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Surfactant enhanced soil washing technique for removal of trace metals from contaminated soils Xu, Beini 2010

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SURFACTANT ENHANCED SOIL WASHING TECHNIQUE FOR REMOVAL OF TRACE METALS FROM CONTAMINATED SOILS  by BEINI XU B.Sc. (Environmental Science), University of Taiyuan Technology & Science, 2005  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (SOIL SCIENCE)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) October, 2010 ©Beini Xu, 2010  Abstract Increasingly stringent environmental regulations and legislation around the world are demanding the development of environmentally friendly technologies for contaminated site remediation. Researchers have recognized soil washing as an economically promising in-situ treatment method. Despite research indicating the effectiveness of soil washing with the aid of aqueous acids or chelating agents such as HCl and EDTA, the need to minimize the environmental impact of the remediation process itself has prompted investigations into alternative soil washing agents such as surfactants, particularly degradable compounds.  This thesis examines two surfactants in their effectiveness of removing cadmium (Cd) and lead (Pb) from artificially contaminated kaolinite and illite clay minerals to determine the optimum conditions (concentration of surfactants and reaction time) for removing metals from contaminated urban sediments from two locations: a Wetland and a parking lot in Vancouver B.C. Selective sequential extraction was used to investigate geochemical fractionation before and after treatment of sediments by the surfactants.  The optimum effective concentration for removing Cd and Pb from kaolinite and illite was 20 mM for Rhamnolipid for 0.5 h and Texapon at a concentration of 100 mM for 0.5 h. Thus, the concentration of 20 mM Rhamnolipid and 100 mM Texapon and reaction time of 0.5 h were selected to apply to remediate the two contaminated urban sediments. The removal of total metal content (Cu, Mn, Pb, and Zn) under laboratory conditions for the Wetland was 31%, 26%, 43%, and 27% after treatment by Rhamnolipid; and 31%, 27%, 58% and 31% after treatment with Texapon. The removal of these metals was 28%, 26%, 60%, and 31% by Rhamnolipid and 39%, 18%, 86%, and 40% by Texapon. Removal of metals from exchangeable and reducible fraction which have the potential to be released into environment approached up to 100%.  ii  Determination of Rhamnolipid and Texapon concentration remaining in Wetland and parking lot sediments after treatment revealed that more than 99% of remaining surfactants were removed from the two sediments after two washes with distilled water. The residual Rhamnolipid and Texapon were below the LD50/LC50 and toxicity limits for aquatic life.  iii  Table of Contents Abstract ............................................................................................................................... ii Table of Contents ............................................................................................................... iv List of Tables .................................................................................................................... vii List of Figures .................................................................................................................... ix List of Abbreviations ......................................................................................................... xi Acknowledgements ........................................................................................................... xii 1. INTRODUCTION .......................................................................................................... 1 1.1Statement of Problem ............................................................................................. 1 1.2 Scope and Objective .............................................................................................. 5 1.3 Research Plan ........................................................................................................ 6 1.4 Organization of Thesis........................................................................................... 8 2. BACKGROUND REVIEW ............................................................................................ 9 2.1 Trace Metals and Soil Interactions ........................................................................ 9 2.1.1 Cation exchange .......................................................................................... 9 2.1.2 Inner-sphere complexation ........................................................................ 10 2.1.3 Precipitation .............................................................................................. 11 2.2 Desorption Mechanisms ...................................................................................... 11 2.2.1 Chelation ................................................................................................... 11 2.2.2 Ion exchange ............................................................................................. 12 2.2.3 Metal-surfactant ........................................................................................ 12 2.3 Factors Affecting the Effectiveness of Metal Removal from Soil ...................... 13 2.3.1 Soil type..................................................................................................... 13 2.3.2 Effect of different clay minerals on metal desorption ............................... 14 2.3.3 Effect of H+ availability in washing solution ............................................ 15 2.4. Effectiveness of Surfactant-enhanced Extraction of Metal-contaminants ......... 15 2.4.1 Surfactant fundamentals ............................................................................ 15 2.4.2 Comparison of surfactants in past researches ........................................... 16 2.4.3 Properties of surfactants ............................................................................ 21 2.5. Selective sequential extraction (SSE) ................................................................. 26 iv  2.6 Environmental Concerns with Surfactant ............................................................ 27 2.6.1 Biodegradability and toxicity of Rhamnolipid .......................................... 28 2.6.2 Biodegradability and toxicity of Texapon ................................................. 29 3. MATERIALS AND METHODS .................................................................................. 31 3.1 Materials .............................................................................................................. 31 3.1.1 Surfactants ................................................................................................. 31 3.1.2 Clay mineral .............................................................................................. 31 3.1.3 Urban Sediments ....................................................................................... 32 3.2 Methods ............................................................................................................... 35 3.2.1 Batch adsorption test ................................................................................. 35 3.2.2 Batch desorption test ................................................................................. 36 3.2.3 Sampling.................................................................................................... 37 3.2.4 Characterization of street sediments ......................................................... 37 3.2.5 Selective sequential extraction (SSE) ....................................................... 40 3.2.6 Determination of surfactant remaining in urban sediments ...................... 41 3.2.7 Quality assurance and quality control (QA/QC) ....................................... 41 4. RESULTS AND DISCUSSION ................................................................................... 43 4.1 Batch Adsorption Test ......................................................................................... 43 4.2 Clay Mineral Effect ............................................................................................. 43 4.2.1 Effect of [H+] on desorption ...................................................................... 43 4.2.2 Surfactant effect ........................................................................................ 45 4.3 Characteristics of Sediments ............................................................................... 53 4.3.1 Total metal content in sediments ............................................................... 54 4.3.2 Easily extractable metal in sediments ....................................................... 57 4.3.3 Geochemical distribution of trace metals .................................................. 59 4.4 Effectiveness of Removing Trace Metals by Surfactants .................................... 62 4.4.1 Total metal content in sediments after treatment with surfactants ............ 62 4.4.2 Easily extractable metal in sediments after treatment with surfactants .... 66 4.4.3 Selective sequential extraction after treatment with surfactants ............... 69 4.5 Surfactant Residual in Sediments ........................................................................ 75 5. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS................................. 78 v  5.1 Summary .............................................................................................................. 78 5.1.1 Surfactant enhanced removal of Cd and Pb from clay minerals ............... 78 5.1.2 Surfactant enhanced removal of four trace metals (Cu, Mn, Pb and Zn) from contaminated urban sediments .................................................................. 79 5.2 Conclusions ......................................................................................................... 80 5.3 Recommendations for Future Research ............................................................... 81 REFERENCES ................................................................................................................. 82 APPENDICES .................................................................................................................. 93 Appendix A- Raw data of pH effect on clay minerals (mg/kg)................................. 93 Appendix B- Raw data of surfactant concentration effect on clay minerals (mg/kg) 95 Appendix C- Raw data of trace metal content in two sediments before treatment with surfactants (mg/kg) .................................................................................................. 103 Appendix D- Raw data of trace metal content in two sediments after treatment with surfactants (mg/kg) .................................................................................................. 104  vi  List of Tables Table 2-1Summary of effectiveness of acid/base-enhanced soil washing for removal of metals………………………………………………………………….….…...18 Table 2-2 Summary of effectiveness of surfactant-enhanced soil washing for removal of metals…………………………………………………………………………19 Table 2-3 Summary of effectiveness of other washing agents-enhanced soil washing for removal of metals…………………….……………………………………….20 Table 2-4 Properties of surfactants…………………………………………………........21 Table 2-5 Toxicity of Rhamnolipid...................................................................................29 Table 2-6 Biodegradability of Texapon.............................................................................29 Table 2-7 Toxicity of Texapon..........................................................................................30 Table 3-1 Characterization of studied clay minerals……...……………………………...32 Table 3-2 Desorption experimental program for Cd and Pb spiked clay minerals………36 Table 3-3 Tessier sequential extraction procedure for 1g sample……………………….40 Table 3-4 Accuracy of AAS technique checking with known concentration of trace metal standard soil……...………………..……………………….…………………42 Table 4-1 Adsorbed concentrations of metal ions in the spiked clay mineral samples by using 150 ppm Cd(NO3)2 and 150 ppm Pb(NO3)2 for 24 h………43 Table 4-2 Percentage of desorbed metals from kaolinite and illite at various pH values..45 Table 4-3 Percentage of Cd and Pb extraction from kaolinite and illite by different concentration of Rhamnolipid and Texapon for different reaction time……..49 Table 4-4 characteristics of urban sediments collected from two sites in Vancouver B.C…………...…………………………………………………………….….54 Table 4-5 Comparison of metal in samples and Canadian limits for protection of all land uses...................................................................................................................56 Table 4-6 Concentration of trace metal in previous studies and this study……...………57  vii  Table 4-7 Percentage of easily extracted metal by 0.5 M HCl in Burnaby Lake and Wetland……………………………………...…………58 Table 4-8 Four trace metal (Cu, Mn, Pb, and Zn) content before treatment with surfactants and percentage of removal with surfactants (20 mM Rhamnolipid and 100 mM Texapon) for 0.5 h from two contaminated sediments in Vancouver B.C………………………………………………………………...65 Table 4-9 Concentration of surfactants remain in sediments after two washes with distilled water………………………………………………………………….75  viii  List of Figures Figure 1-1 Experimental flow chart of surfactant enhanced soil washing technique........7 Figure 2-1 Chemical structure and chemical name of Rhamnolipid.................................25 Figure 2-2 Chemical structure and chemical name of Texapon........................................25 Figure 3-1 Sampling points in Lost Lagoon in Stanley Park, Vancouver BC…………...33 Figure 3-2 Sampling points at 4575 W10th Avenue, Vancouver BC……………………34 Figure 4-1Concentration of desorbed metals from (a) kaolinite and (b) illite at various pH values adjusted by HNO3 for 0.5 h (arithmetic mean ± standard deviation, n=3)…………………………..……………...………………….....45 Figure 4-2 Cd desorption from spiked kaolinite and illite at different concentrations of two surfactants (Rhamnolipid and Texapon) for different desorption periods..............................................................................................................47 Figure 4-3 Pb desorption from spiked kaolinite and illite at different concentrations of two surfactants (Rhamnolipid and Texapon) for different desorption periods..............................................................................................................48 Figure 4-4 Process of Texapon adsorbing Cd2+………………………………………….51 Figure 4-5 Time effect on Cd or Pb desorption from kaolinite and illite with initial concentration sorbed onto kaolinite and illite. Initial concentration: 285 mg Cd2+ and 325 mg Pb2+ sorbed onto kg kaolinite; and 1130 mg Cd2+ and 1210 mg Pb2+ sorbed onto kg illite...........................................................................52 Figure 4-6 Total trace metal (Cu, Mn, Pb, and Zn) content in Stormwater retention wetland and Parking lot sediments..................................................................56 Figure 4-7 Sequential extraction results of Wetland and Parking lot sediment samples (< 2mm)..............................................................................58  Figure 4-8 percentage of geochemical fraction of four trace metals (Cu, Mn, Pb, and Zn) associated with contaminated sediments from Vancouver, B.C……..………61 Figure 4-9 Total content of four trace metals (Cu, Mn, Pb, and Zn) before (N) and after treatment with two surfactants (20 mM Rhamnolipid- R and 100 mM Texapon- T) for 0.5h from contaminated sediments in Vancouver, BC....................................................................................................................64 ix  Figure 4-10 Easily extractable metal adsorbed onto sediment (< 2 mm) before (N) and after treatment with two surfactants (20 mM Rhamnolipid - R and 100 mM Texapon - T) for 0.5 h from contaminated sediments in Vancouver, B.C.................................................................................................................68 Figure 4-11 Geochemical distribution of four trace metals (Cu, Mn, Pb, and Zn) in contaminated sediments before (N) and after extraction with two surfactants (20 mM Rhamnolipid - R and 100 mM Texapon - T) for 0.5h……………..73 Figure 4-12 Percentage of geochemical fractions of four trace metals (Cu, Mn, Pb, and Zn) in two contaminated sediments before (N) and after extraction with two surfactants (20 mM Rhamnolipid - R and 100 mM Texapon - T) for 0.5h...74 Figure 4-13 Concentration of surfactants removed from sediments after two washings with distilled water………………………………………………………….76  x  List of Abbreviations ℃…………………………….…………………………………………....degrees Celsius µm……………………………………………………………………..micrometer (10-6 m) AAS…………………………….………………………..atomic absorption spectroscopy CEC……………………………….……………………………..cation exchange capacity CMC…………………………….…………………………..critical micelle concentration EDTA……………………………………………………ethylene diamine tetraacetic acid h………………………………………………………………………………………..hour H+…………………………………………………………………..…………hydrogen ion HCl……………………………………………………………………….hydrochloric acid HNO3…………………………………………………………………………….nitric acid L or l…………………………………………………………………………………...litre LC50………………………………………………….……………..lethal concentration 50 LD50……………………………….…………………………………………lethal dose 50 kg………………………………………………………………………………….kilogram meq....……………………………………………………………………..milliequivalents mg……………………………………………………………………..…………milligram mL………………………………………………………………………………..millilitre mm………………………………………………………………………….……millimetre mM………………………………………..……………….…………………… 10-3 mol/L M……………………………………………………………………………………. mol/L ppm……………………………..…………………………………………parts per million rpm…………………………………………………………….……revolutions per minute SDS……………………………………………………...