WWW.DISSERTATION.XLIBX.INFO
FREE ELECTRONIC LIBRARY - Dissertations, online materials
 
<< HOME
CONTACTS



Pages:     | 1 |   ...   | 2 | 3 || 5 | 6 |   ...   | 12 |

«THERMODYNAMIC MODELING OF METAL ADSORPTION AND MINERAL SOLUBILITY IN GEOCHEMICAL SYSTEMS A Dissertation Submitted to the Graduate School of the ...»

-- [ Page 4 ] --

In the experiments conducted at an ionic strength of 10"1 M, adsorption of Li and Rb was ' approximately 5% or less under the pH conditions studied; in experiments with an ionic strength of 10"25 M, the maximum extent of Li and Rb adsorption that was observed under any of the pH conditions was 10-15%. To compare, the Cd adsorption experiments reported here were conducted at an ionic strength of 0.1 M, using the same bacterial concentration as we used in the Li and Rb experiments. Although the Cd molality in these experiments is nearly four times that of Li or Rb in their adsorption experiments, approximately 75% of the Cd in solution adsorbed onto cell walls at pH 5 (Figure 2.3 A), compared to less than 5% adsorption for the Li and Rb.

2.4 Discussion 2.4.1 Thermodynamic Modeling The objective of the thermodynamic modeling of the experimental data was to determine if a stability constant for the monovalent-bacterial surface complex could account for the adsorption behavior as a function of NaC104 content for each cation studied. We use a non-electrostatic surface complexation model to describe proton and 5.5

–  –  –

metal adsorption onto the cell wall functional groups of B. subtilis. A system of mass action equations is used to calculate the distribution of protons and metal cations between the bacterial cell wall functional groups and the solution. In this approach, the

proton-activity of the cell wall is ascribed to the deprotonation behavior of cell wallassociated organic acid functional groups:

–  –  –

where Ai represents a distinct organic acid functional group type, and R represents the bacterial cell wall macromolecule to which the functional group A/ is attached. The

mass action equation for the deprotonation reaction is:

–  –  –

represent molar concentrations of the bacterial surface species, and aHt is the activity of aqueous protons in the bulk solution. We use a four-site ( 7 = 1 - 4) non-electrostatic model (NEM), with protonation constant (pKa) values of 3.3, 4.8, 6.8, and 9.1, to describe proton binding onto the cell wall (Fein et al. 2005). We refer to these sites as Sites 1 - 4, respectively.

Bulk adsorption observations can not be used to distinguish between cation binding to specific bacterial surface sites and non-specific cation binding that results from electrostatic attraction by a surface electric field. Our objective is to model this interaction as binding to specific sites, and therefore as a competition reaction.

Experimental measurements of the extent of adsorption as a function of pH in singlemetal systems can be used to constrain which sites are involved in the adsorption reactions and to determine the stability constants for the important bacterial surface complexes (e.g., Fein et al. 1997; Cox et al. 1999; Haas et al. 2001; Ngwenya et al.

2003). However, there are two competing types of monovalent cations present in each of our experimental systems: Li+ or Rb+ as the adsorbing metal of interest, and Na+ from the NaC104 ionic strength buffer. We explicitly account for competition by including metal binding reactions for both cations that are present in each system in our models

according to:

–  –  –

where ht represents the monovalent metal of interest (Li+ or Rb4) in equation (3). The

equilibrium constants (Keq) for complexation reactions (3) and (4) are defined by:

–  –  –

functional group A,-, [R-A£Mf] represents the concentration cell wall functional group A, that is complexed with metal M, and OM+ is the activity of the monovalent metal of interest in solution after equilibrium is attained.

Equations (2), (5), and (6) can be used, together with pH measurements, measurements of the extent of Li or Rb and Na adsorption, and mass balance constraints on Na and Li or Rb, to determine the unknown values of KM and K^a. However, because the extent of Na that adsorbs in each experiment cannot be measured directly, it is not possible to solve for KN0 directly. We can use multiple measurements of Li or Rb adsorption, in experiments conducted with varying total Na concentrations, to constrain the value of Km using an iterative approach to determine simultaneously the best-fitting stability constant values for Na and the adsorbing metal of interest. In this approach, we fix a value for Ksa, and use the data to solve for a value for KM- We systematically vary the fixed value for K^a over a wide range of possible values, determining the value that yields the best overall fit to the data. The fixed value of log KN0 was initially varied between 0 and 10, in increments of 1. For both the Li and Rb data, the model best fits the data when the log K^a value was fixed at 2. To more precisely determine the KN0 value, the value of log K^a was then varied between 1.0 and 3.0 in increments of 0.1 to determine the overall best fit for each metal.

