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Heavy Metals and Colloid Mobility in Soils

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HEAVY METALS AND COLLOID MOBILITY IN SOILS By YAN DONG 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 1999 Copyright 1999 by YAN DONG ACKNOWLEDGMENTS First among those deserving credit for their contributions is the committee chairman, Dr. Lena Q. Ma. Her many contributions to the form and content of this dissertation are appreciated, but equally important were the opportunities and directions that she provided for developing skills that are of considerable benefit to my career in research and teaching. Dr. R. Dean Rhue deserves special thanks for patiently leading me through all the difficulties in finishing Chapter 3. Dr. Willie Harris, Dr. Peter Nkedi-Kizza and Dr. Timothy G. Townsend provided much of the initial direction and a great deal of instructive suggestion to this study. Their efforts were indispensable and are much appreciated. Special thanks also go to Kennelley, E., Schwandes, L., Thomas, J., Reve, W., Lewis, K., Awuma, K., and Choate, A., for their help with instrumental analysis. iii TABLE OF CONTENTS page ACKNOWLEDGMENTS HI LIST OF TABLES IV LIST OF FIGURES VII ABSTRACT X CHAPTERS 1 INTRODUCTION 1 2 COLLOID DEPOSITION, RELEASE AND ASSOCIATION WITH HEAVY METALS IN SOILS 1 5 Introduction 5 The DLVO Theory 10 The Characteristics of Colloids 13 Charge development 13 Electrical double layer (EDL) in metal oxides-water interface 14 Charge development in soil particles 21 Charge development in mobile colloids 22 Hydration 24 Size development of mobile colloids 25 The Characteristics of Porous Media 26 Deposition of Colloids 27 Theoretical background in well-defined porous media 27 Colloid deposition in soil 29 Release of Colloids in Soil 31 The processes of colloid release 33 Mobile colloids and water-dispersible clay 34 Influenes of exchanegable soldium percentage (ESP) on stability of water-dispersible clay and mobilization of soil colloids 35 Ion transfer processes during the release of colloids 37 The ion transfer during soil colloid mobilization in literature 38 Ion transfer during soil colloid release in our research 41 Association of Colloids with Heavy Metals 43 Adsorption of heavy metals to surface hydroxyl of colloids 44 Effects of heavy metal adsorption on the charges of soil colloids 47 Partitioning of heavy metals in soil colloids 49 iv 3 Concluding Remarks 52 3 RELATION OF PB SOLUBILITY TO FE PARTITIONING IN SOILS 55 Introduction 55 Materials and Methods 58 Location and characteristics of soil sample 58 Column experiment 58 Sample separation and analysis 61 Results and Discussion 61 Pb solubility 61 Pb solubility and Fe partitioning 64 Pb solubility and Fe partitioning using published data 68 Implication of this Research • 72 Conclusion 73 4 Heavy metal mobility in contaminated soils: Part 1. The role of exchange sites in controlling solubility and mobility of heavy metals 74 Introduction 74 Materials and Methods 76 Location and characteristics of soil samples 76 Column Experiment 78 Analysis of pore water of soil 79 Results and Discussion 79 Changes in heavy metal solubility with incubation 79 Heavy metal mobility with incubation 86 Implication of this Research 90 5 HEAVY METAL MOBILITY IN CONTAMINATED SOILS: PART 2. COLLOID-FACILITATED METAL MOBILITY IN A PB- CONTAMINATED SOIL 92 Introduction 92 Materials and Methods 95 Characteristics of soil samples 95 Column experiment 97 Analysis of Fe(II) and Ca in pore water 97 Analytical methods 98 Result and discussion 99 Colloid mobility and soil redox status 99 Colloid elution curves 105 Colloid-facilitated Pb mobility 110 Conclusion Ill 6 RELEASE AND DISPERSABILITY OF COLLOIDS IN TWO CONTAMINATED SOILS 1 1 v ' Introduction Materials and Methods 1 1? Column preparation 1 1 Column leaching test Water dispersability test Estimation of relative colloid stability ratio (RW) 119 123 Result and Discussion : Conclusion 131 7 CONCLUSION 132 State of colloid deposition and release in soil and their association with heavy metals 132 Colloidal metal mobility in contaminated soils 132 Metal solubility and mobility in soil 134 REFERENCES 136 BIOGRAPHICAL SKETCH 149 vi LIST OF TABLES Table page 3- 1 Characteristics of the Florida soil used 59 4- 1 Selected characteristics of the soils used in this study 77 5- 1 Selected properties of the Pb contaminated soil used in this study 96 5-2 Minerals in the soil and their Point of zero charge (PZC) 104 6-2 Relative colloid stability ratios (RW) for two soils under different water-flooding time 125 vii LIST OF FIGURES Figure page 1- 1. A road map of this dissertation 3 2- 1. Schematic of potential energy profile of the interaction of surfaces