……….sodium dodecyl sulphafe  xi  Acknowledgements I would like to thank my supervisor Dr. Loretta Li, for her constant support and patience throughout the course of the research, and my supervisory committee Dr. Ken Hall and Dr. Les Lavkulich for their valuable suggestion and insights and giving me this opportunity to pursue my area of interest. Your support, encouragement, and guidance throughout the years have been deeply appreciated. Thank you also for editing this thesis.  Without the kind assistance of lab managers and technicians Susan Harper, Paula Parkinson, and Tim Ma, these experiments would not have been possible.  I would also thank my colleague Lisa Walls and the visiting scholar from China Li Huang this year for creating an entertaining and educational experience and making my graduate experience incredibly memorable.  My family has continued to support me in pursuing my interests, for which I am very grateful. Thank you to my friends who have been so considerate about the time that my school life demands of me. I am also extremely grateful to Ming who was always there to give me support.  Lastly, I would like to thank the UBC Land and Food System Faculty for providing me exceptional academic opportunities.  xii  1. INTRODUCTION  1.1Statement of Problem Mining, smelting, burning waste, vehicle emissions, and industrial activities have caused extensive metal contamination of the environment. These activities contribute metals to the surrounding atmosphere, waterways, and soil. Metal contamination from industrial activities is distributed in the urban area by wind, precipitation and surface runoff. Metals in urban soils have been shown to be very useful tracers of environmental pollution (Davies and Houghton, 1984). The centralization of industry and the presence of intensive human activities in urban areas have exacerbated the problem of trace metal contamination in urban soils (Wang and Qin, 2006). Urban soils are known to have peculiar characteristics such as unpredictable layering, poor structure, and high concentrations of trace elements (Kabata-Pendias and Pendias, 1992; Tiller, 1992). In areas where public gardens and parks are exposed to significant pollution levels, dust from the ground may have toxic effects as a consequence of inhalation or ingestion by humans, particularly children (Culbard et al., 1988; Folinsbee, 1993; Sanchez-Camazano et al., 1994). Furthermore, any contamination of urban soils could cause groundwater contamination because metal-polluted soils tend to be more mobile than unpolluted ones (Steinmann and Stille, 1997; Wilcke et al., 1998). It is now widely recognized that the toxicity and mobility of metal pollutants depend strongly on their specific chemical forms and on their binding state such as precipitated with primary or secondary minerals and complexed by organic ligands.  Cadmium (Cd), copper (Cu), manganese (Mn), lead (Pb) and zinc (Zn) are the most common metal contaminants along roadside and high traffic volume area from vehicle emissions and gasoline spills. These five elements are dominant in different fractions of soil. Cd is a relatively difficult environmental substance to assess in terms of its ecological effects and its impact on human health. It occurs naturally in the earths' crust, and as a result is found in varying concentrations in virtually all components of 1  freshwater, marine and terrestrial ecosystems (Yost, 1984). Cd negatively affects the renal system, cardiovascular system and the skeleton, while causing cancer of the prostate gland and lungs (Yasumura et al., 1980; Ferguson, 1990). Cu causes tremors, laboured respiration and hemolysis (Crosby, 1998). Mn has particularly strong affinity with mitochondra and causes the inhibition of ATP activity resulting in damaging neural system (Crosby, 1998). Generally, Mn in urban soil is from vehicle emission originating from the MMT (methylcyclopentadienyl manganese) used as a fuel additive (Crosby, 1998). Pb is one of the most common contaminants at battery disposal and recycling sites (Nedwed 1996). Pb is also the most difficult element to be removed from soil. It can be taken up by many plants, thereby accumulates in the human body by food chain transfer. Ingested lead accumulates and affects the nervous system (Nakatsuka et al., 1990). Zn is an essential trace element, ubiquitous in soils, and fundamental to the healthy functioning of biological systems. It is also a potential toxicant when present at elevated concentrations. Consequently, the dynamics of Zn in soils are of widespread interest, both in relation to crop nutrient deficiencies and associated impacts on farm yield and agricultural economy (Brown et al., 1993; Alloway, 2003) and in terms of soil health (McLaughlin et al., 2000).  When metal concentration exceeds permissible concentration in soil, remediation will be required. Technologies available for remediating metal contaminated soils can be divided into two groups, namely, immobilization methods and separation/concentration methods. In the first type of remediation, contaminants are immobilized thereby preventing the leaching of contaminants into the groundwater. Containment, in-situ and ex-situ solidification and stabilization, in-situ and ex-situ vitrification fall under this category. The second-type of remediation deals with separating the contaminant from the soils or reducing the volume of contaminated soil. Pump-and-treat is one of the methods of separating the contaminant. The reduced volume of the soil may be deposited in the landfills and the separated contaminants may be treated on-site or off-site with suitable treatment methods (Khodadoust et al. 2005). Several physicochemical and biological remediation methods exist for restoring metal contaminated soil, such as soil washing, soil flushing, phytoremediation and electrokinetics. Soil washing has been evaluated with 2  increasing thoroughness during the last 25 to 30 years. It is now entering a phase of actual use in the field as its applicability and economics become better defined. Soil washing involves the separation of contaminants from soil fines by solubilizing or suspending them in a washing solution. The technology is an ex-situ method, employing acids, bases, chelating agents, surfactants, alcohols, or other additives as the extracting solvent (Pichtel and Pichtel, 1997).  Among the remediation technologies, soil washing is widely used to treat contaminated sites (Asci et al., 2007; Zhang et al., 2007; Shin et al., 2005). The time required for the removal of trace metals by soil washing is often greater than is economically acceptable due to sorption interactions of the contaminant with the soil (Tan et al. 1994); another major problem is the difficulty in getting the metals to the surface for subsequent treatment. These problems have promoted the need for the development of methods to enhance the mobilization of trace metals to shorten the time required for soil washing remediation (Nivas et al. 1996; Tan et al. 1994; USEPA 1997b). Metal removal efficiencies during soil washing depend on the soil characteristics (e.g., particle size), metal characteristics (crystallinity, exchangeable, water-soluble, etc.), extractant chemistry and processing conditions. Metals that are less soluble in water often require chelating agents or other solvents for successful washing. A chelating agent such as ethylenediaminetetracetic  acid  (EDTA)  completes  with  metal  and  facilitates  solubilization in the extraction medium. The ability to form stable metal complexes makes chelating agents like EDTA effective extractants for metal-contaminated soils (Brown and Elliott, 1992). Anionic surfactants (e.g., sodium dodecyl sulfate, SDS) have shown promise for metals removal from soils by virtue of their ability to form colloidal micelles that solubilize metals (Hessling et al., 1986). Several soil washing studies have gained achievement with different extracting solvents, such as EDTA, humic acid, Rhamnolipid, Texapon, and SDS etc (Zhang et al., 2007; Asci et al., 2007; Hong and Pintauro, 1996). Most studies using these extracting solvents are based on artificial spiked single metal contamination to a pure clay mineral such as kaolinite. There is limited research on the role of clay minerals on the effectiveness of extracting trace metals (Li and Li, 2000a). 3  Previous studies reported in the literature have revealed that biosurfactants can mobilize or remove trace metals from soils or effluent streams in many ways. Miller (1995) showed anionic biosurfactants can complex with trace metals, thus decreasing the solution-phase activity of metal partitioning and then, leading to easier desorption from contaminated soils according to Le Chatelier’s principle. Recently, Mulligan and coworkers (Mulligan, 2005; Mulligan et al., 1999a; Massara et al., 2007) reported metal removal performed through soil-washing procedures could be improved by using anionic biosurfactants. In their series of studies, the washing material they proposed is surfactin, a negatively charged biosurfactant, was able to remove trace metals through sorption at the soil–liquid interface, desorption by reducing interfacial tension and heightening forces of liquid streams, and then forming micellar surfactant–metal complexes in solutions. Most previous studies have placed emphasis on the effectiveness of different type of agents. Nonetheless, there is little information on metal partitioning, i.e. amount of removed metal in particular fraction.  Since the effectiveness of soil washing procedures is difficult to predict, it is helpful to obtain information on the geochemistry partitioning of the metals as a function of the strength by which they are held in the soil, for example exchangeable, reducible, oxide, organic and residual fractions in the soil via sequential extraction procedures. Sequential extraction analysis can help identify the geochemical fractions of metals in soil (Tessier et al., 1979). Basically, the more stable the metal binding is with the soil, the stronger extractants are required. Trace metals in exchangeable and reducible forms are easily solubilized by acids. In contrast, metals bound to organic and crystalline lattice are difficult to extract (Gleyzes et al., 2002). These extraction procedures could assist in the determination of which additives might be beneficial for soil washing. Different extractants solubilize different fractions of metals. By sequentially extracting with solutions of increasing strengths, an evaluation of the different metal fractions can be obtained (Tessier et al., 1979). To understand the effectiveness of surfactant as a means of enhancing metal removal, sequential extraction procedures can be used before and after surfactants washing. 4  Surfactants have been applied to natural soils or sediments that were spiked to enlarge metal content in the study by Mulligan et al. (1999b). Metal content in most natural contaminated areas, even contaminated sites, is not as high as spiked concentration. This study investigates the effectiveness of surfactant not only on spiked clay minerals but on real (unspiked) street sediments. Even though much research has been focused on effectiveness of washing agents, the introduction of secondary contamination due to these washing agents has been ignored. The residual surfactant concentration will be determined after treatment in this study. The adsorption and desorption capacity of metals depends on surface charge of clay minerals. Permanent and variable surface charged clay minerals are studied in this research. Based on practical, low cost, ease of operation of soil washing, the technique was applied in this study to remove trace metals from clay minerals and urban sediments. Rhamnolipid (bio-surfactant) and Texapon (anionic surfactant) were selected for this study since they have low toxicity, are ready biodegradability, and easy to use (low foaming and mild odour).  1.2 Scope and Objective This study is aimed on remediation of the trace metal from contaminated soils by two commercially available surfactants. The specific objectives are as follows: 1. To investigate the factors affecting surfactants enhanced soil washing; 2. To find the optimum concentration of surfactants, reaction time and pH on desorption of metals from clay mineral; 3. To evaluate the effectiveness of surfactant for removal of total trace metal content from contaminated urban sediment; 4. To explore the removal of trace metal in particular geochemical fraction of urban sediments; and 5. To determine how much surfactant remains in urban sediments after application of surfactant and to study removal by washing techniques.  5  1.3 Research Plan To achieve above objectives, refer to Figure 1-1, the study was initiated with an assessment of the removal of Cd and Pb from kaolinite and illite by Rhamnolipid and Texapon at different concentrations for different reaction time to determine the optimum conditions for desorption. The most effective conditions (surfactant concentration and reaction time) were selected to apply to urban sediments to remove trace metals.  Figure 1-1 outlines the various aspects of the study. On the left side of the figure is an outline of preliminary work on standard clay minerals, illite and kaolinite. This was conducted as a pilot project to determine optimal conditions for surfactant treatments. Illite and kaolinite were selected as model or representative clay minerals that are common in soil and sediments. They differ in their composition and change characteristics and thus serve as simplified models to aid in the understanding of the processes involved. Figure 1-1 also provides the outline of sediments analysis.  6  Figure 1-1 Experimental flow chart of surfactant enhanced soil washing technique 7  1.4 Organization of Thesis The thesis is presented in five (5) chapters, as follows:  Chapter 1: Presents the scope, objectives, and research plan.  Chapter 2: Describes background information on the removal of trace metals by surfactants enhanced soil washing are provided.  Chapter 3: Describes the equipment, materials, and methods used in this study.  Chapter 4: Presents the results from research program. In addition, adsorption and desorption behavior of trace metals, and compares the effectiveness of different surfactants and different soils. Discussion in context of what has already been published.  Chapter 5: Presents conclusions and recommendations for future study.  8  2. BACKGROUND REVIEW In order to investigate desorption of metal-contaminant from soil, the interaction between metals and soil needs to be reviewed. Desorption mechanisms will be reviewed for giving information about reaction of contaminant and desorption agents. The factors which affect desorption such as H+ concentration, soil type, desorption agent type and concentration, and reaction time will be stated in detail.  2.1 Trace Metals and Soil Interactions The three dominant mechanisms for trace metal retention in soils are cation exchange, the formation of inner-sphere complexes, and precipitation.  2.1.1 Cation exchange Cation exchange describes the phenomenon in which cations electrostatically adsorb onto negatively charged soil particles. The electrostatically held cations are easily displaced by other cations and are therefore mobile and potentially bioavailable (Evans, 1989). The exchange of cations depends on the concentration of ions in the pore water/soil solution. Cations of higher concentrations displace those of lower concentrations, and high valence cations displace the low valence cations (Tan, 1998). In general, soil organic matter possesses the highest cation exchange capacity (CEC cmol/kg), range from 100-300 cmol/kg (Troeh et al., 1993); clay minerals are second, range from 3-100 cmol/kg (Troeh et al., 1993); followed by the rest of the inorganic minerals e.g. 0-3 cmol/kg (Troeh et al., 1993).  9  2.1.2 Inner-sphere complexation When the surface functional group of a soil particle interacts with an ion present in the soil solution to create a stable molecular entity, a surface complex forms (Sparks, 1995). Outer-sphere complexes are bound ionically. By retaining their water of hydration, ionic bonds are considered nonspecific and are classified under cation exchange. Inner-sphere complexes are bound covalently. These are strong bonds in which electrons are shared amongst the bound ions.  For minerals, the hydroxyl groups are important surface functional groups. The divalent transition metals readily form inner-sphere complexes with hydroxyl groups by displacing a H+ from the hydroxyl group and bonding to the -O-. Being divalent, the metal may bond to one or two oxygen atoms (Sparks, 1995).  As for soil organic matter, many surface functional groups are available for complexation. Donor atoms generally are the more electronegative nonmetallic elements (such as O, N, and S), these elements are contained within the basic functional groups (such as amino, carbonyl, alcohol, thioether), and the acidic groups (such as carboxyl, phenolic, enolic, and thiolic) (Evans, 1989; Sparks, 1995).  Livens (1991) states that for soil organic matter the ease and strength of bonding depends on the following: 1. The affinity of metal ion for that type of site; 2. Stereochemical factors, i.e. the amount of room for the metal ion to fit into the site. This can be affected by the size of any other ligands on metal; and 3. The chemical environment of the site. The nature of the functional groups around the actual complexing group can influence its behavior.  10  2.1.3 Precipitation Precipitation is the formation of an insoluble product from a reaction that occurs in solution (McQuarrie and Rock, 1991). The extent of precipitation and dissolution of a mineral can be described by its solubility product (Tan, 1998). Precipitation will occur when the product of the metal ion and ligand concentrations exceed their solubility product. Among the most important precipitation reactions, are those that involve the hydroxide ligand. Metals that are expected to precipitate as hydroxides are Fe3+, Al3+, Cu2+, Fe2+, Zn2+, and Cd2+ (Evans, 1998). In addition, metal ions also commonly precipitate as carbonates (CO32-) and sulphides (S2-). Metals that are expected to precipitate as carbonates are Ca2+, Sr2+, Ba2+, Fe2+, Zn2+, Cd2+, and Pb2+. Although carbonates occur in both oxidizing and reducing conditions, sulphides are stable only under reducing conditions. Metals that occur as sulphides in reducing conditions include Ag+, Ni2+, Zn2+, Cd2+, Hg2+, and Fe3+ (Evans, 1989).  