We used the computer program FITEQL 2.0 (Westall 1982) to solve for the stability constants for the metal-bacterial surface complexes. This program accounts for the aqueous speciation of each metal, and all metal-surface complexes. Li, Rb, and Na are present almost exclusively as free monovalent cations in solution under our experimental conditions. We include aqueous cation hydrolysis reactions, using the constants reported by Baes and Mesmer (1976). The relative goodness of fit of each model is determined by comparing the overall variance parameter, V(Y), calculated by FITEQL.





2.4.2 Modeling of monovalent cation adsorption to B. subtilis Little adsorption of Li or Rb was observed at pH 3, and significant adsorption was observed in the pH 5, 7, and 9 experiments. Thus, we conclude that Site 1 (with a pKa value of 3.3) on the bacterial surface does not significantly contribute to the overall adsorption of monovalent cations. Adsorption of both Li and Rb increases significantly from pH 3 to pH 5, and we ascribe this increase to Li and Rb binding directly onto Site 2 (the site with a pKa value of 4.8). Thus, we determine the binding constants for the bacterial surface complexes that are formed by the binding of the monovalent cations onto Site 2, using the pH 5 data only and assuming that the adsorption under these pH conditions involves binding onto Site 2 only. This approach is reasonable because at pH 5 more than 98% of the Site 3 (with a pKa value of 6.8) functional groups are protonated and, therefore, are unlikely to contribute significantly to Li, Rb, or Na binding.

The best-fitting models to the pH 5 data for Li+ and Rb+ adsorption are shown as solid curves in Figures 2.IB and 2.2B, respectively. We calculate a log Ku value of 2.0, and a log K^a value of 2.3 using the pH 5 Li+ adsorption data; and a log KM value of 1.9 and a log KNQ value of 1.5 using the pH 5 Rb+ adsorption data. To constrain the error of the log KM and Log Ku values, we fixed the log K^a values in each model, and systematically varied the log KM and Log Ku values in increments of ±0.1 log units, calculating the extent of adsorption that would be predicted in each case. A variation of ±0.2 log units in the Rb and Li log lvalues (plotted as dashed curves in Figures 2.2B and 2.IB, respectively) is sufficient to describe the variation in the data.

In order to test whether the monovalent cations adsorb to Sites 3 or 4 under our experimental conditions, we used the calculated KNa, KL„ and KM stability constants for Site 2 to predict the extent of Li or Rb adsorption that would occur at pH 7 and 9, assuming that only cation-Site 2 binding occurs for each metal. The results of this calculation for pH 7 and 9 appear in Figures 2.1 A and 2.2A as grey and dashed curves, respectively. Li and Rb adsorption is predicted to increase somewhat from pH 5 to 7 and to remain essentially unchanged between pH 7 and 9 (Figures 2.1 A, 2.2A). The predicted increase from pH 5 to 7 arises due to the higher concentration of deprotonated Site 2 sites at pH 7 relative to pH 5. From pH 7 to 9, there is little change in the concentration of deprotonated Site 2 sites, so the extent of cation binding onto Site 2 is predicted to remain constant for both Li and Rb. The predicted increase in the extent of Rb adsorption from pH 5 to 7 is larger than that predicted over the same pH interval for Li adsorption because KN0 in the Li model is larger than Ku, so as sites deprotonate going from pH 5 to 7, Na outcompetes Li for the available sites. The opposite trend occurs in the Rb model, where KNG is smaller than KM so Rb can better compete with Na than does Li under the same circumstances. The observed extents of Li and Rb adsorption agree within experimental uncertainty with the predicted adsorption behaviors for the pH 7 and 9 conditions, suggesting that there is no significant interaction between the monovalent cations and Sites 3 or 4. Therefore, the only stability constants that we can determine from our data are those for the monovalent cations bound to Site 2.

The similarities in the log K values calculated for Li, Rb, and Na, and the relatively large uncertainties associated with them lead us to propose that reasonable estimates of the adsorption behavior of monovalent cations can be obtained by using a single averaged value for the stability constant for all monovalent cation-bacterial

–  –  –

monovalent metal adsorption onto Site 2 of B. subtilis is 1.9 ± 0.3.

The Li- and Rb-Site 2 stability constants are small relative to those of divalent and trivalent metals, consistent with our observations of less extensive monovalent metal adsorption compared with that of higher charged cations. For example, using the same modeling approach applied here and the same reaction stoichiometrics, Gorman-Lewis et al. (2005) report a log stability constant value of 6.2 ± 0.3 for the binding of the uranyl cation (UC^24) to Site 2 of B. subtilis. Similarly, Borrok et al. (2007) calculate Site 2 log stability constant values of 3.3 for Ni and 4.7 for Pb. Although these constants are large relative to those we calculate for monovalent cations in this study, monovalent cations are often present in natural systems and in laboratory experiments at concentrations that are orders of magnitude greater than those of the higher-charged cations of interest. Thus, monovalent cations may be able to compete effectively for adsorption onto bacterial surface functional groups in these experiments.