with inclusion of van der Walls attraction, electrical repulsion, and Born repulsion, which shows both primary and secondary minima and an energy barrier as well as the zones in which release and deposition take place 1 6 2- soil in the three size fractions 2. Cumulative mass of metals leached from the . after switching salt solution to deionized water. Size separation was by 450- nm membrane filter and 1 -nm cellulose ultrafiltration membrane (data from table 4-6 in Amrhein et al , 1993) 50 3- 1. Relation between Pb solubility and leachate pH, dissolved organic carbon (DOC), leachate Fe concentration, and ratio of aqueous Fe to sorbed Fe(II) concentrations in a sandy soil. Data from 2.90 mmole kg-1 Pb loading rate read from left y-axis and data from 0.36 mmole kg-1 Pb loading rate read from right y-axis 62 3-2. Relationship between Pb concentrations in pore water and the ratio of aqueous and sorbed Fe (Fe partition index) in a contaminated sediment. Data are taken from Lee et al., 1997 69 3- 3. Relationship between soluble Pb concentrations and the ratio of soluble to sorbed Fe in contaminated soils. Data are taken from Karczewska, 1996 70 4- 1 . Pb and Fe (II) concentrations in pore water of Montreal soil 80 4-2. Pb, As, Cu and Fe(II) in pore water of Tampa soil 81 4-3. Cumulative Pb and Fe leached after 3 1 .8 pore volumes of 0.01 M CaC12 in Montreal soil 84 4-4. Cumulative Pb, As, Cu and Fe leached after 31.8 pore volumes of 0.01 CaCb in Tampa soil 85 5- 1. Changes of effluent turbidity with pore volumes under different incubation times. The insert is a typical breakthrough curve of deionized water displacing CaCl2 100 viii 5-2. Effects of incubation on aqueous Fe (II) and Ca in the pore waters of soil columns and the cumulative colloidal Fe and Al in the effluents after 23 pore volumes 10* 5-3. Elution curves of colloidal Fe, Al, and Pb concentrations in effluents with pore volumes under various incubation times. Each point presents the mean of two replicates 106 5-4. Relationship among colloidal Fe and Al, dissolved Ca and pH in effluents after 3 d of incubation. Each point presents the mean of two replicates : 107 6- 1 Schematic representation of typical absorbency-time curves observed. Linear regression was used to calculate an apparent flocculation rate indicated by solid line. The curves are not drawn in the same time and absorbancy scales. Curve "a" stands for those observed for the Montreal soil in 0.06 NaCl M solution, and Curve "b" for those for the Tampa soil in 0.06 M NaCl and in solution 122 0.01 M CaCl2 solutions, and the Montreal soil in 0.01 M CaCl2 6-2. Absorbency-time curves observed in Ca-saturated Tampa soil suspended in 0.06 M NaCl solution 124 6-3. Relation of cumulative colloids and relative stability ratio (RW) 128 ix Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy HEAVY METAL AND COLLOID MOBILITY IN SOILS By Yan Dong December 1999 Chairman: Lena Q. Ma Major Department: Soil and Water Science Mobility of heavy metals in soils is of environmental significance due to their toxicity to both humans and animals. In general, heavy metal mobility is low because of its low solubility. However, enhanced heavy metal mobility has been reported under both laboratory and field conditions. It has been attributed to enhanced solubility of heavy metals and colloid-facilitated metal transport. In this study, the solubility and mobility of heavy metals were examined in a Pb- spiked sandy soil and two Pb-contaminated soils. For the Pb-spiked soil, water-flooded and non-water-flooded incubations were used to alter soil solution chemistry in soil columns, which were then leached with de-ionized water. It was found that Pb concentrations in leachates were related to the ratios of Fe concentration in the leachates to Fe concentrations extracted with HC1. Enhanced Pb mobility occurred only when the Fe ratios were lower than a threshold value for a given soil. The two Pb-contaminated soils were incubated for different times under water flooded condition to alter their redox x status. Metal solubility was examined by analyzing the pore water of the incubated soil columns whereas metal mobility was examined by leaching the columns with 0.01 M in pore water and metal mobility in CaCl2 CaCl2 . The data showed that metal solubility solution were not always directly related. There has been sufficient evidence that a reduction in cation exchange capacity (CEC) occurs with Fe reduction dissolution. However, the consequent redistribution of metals between solution and exchange phases with incubation was determined not only by the magnitude of CEC, but also the characteristics of metal ions, the competing co-ions and counterions (ligands).
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