2.2 Desorption Mechanisms 2.2.1 Chelation Chelation is the binding or complexation of a bi- or multidentate ligand with a metal. These ligands, which are often organic compounds, are called chelating agents. Chelating agents form multiple bonds with a single metal ion. Chelants are chemicals that form soluble, complex molecules with certain metal ions, inactivating the ions so that they cannot normally react with other elements or ions to produce precipitates or scale. The ligand forms a chelate complex with the substrate. Application of chelating agents directly produces a complex with metal ions which moves from soil to aqueous phase (Eykholt, 1992). It may also dissolve soil organic matter and hence be capable of removing metal sorbed on soil organic matter (Khodadoust et al., 2005).  11  2.2.2 Ion exchange Ion exchange is of great importance for metal desorption from metal-contaminated clay minerals, because the physical properties of clay minerals are dependent to a large extent on the exchangeable ions carried by clay. One cation can be readily replaced by another of equal valence, or by two of one-half the valence of the original one. If a clay containing sodium, as an exchangeable cation, is washed with a solution of calcium chloride, each calcium ion will replace two sodium ions, and the sodium can be washed out in solution. This process can be written as: Na2 clay + CaCl2 → Ca clay + 2NaCl The cation exchange capacity of clay minerals is important to study because cations, which balance or are equal to the amount of negative charge on the clay mineral. Release (desorption) of previously sorbed metal ions can occur when saturation sorption occurs and when the concentration of ions in the surrounding solution is lower than initial sorbed ions (Yong et al. 1992; Bolt, 1979).  2.2.3 Metal-surfactant The addition of a biosurfactant, such as Rhamnolipid, can effectively decrease the interfacial tension between solid surface and contaminants, therefore increasing contaminant mobility. This may also be applicable for explaining desorption of weakly bound trace metals from solid surfaces (Wang and Mulligan, 2009). Rhamnolipids are known to be able to form micelles at concentrations above the critical micelle concentration (CMC), therefore, increasing the mobilization of metals or organic contaminants from soils and sediments (Mulligan, 2005; Mulligan et al., 1999b). According to Mulligan et al. 1999b, Rhamnolipid adsorption is essential for metal mobilization from soil and sediments. Since the Rhamnolipid is negatively-charged, it may form metal-biosurfactant with metallic cations (Wang and Mulligan, 2009).  12  In addition, anionic surfactants may enhance the release of trace metals from soil through ion exchange, electrostatic attractions, as well as, the release of metals bound soil to organic matter (Shin et al., 2005). Water soluble anionic surfactants have free anionic ions, which form complex with metal cations. Metal ions sorbed on soil are extracted into solution by a surfactant, such as sodium dodecyl sulfate (SDS) and Texapon (Romanell et al., 2004).  2.3 Factors Affecting the Effectiveness of Metal Removal from Soil  In order to investigate extraction of metals from contaminated soil, the factors affecting the extraction effectiveness such as soil type, pH, surfactant type, surfactant concentration, and reaction time need to be considered.  2.3.1 Soil type Most soils contain four basic components: mineral particles, water, air, and organic matter. Organic matter can be further sub-divided into humus, roots, and living organisms (Mitchell, 1993). In this study, two types of clay minerals-variable and permanent charged- were investigated, since they are representative clay minerals of the two general charged clays types (Yong et al., 1992).  The reactivity of clay minerals is controlled by their large specific surface area (Ko et al., 2006; Bradl, 2004; Davis, 2000) and surface charge (Yong, 2001). A large surface area results in a greater exposure of the clay to solutes through increased availability of reactive sites (Bradl, 2004; Yong, 2001); In essence, increased surface area translates to more adsorption of metal contaminants (Sposito, 1989). In addition, electrostatic interactions occur between the charged surface of clay particles and metal ions (Bradl, 2004; Yong, 2001). There are two sources of this surface charge: isomorphous substitution and broken edge bonds. The two representative types of clay minerals are discussed below: 13  Kaolinite minerals  Broken bonds at the edge of a lattice result in a variable charge surfaces, such as found in kaolinite (Yong, 2001; Li and Li, 2000). These exposed edges have surface hydroxyl groups-silanol or aluminol-that can undergo protonation and deprotonation to produce net negative or positive charges (Bradl, 2004; Yong, 2001; Li and Li, 2000a). This is affected by the surrounding pH. Acidic conditions yield more protonated sites, which repel positively charged metal ions and enhance their mobility (Erikkson, 1989; Abd-Elfattah, 1981). At a pH below 4, kaolinite has a net positive charge and repels cations, while at above pH 4, the surface is negatively charged and an increase in cation exchange capacity favours the bindings of cations (Li, 2006; Li, 2003).  Illite minerals  Illites have an aluminosilicate structure, comprised of alumina and silicon (Yong, 2001). Isomorphous substitution within the lattice, where an atom is replaced by another without disruption of the overall lattice structure, leads to a permanent or fixed charged surface (Yong, 2001; Li and Li, 2000a). For instance, if an Al3+ replaces a Si4+, there will be a net negative charge (Yong, 2001; Li and Li, 2000a).  2.3.2 Effect of different clay minerals on metal desorption Kaolinite is a pH-dependent clay mineral, meaning that at low pH, the cation exchange capacity decreases and anion exchange capacity increases because the surface charge of kaolinite changes to positive. When the surface charge changes from negative to positive, the adsorbed trace metal ions (cations) are repelled from the charged surface of kaolinite (Li, 2006). Illite has a high crystal charge as a result of isomorphous substitution of Al3+ for Si4+ in tetrahedral sites and Mg2+ for Al3+ in octahedral sites (Sposito, 1984). Most cation exchange sites result from permanent charges and, to a lesser extent, OH- ions.  14  Unlike kaolinite, the cation exchange of illite is not pH-dependent; low pH does not improve the desorption (Li, 2006).  2.3.3 Effect of H+ availability in washing solution Based on the solubility of trace metals and the surface properties of clay minerals, desorption of metal ions in soil systems occurs as the pH of washing agents reaches the solubility range of the trace metal or is lowered to the point of zero charge of the clay minerals. When pH is below the point of zero charge of clay minerals, surface charge of variable charged clay will be changed from negative to positive, causing the clay minerals to repel metal cations. H+ ions have high metal removal potential for kaolinite, but not for illite, because kaolinite is a variable-charge mineral. Thus, any change of surface H+ ions activity (pH) affects the kaolinite surface immediately.  In addition, as the pH environment changes, adsorption and desorption processes may be significantly affected. Dissolution of precipitates (pH lowering) may occur causing release of the previously sorbed contaminants. The retention capacity is markedly increased when the soil solution pH exceeds the value required for precipitation or formation of metal hydroxyl species, M(OH)n (Yong et al, 1992).  2.4. Effectiveness of Surfactant-enhanced Extraction of Metalcontaminants 2.4.1 Surfactant fundamentals More environmentally friendly yet effective desorption reagents are being sought after, with properties such as biodegradability, specificity, and chemical stability (Juwarkar et al., 2007). Surfactants are being proposed as viable alternatives to acids and chelating agents (Chu, 2003; Mulligan et al., 2001). Surfactants are molecules comprised of lyophilic, or solvent-loving, and lyophobic, or solvent-fearing groups (Rosen, 1989). 15  Surfactants exist in the anionic, cationic, zwitterionic, or nonionic forms (Urum and Pekdemir, 2004). The classification is reflective of the charge on the hydrophilic group (Rosen, 1989).  The behavior of the surfactant is determined by the nature of, and interactions, with the solvent. When at a low concentration in solution, the surfactant molecules commonly reduce the interfacial tension by adsorbing to an interface in an oriented manner (Rosen, 1989). Alternatively, this means that an increase in the free energy of the system, created by the distortion of the solvent matrix due to the presence of lyophobic groups, leads to a decrease in the work required to gain a unit area increase at the interface (Rosen, 1989). As the surfactant concentration increases and reaches the critical micelle concentration (CMC), another mechanism for free energy reduction of the system occurs when surfactant monomers begin to aggregate to form micelles (Rosen, 1989). The monomers arrange themselves such that they are oriented towards the interior of the cluster from the solvent (Rosen, 1989). Various factors influence the concentration at which micelle formation begins, including the surfactant structure and solvent characteristics (Rosen, 1989).  The mechanisms that have been attributed to surfactant-facilitated metal removal: 1. At or above the CMC: solubilization of the metal into the micelle (Juwarkar et al., 2007; Shin et al., 2005;Desphande et al., 1999); 2. Below the CMC: interaction with and desorption of the metal from the soil surface as surfactant gathers at the soil-solution interface and is agitated (Giannis et al., 2007; Desphande et al., 1999); and 3. Binding of free metal ions (Chang et al., 2005).  2.4.2 Comparison of surfactants in past researches Over the last twenty years, a variety of research activities related to surfactant enhanced remediation of metal contaminated soil has been done. Generally there are three types of reagents: acid and base (Table 2-1) including HCl, HNO3 and NaOH; surfactants (Table 16  2-2) such as SDS, Texapon, and rhamnolipid etc; and chelating agents (Table 2-3) such as EDTA, DPTA etc.  Among the previous studies given in Table 2-1, the lower the pH, the greater the removal of Cd and Pb from sediment can be achieved when acid is applied (Nystroem et al., 2006). Nitric acid was found to be efficient for removal of Cd and Pb from clay minerals (Farrah and Pickering, 1977). In addition, removal of metals from coarser particles, such as found in sandy soil, is much easier than from finer particles, such as sediment (Legiec, 1997). Table 2-1 shows that removal of metals from contaminated soil by some chelating agents and most acids was more than that removed by surfactants. However, surfactants are selected as washing agent in many cases (Asci et al., 2007; Zhang et al., 2007; Chang et al., 2005) since they are environmentally friendly and have no secondary pollution.  17  Table 2-1 Summary of effectiveness of acid/base-enhanced soil washing for removal of metals Acid/Base  Contaminant  Effectiveness Final Conc. % 66 62  Soil type  Time (h)  Author (s)  sediment  48  Nystroem et al., 2006  Name  Conc.  pH  Type  HCl  0.6 M  0.4  Pb Cd  Conc. mg/kg 56.5 3.39  Lactic acid  1M  2.7  Pb Cd  56.5 3.39  38 58  sediment  48  Nystroem et al., 2006  Citric acid  1M  2.0  Pb Cd  56.5 3.39  42 55  sediment  48  Nystroem et al., 2006  Ammonium citrate  0.5 M  8.0  Pb Cd  56.5 3.39  28 39  sediment  48  Nystroem et al., 2006  Nitric acid  0.1 M  1.4  Pb Cd Pb Cd  100 50-65 25-45 70-85  Kaolin  24  Farrah and Pickering, 1977  Illite  HCl  1.0 N  2.5  Pb  88.6  Sandy soil  24  Legiec, 1997  Citric acid  1.0 N  3.42  Pb  79.9  Sandy soil  24  Legiec, 1997  18  Table 2-2 Summary of effectiveness of surfactant-enhanced soil washing for removal of metals Surfactant  Contaminant  % removal from soil  Soil type  Time (h)  Author (s)  Name  Conc.  pH  Type  Conc.  SDS (Anionic)  5 g/L 20 g/L  7  Pb  34  23 30  Sandy soil  6  Zhang et al., 2007  Rhamnolipid  0.5%  7  Cu Zn  110 3300  65 18  Sediments  24h  Mulligan et al., 2005  SDS  69 mM  5-11  Cd  20  6  Sandy soil  3  Chang et al., 2005  Triton X-100  31 mM  5-11  Cd  20  6  Sandy soil  3  SDS  0.1 M  4-11  Pb  30-40  Mixture of native soil and industrial waste  5  Pichtel and Pichtel, 1997  Triton X-100 + 0.036mol/L I-  0.1 M  6.8  Pb Cd  1165 15.6  0.6 35  Sandy soil  24  Shin and Barrington, 2005  SDS  0.1 M  6.8  Pb  1165  0.2  Sandy soil  24  Surfactin with NaOH  0.1%  Cd  5 15  Sediment  24  Mulligan et al., 1999  Rhamnolipid  80 mM  Cd  71.9  Kaolin  72  Asci et al., 2007  Rhamnolipid  10 mM  6.87.0 7.1  Pb  15.3  Sandy loam  Neilson et al., 2003  3  Cd  99  Montmorillonite  10 wash  CBDA (cationic)  Malakah et al., 1998  19  Table 2-3 Summary of effectiveness of other washing agents-enhanced soil washing for removal of metals Other reagent Name  Contaminant Type Conc. mg/kg Pb 65,200 Cd 52 Pb Cd Cd  % removal from soil  Soil type  Time (h)  Author (s)  86 96 84 100 100  Sediment  0.5-5  Steele and Pichtel, 1998  Kaolin  24  Cd  98  Kaolin  24  Hong and Pintauro, 1996  >6 <3.5  Cd  100  Kaolin  24  2.512 7  Cd  100  Kaolin  24  Pb  34  Sandy soil  6  Zhang et al., 2007  5-11  Cd  20  Sandy soil  3  Chang et al., 2005  7  Pb  34  Sandy soil  6  Zhang et al., 2007  7.5  Pb Cd  56.5 3.39  79 84 82 30-50 >80 97 90 87 1 1.5  0.6 M  7.3  0.001 M  7.2  56.5 3.39  EDTA  0.1 M  NTA Metaset-Z  0.1 M  4.3 12 4.5 5.5-7  20 58 100 100 100 96.2 38 85  Sediment  EDTA  Pb Cd Pb Cd Pb  Conc.  pH 4.5  ADA  0.0225 M 0.0375 M 0.075 M  NTA  20 μM  EDTA  20 μM  8 <3.2 8  EGTA  20 μM  DCyTA  20 μM  EDTA EDTA +SDS EDTA +SDS LED3A EDTA EDTA EDTA+SDS EDTA+SDS Distilled water  0.27 M 5 g/L 20 g/L 0.01 M 0.01 M 0.54 M 5 g/L 20 g/L  NaCl  EDTA  6.5  Pb Pb  Sediment  Kaolin Illite Mixture of native soil and industrial waste Real soil and surrogate  Nystroem 2006 24 5 5 7  et  al.,  Farrah and Pickering, 1977 Pichtel and Pichtel, 1997 Rampley Ogden, 1998  and  20  2.4.3 Properties of surfactants A variety of surfactants have been tested in the laboratory for metals remediation including sodium dodecyl sulphate (SDS) (Doong et al., 1998), cetyltrimethylammonium bromide (CTMB) (Doong et al., 1998), Rhamnolipid biosurfactants (Mulligan et al., 2001), and Texapon (Takeda, 2008). The properties of common surfactants are shown in Table 2-4.  Table 2-4 Properties of surfactants Property Phase  Rhamnolipid (Jeneil, 2008) Liquid  Texapon (Cognis, 2006) Paste  Colour  Dark brown and visible suspension  Water white  Odour  Mild cooked  Conform to standard  Chemical formula C32H58O13 and C26H48O9  CH3(CH2)11OSO3Na  Mol weight  504/650  382 g/mol  pH  6.5-7.5  7-9 (4% solution)  Specific Gravity  1.12-1.14 (25℃)  1.1 (25℃)  Kow/Koc  1.082±0.009×10-2μM-1 min-1  N/A  Water Solubility  150mg/L at pH 5  Soluble  Stability  Stable at 25℃  Stable at 25℃  Volatility  Not volatile  Not volatile  Biodegradability  Readily degradable  Readily degradable: BOD28/COD > 60 %  Suitable Diluents  Water, most common alcohol  N/A  Materials to avoid  N/A  Strong acids, bases, oxidizing agents  Toxicity  Oral LD50 (rat) is greater than 5,000 mg/kg LD50 (rat) is not available LC50 > 10 - 100 mg product/L to fish  21  Table 2-4 Continued Property  EDTA (Fisherbrand)  Triton X-100 (Sigma Aldrich Canada Ltd.)  Phase  Solid  Clear liquid  Colour  Colourless  Light yellow  Odour  Odourless  Odourless  Chemical formula  [CH2N(CH2CO2H)2]2  C33H60O10  Mol weight  372.24 g/mol  646.85 g/mol  pH  N/A  9.7  Specific Gravity  N/A  1.06  Kow/Koc  N/A  9.36±0.43×10-3 μM-1 min-1  Water Solubility  1650 g/L at 22℃  Soluble in hot water and cold water  Stability  Stable at 25℃  Stable at 25℃  Volatility  Not volatile  <0.5% (v/v)  Biodegradability  not degradable  Possibly hazardous short term degradation products are not likely  Suitable Diluents  Water  Water  Materials to avoid  Strong oxidizing agents  Reactive with oxidizing agents, reducing agents  Toxicity  LD50 (rat) of 2.0 – 2.2 g/kg  Oral: LD50 (rat) > 10 - 100 mg product/L to fish  22  Table 2-4 Continued Property  Standapol (Cognis)  Saponin (Sigma Aldrich Canada Ltd.)  Phase  Clear viscous liquid  Very fine powder  Colour  Water white to pale yellow  Light yellow  Odour  Odourless  Odourless  Chemical formula  C12H25NaO4S  C71H116O36  Mol weight  N/A  N/A  pH  7.5 (10% solution)  Not determine  Specific Gravity  1.03  N/A  Water Solubility  Soluble  Soluble in cold water  Stability  Stable at 25℃  Stable at 25℃  Volatility  Not volatile  N/A  Biodegradability  Degradable  N/A  Suitable Diluents  Water  Water, alcohol, organic solvents  Materials to avoid  Strong acids, bases, oxidizing agents  Strong oxidizing agents, acids  Toxicity  unavailable  LD50: Not available.LC50: Not available.  Property  Sodium Dodecyl Sulfate (Cognis)  Phase  Fine powder  Colour  white or slightly yellow  Odour  Slight fatty odor  Chemical formula  C12H25OSO3Na  Mol weight  288.38  pH  N/A  Specific Gravity  0.4 at 15C/4C  Water Solubility  10 g/100 g water  Stability  Stable under ordinary conditions of use and storage  Volatility  Not volatile  Biodegradability  Readily degradable  Suitable Diluents  Water, most common alcohol  Materials to avoid  Strong oxidizers, acids  Toxicity  Oral rat LD50: 1288 mg/kg; Inhalation rat LC50: > 3900 mg/kg  23  One natural surfactant with low toxicity is Rhamnolipid or JBR210. In aqueous solutions, Rhamnolipid has a very low Critical Micelle Concentration indicating strong surface activity shown at low concentrations, characterized by low surface tension for water, and electrolyte solutions with very low interfacial tensions for water/hydrocarbon systems (Mulligan et al., 2001). Rhamnolipid can produce stable closed-celled foams in aqueous solutions and act as a foam stabilizer for other surfactants, particularly anionic and amphoteric compounds. The chemical structure and chemical names of Rhamnolipid is shown in Figure 2-1.  