Scholars' Mine Doctoral Dissertations Student Theses and Dissertations Fall 2007 The leaching behavior of arsenic, selenium and other trace elements in coal fly ash Tian Wang Follow this and additional works at: https://scholarsmine.mst.edu/doctoral_dissertations Part of the Civil Engineering Commons Department: Civil, Architectural and Environmental Engineering Recommended Citation Wang, Tian, "The leaching behavior of arsenic, selenium and other trace elements in coal fly ash" (2007). Doctoral Dissertations. 2301. https://scholarsmine.mst.edu/doctoral_dissertations/2301 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. THE LEACHING BEHAVIOR OF ARSENIC, SELENIUM AND OTHER TRACE ELEMENTS IN COAL FLY ASH by TIAN WANG A DISSERTATION Presented to the Faculty of the Graduate School of the UNIVERSITY OF MISSOURI-ROLLA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY in CIVIL ENGINEERING 2007 _______________________________ _______________________________ Jianmin Wang, Advisor Craig D. Adams _______________________________ _______________________________ Joel G. Burken Glenn C. Morrison _______________________________ _______________________________ Charles Chusuei Ken Ladwig 2007 Tian Wang All Rights Reserved iii PUBLICATION DISSERTATION OPTION This dissertation has been prepared in the form of seven journal articles for peer- review. These articles are presented in Paper I through Paper V. Paper I has been prepared according to the style used by Waste Management and pages 13 to 43 have been submitted to this publication. Paper II has been prepared in the style used by the Journal of Environmental Quality and pages 44 to 73 have been submitted to this publication. Paper III has been prepared in the style used by Chemosphere and pages 74 to 99 have been submitted to this publication. Paper IV has been prepared in the style used by Environmental Science and Technology and pages 100 to 124 have been submitted to this publication. Paper V has been prepared in the style used by Environmental Science and Technology and pages 125 to 149 have been submitted to this publication. NOTE: The sections of Introduction, Purposes and Objectives, Materials and Experimental, Conclusions, Significance and Impacts, Future Works, and Appendices contain supplemental information for the journal articles. They present some information required to complete this dissertation but not necessary for submission to any of the aforementioned journals. iv ABSTRACT Trace elements in coal fly ash have long been an environmental concern in terms of their toxicity and mobility. Among them, arsenic and selenium are two oxyanionic elements of greatest concern, the regulation for arsenic in drinking water is even stricter with MCL of 10 ug/L since January 2006. Therefore, understanding the leaching process of these trace elements in fly ash during ash disposal and reuse is important in developing novel methods to control their leaching and protecting water quality. The goals of this study are four fold, they are: (1) to investigate the leaching behavior of arsenic and selenium from fly ash as well as their affecting factors; (2) to analyze the speciation of arsenic and selenium in fly ash leachate; (3) to develop a modeling approach to quantify the availability and stability of trace cationic elements in fly ash; (4) to apply this model to describe the leaching/adsorption behavior of arsenic and selenium on fly ash, as well as the calcium effect on arsenic (V) adsorption process. This research shows that pH is one of the most important factors affecting arsenic and selenium leaching from fly ash, which is also dependent upon the types of fly ash, solid-to-liquid ratio and leaching time. The leaching of arsenic and selenium from fly ash is governed by adsorption/desorption process in samples with low calcium concentration, but likely controlled by the calcium phase in samples with high calcium concentration. The total leachable mass and adsorption constant of trace cationic elements in fly ash can be determined with the modeling approach developed in this study. The adsorption of arsenic and selenium on bituminous coal fly ash was also successfully quantified with a speciation-based adsorption model. The speciation of arsenic and selenium in fly ash leachate varied with samples and was affected by the S/L ratio and leaching time. v ACKNOWLEDGMENTS The endless support and help I received from faculty, staff, friends, and family has led me to where I am today. Many of them deserve further recognition, but to all of them I am very thankful. I would like to express my sincere thanks to my advisor, Dr. Jianmin Wang, for his guidance, time, and support. Without these, I can’t image how these projects and my dissertation would have been completed. Also, I would like to thank my committee – Drs. Craig Adams, Joel Burken, Glenn Morrison, Charles Chusuei and Mr. Ken Ladwig – for their time, guidance, and constructive comments. Many thanks go to Ms. Honglan Shi and PerkinElmer technicians who have been invaluable in helping me on the method development for arsenic and selenium speciation analysis and to Mr. Gary for his remarkable work on maintaining laboratory instrumentations and fixing problems. I would like to thank my colleagues in Dr. Wang’ research group, Xiaohong Guan, Harmanjit Mallhi, Tingzhi Su and Shi Shu for their collaboration and hard work on the research projects and filling their sense of humor during tedious bottle-washing time. Special thanks to all other fellow students in the ERC for giving me a good time at UMR. I am very grateful to my family in China and my friends both in the U.S. and back in China for their understanding, support, and friendship that helped me overcome so many difficulties in studying abroad. There is no word that can express my gratitude. Last but not least, I would like to thank my husband, Yu Liu, for always encouraging me and standing by me in all these years, for his love and support, no matter what. vi TABLE OF CONTENTS Page PUBLICATION DISSERTATION OPTION................................................................... iii ABSTRACT...................................................................................................................... iv ACKNOWLEDGMENTS .................................................................................................. v LIST OF ILLUSTRATIONS........................................................................................... xii LIST OF TABLES.......................................................................................................... xiv SECTION 1. INTRODUCTION...................................................................................................... 1 1.1. LEACHING METHODS TO EVALUATE THE LEACHING BEHAVIOR OF TRACE ELEMENTS FROM FLY ASH.................................................... 2 1.2. ARSENIC AND SELENIUM IN FLY ASH AND THEIR ENVIRONMENTAL CONCERN.................................................................... 3 1.3. MECHANISM AND MODELING STUDY ON LEACHING OF ARSENIC AND SELENIUM FROM FLY ASH............................................................... 5 1.4. SPECIATION OF ARSENIC AND SELENIUM IN FLY ASH AND THE GENERATED LEACHATE ............................................................................ 6 2. PURPOSES AND OBJECTIVES.............................................................................. 9 3. MATERIAL AND EXPERIMENTAL.................................................................... 12 PAPER I. QUANTIFYING THE AVAILABILITY AND THE STABILITY OF TRACE CATIONIC ELEMENTS IN FLY ASH............................................. 13 Abstract ............................................................................................................ 13 1. Introduction .................................................................................................. 14 2. Theoretical aspects ....................................................................................... 16 vii 3. Materials and methods.................................................................................. 19 3.1. Fly ash............................................................................................. 19 3.2. Batch partitioning of washed ash.................................................... 20 3.3. Batch leaching of raw ash............................................................... 20 3.4. EDTA extraction............................................................................. 21 3.5. Analytical method........................................................................... 21 3.6. Data analysis ................................................................................... 22 4. Results and discussion.................................................................................. 22 4.1. Surface site characterization ........................................................... 22 4.2. Metal partitioning with washed ash ................................................ 23 4.3. Batch leaching of raw ash with and without external element addition .......................................................................................... 24 4.4. The total leachable mass ................................................................