2.4.3 Monovalent cation competition with Cd Most experiments that have measured metal adsorption onto bacteria have been conducted using a monovalent electrolyte that is present at concentrations up to several orders of magnitude greater than that of the adsorbing metal of interest. Under these conditions, monovalent cations can compete effectively for surface sites. If metal adsorption in these studies is modeled using a non-electrostatic approach and if the competition by monovalent cations is not accounted for in the thermodynamic calculations, then the calculated stability constants for the metal-bacterial surface complexes would need to be corrected. We determine the magnitude of this correction for Cd-bacterial surface complexes, using Cd-J5. subtilis adsorption data from pHdependent adsorption experiments reported in this study (Figure 2.3A) and from isotherm adsorption data reported in Mishra et al. (2008) as examples. The data of Mishra et al. (2008), shown in Figure 2.4, were selected because they are isotherm experiments conducted as a function of Cd concentration at pH 5.9, so all of the Cd adsorption in these experiments can be attributed to Cd-Site 2 binding. The experiments in Mishra et al. (2008) were conducted with 10 g l"1 bacteria suspended in a 0.1 M NaClC4 electrolyte at afixedpH of 5.9 ± 0.2. Initial Cd solution concentrations in the TO U 20 Total Cd in System (ppm) Figure 2.4: Cd adsorption to 10 g l"1 B. subtilis cells in 0.1 M NaC104 electrolyte at pH

5.9±0.2. Adsorption models with and without Na-Site 2 complexation included yield identical best fits (solid curve) to the data. Data are from Mishra et al. (2008).

experiments varied between 5 and 205 ppm. We use the same modeling approach employed by Mishra et al. (2008), but account for Na+ binding to Site 2 in order to determine the magnitude of change in the calculated Cd stability constant for this site.

The models with and without Na+-Site 2 binding provide identical fits to the Cd adsorption data (Figure 2.4), but the stability constant calculated for the Cd-Site 2 surface complex increases significantly when the Na+ competition reaction is considered.

Without considering direct competition of Na+ with Cd2+, the calculated best-fitting log stability constant value for the Cd-Site 2 complex is 3.4. Including the Na-Site 2 complexation reaction in the model yields an increased calculated best-fitting Cd-Site 2 log stability constant value of 4.4.

We model pH-dependent adsorption data between pH 2 and 5.5 (Figure 2.3A) using the same modeling approach. The calculated log stability constant value for the Cd-Site 2 complex is 3.8 without Na+ competition considered (dashed curve), and 4.4 with Na+ competition at Site 2 (solid curve). Notably, the model that includes the Na+ competition reaction at Site 2 fits the data better than the model without this reaction.

Additionally, the magnitude of the correction should be less for cations such as UC2+2 that display a higher affinity for the bacterial sites than does Cd+2.



Pages:     | 1 |   ...   | 2 | 3 || 5 | 6 |   ...   | 12 |


Similar works:

«Chapter from Achin Vanaik (editor), Selling US Wars (Interlink Publishing, 2007) The Empire of Fear Zia Mian Whatever they fear from you, you’ll be threatened with. —Seneca (Roman philosopher and statesman, 4 BCE–65 CE) In late February 2001, a year after President George W. Bush took office, his secretary of state, Colin Powell, spoke on the subject of Iraq and its military capabilities. Ten years had passed since the 1991 Gulf War, a decade marked by international inspections aimed at...»

«Humanities 2015, 4, 885–904; doi:10.3390/h4040885 OPEN ACCESS humanities ISSN 2076-0787 www.mdpi.com/journal/humanities Article The Ubiquity of Humanity and Textuality in Human Experience Daihyun Chung Department of Philosophy, Ewha Womans University, Seoul 120-750, South Korea; E-Mail: chungdhn@ehwa.ac.kr; Tel.: +82-10-6286-9233 Academic Editor: Albrecht Classen Received: 16 June 2015 / Accepted: 19 November 2015 / Published: 27 November 2015 Abstract: The so-called “crisis of the...»

«Families Precede Nation and Race?: Marriage, Migration, and Integration of Japanese War Brides after World War II A DISSERTATION SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY Masako Nakamura IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY (History) Erika Lee and Elaine Tyler May August 2010 © Masako Nakamura, 2010 Table of Contents List of Figuresii Introduction-1 Chapter 1 Families Precede Nation and Race?: The 1947...»