Texapon N70, or sodium laureth sulphate, is used as a cleaning product. Texapon N70 is a highly concentrated sodium lauryl ether sulphate derived from natural fatty alcohols. Due to its high content of washing active substance, Texapon N70 is particularly suited for highly concentrated end products, or if raw materials with lower water content are required (Cognis Care Chemicals, 2006). The chemical structure of Texapon is shown in Figure 2-2. According to the surfactant properties, surfactant has both lyophilic and lyophobic groups, such as shown in Figure 2-2, Na-OSO3- is lyophilic, which can absorb metal ions from soil thereby releasing the metal into solution.  24  Formula: R1 or RLL: C26H48O9 Molecular Weight: 504  Formula: R2 or RRLL: C32H58O13 Molecular Weight: 650 Figure 2-1 Chemical structure and chemical name of Rhamnolipid (http://ag.arizona.edu/swes/maier_lab/surfactants.htmL)  Chemical name: Sodium laureth sulphate Figure 2-2 Chemical structure and chemical name of Texapon (extracted from CAS No.: 9004-82-4)  25  2.5. Selective sequential extraction (SSE) A widely-used technique for understanding element distribution in the solid phase is based on the application of selective sequential extractions (SSE). There are other methods of metal extraction that provide similar results as SSE, such as BCR (Rauret et al., 1999), continuous-flow approach (Shiowatana et al., 2001), ultrasonic bath and microwave method (Filgueras et al., 2002), and Rotating coiled column (Fedotov et al., 2005). These methods are based on the rational use of a series of more or less selective reagents chosen to solubilize successively the different mineralogical fractions thought to be responsible for retaining the larger part of the trace elements (Gleyzes et al., 2002). In this study, selective sequential extraction was used to determine the quantity of metals that were adsorbed to different soil geo-chemical fractions before and after desorption. The SSE method used in this study was a five-step procedure originally developed by Tessier, 1979.  Fraction 1. Exchangeable. This fraction includes weakly adsorbed metals retained on the solid surface by relatively weak electrostatic interaction, including metals that can be released by ion-exchange processes etc. Changes in the ionic composition influencing adsorption–desorption reactions, or lowering of pH could cause remobilisation of metals from this fraction. (Krishnamurti et al., 1995; Arunachalam et al., 1996; Narwaletal, 1999; Ahnstrom and Parker, 2001). Exchangeable metal ions are a measure of those trace metals which are released most readily into the environment. Metals corresponding to the exchangeable fraction usually represent a small portion of the total metal content in soil, sewage sludges, and sediments and that can be replaced by neutral salts (Rauret, 1998).  Fraction 2. Bound to Carbonates. Carbonate can be an important adsorbent for many metals when organic matter and Fe–Mn oxides are less abundant in the aquatic system (Stone and Droppo, 1996). The carbonate form is a loosely bound phase and liable to change with environmental conditions. This phase is susceptible to changes in pH, being generally targeted by use of a mild acid. The time required for complete solubilisation of carbonates depend on several factors such as particle size of the solid, type and amount of 26  carbonate in the sample, etc (Beck et al., 2001).  Fraction 3. Bound to Iron and Manganese Oxides. Hydrous oxides of manganese and iron are extracted together and are the well known “sinks” in the surface environment for trace metals. Scavenging by these secondary oxides, present as coatings on mineral surfaces or as fine discrete particles, can occur by any or a combination of the following mechanisms: coprecipitation; adsorption; surface complex formation; ion exchange; and penetration of lattice (Hall et al., 1996). The amorphous oxyhydroxides of iron and manganese strongly sorb trace elements, initially in exchangeable forms, but increasingly with time are transformed to less mobile, specifically adsorbed forms.  Fraction 4. Bound to Organic Matter. Trace metals may be bound to various forms of organic matter: living organisms, detritus, coatings on mineral particles, etc. The complexation and peptization properties of natural organic matter (notably humic and fulvic acids) are well recognized, as is the phenomenon of bioaccumulation in certain living organisms. Under oxidizing conditions in natural waters, organic matter can be degraded, leading to a release of soluble trace metals.  Fraction 5. Residual. Once the first four fractions have been removed, the residual solid should contain mainly primary and secondary minerals, which may hold trace metals within their crystal structure. These metals are not expected to be released in solution over a reasonable time span under the conditions normally encountered in nature.  2.6 Environmental Concerns with Surfactant Surfactants, as detergent active substances, are an important source of pollution causing biological adverse effects to aquatic organisms. Research (Romanell et al., 2004) has reported ecological impact due to the high concentration of surfactants on receiving waters and from wastewater treatment plants. The studied surfactants-Rhamnolipid and Texapon-are discussed below.  27  2.6.1 Biodegradability and toxicity of Rhamnolipid Biodegradability OECD (Organization for Economic Cooperation and Development) tested Rhamnolipid by using techniques such as 301D, OECD 209, and OECD 202 for readily biodegradability, Activated Sludge Respiration Inhibition (ASRIT) and aquatic toxicity to daphnia. These results were to determine whether or not the chemical has the potential to cause problems in waste treatment plants or in the environment. The biosurfactant Rhamnolipid is a particular surfactant, which has no toxicity and can be degraded by Bacillus subtilis and compost microorganisms, however it cannot be utilized by its producing bacterium Pseudomonas aeruginosa. Among these three bacteria, the compost consortium had the strongest degradation capacity on the tested surfactants due to their microorganisms’ diversity. In compost matrix rhamnolipid could be degraded during composting, but not preferentially utilized.  Rhamnolipid showed ready biodegradability by demonstrating a biodegradability rate of 68.4% on day 10 of the 28-day test cycle (Jeneil Co.). This is an excellent test result clearly demonstrating that Rhamnolipid JBR210 is readily biodegradable. The term half maximal effective concentration (EC50) refers to the concentration of a drug, antibody or toxicant which induces a response halfway between the baseline and maximum after some specified exposure time (GraphPad, 2003). The biosurfactant showed no toxicity to activated sludge biomass with an EC50 (effective concentration) > 1000 mg/l. This is the best test result possible. This means that this surfactant could be discharged to a waste treatment plant at concentrations >1000 mg/L or 0.1% with no adverse effects (Jeneil Co.). Rhamnolipid demonstrated acute toxicity to Daphnia magna with an EC50 of 36.1 mg/L. This is an extremely low toxicity for a commercial surfactant.  Toxicity Toxicity testing was done in accordance with U. S. EPA guidelines (1996) by an independent laboratory. In toxicology, LD50 (abbreviation for “Lethal Dose, 50%”), LC50 (Lethal Concentration, 50%) of a toxic substance or radiation is the dose required 28  to kill half the members of a tested population after a specified test duration. LD50 figures are frequently used as a general indicator of a substance's acute toxicity (Hodgson, 2004). A 9.5% Rhamnolipid concentration aqueous solution was tested except as noted. Results follow (Table 2-5):  Table 2-5 Toxicity of Rhamnolipid for rat (Source: Jeneil Biosurfactant Co.) Pathway  Toxicity  Acute oral  LD50>5,000 mg/kg  Acute dermal  LD50>5,000 mg/kg  Acute inhalation  LC50>2.05 mg/L  Dermal irritation  Slightly irritating. Irritation cleared by 72 hours  Ocular irritation  Moderately irritating  2.6.2 Biodegradability and toxicity of Texapon Biodegradability Biodegradability of Texapon is reported as readily degradable by the Organization for Economic Cooperation and Development. Detail is listed as following Table 2-6.  Table 2-6 Biodegradability of Texapon (Source: Cognis Care Chemicals) Biodegradability BOD28/COD > 60 % > 90 % MBAS decrease  Tested Method OECD 301D (Closed Bottle Test) OECD Screening Test  29  Toxicity The toxicity of Texapon was provided on product safety datasheet by Cognis Canada Corporation. Detail is shown in Table 2-7.  Table 2-7 Toxicity of Texapon (Source: Cognis Canada Co.) Pathway  Toxicity  Tested Method  Acute fish  LC50>10 - 100 mg product/l  OECD 203  Acute bacteria  EC0 > 100 mg product/l  OECD 209  Acute daphnia  EC50 > 100 mg product/l  OECD 202/1  Acute algae  EC50 > 1 - 10 mg product/l  OECD 201  These two surfactants are of particular interest for use in remediation technologies for an important reason, which is that they are generally degradable. Very limited information is available on comparison of toxicity standard (i.e. LC50/LD50) and remaining surfactant in sediment after treatment with surfactants.  This study examined the remaining  surfactant concentration in sediments after treatment with surfactants, to assess if the remaining concentration had any adverse impact on aquatic life.  30  3. MATERIALS AND METHODS The materials used in this study were surfactants (Rhamnolipid and Texapon), clay minerals (kaolinite and illite) and urban sediments (Wetland and parking lot). The methods applied included batch adsorption and desorption tests, characterization of sediments, selective sequential extractions and determination of surfactant concentration.  3.1 Materials 3.1.1 Surfactants Rhamnolipid JBR 210 was purchased from Jeneil Biosurfactant Corporation and Texapon N70 was supplied by Cognis Canada Corporation. The properties of the two surfactants are shown in Table 2-4.  3.1.2 Clay mineral Two clay minerals were employed in this study: (ⅰ) Hydrite PX, dominated by kaolinite, from Georgia Kaolin Company of Elizabeth, New Jersey, designated here as kaolinite; and (ⅱ) Grundite, dominated by illite, from Illinois Clay Products Company of Joliet, Illinois, referred to as illite. The characterization of these two clay minerals was detailed in Li 2006 (Table 3-1).  31  Table 3-1 Characterization of studied clay minerals (Li and Li, 2000) Kaolinite Soil pH (1:10 H2O) CEC (cmol/kg) Surface area (×10-3m2/kg) Organic content (%wt) Carbonate content (%wt) Mineral composition  4.5 8 12 0 0 Kaolinite  Illite 3.9 55 197 Not detected 0 Illite, traces chlorite, quartz, and feldspar  3.1.3 Urban Sediments Location A-The studied stormwater retention wetland - Lost Lagoon, Vancouver BC Lost Lagoon is an artificial, captive 16.6-hectare (41 acre) body of water, located at 49.3N and 123.1W, west of Georgia Street, near the entrance to Stanley Park in Vancouver, Canada. Surrounding the lake is a 1.75 km trail, and it features a lit fountain that was erected to commemorate the city's golden jubilee. It is a nesting ground to many species of birds, including non-native Mute Swan (whose wing tendons have been clipped to prevent escaping), Canada geese, numerous species of ducks such as mallard ducks and Great Blue Herons. The road dust from highway 99 where it crosses over the lagoon is washed down into the water by rain and the trace metal from vehicles precipitates at the bottom, binding with the sediment particles. Highway 99 is a main road with dense traffic volume connecting Vancouver City and North Vancouver. There are an average of 63,369 cars that go through Highway 99 which cross over the lagoon everyday (B.C. Ministry of Transportation, 2010). North of the lagoon is Stanley Park. Sediments were taken from a constructed wetland that received the street runoff from the causeway in Stanley Park. The dust with contaminants from vehicles directly accumulates on the north bank of the lagoon. Samples (simply referred to as “Wetland” here after) were taken at the sampling points in the constructed area on north bank of Lost Lagoon marked in Figure 3-1. Photo 3-1 shows Lost Lagoon. Detailed sampling methods are given in Section 3.2.3 for urban sediments.  32  Figure 3-1 Sampling points in Lost Lagoon in Stanley Park, Vancouver BC is the sampling point  Photo 3-1 Wetland-Lost Lagoon in Stanley Park, Vancouver B.C.  33  Location B-Parking lot on W10th Avenue, Vancouver BC The second study site is located at 4575 W10th Avenue Vancouver BC (49.3N and 123.2W). W10th Avenue is a main street connecting the UBC area and Vancouver Westside District with high traffic density. There are two driving lanes on each side of the road and parking spaces along the road on W10th Avenue. Samples were taken in a trap at a parking lot outside of the supermarket. The metals from vehicle tires and gasoline spills are collected in the trap. Samples (referred to as “Parking lot” here after) were taken at sampling point marked in Figure 3-2. The surrounding of sampling points is shown in Photo 3-2. Detailed sampling methods are given in Section 3.2.3 for urban sediments.  Figure 3-2 Sampling points at the parking lot near W10th Avenue, Vancouver BC is the sampling point  34  Photo 3-2 Parking lot near W 10th Avenue, Vancouver B.C.  3.2 Methods 3.2.1 Batch adsorption test Based on adsorption isotherms from prior investigations using the same kaolinite and illite clay minerals (Li, 2006), it was determined that for this set of experiments, target adsorbed cadmium and lead concentrations of 150 ppm for both kaolinite and illite samples would be appropriate. In order to get kaolinite and illite partially saturated with Cd and Pb, 150 ppm of Cd and Pb were used to spike the clay minerals. The concentrations of the elements studied were based on the adsorption isotherm determined in previous batch adsorption tests by Li and co-workers (Li and Li, 2000; Li, 2003; Li and Hui, 1999; Li and Lai, 1999). These spiked samples were partially saturated with Cd2+ or Pb2+ on their charged surfaces.  The batch equilibrium test technique of USEPA (USEPA, 1987) was used to investigate the Cd2+ and Pb2+ adsorption characteristics of both clay minerals. The solid: solution ratio was 1:10 (by weight), according to the standard EPA procedures. In this study, 40 mL of solution were added to 4 g of solid sample and rotated on an end-over-end rotator for 24 h to achieve chemical equilibrium. Kaolinite and illite were spiked with 150 ppm lead nitrate and 150 ppm cadmium nitrate separately. pH of all the solution was adjusted to 3.5 by dilute nitric acid to prevent metal ions from precipitation. Triplicate samples 35  were prepared for each solution to verify reproducibility. The supernatant was separated from the clay by centrifuging at 4000 rpm for 10 minutes. The residual concentration of Cd2+ and Pb2+ ions in solution were analyzed using the Atomic Absorption Spectrometer (Varian SpectrAA 220FS), while the solid was oven-dried at 50℃ for 36 h. The dried clay was ground using a mortar and pestle and stored in a fridge. The amount of Pb2+ and Cd2+ ions (by weight) adsorbed per kilogram of soil were calculated based on a mass balance approach, where the difference between the initial concentrations of the solution applied to the soil and the residual concentrations after equilibration using the following equation:  3.2.2 Batch desorption test The desorption procedure was similar to the batch adsorption test (USEPA, 1987), i.e. the solid: solution ratio is 1:10 with the actual weight ratio being 2 g spiked clay mineral sample (with Cd or Pb) to 20 mL washing solution at designated concentration. Triplicate samples were reacted at room temperature in 50 mL polypropylene centrifuge tubes. To determine desorption kinetic, for practical purpose, shorter reaction time is more economical. Therefore, 0.5 h, 1 h, 2 h, 12 h, and 24 h reaction times were investigated. Each metal-ion-spiked clay sample was washed with one of the reagent solutions and pH effect is shown in Table 3-2. Table 3-2 Desorption experimental program for Cd and Pb spiked clay minerals Effect Examined  Reagent  Surfactant concentration  Rhamnolipid Texapon  Reaction time  Rhamnolipid Texapon  pH  HNO3  Conc./time/pH 10, 20, 30, 40, 50, 60, 70 (mM) 10, 50, 100 (mM) 0.5, 1, 2, 12, 24 h 0.5, 1, 2, 12, 24 h 1.5, 2.5, 3.5, 4.5, 5.5, 6.5  36  3.2.3 Sampling Samples were taken from the two locations in June, summer of 2009. At the Wetland, three samples were taken in constructed wetland on the north bank of Lost Lagoon. A plastic spoon was used to collect the sediment samples to prevent introducing metal contamination. At the parking lot location, three samples were also taken from the trap in the parking lot using the plastic spoon. Approximately 2 kg was collected for each sample in a plastic bag, store at 4℃ cooler, and then transported to UBC lab for further sample preparation.  3.2.4 Characterization of street sediments Sample pretreatment In this study, all samples were oven-dried at 50℃ for 36 h to dry the sample but not to destroy any organic materials within the sample. The samples were disaggregated using a mortar and pestle. After drying, sieving to obtain the appropriate particle size of smaller than 2 mm. was made using nylon sieves in order to avoid metal contamination. In order to understand metal binding with finer particles and coarser particles, the smaller particle size of sediments (< 63 μm) was analyzed for comparison with sediments < 2 mm. Split sampling before analysis was used to avoid segregation of particles in the bottles. After the preparation, samples were labeled and stored in fridge (4℃).  