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Studies on Chernical Speciation of Some Trace Metals in the Aquatic

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Studies on Chernical Speciation of Some Trace Metals in the Aquatic Studies on Chernical Speciation of Some Trace Metals in the Aquatic and the Terrestrial Environment Tat Ting Michael Lam, B.Sc., B.Ed. A thesis submitted to the Faculty of Graduate Studies and Research in partial fûlfilment of the requirements for the degree of Doctor of Philosophy Department of Chernistry Copyright O Carleton University Ottawa, Ontario 1998, Michael T. Lam National Library Bibliothèque nationale I*m of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. nie Wellington Ottawa ON K1A ON4 OttawaON K1AON4 Canada Canada Your fila Votre refermce Our fik Notre réference The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant a la National Library of Canada to ~ibliothe~uenationale du Canada de reproduce, loan, distribute or sell reproduire, prêter, distribuer ou copies of this thesis in microfom, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/fb, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantiai extracts fkom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimes reproduced without the author7s ou autrement reproduits sans son permission. autorisation. New analytical techniques and methods for detennining chernical speciation of sorne trace metals in the aquatic and the terrestrial environment have been investigated and developed. Rotating disk electrode voltamrnetry (RDEV) in conjunction with anodic stripping voltamrnetry (ASV) with a thin mercury film electrode (TMFE), or with a Nafion-coated thin mercury film electrode (NCTMFE) has been evaluated far direct determination of lead and cadmium speciation in aqueous solutions containing dissolved organic matter. The RDEV technique has been also employed to estimate dissociation rate constants and diffusion coefficients. Pseudopolarographic analysis of aqueous sarnples containing Cd or Pb and a well-charactenzed fulvic acid. and of samples of Rideau river surface water show that NCTMFEs provide interference-free determination, and give well-defined pseudopolarograms for determination of stability constants. For detemination of dissociation rate constants of nickel complexes, Cornpetitive Ligand Exchange / Adsorptive Cathodic Stripping Voltarnrnetry (CLE/AdCSV) usin; high- frequency square-wave voltamrnetry has been developed as Anodic Stripping Voltarnrnetry cannot take advantage of high-frequency square-wave voltarnmetry to achieve the extremely high sensitivity required for determininç trace concentrations of nickel in unpolluted waters. Application of the CLE/AdCSV method to aqueous samples containing dissolved organic mafier shows that complexes having dissociation rate constants from 10" s-l to 10" s-' cm be resolved from very labile complexes, and also from inert complexes. For detemination of chernical speciation of Zn and Cd in soil, High Performance Liquid Chromatography - Microfiltration Method was developed for determination of solution phase, labile-bound, and nonlabile Zn and Cd species. Extraction of metals fiom soil solids was accomplished by using online mircrofiltration which trapped soil solids fiom an injection of a soi1 slurry and allowed the mobile phase to extract metals and cany them to the chromatographie column for separation. The results of this kinetic study of cadmium and zinc sorption/desorption on a well- characterized soi1 show that the metal sorption on the soi1 is a two-step process, involving an initial fast binding followed by a much slower sorption. Experimental diKerentiation of the Cd and Zn species on soi1 was found to be usefùl for understanding the mechanisms of sorption/desorption reactions of Zn(TI) and Cd(Q on soil. 1should like to express my most sincere thanks to Drs. C.L. Chakrabarti and Dr. D.S. Gamble for their supervision, support and guidance. 1should iike to extend my gratitude to the membee of the research laboratory, past and present: John Murimboh, Nouri Hassan, Amina Sekaly, Victor Pavski, Rupa Mandal, Mufida Benyounes for their help. 1 should also like to acknowledge the help of the technical staff: Jim Logan, Michel Grenier and Ali Ismaily. Lastly. I thank rny wife Christine for her love, understanding and support. TBLE OF CONTENTS ... Abstract ..................................................................................................... iii Acknowledgements ........ ........... ........................................................................................ v ......... Table of Contents ....................... ..... ....... ......... ................ vi List of Figures .............................. ........... .......................................................................... s List of Tables ..................................................................................................................... xiv Introduction .................................................................................................................... 1 - - Chemical Speciation.. ... .. ......................................................................................... -7 Speciation Parameters ............................................................................................. 8 Organic Complexants such as Humic Substances in the Natural Environment, and their Effects on Meta1 Speciation in the Freshwater Environment .................... ... 10 Objectives and Goal .............................................................................................. 1 1 Pseudopolarography using Rotating Disk Electrode / Anodic Stripping Voltamrnetry with Thin Mercury Film Electrodes for Determination of Speciation Parameters ...... 13 L. I Introduction .............................. .........................................................................14 The Advantages of Rotatuig Disk Electrode Voltammetry (RDEV) ............ 14 Definition of Lability .................................................................................... 14 Rotating Disk Electrode Voltarnmery/Anodic Stripping Voltarnrnetry using a Thin Mercury Film Electrode ..................................................................... 15 Pseudopolarography ...................................................................................... 18 Nafion-Coated Thin Mercury Film Electrodes (NCTMFE) ......................... 19 2.2 Experimental ...................................... ,. .....22 2.2.1 Chernicals and Reagents ...... .......................................................................... 22 2.2.2 Armadale Fulvic Acid .................................................................................. 23 2.2.3 Samples .... ...................................................................................... 24 2.2.4 Apparatus ......................................................................................................24 2.2.5 Formation of Thin Mercury Film Electrodes (TMFEs) ................................25 2.2.6 Formation of Nafion-Coated Thin Mercury Film Electrodes ....................... 25 2.2.7 Experimental Procedure ................................................................................26 2.3 Resuits and Discussion ..........................................................................................27 2.3.1 The Effective Surface Area of the Electrode .................... .,, ..,,..... .....27 2.3.2 Effects of Organic Matter .............................................................................. 28 2.3.3 Complexation of Cadmium by Fulvic Acid in Mode1 Aqueous Solutions ... 40 2.3 -4 Complexation of Lead by Fulvic Acid in Model Aqueous Solutions ........... 48 2.3 -5 Pseudopolarographic Analysis of a Rideau River Surface Water Sample .... 50 3 . Determination of Kinetic Speciation Parameters Using Rotating Disk EIectrode / Anodic Stripping Voltamrnetry .................................................................................... 65 3.1 Introduction ....................................................................................................... .... 66 3.2 Theory ................................................................................................................ 67 3.2.1 Rotating Disk Electrode Voltammetry ....................................................... 67 3 -3 Expenmental ......................................................................................................... 74 3.4 Results and Discussion .......................................................................................... 74 3.4.1 Determination of Difision Coefficients .......................................................74 vii 3 A.2 Kinetic Study of Cd-FA and Pb-FA Complexes in Mode1 Aqueous Solutions. 3.4.3 Kinetic Study of Ultrafiltered Samples of Rideau River Surface Waters ..... 76 4 . Determination of Chernical Speciation of Nickel in Solutions containing Organic Complexants by Competitive Ligand Exchange / Adsorptive Cathodic Stripping 4.1 Introduction ........................................................................................................... 93 4.1.1 Adsorptive Cathodic Stripping Voltamrnetry (AdCSV) ............................... 93 4.1.2 Literature Survey of Electrochernical Determination of Ni(DMG)? Complexation ...........................................................................................................
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