hg+ + 2 Cl- TERM 82 concept of pe DEFINITION 82 free e- do not exist in aqueous solns we can still quantify degree of e- availability (e-) symbolizes electron activity measures tendency of soln to accept or donate e-s Eh (volts) = 0.059 pe Eh and pe for half runs are interchangeable in soils pe values range from -6 (strongly reduced) to 12 (strongly oxidized) TERM 83 Reducing soils have ___ value of (e-), ____ pe DEFINITION 83 highlow TERM 84 oxidizing solns have ____ value of (e-), ___ pe DEFINITION 84 lowhigh TERM 85 Depletion of O2 in H2O-Logged Soil DEFINITION 85 microbial activitylow H2O solubility (8ug/l) TERM 96 Redox Couple: Nitrogen DEFINITION 96 nitrate (NO3^-) most stable form in aerated soils moderate reducing conditions NO3^- -->N2 (denitrification) strongly reducing conditions N2 --> NH4^+ thermodynamically possible (enzyme catalyzed in algae/plants N-fixation) oxidation of N2 to NO3^- thermodynamically favorable in aerated soils, yet it does not occur TERM 97 Redox Couple: Sulfur DEFINITION 97 -aerobic soils SO4^-2 is the stable form-reducing conditions SO4^-2 biologically reduced to H2S(g)-exposure to atmosphere produces acid sulfate soils-semiarid regions sulfate reduction causes a build-up of alkalinity Na2SO4 --> NaHCO3 + H2S(g) ph may increase to greater than 8 TERM 98 Redox Couple: Sulfides DEFINITION 98 Kso= (M^2+)(S^2-) TERM 99 Use of Redox Potentials DEFINITION 99 Determine depletion of oxidants (Nitrate and oxygen) conditions favorable for increased bioavailability of heavy metals charges in plant metabolism location of wetlands TERM 100 Redox Potentials measured in the field are unreliable, Why? DEFINITION 100 mixed potentials EMF function of concentration numerous solids and molecules negligible effect on electrode measurements (inert behavior O2 NO3^- N2, appropriate choice of solid phase Mn) soils seldom if ever at equilibrium more value for anaerobic systems compared to aerobic TERM 101 alternatives to Eh DEFINITION 101 -Indicators (also pH indicators, react with soil components)-Cr oxidation-Ferrous Fe test-Common scents TERM 102 Bartlett and Berner DEFINITION 102 due to difficulty of measuring a thermodynamically meaningful Eh in soils a new system of classification proposed by them Bartlett: soils separated into 6 categories according to redox behavior in fieldeach category represents a range in electron liability (el) or reactivity/availabilityBerner: initial distinction based on oxygen content TERM 103 Oxic Characteristic Phases DEFINITION 103 Fe-oxides, Mn-oxides, no OMDissolved Gases: O2>30 TERM 104 Suboxic and Anoxic Characteristic Phases DEFINITION 104 Fe-oxides, Mn oxides, minor OMDissolved Gases:Suboxic: O2<30 and >or= 1Anoxic: O2<1 TERM 105 Sulfidic and Nonsulfidic Characteristic Phases DEFINITION 105 OM, pyrite, marcasite, rhodocrositeDissolved Gases:Sulfidic: H2S>or=1Nonsulfidic: H2S<1 TERM 106 Postoxic Characteristic Phases DEFINITION 106 Low-temp Fe2+ and Fe3+ silicates, siderite, rhodocrosite, minor OM, no silfide minerals TERM 107 Methanic Characteristic Phases DEFINITION 107 Siderite, rhodocrosite, earlier formed sulfide minerals, OM TERM 108 superoxic, very low el DEFINITION 108 soils contain very high levels of oxidants, especially Mn- oxidesMany rhizosphere soils and certain dark colored A horizons developed from calcareous rock very high in Fe and Mn TERM 109 manoxic, low el DEFINITION 109 highly oxidizing soils that are well-drained, contain mature humus, are mineralizing and nitrifying when moist, and are free of gluey mottles throughout the profileExamples, tall corn or alfalfa fields, beech-maple climax forests TERM 110 Suboxic, medium el DEFINITION 110 These soils are oxidized and have nitrates present, but they also have significant potentials for reduction.Reducing tendency is balanced against oxidizing propensity.Examples: organic horizons in well- to moderately-drained forest soils, well cured composts, and recently manured well or moderately-well drained soils TERM 121 structural environment of metal will alter its _____________ DEFINITION 121 reduction potentialFe in silicate vs. Fe in oxide vs. Fe in solution TERM 122 Two dimensions vs three dimensions DEFINITION 122 - presence of other cations and ligands:competitive adsorptionprecipitation and coprecipitation-kinetics vs thermodynamics-important engineered remediation technique TERM 123 ferrolysis DEFINITION 123 overall process of soil acidification by alternating iron reduction and oxidation TERM 124 acid sulfate soils DEFINITION 124 oxidation of exposed sulfide minerals generating acidity and sulfate minerals TERM 125 pe DEFINITION 125 similar to pH it is the negative log of the electron activity sometimes referred to as virtual electron activity TERM 126 singlet oxygen DEFINITION 126 no unpaired electrons (excited oxygen) TERM 127 Triplet oxygen DEFINITION 127 two unpaired electrons (ground state) TERM 128 aluminol group DEFINITION 128 edge AlOH group TERM 129 hard base DEFINITION 129 the donor atom is of low polarizability and high electronegativity, is hard to reduce, and is associated with empty orbitals of high energy and is thus unaccessible TERM 130 acceptor acid DEFINITION 130 the acceptor atom is of high positive charge and small size, and does not have easily excited outer electronsnot polarizable and associates with hard bases through ionic bonds TERM 131 inner-sphere complex DEFINITION 131 when metal ions and ligands directly interact in solutionno water molecules are present between the metal ion and ligand TERM 132 lewis acid DEFINITION 132 an electron pair acceptor TERM 133 lewis base DEFINITION 133 electron pair donor TERM 134 outer-sphere complex DEFINITION 134 when a water molecule is positioned between the metal ion and the ligand TERM 135 silanol group DEFINITION 135 edge SiOH group