Characterization of samples Soil pH: Soil pH was measured in a solution with a soil to water ratio of 1:1 and 1:2.5 (Shoemaker et al., 1961; Webber et al., 1977; Adams and Evans, 1962). The actual procedure was to 20 g of soil in a 50 mL beaker, was added 20 mL and 50 mL of distilled water and the suspension stirred several times during the next 30 min. the suspension was allowed to settle for 30 min and the pH was measured using an Orion 720A pH meter.  Cation exchange capacity (CEC): The cation exchange capacity (CEC in mol (+)/kg) of the sample was estimated by the sum of base cations obtained by measuring displaced K, 37  Na, Ca, Mg by 1.0 M ammonium acetate extract adjusted to pH 7.0 (McKeague, 1978). These cations were measured by AAS FS220. Since pH of sediments was less than 6, this could be an under estimate of the CEC (exchangeable H+/Al3+ was not measured).  The procedure was weigh 10 g of 2 mm air dried soil into 250 mL Erlenmeyer flask and add 50 mL of neutral 1.0 M ammonium acetate. Stopper the flask and rotated for 30 min and then filter the extract through Whatman No. 2V filter paper and save the filtrate for AAS analysis.  Organic matter content (OM): Organic matter content was determined by K2Cr2O7 volumetric method (ASTM D 2974). The procedure was to determine and record the mass of an empty, clean, and dry porcelain dish (MP), into which was placed a fraction or the entire oven-dried test specimen from the moisture content experiment in the porcelain dish and the mass of the soil specimen was determined and recorded (MPDS). The dish was then placed in a muffle furnace and the temperature was gradually increased in the furnace to 440oC. Specimens were left in the furnace overnight. The porcelain dish was removed carefully using tongs, and allowed it to cool to room temperature in a dessicator. The mass of the dish containing the ash (burned soil) (MPA) was determined and recorded. Data analysis: Mass of the dry soil: MD=MPDS-MP Mass of the ashed (burned) soil: MA=MPA-MP Mass of organic matter: MO=MD-MA Organic matter content: OM=  MO  MD  × 100  Total metal content: The trace metal content was measured after digesting using aqua regia (36% HCl: 70% HNO3 at the ratio of 3:1) by AAS. 12 mL aqua regia was added in 0.5 g soil sample on a hot plate for 3 h at 110℃. After evaporation near dryness, the sample was diluted with 20 mL of 2% HNO3 (v/v with distilled water) and transferred into 100 mL volumetric flask after filtering through Whatman No.42 paper and dilute to 100 mL with distilled water. The filtrate was saved for analysis. The same procedure was used to the sediments after treatment with surfactants. 38  Easily extractable metal (EE): For easily reduced metal, which might be considered as bio-available fraction, 2 g of sample was extracted at room temperature with 20 mL of 0.5 M HCl in 50 mL centrifuge tubes on a rotator and measured after filtering through Whatman No.42 paper. The filtrate was saved for analysis by AAS. The same procedure was used for the sediments after treatment with surfactants.  Specific surface area: Specific surface area was measured using ethylene glycol monoethyl ether (EGME) method (Cihacek and Bremner, 1979). The soil was disaggregated to remove particles larger than 250 µm using 60-mesh sieve. Placed 1.1 g of soil in a 600 mL beaker and added 10 mL 0f H2O2 (30%) to destroy organic material, warmed slightly on a hotplate. After reaction finished, more H2O2 was added with warming until no observable reaction occurred. Samples were dried on a hotplate and rinsed with 1 M CaCl2 in a plastic centrifuge tube and shaken, and centrifuged. The residue was washed twice more with CaCl2 and 3 times with distilled water, discarding the supernatant. Samples were air-dried and disaggregated. After the preparation of soil, EGME retention was determined by the following procedure: 1. Weigh the prepared soil into an aluminum weighing dish. Dry to constant weight in an evacuated dessicator over P2O5. Check that constant weight was obtained by periodic measurement. 2. Added 1.5 mL of reagent grade EGME to cover the dried sample. Let this to equilibrate for 1 hour. 3. Meanwhile, removed the P2O5 from the bottom of the dessicator. Fill the dessicator with approximately 130 g CaCl2-EGME solvate: weigh 120 g CaCl2 (40 mesh) into a 1 liter beaker. Dry in oven 1 hour. Weigh 30 g EGME into 400 mL beaker. Added 100 g of the hot dry CaCl2 to EGME, mixing thoroughly with a spatula. After cooling spread in bottom of dessicator. 4. Place sample-EGME slurry in an aluminum dish in a Petri dish and lay cover over. Evacuate with high vacuum pump for 45 min. leave dessicator closed 1 hour, then weigh the sample. 5. Evacuate for 45 min, then reweigh at successively longer internals until constant weight is reached. 39  3.2.5 Selective sequential extraction (SSE) The sequential extraction analysis was conducted as described by Tessier et al. (1979), except that the aqua regia digest method was used in the final extraction (modified by Li and Li, 1999) rather than digestion with HF-HClO4 mixture. A description of the analytical grade reagents, procedures and the experimental conditions are provided in Table 3-3. For each extraction step the samples were rotated on a rotator at 80 rpm for the times listed in the procedure. Following each extraction, the samples were centrifuged at 4000 rpm for 30 minutes, the solution was filtered through a 0.45 μm pore size paper and the filtrate was analyzed for Cu, Fe, Mn, Pb, and Zn. Measurements for all the metals were performed on Atomic Adsorption Spectrometer AA 220FS. Between each step, the residue was washed by 16 mL distilled water. As a final step, the residue was digested by the same method as measuring total metal content.  Table 3-3 Tessier sequential extraction procedure for 1g sample (Tessier et al. 1979) Stage  Fraction  Reagent  Experiment conditions  1  Exchangeable  8 mL of 1 mol/L MgCl2 (pH 7)  1 h at 25℃ continuous stirring  2  Associated with carbonates  8 mL of 1 mol/L NaOAc (pH 5 with acetic acid)  5 h at 25℃ continuous stiring  3  Associated with Fe-Mn oxides  20 mL of NH2OH·HCl, 0.04 mol/L in 25% w/v HOAc (pH~2)  4  Associated with organic matter  3 mL of 0.02 mol/L HNO3/5mL of 30% m/v H2O2, +3 mL of 30% m/v H2O2 +5 mL of 3.2 mol/L NH4OAc  5  Residual fraction*  12 mL of aqua regia 20 mL of 20% HNO3  6 h at 96℃  2 h at 85℃ 3 h at 85℃ 30 min at 25℃ Occasional agitation 3 h at 110℃  * Li and Li, 1999  40  3.2.6 Determination of surfactant remaining in urban sediments Concentration of surfactant was determined by measurement of total organic carbon (TOC). Both anionic (Texapon) and non-ionic (Rhamnolipid) surfactant can be determined by this method. Pre-determined concentrations of Texapon and Rhamnolipid (0, 1, 3, 5, 10, 20, 50, 100 mg/L) were prepared for a linear surfactant standard curve. After preparation of the calibration curve, the samples were tested and sample blanks were measured as control. The solution after treatment with Rhamnolipid and Texapon, after first wash and after second wash were tested for surfactant concentration. The concentration of surfactant residue in sediment after two washes with distilled water was compared with toxicity standards of the two surfactants. Each sample was analyzed in triplicate. 3.2.7 Quality assurance and quality control (QA/QC) Quality control measures were taken as follows: each sample was prepared in triplicate to enable identification of any significant variability in measurements. In addition, reagents and sample blanks were measured for metal concentration to control for contaminations. Because the sensitivity ranges of the AAS, the samples whose concentrations exceeded the limit of the instrument were diluted to within range. To check that dilutions were prepared correctly, a standard with known metal concentration was run through the AAS.  The coefficient of variation of all data was calculated to verify the accuracy of all experiments. The coefficient of variation was less than 2%. Calculation of coefficient of variation followed the equation: Coefficient of variation=  standard deviation average value  ×100%  To determine the accuracy of AAS technique, standard soil from Soil Laboratory of Department of Land and Food System with known concentration of trace metal was measured. Results are shown in Table 3-4.  41  Table 3-4 Accuracy of AAS technique checking with known concentration of trace metal standard soil Trace metal  Tested conc. (mg/kg)  Certified conc. (mg/kg)  Mean±S.D.  Mean±S.D.  Cu  44.5±1.25  45.1±0.25  Mn  351.6±5.80  352±4.50  Pb  90±1.63  90.8±0.65  Zn  47.1±0.87  48±1.59  42  4. RESULTS AND DISCUSSION 4.1 Batch Adsorption Test In order to compare the adsorption capacity of kaolinite and illite, the two samples were spiked at similar concentrations. The amount of adsorped cadmium and lead are given in Table 4-1. The results agree with a previous study by Li (2006). Both Cd and Pb were more strongly adsorbed on illite (3 × more) than kaolinite. Kaolinite has a lower adsorption capacity than illite because of smaller surface area and lower CEC (Table 3-1).  Table 4-1 Adsorbed concentrations of metal ions in the spiked clay mineral samples by using 150 ppm Cd(NO3)2 and 150 ppm Pb(NO3)2 for 24 h Clay  Applied [Cd2+] (ppm)  Applied [Pb2+] (ppm)  Adsorbed Cd (mg/kg)  Adsorbed Pb (mg/kg)  Kaolinite  131  130  285  325  Illite  128  125  1130  1210  4.2 Clay Mineral Effect 4.2.1 Effect of [H+] on desorption The influence of [H+] of kaolinite and illite clay minerals on desorption is demonstrated by desorption at pH’s 1.5, 2.5, 3.5, 4.5, 5.5, and 6.5 with nitric acid (HNO3) (Figure 4-1) (The experimental data is given in appendix A). The removal of metal ions from spiked kaolinite and illite clay minerals differed significantly. As indicated in Table 4-2 a single wash of Cd-spiked and Pb-spiked kaolinite with pH 6.5, decreasing to pH 3.5 HNO3 solutions, removed only 4.7%-10.9% and 1.5%-11.1% of the adsorbed Cd2+ and Pb2+ respectively, whereas HNO3 solution at pH 2.5 removed 52.4% and 76.6% of adsorbed 43  Cd2+ and Pb2+ from the kaolinite. The removal of Cd2+ and Pb2+ increased to 98.4% and 97% at pH 1.5. Kaolinite is a pH-dependent charge clay mineral, meaning that at low pH below 3.5 (point of zero charge of kaolinite), the cation exchange capacity (CEC) decreases and the anion exchange capacity increases. As the surface charge of kaolinite changes from negative to positive, the adsorbed metal ions (cations) are repelled from the charged surface of kaolinite. The acid wash with HNO3 at pH 1.5 and 2.5, are lower than the pH at the point of zero charge of kaolinite, and thus effective in the removal of metal ions from the kaolinite. The removal of adsorbed Cd2+ and Pb2+ from illite with HNO3 solutions at the same pH values as those used for kaolinite was found to be 9%-12.9% and 13.3%-21% of the original adsorbed Cd2+ and Pb2+. Illite has a high crystal charge as a result of isomorphous substitution of Al3+ for Si4+ in tetrahedral sites and Mg2+ for Al3+ in octahedral sites (Yong and Phadungchewit, 1993). Unlike kaolinite, the cation exchange of illite is not pH-dependent. Thus change of pH does not improve desorption. The results indicated that using nitric acid (pH < 3.5) as a washing reagent to remove metals from kaolinite was very effective. In order to save costs, application of nitric acid alone can be considered as an efficient removal agent for kaolinite, but not illite.  This result agreed with previous study by Li (2006). Her results showed HNO3 removed ~50% Cd2+ and 70-90% of the adsorbed Pb2+ ions from kaolinite at pH 2. The cation exchange of illite was not pH-dependent; low pH did not improve desorption.  44  Figure 4-1Concentration of desorbed metals from (a) kaolinite and (b) illite at various pH values adjusted by HNO3 for 0.5 h (arithmetic mean ± standard deviation, n=3) Table 4-2 Percentage of desorbed metals from kaolinite and illite at various pH values (average value for n=3) Kaolinite (%) pH  Cd desorbed  Illite (%)  Pb desorbed  Cd desorbed  Pb desorbed  1.5  98.4  97  12.9  21  2.5  52.4  76.6  10.2  17  3.5  10.9  11.1  13  21  4.5  8.6  3.1  10  18.9  5.5  6.2  3.1  10  19.8  6.5  4.7  1.5  9  13.5  4.2.2 Surfactant effect Although the effect of pH on Cd and Pb removal from spiked clay sample has been previously demonstrated, the effect of the surfactant concentration is not clear. In order to investigate the most efficient condition for desorption of Cd and Pb, different surfactant concentrations and reaction time were applied. The results for effects of surfactant 45  concentration and reaction time are shown in Figure 4-2, 4-3, and 4-4. It is worth noting that both of the surfactants (Rhamnolipid JBR210 and Texapon N70) were tested for metals and showed no contamination.  Concentration of surfactants Cd and Pb extraction from kaolinite and illite by different concentrations of Rhamnolipid and Texapon for different reaction times (0.5-24 h) are shown in Figure 4-2 and Figure 43. Detail of experimental data is provided in appendix B. Percentage of Cd and Pb extracted from kaolinite and illite by different concentration of Rhamnolipid and Texapon for different reaction times (0.5-24 h) are given in Table 4-3.  46  Figure 4-2 Cd desorption from spiked kaolinite and illite at different concentrations of two surfactants (Rhamnolipid and Texapon) for different desorption reaction time (arithmetic mean ± standard deviation, n=3)  ----  Cd original concentration  47  Figure 4-3 Pb desorption from spiked kaolinite and illite at different concentrations of two surfactants (Rhamnolipid and Texapon) for different desorption time (arithmetic mean ± standard deviation, n=3) Pb original concentration  48  Table 4-3 Percentage of Cd and Pb extraction from kaolinite and illite by different concentration of Rhamnolipid and Texapon for different reaction time (average value for n=3) Cd removal (%) Time* Kaolinite with Rhamnolipid (h)  Illite with Rhamnolipid  Kaolinite with Texapon  Illite with Texapon  10 20 30 40 50 60 70  10 20 30 40 50 60 70  10 50 100  10 50 100 (mM)  0.5 66 72 70 74 75 76 76  19 22 20 22 17 19 19  28 80 99  9 22 22  1  66 75 76 81 78 81 74  20 23 22 19 20 17 17  28 76 97  9 24 25  2  64 69 75 81 81 83 83  22 22 19 19 19 20 20  39 80 100  10 20 25  12  65 66 75 75 81 83 83  19 20 20 18 19 18 20  40 85 99  10 21 25  24  66 67 75 75 80 83 80  20 19 19 20 19 18 16  44 83 100  11 21 25  * Time - Extraction Time Table 4-3 Continued Pb removal (%) Time* Kaolinite with Rhamnolipid  Illite with Rhamnolipid  Kaolinite with Texapon Illite with Texapon  (h)  10 20 30 40 50 60 70  10 20 30 40 50 60 70  10 50 100  10 50 100 (mM)  0.5  87 100 94 100 91 94 93  10 10 12 13 17 20 18  26 36 92  4  4  16  1  92 100 100 100 89 89 91  7 13 16 16 13 17 17  25 48 100  3  18  24  2  96 100 98 94 93 66 93  9 12 17 11 18 11 17  33 39 98  4  20 22  12  92 87 85 72 61 35 47  11 13 11 13 12 11 12  33 40 100  4  20 23  24  52 85 75 67 57 19 30  11 16 13 9 11 13 13  36 48 97  3  20 24  * Time - Extraction Time  Removal of Cd from kaolinite and illite by Rhamnolipid and Texapon: The removal of Cd revealed no significant difference by increasing the concentration of Rhamnolipid. Asci (2007) found that the removal of Cd2+ from kaolinite increased with increasing Rhamnolipid (JBR 425) concentration up to 100 mM, and Cd2+ recovery efficiency reached a plateau value of 70.3-71.5% of sorbed Cd2+. In this study, removal efficiency of Cd2+ reached 72-75% at different desorption time with the Rhamnolipid (JBR 210) concentration of 20 mM (Table 4-3). The removal of Cd2+ reached 76% of sorbed Cd2+ when Rhamnolipid concentration increased to 70 mM. Rosen (1989) indicated that 49  nonionic surfactants generally have lower CMC values than those of ionic surfactants. In this case, micelles were formed and started to absorb Cd2+ ions at Rhamnolipid concentration of 20 mM. Removal of Cd2+ reached a plateau value of approxinate 75% when the concentration of Rhamnolipid was above 30 mM. For illite, Rhamnolipid was not as effective as  kaolinite due to the stronger adsorption capacity of illite. The  desorption efficiency was 19-22% by increasing Rhamnolipid concentration from 10 mM to 70 mM. The most effective concentration of Rhamnolipid among seven concentrations tested was 20 mM, where desorption of Cd2+ was 22%.  The other surfactant applied to remove Cd was Texapon. Unlike Rhamnolipid, Texapon was concentration dependent, i.e. the removal of Cd significantly increased with increasing Texapon concentration. The removal of Cd2+ from spiked kaolinite was only 28.1% at low Texapon concentrations of 10mM. Increasing the Texapon concentration to 50 mM and 100 mM, desorption rate increased to 79.6% and 98.6%. According to the Texapon structure with a hydrophilic head and a hydrophobic tail, when the concentration of Texapon was 100 mM, micelles were formed with a hydrophilic exterior (the hydrophilic heads were oriented to the exterior of the aggregate) and a hydrophobic interior (the hydrophobic tails were oriented to the interior aggregate) as shown in Figure 4-4. Cd2+ ions were adsorbed on the surface of micelles as well as Pb2+ ions. Therefore the high concentration of Texapon (100 mM) showed the most efficiency. However, even though Texapon concentration played an important role on desorbing Cd2+, the removal rate from spiked illite was only 9%, 22%, and 22% at Texapon concentration of 10 mM, 50 mM, and 100 mM respectively. This is probably because illite has much higher surface area and CEC than kaolinite, thus the metal adsorbing ability of illite is much stronger than kaolinite. Cd2+ was difficult to be extracted even if the concentration of Texapon was 100 mM.  50  Figure 4-4 Process of Texapon adsorbing Cd2+  Removal of Pb from kaolinite and illite by Rhamnolipid and Texapon: The removal of Pb showed a similar trend to Cd removal, this is expected as the ionic radius of Cd (0.148 nm) is similar to Pb (0.146 nm). The extraction of Pb indicated no significant difference by increasing concentration of Rhamnolipid. Desorption of Pb2+ from kaolinite was 84 100% when Rhamnolipid concentration increased from 10 mM to 20 mM. When the concentration of Rhamnolipid was 30 mM to 70mM, the removal of Pb2+ reached a plateau value of 91-100%. For lead spiked illite, there was a slight difference as the Rhamnolipid ranged from 10 mM to 70 mM. The range was 10-20%. Illite has higher surface area than kaolinite, with the consequence that it has a stronger adsorption ability to bind metal ions tightly, meaning that metal ions adsorbed on illite are difficult to release into solution.  