«UNIVERSITÀ DEGLI STUDI DI NAPOLI “FEDERICO II” FACOLTÀ DI INGEGNERIA DOTTORATO IN INGEGNERIA DEI MATERIALI E DELLE STRUTTURE XXIV CICLO TOWARD A NEW THERMOPLASTIC EPOXY-BASED SYSTEM: NANOCOMPOSITE AND FIBRE REINFORCED MATERIAL BY REACTIVE PROCESSING Ph.D. Dissertation Candidate: Angelo Petriccione TUTOR: PROF. ING. MICHELE GIORDANO CO-TUTOR: DOTT. ING. MAURO ZARRELLI COORDINATOR: PROF. ING. GIUSEPPE MENSITIERI DECEMBER 2011 This thesis is submitted in fulfilment of the requirements for...»

«The Riddles of Philosophy By RUDOLF STEINER THE ANTHROPOSOPHIC PRESS SPRING VALLEY NEW YORK This volume is a translation of Die Rätsel der Philosophie (Vol. 18 in the Bibliographic Survey, 1961). Copyright © 1973 by Anthroposophic Press, Inc. Library of Congress Card No. 73-89784 This translation has been authorized for the Western Hemisphere by the Rudolf Steiner Nachlassverwaltung, Dornach, Switzerland Printed in the United States of America TABLE OF CONTENTS Introduction by Fritz C. A....»

«CONTACT STRUCTURES ON OPEN 3-MANIFOLDS James J. Tripp A Dissertation in Mathematics Presented to the Faculties of the University of Pennsylvania in Partial Fulllment of the Requirements for the Degree of Doctor of Philosophy John B. Etnyre Supervisor of Dissertation David Harbater Graduate Group Chairperson Acknowledgments Thank you to John Etnyre, my advisor, and Stephan Sch¨ nenberger for many helpful o conversations and for reading drafts of this work. Also, thank you to Ko Honda, Will...»

«DEVELOPMENT OF IMPROVED TRAVELER SURVEY METHODS FOR HIGHSPEED INTERCITY PASSENGER RAIL PLANNING A Dissertation by BENJAMIN ROBERT SPERRY Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY May 2012 Major Subject: Civil Engineering Development of Improved Traveler Survey Methods for High-Speed Intercity Passenger Rail Planning Copyright 2012 Benjamin Robert Sperry DEVELOPMENT OF IMPROVED TRAVELER...»

«K O E FANĀ FOTU´: SUCCESS IN MOTION, TRANSFORMING PASIFIKA EDUCATION IN AOTEAROA NEW ZEALAND 1993-2009 A thesis submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy in Pacific Studies and Education at the University of Canterbury Christchurch New Zealand Lesieli Pelesikoti Tongati‘o © ii MINISTRY OF EDUCATION STATEMENT 15 April 2010 Approval is given for Lesieli Pelesikoti Tongati‘o to use and analyse information and data, gathered during the course of her...»

«An Investigation into Communication Strategy Usage and the Pragmatic Competence of Taiwanese Learners of English within a Computer Mediated Activity Thesis Submitted for the Degree of Doctor of Philosophy at the University of Leicester by Ying-Chuan, Wang School of Education University of Leicester September 2008 ABSTRACT In order to increase the competitiveness of Taiwan to international environment, Taiwanese Government has become aware of the importance of English in reforming English...»

«COMPOSITE SERVICE DISCOVERY, DESCRIPTION AND INVOCATION By QIANHUI ALTHEA LIANG A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA Copyright 2004 by QIANHUI ALTHEA LIANG To My Mother and Father ACKNOWLEDGMENTS First and foremost, I would like to express my deepest gratitude to my advisor, Dr. Stanley Su, for giving me the opportunity to work with him and to study...»

«Murderous Visions of Relativity In the Novels Das Parfum and Oceano mare Mattia Marino by BEYOND MOURNING Social rites attempt to fill in the bodily gaps left by death. The aesthetic rituals of the novels Das Parfum (1985) by Patrick Süskind and Oceano mare (1993) by Alessandro Baricco come to terms with death in representations of murder which convey a relativist conception of being as presence, based on creative and critical dissent from the social resentment revolving around the dualist...»

«Body and Soul in Ancient Philosophy Edited by Dorothea Frede and Burkhard Reis Walter de Gruyter · Berlin · New York Contents Introduction....................................... 1 I. Presocratics Carl Huffman The Pythagorean conception of the soul from Pythagoras to Philolaus.......................................... 21 Christian Schäfer Das Pythagorasfragment des Xenophanes und die Frage nach der Kritik der...»





 
<<  HOME   |    CONTACTS
2016 www.dissertation.xlibx.info - Dissertations, online materials

Materials of this site are available for review, all rights belong to their respective owners.
If you do not agree with the fact that your material is placed on this site, please, email us, we will within 1-2 business days delete him.