Immobilization of Mercury Using Iron Sulfide Minerals
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IMMOBILIZATION OF MERCURY USING IRON SULFIDE MINERALS Except where reference is made to the work of others, the work described in this thesis is my own or was done in collaboration with my advisory committee. This thesis does not include proprietary or classified information. ____________________________________ Julia Michelle Bower Certificate of Approval: ________________________ _______________________ Willie F. Harper Mark O. Barnett, Chair Assistant Professor Associate Professor Civil Engineering Civil Engineering ________________________ _______________________ Dongye Zhao Joe F. Pittman Associate Professor Interim Dean Civil Engineering Graduate School IMMOBILIZATION OF MERCURY USING IRON SULFIDE MINERALS Julia Michelle Bower A Thesis Submitted to the Graduate Faculty of Auburn University in Partial Fulfillment of the Requirements for the Degree of Master of Science Auburn, Alabama August 4, 2007 IMMOBILIZATION OF MERCURY USING IRON SULFIDE MINERALS Julia Michelle Bower Permission is granted to Auburn University to make copies of this thesis at its discretion, upon request of individuals or institutions and at their expense. The author reserves all publication rights. _____________________________ Signature of Author _____________________________ Date of Graduation iii THESIS ABSTRACT IMMOBILIZATION OF MERCURY USING IRON SULFIDE MINERALS Julia Michelle Bower M.S., August 4, 2007 (B.S. Auburn University, 2005) 95 Typed Pages Directed by Mark O. Barnett Mercury is a pervasive pollutant that has caused environmental and health problems throughout the world. Numerous industries including coal-fired power plants and chlor-alkali plants have discharged mercury into the environment. A common remediation technique at contaminated sites has been excavation and incineration of soils, which is costly and can emit harmful mercury vapor. An alternative approach is in situ immobilization of subsurface mercury using iron sulfide minerals. In this study, pyrite was chosen for mercury immobilization studies because it is the most abundant metal sulfide in nature. Iron monosulfide (FeS) was selected because the Fe2+ has been shown to readily exchange with Hg2+ to form HgS(s). Additionally, both of these minerals are known as scavengers of mercury in the environment. iv Batch experiments were conducted to investigate the kinetic and thermodynamic parameters involved in Hg(II) immobilization. Parameters such as pH, reaction time, and initial Hg(II) concentration were varied to determine optimal conditions. Batch studies revealed that both of these minerals can effectively remove Hg(II) from aqueous solution along a broad pH range. Additionally, the Hg(II) removal rates for both pyrite and FeS(s) increased with increasing pH. FeS(s) was found to be more efficient at removing Hg(II), most likely due to the formation of HgS(s). Column experiments were conducted to provide insight into the environmental behavior of Hg(II) under dynamic (flow) scenarios. Furthermore, models were generated using CXTFIT (version 1.0.001) to aid in the development of long-term barrier systems, such as permeable reactive barriers (PRBs). Column studies revealed that transport of the Hg(II) was significantly retarded in the presence of pyrite, indicating its ability as a potential barrier material. Due to nonequilibrium, the local linear equilibrium (LLE) model over predicted the BTCs; however, the presence of an irreversible fraction of Hg(II) on the pyrite acted to counteract the increased mobility. The asymmetric shape of the BTCs, which is indicative of rate-limited and/or non-linear adsorption, corresponded with the findings of the kinetic and equilibrium batch experiments. v ACKNOWLEDGEMENTS The author would like to acknowledge the excellent instruction, support, and guidance of her advisor, Dr. Mark Barnett. Additional thanks to Dr. Dongye Zhao and Dr. Willie Harper for their knowledge and support during the author’s term at Auburn University. The author would like to thank Jinling Zhuang for his technical assistance and training in the environmental laboratory at Auburn University. The author would like to acknowledge the EPA (Grant Number GR832212) for providing financial support for the author’s term at Auburn University. vi Style manual or journal followed: Auburn University Graduate School: Guide to Preparation and Submission of Theses and Dissertations. Computer software used: Microsoft Office XP: Excel, PowerPoint, Word; VisualMINTEQ; and CXTFIT vii TABLE OF CONTENTS LIST OF TABLES ...................................................................................................... xi LIST OF FIGURES.................................................................................................... xii CHAPTER I. INTRODUCTION .................................................................................. 1 1.1 Problem Statement ...................................................................................... 1 1.2 Objectives ................................................................................................... 1 1.3 Organization................................................................................................ 2 CHAPTER II. LITERATURE REVIEW ...................................................................... 3 2.1 Risk............................................................................................................. 3 2.2 General Chemistry of Mercury .................................................................... 3 2.3 Sources of Mercury Release ........................................................................ 6 2.4 Mercury Remediation Methods ................................................................... 7 2.5 Mercury Immobilization Mechanisms ......................................................... 9 2.6 Mercury Sulfide in the Environment.......................................................... 12 2.7 Pyrite Oxidation ........................................................................................ 13 2.8 Comparison of Iron Sulfide Minerals......................................................... 14 CHAPTER III. IMMOBILIZATION OF MERCURY BY PYRITE ........................... 16 3.1 Introduction............................................................................................... 16 3.2 Materials and Methods .............................................................................. 19 3.2.1 Pyrite.......................................................................................... 19 viii 3.2.2 Batch Experiments...................................................................... 21 3.2.3 Column Experiments .................................................................. 22 3.2.4 Analytical Methods..................................................................... 23 3.3 Results and Discussion.............................................................................. 24 3.3.1 Batch Experiments...................................................................... 24 3.3.2 Column Experiments .................................................................. 39 3.4 Conclusions............................................................................................... 49 CHAPTER IV. INVESTIGATION OF HG(II) REMOVAL BY IRON SULFIDE...... 50 4.1 Introduction............................................................................................... 50 4.2 Materials and Methods .............................................................................. 52 4.2.1 Iron Sulfide................................................................................. 52 4.2.2 Pyrite and Pyrrhotite ................................................................... 52 4.2.3 Batch Experiments...................................................................... 52 4.2.4 Analytical Methods..................................................................... 53 4.3 Results and Discussion.............................................................................. 54 4.4 Conclusions............................................................................................... 67 CHAPTER V. CONCLUSIONS AND RECOMMENDATIONS .............................. 68 5.1 Conclusions.............................................................................................. 68 5.2 Recommendations.................................................................................... 69 REFERENCES........................................................................................................... 70 APPENDICES............................................................................................................ 77 ix LIST OF TABLES Table 2.1. Mercury Reactions with Pyrite and FeS(s)................................................... 9 x LIST OF FIGURES Figure 2.1. Biogeochemical Mercury Cycle .................................................................. 6 Figure 3.1. SEM Microphotograph of Pyrite ............................................................... 20 Figure 3.2. Hg(II) Sorption onto Pyrite as a Function of pH........................................ 26 Figure 3.3. Hg(II) Sorption onto Pyrite as a Function of Time..................................... 28 Figure 3.4. Linearization of Hg(II) Sorption onto Pyrite as a Function of Time........... 30 Figure 3.5. Hg(II) Sorption Isotherm Data at pH 4.1, 6.4, and 10.4 ± 0.2 .................... 32 Figure 3.6. Hg(II) Sorption Isotherms at pH 4.1 and 6.4 ± 0.2..................................... 33 Figure 3.7.