The other surfactant applied to remove Pb was Texapon. Unlike Rhamnolipid, desorption of Pb2+ on kaolinite was only 27% and 36% at Texapon concentration values of 10 mM and 50 mM. The removal reached 92% for kaolinite at a Texapon concentration of 100 mM. Removing Pb2+ from lead spiked illite had the same pattern as the desorption of Cd2+ from cadmium spiked illite. Texapon concentration made a significant difference on Pb2+ removal with levels of 4%, 4%, and 16 % from illite as Texapon concentration increased from 10 mM, 50 mM, and 100 mM.  51  For further investigation, Rhamnolipid concentration of 20 mM was selected for further work due to insignificant difference of Cd2+ and Pb2+ removal from 20 mM to 70 mM and a Texapon concentration of 100 mM was selected for application in any further study.  Reaction time An important factor affecting removal rate of cadmium and lead from clay minerals is the reaction time. Desorption of Cd2+ and Pb2+ from kaolinite and illite with Rhamnolipid concentration of 20 mM and Texapon concentration of 100 mM had slight differences comparing 0.5 h and 24 h reaction times (Figure 4-5).  Kaolinite 400  400  20 mM Rhamnolipid  300 250 200 150 100 50  400 350 300 250 200 150 100 50 0  0.5 h  1h  2h  12 h  100 mM Texapon  0.5 h  1h  2h  12 h  300 250 200 150 100 50 0  24 h  Cd Pb desorbed (mg/kg)  Cd Pb desorbed (mg/kg)  0  20 mM Rhamnolipid  350 Cd Pb desorbed (mg/kg)  350 Cd Pb desorbed (mg/kg)  Illite  24 h  400 350 300 250 200 150 100 50 0  0.5 h  1h  2h  12 h  24 h  100 mM Texapon  Cd Pb 0.5 h  1h  2h  12 h  24 h  Figure 4-5 Effect of time on Cd or Pb desorption from kaolinite and illite with initial concentration sorbed onto kaolinite and illite. Initial concentration: 285 mg Cd2+ and 325 mg Pb2+ sorbed onto kg kaolinite; and 1130 mg Cd2+ and 1210 mg Pb2+ sorbed onto kg illite (average value for n=3, S. D. ~ 2%)  52  Recognizing the need for an economical and feasible process to achieve end goal field usage, the reaction time must be as short as possible but long enough to attain the desire level of contaminant removal, within a margin of safety.  During the first half an hour of mixing, 20 mM Rhamnolipid showed that 72% and 22% of Cd2+ was removed from spiked kaolinite and illite. This was similar to the desorption of Pb2+ from lead spiked kaolinite and illite, which was 100% and 13% of Pb2+ removed in first half an hour. In addition, removal of Cd2+ and Pb2+ from spiked kaolinite by 100 mM Texapon was 99% and 92%; and also removal of these two elements from spiked illite was 22% and 16% in the first half an hour. By increasing the reaction time from 1 h to 24 h, the slurries had an opportunity to undergo more thorough mixing and be exposed to the washing agents for an extended period of time. Interestingly, the results did not reflect a simple relationship between time and effectiveness (Figure 4-5). In general, there were no significant enhancements in Cd and Pb removal after waiting an additional 23 and a half hours.  There is limited research that focused on reaction time effect on Cd and Pb removal by Rhamnolipid and Texapon. However, treatment with other surfactants such as SDS and Triton X-100 showed similar results (Takeda, 2008; Liu et al., 1995); results showed there was an only slight difference of removing metals from soil between first hour and additional hours. Therefore, 0.5 h was selected as the reaction time for urban sediment studies.  4.3 Characteristics of Sediments Characteristics of two urban sediments are given in Table 4-4. The soil pH in both Wetland and Parking lot was below 7, meaning that the two samples did not contain carbonate. Particle size of Parking lot sediment was coarser than Wetland. Organic matter content in Wetland was three times higher than in Parking lot sediment, because finer particles of Wetland bind more organic materials in a biodiverse wetland ecosystem. The 53  fraction of <63µm was 55.7% in Wetland and 37% in Parking lot sediment. The experiment data is presented in appendix C.  Table 4-4 Characteristics of urban sediments collected from two locations in Vancouver B.C. Properties  Wetland  Parking lot  pH ( water (1:1))  5.2  6.3  pH ( water (1:2.5))  5.4  6.4  pH (0.01M CaCl2(1:2))  4.9  5.6  Organic matter(g/kg) ( K2Cr2O7 volumetric methods )  200  74.9  Particle size (%) (<63µm)  55.7%  37%  Exchangeable K (cmol/kg) 1.0 N ammonium acetate extract)  0.10  0.07  Exchangeable Na (cmol/kg)  0.71  1.63  Exchangeable Ca (cmol/kg)  3.10  0.23  Exchangeable Mg (cmol/kg)  0.69  0.39  Specific Area (EGME) (m2/g)  101  76.7  4.3.1 Total metal content in sediments The total metal content of < 2mm sieved Wetland samples were nearly twice as high as that found for the Parking lot sediment (Figure 4-6). The particle size of Wetland samples was finer than Parking lot sediments, which would result in a higher adsorption ability of Wetland over Parking lot sediments. Cu content in Wetland and Parking lot sediments was 174.87 mg/kg and 81.33 mg/kg, both concentration exceeded sediment critical limit of Canada (Table 4-5) (De Vries and Bakker, 1998). Total Mn content of Wetland and Parking lot sediments was 271.47 mg/kg and 147.93. Mn probably originated from oil spills and vehicle emissions the result of the use of MMT (methylcyclopentadienyl 54  manganese) as a fuel additive (Crosby, 1998). The amount of Pb in Wetland and Parking lot sediments was relatively similar 130.67 mg/kg and 128 mg/kg, which exceeded the 25 mg/kg of Pb given in Canadian sediment quality criteria (De Vries and Bakker, 1998). Zn content in Wetland was 292.39 mg/kg, twice the 140.77 mg lead per kg of Parking lot sediments. Both Wetland and Parking lot sediments exceeded Canadian sediment criteria for Zn (De Vries and Bakker, 1998). The Pb and Zn probably originated from precipitation of air contaminants of traffic activities (Preciado and Li, 2006).  Recent sediment contaminant research of a freshwater river by Li et al. (2009) has shown similar results to those found in the Wetland in this study (Table 4-6). Compared to research related to urban soil contaminant in the city of Palermo Italy by Manta et al. (2002), Mn concentration in analyzed sediment are much lower than those reported from Palermo. Cu, Pb, and Zn were generally similar to Palermo values (Table 4-6).  For samples less than 63 µm, the elements adsorbed onto these particles were much higher in amount than in the <2 mm (Figure 4-6). Cu, Mn, Pb, and Zn bound on Wetland samples were 445.13 mg/kg, 349.27 mg/kg, 278.67 mg/kg, and 735.39 mg/kg respectively; and those bound on Parking lot sediments were 159.13 mg/kg of Cu, 248.07 mg/kg of Mn, 137.33 mg/kg of Pb, and 292.07 mg/kg of Zn. These results agreed with the theory that finer particle have larger specific areas, which have higher absorbing ability for metals.  55  Wetland  800  Parking lot  mg element sorbed onto kg sediment  700 600 500 400  < 63 µm < 2 mm  300 200 100 0 Cu  Mn  Pb  Zn  Cu  Mn  Pb  Zn  Figure 4-6 Total trace metal (Cu, Mn, Pb, and Zn) content in Wetland and Parking lot sediments (arithmetic mean ± standard deviation, n=3)  Table 4-5 Comparison of metal in samples and Canadian limits for protection of all land uses (De Vries and Bakker, 1998) Unit: mg/kg dry weight Cu  Mn  Pb  Zn  Canadian critical limit*  30  ---  25  50  Wetland (<2 mm)  175  271  131  292  Parking lot (<2 mm)  81  148  128  141  Wetland (< 63 µm)  445  349  279  735  Parking lot (<63 µm)  159  248  137  292  * CCME, 1997  56  Table 4-6 Comparison of concentration of trace metal in other studies and this study Trace metal  Brunette River  (mg/kg)  (Li et al., 2009)  Wetland  Palermo Italy  Parking lot  (Manta et al., 2002)  Cu  125  175  63  81  Mn  321  271  519  148  Pb  135  131  121  128  Zn  56  292  138  141  4.3.2 Easily extractable metal in sediments Easily extractable metals have been proposed as a measure to evaluate potential bioavailability of trace metal contaminants in sediments (Sutherland, 2002). Easily extractable metals (with 0.5 M HCl) associated with the two sediments are presented in Figure 4-7. In Wetland, 34.6%, 5.9%, 20.2%, and 29.5% of the particulate bound metals (Cu, Mn, Pb and Zn) were in the easily extractable fraction (Table 4-7). In the trap at the Parking lot, the easily extractable metal content of the four elements (Cu, Mn, Pb, and Zn) was 19%, 3.6%, 8.2%, and 27.1% (Table 4-7).  Generally, percentage of easily  extractable Mn and Zn from Wetland and Parking lot sediments was similar. Cu extracted by HCl from Stormwater retention was much higher than Parking lot, since a large portion of Cu was associated with organic matter.  A previous study of a freshwater lake by Li et al. (2009), provided results that showed most metals were extracted by 0.5 M HCl (Table 4-7). This is attributed to characteristics of the sediments. Metals were loosely bound on coarser particles, since the sediment was sandy sediment in their research. Values for easily extracted metal concentration in urban parking lots or streets are scarce in the literature.  57  Wetland  350  parking Lot  mg Metal absorbed on kg sediment  300 250 Easily Extractable 200  Total Digestion residual organic matter  150  Fe-Mn oxide reducible  100  exchangeable 50 0 Cu  Mn  Pb  Zn  Cu  Mn  Pb  Zn  Figure 4-7 Sequential extraction results of Wetland and Parking lot sediment samples (< 2 mm) (arithmetic mean ± standard deviation, n=3)  Table 4-7 Percentage of easily extracted metal by 0.5 M HCl in Burnaby Lake and Wetland Easily extracted metal  Burnaby Lake (Li et al., 2009)  Wetland  Parking lot  Cu  65  34.6  19  Mn  58  5.9  3.6  Pb  82  20.2  8.2  Zn  82  29.5  27.1  58  4.3.3 Geochemical distribution of trace metals The geochemistry of the sediment-associated trace metals can affect their transport dynamics as well as their potential availability to aquatic organisms (Li et al., 2009). Figure 4-8 presents the percentage of the trace metals associated with five geochemical phases for the sediments.  The largest percentage of Cu was associated with the organic component of both Wetland and Parking lot sediments. The percentage in this phase was 77% in Wetland, and was higher than 55% in Parking lot. The difference is probably due to higher organic matter content in Wetland. Recent sediment contaminant research has shown a similar trend in both freshwater (Fytiano and Lourantou 2004-lakes in N. Greece; Wang et al., 2004wetlands in China) and coastal marine sediments (Burton et al., 2005-Queensland, Australia; Morillo et al., 2007-S. Spain). The proportion of Cu in the exchangeable phase was 2.2% and 3.3% in Stormwater and Parking lot, respectively (Figure 4-8). This exchangeable form of Cu should be more mobile and easily bioavailable. This source of Cu could be from the wear of automobile brake linings (Kayhanian et al., 2003).  Mn geochemistry is dominated by the residual phase (72% in Wetland and 74% in Parking lot), with very little Mn associated with the exchangeable phase (2.2% and 3.3% in Wetland and Parking lot, respectively). The residual phase containing Mn is not readily bioavailable, but could be important in the geochemical distribution of other elements due to the adsorptive properties of their oxides (Jenne, 1968). Previous studies have reported that a relatively high proportion of Mn (30%) is found in Fe-Mn oxide phase (Pardo et al., 2004; Wang et al., 2004). This component was also found in both Wetland and Parking lot with 10.2% and 9.7% (Figure 4-8). However, Mn was also dominant in the residual phase in these two locations.  Sediment geochemical studies report considerable Pb associated with Fe-Mn oxides (Pardo et al., 2004; Wang et al., 2004), which was also the case for Wetland and Parking lot sediments in this study (44.6% and 43.3% of Pb associated with Fe-Mn oxide). Pb 59  bound to organic was 16.3% and 17.7% in Wetland and Parking lot, followed by the exchangeable phase (15.6% and 16.5% in wetland and Parking lot). Even though the amount of Pb bound to the exchangeable phase was very low, grazing of organic detritus could make Pb in organic phase more readily available to benthic invertebrates as with Cu, (Li et al., 2009).  The largest percentage of Zn was associated with Fe-Mn oxide phase with 52.3% and 45.1% in Wetland and Parking lot sediments, respectively. A previous study of the Brunette River by Li et al. (2009) showed similar results, namely that the geochemical fractions for Zn ranked in order Fe-Mn oxide > residual phase > organic > exchangeable. However, Zn bound to organic matter can also be important and will depend on the organic matter characteristics of the sediments. In the high organic Wetland sediments, 13.3% of Zn was in organic phase compared 9.9% in organic of Parking lot (Figure 4-8). Corrosion of galvanized components on vehicles followed by washing into urban streams is believed to be a major source of Zn contaminants on roadways (Li et al., 2006).  A comparison of the HCl extractable metals to the sum of the first four sequential metal extracts indicated that for Cu, Mn, Pb and Zn a higher proportion is extracted by the series of sequential extractions. This was especially true for Cu, Pb and Zn since most Cu was associated with the organic phase and most Pb and Zn were associated with Fe-Mn oxides. The sum of the four phases for Mn was slightly higher than HCl extracted due to largest proportion of Mn associated with residual phase.  60  Wetland  100%  Parking lot  90% 80% 70% 60%  residual  50%  organic matter  40%  Fe-Mn oxide  30%  reducible  20%  exchangeable  10% 0% Cu  Mn  Pb  Zn  Cu  Mn  Pb  Zn  Figure 4-8 Percentage of geochemical fraction of four trace metals (Cu, Mn, Pb, and Zn) associated with contaminated sediments from Vancouver, B.C.  61  4.4 Effectiveness of Removing Trace Metals by Surfactants 4.4.1 Total metal content in sediments after treatment with surfactants The adsorbed metals on sediments (Wetland and Parking lot) decreased after treatment with two surfactants-Rhamnolipid and Texapon. Figure 4-9 shows the ratio of the final to the initial concentration of trace metals (Cu, Mn, Pb and Zn). The experiment data is provided in appendix D.  Treatment with Rhamnolipid Table 4-8 shows that 31% and 28% Cu was removed from Wetland and Parking lot sediments. Total Mn removal in two samples with Rhamnolipid was similar, 26% (Wetland) and 26% (Parking lot). Pb removal was the most among all elements tested at 43% in Wetland and 60% in Parking lot sediments with treatment of Rhamnolipid. Zn removal was similar to Cu, 27% was removed from Wetland and 31% was removed from Parking lot.  These metals were removed by forming complexes with Rhamnolipid on the sediment surface, then being detached and released into the solution due to the lowering of the interfacial tension, and hence reacting with Rhamnolipid micelles, as discussed in metal removal from clay minerals (Figure 4-4). Rhamnolipid micelles are formed immediately as the concentration of Rhamnolipid applied exceeded CMC of Rhamnolipid (0.1mM) (Mulligan and Wang, 2006). Amount of Cu2+, Mn2+ and Zn2+ adsorbed on Rhamnolipid micelles was similar as a result of their similar ionic radius. Pb2+ was the most competitive ion with respect to adsorption onto the surface of micelles. The unhydrated radii are Cu2+ (0.072 nm), Mn2+ (0.080 nm), Pb2+ (0.120 nm), and Zn2+ (0.074 nm) (Sposito, 1984). However, the hydrated radii is in reverse order Cu>Zn>Mn>Pb. The larger hydrated radii imply reduced bond strength between ion and micelle, while smaller hydrated radii would result from stronger bonding forces between ion and micelle.  62  Treatment with Texapon Cu removal of 31% and 39% was recorded from Wetland and Parking lot sediments respectively by application of Texapon (Table 4-8). And 27% Mn from Wetland and 18% from Parking lot was removed. The removal efficiency of Pb was 58% and 86% from Wetland and Parking lot sediments. Texapon removed 31% and 40% of Zn from these two sediments (Wetland and Parking lot).  The possible mechanism for the extraction of metals by Texapon is the formation of micelles. The process is similar to Rhamnolipid. Several micelles are formed when Texapon concentration reaches a critical value (>CMC of 70%) (Cognis, 2006). The hydrophilic heads with negative charge orient towards the exterior and hydrophobic tails towards interior. These metal cations migrate towards the Texapon micelle a result of their negative charge. Generally, the efficiency of treatment with the two surfactants was similar. However, the amounts of all metals removal from Parking lot was slightly higher than Wetland because Wetland sediment had stronger adsorption ability due to their larger specific area (Table 4-4).  Comparison with previous studies Related previous studies are listed in Table 2-2. Research by Mulligan et al. (2005) showed higher Cu removal of 65% from sediments by 0.5% Rhamnolipid. The sediment they chose for studying has a higher organic content than the analyzed sediment in this study. Cu was dominantly in organic phase. Rhamnolipid removed Cu by dissolving organic matter. Another research by Pichtel and Pichtel (1997) demonstrated 30-40% Pb was removed by 0.1 M SDS (chemical structure is similar as Texapon). This result was similar to this study.  63  Wetland  mg element adsorbed on kg sediments  350  Cu  300  Mn  Pb  Zn  250 200 150 100 50 0  N  R  T  N  R  T  N  R  T  N  R  T  Parking lot 350  Cu  mg element adsorbed on kg sediments  300  Mn  Pb  Zn  250 200 150 100 50 0  N  R  T  N  R  T  N  R  T  N  R  T  Figure 4-9 Total content of four trace metals (Cu, Mn, Pb, and Zn) before (N) and after treatment with two surfactants (20 mM Rhamnolipid - R and 100 mM Texapon - T) for 0.5 h from contaminated sediments (< 2 mm) in Vancouver, B.C. (arithmetic mean ± standard deviation, n=3) 64  Table 4-8 Four trace metal (Cu, Mn, Pb, and Zn) content before treatment with surfactants and percentage of removal with surfactants (20 mM Rhamnolipid and 100 mM Texapon) for 0.5 h from two contaminated sediments in Vancouver B.C. (average mean for n=3)  Wetland No treatment (mg/kg) Cu  Mn  Pb  Rhamnolipid (%)  Texapon (%)  Zn  Cu  Mn  Pb  Zn  Cu  Mn  Pb  Zn  Exchangeable  3.3 8.49 20.7 40.8  73  33  100  49  6.2  43  100  1  Reducible  10  3.95 15.6 32.2  58  60  36  19  0  68  38  55  Fe-Mn oxide  11.5 20.6 59.1 168  35  0  49  26  44  6.9  0  40  Organic matter  116  0  0  14  15  4.2  0  84  26  Residual  9.65 146 15.6 36.3  7.4 9.2  0  0  3  6.9  0  0  Total metal  175 271 131  31  26  43  27  31  27  58  31  12  0  22  14  15  25  0  31  23.1 21.5 42.4 292  Easily extractable 60.6 16 26.4 86.2  Parking lot No treatment (mg/kg) Cu  Mn  Pb  Zn  Rhamnolipid (%)  Texapon (%)  Cu  Mn  Pb  Zn  Cu  Mn  Pb  Zn  Exchangeable  2.02 4.57 15.3 18.2  90  75  100  72  56  79  100  11  Reducible  6.81 1.58 14.2 26.5  63  56  69  56  42  64  66  66  Fe-Mn oxide  10.5 13.4 53  71.7  63  0  51  35  67  0  52  44  Organic matter  33.9 17.1 21.7 15.7  19  0  44  0  33  0  100 67  Residual  7.95 102 18.1 26.8  7.8  15  8.3  0  5.7  17  11  0  Total metal  81.3 148 128 159  28  26  60  31  39  18  86  40  Easily extractable 15.5 5.33 10.5 38.2  6.7  0  67  3.6  0  14  0  19  65  4.4.2 Easily extractable metal in sediments after treatment with surfactants Rhamnolipid and Texapon showed very different efficiency to HCl extractable metal removal, probably result of their different chemical structures. Figure 4-10 shows the HCl extractable metal removal from two sediments (Wetland and Parking lot) by treatment of Rhamnolipid and Texapon. Table 4-8 shows the percentage of easily extractable metal removal from the two sediments.  Treatment with Rhamnolipid The removal efficiency of easily extractable Cu was 12% from Wetland higher than 6.7% from Parking lot sediments, the result is probably because Wetland had higher organic matter content of 200 g/kg than Parking lot sediments of 74.9 g/kg. Rhamnolipid removed Cu from organic phase which adsorbed largest proportion of Cu. Rhamnolipid did not remove any easily extractable Mn from either Wetland or Parking lot sediments. Easily extractable Zn removal was similar to Cu, a result of their similar ionic radii. Rhamnolipid removed 22% easily extractable Pb from Wetland, and less than 67% from Parking lot sediments, the result of Wetland sediments having a larger specific area of 101 m2/g than Parking lot sediments of 76.7 m2/g.  Generally, easily extractable metals removal by Rhamnolipid did not show a high efficiency of total metal removal. 0.5 M HCl used to extract easily extractable metals lost its ability to release metals into solution by Rhamnolipid. Acis et al. (2007) gave an explanatory mechanism, that is, Rhamnolipid forms liposome-like vesicles when pH<5.8.  Treatment with Texapon Easily extractable metal removal by Texapon showed similar results to Rhamnolipid, which had a lower efficiency than removal of total metals. Easily extractable Cu was only 15% and 0 from Stormwater retention and Parking lot sediments. Mn and Zn were similar, 25% and 14% Mn and 31% and 19% Zn were removed from Wetland and Parking lot sediments, respectively. Texapon did not remove any extractable Pb from either of the two sediments. Based on the chemical structure and physical properties of Texapon, 66  easily extractable metals boundon sediment particles were only slightly removed with treatment of Texapon. Texapon in the presence of HCl is less effective in removing adsorbed metals from sediments surfaces, probably because of an interaction between Texapon and HCl. Based on the chemical structure and physical properties, an interaction took place between HCl and Texapon [Na-OSO3-CH3(CH2)11]. The reaction equation is: Na-OSO3-CH3(CH2)11+HCl=H-OSO3-CH3(CH2)11+NaCl The strong acid HCl was changed to weak acid H-OSO3-CH3(CH2)11 and lost the extracting ability of metal ions. In addition, Pb was the most tightly bound ion, thus Pb was the most difficult to be extracted, so easily extractable Pb procedure showed nothing was removed from either sediment.  67  Wetland 100  Cu  mg element adsorbed on kg sediments  90  Mn  Pb  Zn  80 70 60 50 40 30 20 10 0  N  R  T  N  R  T  N  R  T  N  R  T  Parking lot 100 mg element adsorbed on kg sediments  90  Cu  Mn  Pb  Zn  80 70 60 50 40 30 20 10 0  N  R  T  N  R  T  N  R  T  N  R  T  Figure 4-10 Easily extractable metal adsorbed onto sediment (< 2 mm) before (N) and after treatment with two surfactants (20 mM Rhamnolipid - R and 100 mM Texapon - T) for 0.5 h from contaminated sediments in Vancouver, B.C. (arithmetic mean ± standard deviation, n=3)  68  4.4.3 Selective sequential extraction after treatment with surfactants Experiments with sequential extraction were performed on the two sediments (Wetland and Parking lot sediments) after washing with two surfactants, Rhamnolipid and Texapon. Figure 4-11 shows the geochemical distribution of four trace metals (Cu, Mn, Pb and Zn) with and without washing by surfactants.  Cu desorption by surfactants The amount of Cu bound in the exchangeable fraction was reduced from 3.23 mg/kg with no treatment to 0.889 mg/kg after treatment with Rhamnolipid in Wetland sediments. Significant reduction occurred in the reducible fraction and Fe-Mn oxide fraction with treatment by Rhamnolipid, which was found to the 10.01 mg/kg to 4.22 mg/kg in reducible fraction and from 11.5 mg/kg to 6.1 mg/kg in Wetland samples. There was no obvious reduction in the organic matter fraction and residual fraction after application of Rhamnolipid in Wetland samples.  Treatment by Rhamnolipid of Parking lot sediments showed similar effectiveness on Cu removal. From 2.02 mg/kg to 0.20 mg/kg in exchangeable fraction, 6.81 mg/kg to 2.50 mg/kg in reducible fraction, and 10.5 mg/kg to 3.94 mg/kg in Fe-Mn oxide fraction were found after application of Rhamnolipid to Parking lot sediments. Cu bound to the organic matter fraction and residual fraction was similar in amount to no treatment. Treatment by Texapon on Wetland sediments showed slight reduction (< 10%) of Cu in each fraction. However, removal of Cu with application of Texapon in Parking lot sediments showed significant effect in first three fractions with a reduction of Cu from 2.02 mg/kg to 0.90 mg/kg in exchangeable fraction, 6.8 mg/kg to 3.9 mg/kg in reducible fraction and 10.5 mg/kg to 3.5 mg/kg in Fe-Mn oxide fraction.  The results indicated that both Texapon and Rhamnolipid were very effective for removing Cu from relatively easy released fractions, i.e. exchangeable, reducible, and FeMn oxide fraction in both Wetland and Parking lot sediments. Previously, Shin et al. (2005) showed similar results as this study, mainly that most of the Cu is associated with 69  exchangeable and reducible fraction and may be removed by surfactants, such as Triton X-100.  Mn desorption by surfactants Both Rhamnolipid and Texapon were effective in removing Mn from the exchangeable fraction and reducible fraction, but had low effective removal in the remaining fractions in both Wetland and Parking lot sediments. In Wetland samples, Mn removal was from 8.48 mg/kg to 5.72 mg/kg by Rhamnolipid and 4.82 mg/kg by Texapon in exchangeable fraction. Mn bound in the reducible fraction decreased from 3.95 mg/kg with no treatment to 1.56 mg/kg by Rhamnolipid treatment and to 1.25 mg/kg by Texapon. Mn bound with the remaining fractions with treatment of Rhamnolipid and Texapon showed similar adsorption to the original Wetland samples with no treatment. Amount of Mn adsorbed onto exchangeable fraction was 4.56 mg/kg originally to 1.12 mg/kg by Rhamnolipid and to 0.979 mg/kg by Texapon in Parking lot sediments.  The results demonstrated that both Rhamnolipid and Texapon were effective in removing Mn from exchangeable and reducible fraction. There was no Mn removal from the remaining three fractions, as natural occurrence of Mn associated with Fe-Mn oxide, organic and residual fraction was difficult to be extracted by surfactants. Mn associated with exchangeable and reducible originated from human activity was efficiently extracted by surfactants. In addition, the effectiveness of the two surfactants in Wetland is higher than Parking lot sediments due to the lower adsorbing capacity of Parking lot sediments.  Pb desorption by surfactants The amount of Pb bound to the exchangeable fraction in both Wetland and Parking lot sediments with treatment of Rhamnolipid and Texapon showed negative results. The AAS gave negative reading due to low concentration of Pb exceeding detection limits of instrument. Removal of Pb from organic matter fraction demonstrated to be the most effective among all fractions in both Wetland and Parking lot sediments with treatment of Texapon. In Wetland sediments, Pb associated with organic matter decreased from 21.6 mg/kg to 18.4 mg/kg with Rhamnolipid and to 3.44 mg/kg with Texapon. In Parking lot 70  sediments, the amount of Pb bound to organic matter was reduced from 21.8 mg/kg, with no treatment, to 12.1 mg/kg with Rhamnolipid and to negative values with Texapon. The other fractions showed slight reduction in both Wetland and Parking lot sediments.  The results indicated that both Rhamnolipid and Texapon removed most Pb associated with exchangeable and reducible fractions and large amount of Pb associated with the organic matter fraction. Pb is the most tightly bound with surfactant micelle due to its small hydrated radius. When surfactants dissolved organic matter, Pb was adsorbed onto the hydrophilic heads of surfactant micelles. Therefore, Pb removal showed more efficiency by surfactant than other three metals. This result was similar to Huang et al. (1994), where Pb removal efficiency achieved was 99.9% but Ni removal was only 17%.  Zn desorption by surfactants Rhamnolipid removed a large portion of Zn ranging from 40.8 mg/kg to 20.8 in the exchangeable fraction, 32.2 mg/kg to 25.9 mg/kg in the reducible fraction, and 168.3 mg/kg to 125.0mg/kg in the Fe-Mn oxide fraction for Wetland samples. Treatment by Texapon had a slight reduction from 40.8 mg/kg to 40.5 mg/kg in the exchangeable fraction, larger decrease from 32.2 mg/kg to 14.4 mg/kg in the reducible fraction, and 168.3 mg/kg to 100.2 mg/kg in the Fe-Mn oxide fraction of Wetland sediments. Furthermore, Parking lot sediments showed similar tendency of Zn removal by both Rhamnolipid and Texapon. Treatment by Rhamnolipid reduced Zn adsorption from 18.2 mg/kg to 5.15 in the exchangeable fraction, 26.6 mg/kg to 11.6 mg/kg in the reducible fraction, and 71.7 mg/kg to 46.9 mg/kg in the Fe-Mn oxide, while Texapon caused Zn adsorption to be 7.14 mg/kg, 9.04 mg/kg, and 40.4 mg/kg in the first three fractions respectively. The other fractions were constant or gradually reduced.  The results illustrated that Rhamnolipid and Texapon were more efficient on removing Zn from the first three fractions (i.e. exchangeable, reducible, and Fe-Mn oxide) than the other two fractions (organic matter and residual). The reason are similar to those discussed for Mn removal; most Zn associated with the first three fractions was from anthropogenic activities such as vehicle emissions and industrial waste. This Zn is loosely 71  bound to sediments which means easily desorbed into solution. A previous study by Mulligan et al. (2001) showed similar results, that is a large amount of Zn associated with exchangeable, reducible and oxide fraction is removed, compared to no significant change in the organic and residual fractions.  Different efficiency of two surfactants Generally, both Rhamnolipid and Texapon removed large portions of metals associated with the first three fractions (exchangeable, reducible and Fe-Mn oxide fraction) of both Wetland and Parking lot sediments (Figure 4-12). The four metals removal efficiency by Texapon was slightly higher than by Rhamnolipid, because of the different chemical structure of the two surfactants. Texapon, an anionic surfactant, could enhance metal removal from sediments through mechanism of counter ion exchange at micelle surface above CMC. Once Texapon micelles were formed, metal cations moved toward the negatively charged micelles and adsorbed on the surface of the micelles. Unlike Rhamnolipid, a nonionic surfactant, metals were removed by forming complexes, being detached into solution due to lowering of interfacial tension, and hence associating with Rhamnolipid micelles. The hydrophilic heads of Rhamnolipid did not adsorb metal cations as effectively as Texapon because of its uncharged surface.  The results of this study are in agreement with some previous studies. Shin et al. (2005) showed anionic surfactant (SDS) enhanced removal of Cd up to 80%. Huang et al. (1997) also indicated anionic surfactant (Dowfax C10 and C16) achieved Pb removal up to 100%. Nevertheless, nonionic surfactant (Triton X-100) had low effects on metal removal (Huang et al., 1997).  72  mg element adsorbed on kg sediments  Wetland 350 300 250 200 150 100 50 0 N  R  T  N  Cu  R  T  N  Mn  R  T  N  Pb  R  T  Zn  Parking lot  mg element adsorbed on kg sediments  350 300 250 200 150 100 50 0 N  R  T Cu  N  R  T  N  Mn  R  T Pb  N  R  T  Zn  residual organic matter Fe-Mn oxide reducible exchangeable  Figure 4-11 Geochemical distribution of four trace metals (Cu, Mn, Pb, and Zn) in contaminated sediments before (N) and after extraction with two surfactants (20 mM Rhamnolipid - R and 100 mM Texapon - T) for 0.5 h (average value for n=3)  73  100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%  Mn  Cu  N  R  T  N  Stormwater retention wetland  R  T  N  R  T  Stormwater retention wetland  Parking lot  100% 90%  N  R  T  Parking lot  Zn  Pb  80% 70% 60% 50% 40% 30% 20% 10% 0% N R T Stormwater retention wetland  N R Parking lot  T  N  R  T  Stormwater retention wetland  N  R  T  Parking lot  Figure 4-12 Percentage of geochemical fractions of four trace metals (Cu, Mn, Pb, and Zn) in two contaminated sediments before (N) and after extraction with two surfactants (20 mM Rhamnolipid - R and 100 mM Texapon - T) for 0.5 h (average value for n=3)  74  4.5 Surfactant Residual in Sediments Zhang et al. (2007) and Shin et al. (2005) focused on the effectiveness of surfactants on removing metals from contaminated soil but did not determine the amount of surfactant that remained in treated samples. How much surfactant remains in the soil and the toxicity of residual surfactant in soil has been ignored by most researchers. In this study, the remaining surfactant associated with sediments was measured after two washings with distilled water. The results are given in Table 4-9 and Figure 4-13.  Table 4-9 Concentration (mg/L) and percentage of surfactants removed from each washing and remaining in sediments after two washes with distilled water (average mean for n=3) Rhamnolipid Wetland Parking lot Conc. % Conc. % Original 12242 After desorption 11019 739 1st wash 134 2nd wash Remain 349  10.0 3.9 3.1 2.8  12242 11157 860 173 51  9.0 1.8 0.4 0.4  Wetland Conc. % 34969 32377 2007 303 282  6.4 1.7 1.1 0.8  Texapon  Parking lot Conc. % 34969 33511 1312 109 37  4.2 0.4 0.1 0.1  75  Figure 4-13 Concentration of surfactants removed from sediments after two washings with distilled water (arithmetic mean ± standard deviation, n=3)  76  In order to understand the toxicity of the two surfactants to the environment, the amount of surfactant that remains in sediments was determined for comparison with LD50/LC50 of the two surfactants. The results (Table 4-9) showed 10% and 9% of Rhamnolipid remained in Wetland and Parking lot sediments respectively and only 2.8% and 0.4% Rhamnolipid remained on sediments after two washings with distilled water. Table 4-9 indicates there was 349.39 mg/L Rhamnolipid remaining in Wetland sediments and only 51.4 mg/L in Parking lot sediments, which are below oral and dermal LD50 of 5000 mg/kg (Jeneil, 2008).  Residual Texapon in Wetland sediments was 6.4% after desorption and only 0.8% still remained after two washings. Parking lot sediments held 4.2% Texapon after desorption and only 0.1% Texapon remained after two washings with distilled water. Table 4-9 shows that the residue of Texapon in Wetland sediments was 281.6 mg/L, which exceeded LC50 of 100 mg/L to fish and bacteria, suggesting that it might be toxic to aquatic life when the sediment is returned to the Wetland. Texapon that remained in Parking lot sediments was lower than in Stormwater retention, and was below the LC50 to aquatic life of 100 mg/L (Cognis, 2006).  Generally, Wetland held more surfactants, both Rhamnolipid and Texapon, than Parking lot sediments, probably because the specific area of Wetland sediments was larger than Parking lot sediments. In addition, both Rhamnolipid and Texapon have the ability to become associated with organic matter. Wetland sediments had much higher organic matter content than Parking lot sediments, resulting in residual surfactants in Wetland being more than Parking lot sediments.  77  5. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS  5.1 Summary 5.1.1 Surfactant enhanced removal of Cd and Pb from clay minerals 1. Batch adsorption testing demonstrated that illite has substantially higher adsorption capacity for Cd and Pb than kaolinite. The adsorption of Cd and Pb on illite was more than twice than on kaolinite when the same 150 mg/L of original concentration of Cd2+ and Pb2+ was applied. 2. pH effect showed 52% and 77% of adsorbed Cd2+ and Pb2+ was removed with nitric acid from kaolinite when pH was lowered to 2.5. The removal efficiency of Cd2+ and Pb2+ from kaolinite increased to 98% and 97% when pH decreased to 1.5. The removal of Cd2+ and Pb2+ from variable charged kaolinite was improved by lowering pH. However, pH did not affect removal of Cd2+ and Pb2+ from the permanent surface charged mineral illite. 3. Surfactants concentration tested showed that there was no significant difference in the removal of Cd and Pb from both kaolinite and illite by increasing the concentration of Rhamnolipid, which reached a plateau value. However, there was significant increase in the removal of Cd and Pb from kaolinite and illite by increasing the Texapon concentration to 100 mM.  4. Reaction time effect tested showed that desorption of Cd and Pb from both spiked kaolinite and illite by 20 mM Rhamnolipid and 100 mM Texapon was only slightly different by prolonging the reaction time. The reaction time of 0.5 h had the same effect on Cd and Pb desorption, as additional 23.5 h.  78  5. With field application, a lower surfactant concentration and shorter reaction time is desirable because of the economic aspect of using less surfactant per volume solution and completing the remediation process faster. Therefore, 0.5 h of reaction time, 20 mM of Rhamnolipid and 100 mM of Texapon were selected as an optimum condition to employ to remove metals from contaminated urban sediments.  5.1.2 Surfactant enhanced removal of four trace metals (Cu, Mn, Pb and Zn) from contaminated urban sediments Before treatment with surfactants 1. The total metal content of < 2 mm sieve Wetland sediments were nearly twice as high than the Parking lot sediments because of the higher specific area and also their high organic matter content held more metal than Parking lot sediments. 2. Easily extractable metals with 0.5 M HCl test showed that percentage of easily extractable Mn and Zn from Wetland and Parking lot sediments were similar. Cu extracted by HCl from Stormwater retention was much higher than Parking lot since large portion of Cu was associated with organic matter; and HCl was able to extract Cu that was associated with organic matter.  3. Selective sequential extraction analysis showed the geochemical distribution of the metals in the two sediments. A large proportion of Cu was associated with organic phase, which was higher in Stormwater sediments than Parking lot sediment a result of the higher organic matter content. Mn was dominant in the residual phase in these two locations. A Large proportion of Pb and Zn was found associated with Fe-Mn oxide phase.  After treatment with surfactants 1. Total metal removal efficiency by Rhamnolipid from both Wetland and Parking lot sediments was slightly lower than by Texapon, because anionic Texapon surfactant with negatively charged micelles had a higher adsorption capacity for metal cations than Rhamnolipid. 79  2. Applications of Rhamnolipid and Texapon were effective in removing metals that are bound to exchangeable and reducible fractions of Wetland and Parking lot sediments even when removal of total metal content was not significant. They have potential to release metals into the environment, since they are loosely bound on particles. Removal of metals from exchangeable and reducible fraction of both Wetland and Parking lot sediments approached 100%, which would reduce the bioavailability of metals.  3. Determination of Rhamnolipid and Texapon concentration that remained in Wetland and Parking lot sediments after treatment, demonstrated that only a small portion of surfactant residue was left in the samples after two washings with distilled water.  4. More than 99% of surfactants were removed after two washes with distilled water. The residual Rhamnolipid and Texapon were below the LD50/LC50 and toxicity limits for aquatic life. Therefore, the surfactant treated sediments are suggested to submit to at least two washings by distilled water to remove Rhamnolipid and Texapon.  5.2 Conclusions 1. Optimum experimental condition based on the pilot study was that 20 mM Rhamnolipid and 100 mM Texapon and 0.5 h reaction time are the most efficient on desorption of metals.  2. Rhamnolipid and Texapon were effect in removing exchangeable and reducible bioavailable fractions almost 100% from Wetland and Parking lot sediments.  3. Rhamnolipid and Texapon can be removed from sediments after treatment by two washings using distilled water, within the acceptable dosage.  80  5.3 Recommendations for Future Research In the research of surfactant enhanced soil washing technique for removal of trace metals from contaminated soils, there are a number of points that merit further consideration.  1. pH of surfactants conducted in this study were at their original pH. The surfactants efficiency under acidic or basic conditions should be investigated. Acid or base may enhance surfactants efficiency of removal of metals from sediments.  2. Sorption of surfactants by sediments should be investigated in future research. Surfactants can be sorbed onto sediment fractions, reducing their effectiveness. It should be assessed to see if the sediments are saturated with surfactants or not. 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Yost, K.J. 1984. “Cadmium, the environment and human health: an overview.” Experientia 40, Birkhauser Verlag, CH-4010 Basel/Switzerland.  91  Zhang, W., Tsang, D.C.W., Lo, I.M.C. 2007. “Removal of Pb and MDF from contaminated soils by EDTA- and SDS- enhanced washing.” Chemosphere 66: 20252034.  92  APPENDICES Appendix A- Raw data of pH effect on clay minerals (mg/kg) pH effect on illite pH 1.5  2.5  3.5  4.5  5.5  6.5  Cd desorbed A SD Pb desorbed 141 146 4.582576 252.9 147 256.8 150 254.1 115 115.6667 3.05505 205.7 119 202.9 113 207.4 149 146.9667 2.000833 262.1 145 269.8 146.9 266.2 111.9 112.9 2.93087 231.3 110.6 225.2 116.2 229.9 115 112.8 2.151743 235.9 112.7 239.5 110.7 242.6 101.7 101.6 1.352775 166 100.2 163.7 102.9 161.5  A  SD Cd original Pb original 254.6 1.997498 1130 1210 1130 1210 1130 1210 205.3333 2.272297 1130 1210 1130 1210 1130 1210 266.0333 3.852705 1130 1210 1130 1210 1130 1210 228.8 3.195309 1130 1210 1130 1210 1130 1210 239.3333 3.353108 1130 1210 1130 1210 1130 1210 163.7333 2.250185 1130 1210 1130 1210 1130 1210  93  pH effect on kaolinite pH 1.5  2.5  3.5  4.5  5.5  6.5  Cd desorbed 283.1 277.9 280 149 147.2 151.6 30.1 31.2 32.4 22.9 26.2 24.5 20 15.2 17.8 13.4 14.9 11.9  A SD Pb desorbed 280.3333 2.615977 312.2 317.6 315 149.2667 2.212088 249 252.1 246.9 31.23333 1.150362 36 35.2 37.1 24.53333 1.650253 11.3 9.2 10 17.66667 2.402776 10 10.2 9.8 13.4 1.5 5 4.7 5.3  A SD Cd original Pb original 314.9333 2.700617 285 325 285 325 285 325 249.3333 2.615977 285 325 285 325 285 325 36.1 0.953939 285 325 285 325 285 325 10.16667 1.059874 285 325 285 325 285 325 10 0.2 285 325 285 325 285 325 5 0.3 285 325 285 325 285 325  94  Appendix B- Raw data of surfactant concentration effect on clay minerals (mg/kg) Cd spiked illite with treatment of Rhamnolipid Surfacta nt concentr ation 10  20  30  40  0.5h  A  214.6  SD 215.6  1h 1.249  70  226.3  2h 2.26495  A 251  SD 248.8333  2.0599  12h  A  215.8  SD 215.76  24h  2.1501  A  228.1  SD 226.1  1.9519  original 1130  228.7  246.9  213.6  224.2  1130  215.2  224.2  248.6  217.9  226  1130  246  247.93  1.70098  257.9  260.16  2.35442  248.6  248.5333  1.4011  223.9  226  2.1  213.2  214.63  1.4011  1130  249.2  260  249.9  228.1  214.7  1130  248.6  262.6  247.1  226  216  1130  226  225.93  2.30072  248.6  248.46  2.20302  212.6  214.7666  2.2007  224.2  226.26  2.2120  212.9  214.73  1.8502  1130  223.6  246.2  214.7  226  214.7  1130  228.2  250.6  217  228.6  216.6  1130  249.1  248.3  0.98488  193.6  216  214.3  1.93132  212.2  248.6  60  226  SD  217  247.2 50  A  1.35277  223.9  214.9333  2.1594  214.7  214.7 192.2  212.9  2.15019  214.7  203.26  2.8284  205.2  217.2 226.03  201.2  1.4047  214.7  226.23  2.2590  226  203.4 214.5666  224.1  1130  228.6 214.66  2.0502  216.6  1130 1130  214.83  1.7039  1130  190.9  226  213.1  212.6  213.2  1130  192.1  228.2  215.9  216.7  214.7  1130  214.7  214.5  1.21243  193.9  192.3  1.50996  226  226.1  1.9519  205.2  203.4  1.8  203.4  203.6  2.3065  1130  213.2  190.9  224.2  201.6  201.4  1130  215.6  192.1  228.1  203.4  206  1130  216.2  214.5  1.80831  193.2  192.4  0.7  228.6  226.4  3.8682  182.1  180.7  1.4525  183.1  180.6  2.6057  1130  214.7  191.9  226  180.8  177.9  1130  212.6  192.1  224.6  179.2  180.8  1130  95  Cd spiked kaolinite with treatment of Rhamnolipid Surfactant concentration  0.5h 10  189.2  A  SD  1h  186.93 33  2.3007 25  187  30  204.8  2.7153 88  182.6  SD 182.5  1.5524 17  180.9 2.0550 75  192.2  182  A  SD  182.26 67  2.2120 88  180.2  184 212.56 67  12h  3.4530 18  190  187.3  A  SD  187.33 33  2.2501 85  185.1  184.6 195.73333 33  24h  2.4006 94  189.2  285 285  189.6 187.56 67  original  285 191.6  2.4515 3  285  210.6  199.1  187.5  194.1  285  214.7  195.9  185.2  191.5  285  199.2  200.4  1.2  212  216.3  218.36 67  2.1548 4  220.6 2.0550 75  229.2  211.5  214.46666 67  3.0534 13  217.6  218.2 212.16 67  2.2030 28  230.2  214.76 67  1.0598 74  213.8  214.3 231.33 33  214.6  0.8504 9  210.6  215.5  3.0805 84  212.2  215.9 231.03333 33  216  285  218.3 214.46 67  4.1198 71  210.9  285  285 213.9  3.0512 29  285  210.2  233.6  231.9  218.8  213.8  285  214.3  231.2  231  214  217  285  214.6  214.63 33  2.5501 63  218.5  222.7  222.66 67  2.4501 7  220.2  212.1  70  212.4  A  208  217.2  60  2.5579 94  2h  202.6  200.4  50  187.33 33  187.1 205.13 33  201.6  40  SD  184.9  184.6 20  190  A  1.9756 86  229.2  231.63333 33  1.5502 69  233.2  225.1 216.36 67  230.1  2.2030 28  232.2  231.23 33  0.7767 45  232.1  231.6 231.33 33  231  4.4060 56  236  227.16 67  2.6539 28  224.6  230.6 236.46666 67  227  285  229.9 236.03 33  0.8504 9  235.6  285  285 235.93 33  0.3055 05  285  214.6  233.6  241  236.9  236.2  285  216  231.2  236.2  235.2  236  285  215.9  215.7  2.4062 42  212.6  212.8  2.1071 31  236  236.03333 33  0.9504 38  232.2  236.8  4.7031 9  228.9  228.53 33  3.2654 76  285  213.2  210.8  235.1  236.6  225.1  285  218  215  237  241.6  231.6  285  96  Pb spiked illite with treatment of Rhamnolipid Surfactant concentration  0.5h 10  A 125.6  SD 125.5  2.3515 95  123.1  122.9  3.1501 32  1.4502 87  2.2007 57  2.4501 7  239.4  189.5  2.2501 85  205.1  204.6  140.2  151.6  2.5026 65  211.9  2.8536 53  138.6  1.8037  201.5  157.5  162.2  2.5540 82  151.3  138.7  136.1  3.8070 11  154.3  1210 157.3  3.3511 19  2.7024 68  133.9  1210 113.53 33  1.4047 54  1210 138.2  4.1146 08  157.3  1210 157.2  3.0512 29  160.2 3.0501 37  153.9  1210 1210  154.1 151.26 67  1210 1210  138.6 2.3028 97  1210 1210  142.1 138.46 67  1210 1210  113.4 151.43 33  138.6 4.6500 9  115  1210 1210  112.2  140.7 201.53333 33  189.3  160.6 158.53 33  148.8 2.0599 35  153.9  1210  1210 1.2124 36  157.4  154.2 138.36666 67  189.1  original  1210  188.2 3.5042 83  158.8 214.36666 67  1.9008 77  190.6  154.6  140.3 201.9  138.9  SD  138.73 33  138.8 2.4062 42  142.1 138.46666 67  136.2 3.1048 35  157.3  140.6  A  136.8  135.1  214.2 1.4047 54  0.2  160 201.66666 67  217 201.66 67  138.6  24h  155.2  138.6 157.33 33  SD  138.6 1.9078 78  136.6  203 214.33 33  149.8  138.8  A  138.4  198.9 0.9539 39  201.8  242.1 214.3  200.2  2.2  201.5  159.9 2.7513 63  236.6  70  3.1501 32  154.9  199.2 239.5  157.2  113.4  12h  151.4 126.03 33  190.5 201.66 67  204.1  60  189.4  113.4  SD  153.6  188.6  157.3 201.7  2.3501 77  126 157.36 67  155.2  50  122.9  A  115.6 157.26 67  129.2  150.1 159.6  154.9  2h  111.2  159.6 151.53 33  153  40  1.6623 28  157.3  129.2 151.5  SD  88.433 33  86.9 126.03 33  126  30  90.2  A  88.2  127.8 20  1h  1210 157.26 67  3.3501 24  1210  212.1  198.9  206.2  151.3  160.6  1210  216.6  201.7  196.9  148.2  157.3  1210  97  Pb spiked kaolinite with treatment of Rhamnolipid Surfactant concentration  0.5h 10  A 284  SD 284  1h 4  288  325  0.5773 5  2.5166 11  3.5118 85  60  1.1547 01  289  295  290 305  0  305  302  290  4.0414 52  2.5166 11  295  12h  0.5773 5  172  332  332  0  320  304  305  213  299  280  284  4  284 7.5055 53  270  7.0945 99  279 0.5773 5  234  233.66 67  1.5275 25  232  304  203  5.0332 23  112  5.6862 41  150  275  325 243.66 67  4.5092 5  4.1633 32  325  244  325  239  325  216  218  2  188  62  91  325 325 325  187.33 33  5.0332 23  325 325 325  63  7.5498 34  325 325  71 153.33 33  325 325  56  109 5.8594 65  325 7.8102 5  182 113.66 67  120 303.33333 33  248  325 325  192  197 216  original  220 197.66 67  193 8.8881 94  3.5118 85  218  235 2.6457 51  SD  168.66 67  279 277.66 67  284 304.66666 67  280  A  266  288 319.66666 67  226 2.5166 11  165  303  209 294.66 67  24h  311  301 1.5275 25  3.5118 85  169  306 288.66 67  SD  299.66 67  296  305 289.33 33  300  A  311  305  289 302.33 33  0.5773 5  327 332.66 67  287  305 70  289  SD  310.66666 67  312  337 295.66 67  297  305  334  332  333 295  329  310  A  332 3.6055 51  330 329.66 67  330  50  337  2h  332  335  302 326  2.5166 11  342 304.66 67  305  40  340  339.66 67  337  324 307  4.5092 5  305 324.33 33  324  30  SD  300.33 33  296  280 20  300  A  325 95.666 67  4.5092 5  325  305  292  310  152  100  325  300  297  301  158  96  325  98  Cd spiked illite with treatment of Texapon Surfactant concentration  0.5h 10  A 102  102.2 667  SD 2.212 088  100.2 246.6  2.203 028  101.6 667  1.550 269  270  2.300 725  282.5  A 111.3  111.3333 333  SD 2.150 194  1.616 581  224.2  2.354 428  284.2  114.1 667  SD 2.250 185  237.7  0.550 757  282  124.7  A 124.5 667  SD 2.402 776  240.6  241  236.4  284.6  1130 1130  236 2.003 331  1130 1130  4.413 615  232.2 282.1 333  origin al 1130  126.9 2.951 271  240.5 284.8333 333  24h  122.1  243.6  226.8 1.350 309  114.2  A  116.4 226.6333 333  228.9 282.5 333  12h  111.9  113.5 271.4 667  271.2 248.5 333  2h  109.2  273.2  248.6 246.2  101.7  SD  103.2 248.7 333  251 100  A  100.1  104.6 50  1h  1130 284.1 667  1.401 19  1130  250.8  283.9  285.2  280.2  282.6  1130  248.6  281.2  285.1  284.2  285.3  1130  99  Cd spiked kaolinite with treatment of Texapon  Surfactant concentration  0.5h 10  A 80.2  80.56 667  SD 0.907 377  81.6  100  225.9  A 81.8  SD 81.2  0.529 15  80.8  79.9 50  1h  1.150 362  220.6  A 111.3  111.3333 333  SD 2.150 194  109.2  81 227.0 667  2h  2.350 177  224.2  111.9  A 114.1 667  SD 2.250 185  116.4  113.5 218.2 333  12h  2.354 428  240.5  122.1  A 124.5 667  SD 2.402 776  124.7  114.2 226.6333 333  24h  240.6  236  285 285  126.9 2.951 271  origin al  285 236.4  4.413 615  285  228.2  215.9  228.9  237.7  232.2  285  227.1  218.2  226.8  243.6  241  285  281  281.3  1.571 623  276.1  277.0 667  1.850 225  284.2  284.8333 333  0.550 757  280.2  282.1 333  2.003 331  285.3  284.1 667  1.401 19  285  283  279.2  285.2  282  284.6  285  279.9  275.9  285.1  284.2  282.6  285  100  Pb spiked illite with treatment of Texapon Surfactant concentration  0.5h 10  A 48.1  SD 48.3  2.206 808  46.2 45.9  2.250 185  38.46 667  1.955 335  214.2  5.784 75  289.9  A 44.2  46.73333 333  SD 2.454 248  49.1 214.3  2.251 666  239.3  239.3666 667  2.900 575  236.5  216.6 195.4 667  2h  46.9  212.1  48.1 196.9  38.3  SD  40.5 48.13 333  50.4 100  A  36.6  50.6 50  1h  3.308 071  264.7  47.6  A  SD 46.3  24h  1.212 436  37.8  45.2  32.9  239.9  239.9  3.3  2.550 163  277.3  241.1  A  origin al  SD 37.8  4.9  1210 241.5 667  1.266 228  2.250 185  289.2  1210 1210  243 277.3 333  1210 1210  240.6  243.2 264.6666 667  42.7  46.1  236.6  242.3 289.6 333  12h  1210 288.3 333  0.808 29  1210  200.4  286.2  267.2  275.1  288.2  1210  189.1  292.8  262.1  279.6  287.6  1210  101  Pb spiked kaolinite with treatment of Texapon  Surfactant concentration  0.5h 10  A 86  85.66 667  SD 0.577 35  85 86 50  117  117.3 333  2.516 611  115 300  A 81  SD  80.66 667  2h  0.577 35  1.527 525  107 105  81  106  157  157  0  157 300.3 333  A  80  157  120 100  1h  322  324.3 333  2.081 666  126  SD 106  12h 1  107  SD 107  24h 2  105 1.527 525  131 131  129  132 318  2  326  117  A 116.6 667  SD 0.577 35  116  109 127.3333 333  127 316  A  0.577 35  155  325 155.3 333  1.527 525  157 325  319  325 325  154 2.645 751  325 325  117 131.3 333  origin al  325 314.3 333  5.033 223  325  302  326  320  322  315  325  299  325  318  327  309  325  102  Appendix C- Raw data of trace metal content in two sediments before treatment with surfactants (mg/kg) Wetland  exchangeable reducible Fe-Mn oxide organic matter residual ∑ Total  Cu Mn Pb Zn 3.299 8.485 20.667 40.828 10.008 3.947 15.647 32.227 11.507 20.6 59.133 168.26 116  23.051  21.547  42.385  9.65 145.708 15.625 36.258 150.464 201.791 132.619 319.958 174.867 271.467 130.667 292.387  Parking lot  exchangeable reducible Fe-Mn oxide organic matter residual ∑ Total  Cu Mn Pb Zn 2.019 4.565 15.307 18.234 6.808 1.584 14.187 26.564 10.527 13.367 53 71.675 33.936  17.147  21.707  15.681  7.95 101.917 18.083 26.763 61.24 138.58 122.284 158.917 81.333 147.933 128 140.773  103  Appendix D- Raw data of trace metal content in two sediments after treatment with surfactants (mg/kg) Wetland With Cu Mn Pb Zn Rhamnolipid exchangeable 0.888 5.715 0 20.747 reducible 4.224 1.564 10.053 25.976 Fe-Mn oxide 6.13 24.06 30.133 125.038 organic 120.768 33.688 18.427 36.184 matter residual 8.938 132.375 14.75 37.329 ∑ 140.948 197.402 73.363 245.274 Total 120.67 200.01 73.8 212.35  With Texapon exchangeable reducible Fe-Mn oxide organic matter residual ∑ Total  Cu  Mn  3.093 10.747 6.443  4.816 1.252 19.173  111.168  30.685  9.363 135.667 140.814 191.593 119.67 197.423  Pb  Zn  0 40.46 9.733 14.417 26.067 100.164 3.44  31.3  15.792 37.408 55.032 223.749 54.96 200.69  104  Parking lot With Rhamnoipid exchangeable reducible Fe-Mn oxide organic matter residual ∑ Total  With Texapon exchangeable reducible Fe-Mn oxide organic matter residual ∑ Total  Cu  Mn  Pb  Zn  0.203 2.501 3.937  1.12 0.695 13.667  0 4.32 25.867  5.153 11.56 46.918  27.616  17.208  12.08  17.514  7.329 41.586 58.65  86.25 118.94 109.26  Cu  Mn  16.583 26.854 58.85 107.999 51.38 96.463  Pb  Zn  0.896 3.96 3.47  0.979 0.564 13.66  0 4.76 25.6  7.141 9.083 40.382  22.843  14.979  0  5.13  7.496 84.958 38.665 115.14 49.133 121.279  16.125 46.485 17.6  27.363 89.099 85.02  105  

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