Harvey LisztArecibo July 2005 Harvey S. Liszt NRAO, CHARLOTTESVILLE.
FinalPoster · Title: FinalPoster.ppt Author: David Harvey Created Date: 9/13/2006 1:43:11 PM
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Kelly Presutti and David Harvey Kelly Presutti and David Harvey Department of Chemistry and Biochemistry Department of Chemistry and Biochemistry DePauw University DePauw University Greencastle, Indiana Greencastle, Indiana Abstract Abstract The utility of using a sequential extraction procedure to assess the level of hazardous trace metals in sediments has already been well evidenced. 1 A simple digestion of a sediment sample provides insufficient information as to the bioavailability of trace metals because they are contained within different phases, or compartments, within the sediment that differ in reactivity. A sequential Example of a Gel of our PCR product KP would like to thank DePauw University, the Faculty Development Committee, and Dr. David Harvey for making this project possible. Funding for the Varian 220FS atomic absorption spectrometer is from NSF Grant 0125835. Evaluating the Appropriateness of the BCR Procedure for Calcareous Sediments Evaluating the Appropriateness of the BCR Procedure for Calcareous Sediments Introduction Introduction Varying the Concentration of Acetic Acid Varying the Concentration of Acetic Acid Kinetics Using 0.11 M & 0.5 M Acetic Acid Kinetics Using 0.11 M & 0.5 M Acetic Acid Effect of Carbonates Effect of Carbonates Calcareous Samples Calcareous Samples Kinetic Investigation Kinetic Investigation Buffered vs. Unbuffered Acetic Acid Buffered vs. Unbuffered Acetic Acid The Role of pH The Role of pH Future Work Future Work References References Acknowledgements Acknowledgements Procedure Procedure extraction, however, provides a method for determining the speciation of trace metals, allowing one to predict the natural conditions under which the metals might be released. One should also be aware, however, of the difficulties inherent with this type of procedure, in which the sediment phases are operationally defined by the reagents that are used . A sequential extraction procedure determined to be sufficiently consistent was recently developed by the European Commission. This procedure, referred to as the BCR, involves extraction by three reagents, each assigned to attack a particular operational phase of the sediment. 2 The sediment phases identified by the BCR are carbonates, iron and manganese oxides, and organics, attacked by Step 1, 2, and 3 respectively. The literature includes few investigations into the kinetic aspects of sequential extractions. Previous work in our lab concerning the release of trace metals from an Indiana lake sediment over time, however, revealed an unexpected trend. 3 With any extraction, it is expected that the concentration of released metal will gradually increase over time until it reaches a steady-state. This was observed in the Step 1 extraction of manganese. In the Step 1 extraction of zinc and iron, however, an initial increase in concentration was seen, followed by a decrease in concentration that eventually leveled off. This decrease in concentration over time suggests that a significant amount of the zinc and iron reentered the sediment. This observation was further explored by reversing the order of Steps 1 and 2. The majority of released manganese occurred in the first extraction, regardless of whether acetic acid or hydroxylamine was used. Iron again behaved unexpectedly. When Step 1 was performed first, very little iron was released by the acetic acid. When performing Step 2 first, however, the acetic acid extraction released a significantly larger amount of iron. Thus, performing Step 2 first appeared to facilitate the release of iron in Step 1. This research project sought to further explore and attempt to explain these observations, specifically regarding the appropriateness of the BCR for calcareous sediments. Sediment was obtained from core samples collected from Lake Tippecanoe and Lake Wawasee in northern Indiana. The samples, of depths ranging from the sediment-solution interface to 50 centimeters, were dried, ground and combined to create a single sample. The homogeneity of the sediment was evaluated by a 16 hour extraction with 0.5 M HCl (n = 5). The results, shown in Table 2, verified that the sample was sufficiently homogeneous for our purposes, with relative standard deviations of less than 10%. In some studies, the concentrations of trace metals were increased by spiking the sediment. This was done by equilibrating the sediment overnight with a solution containing the dissolved metal ions. Model sediments were created using an iron oxide compound synthesized by adding KOH to a solution of Fe(NO 3 ) 3 and aging the solution at 60º for 24 hours. The compound was tentatively identified as goethite on the basis of its color. All extractions were performed using the standard BCR ratio of 25 mg solid to 1 mL of the extraction reagent. The sediment and solution were shaken in polyurethane bottles using a shaker table, and then gravity filtered. The filtrate was analyzed using a Varian model 220FS atomic absorption spectrometer with an air/acetylene flame. Table 2: Average Concentrations of Trace Metals in Sediment 4.18% 6.39% 7.86% 4.85% 5.30% relative standard deviation 2.10 2.09 776 114 0.844 standard deviation 50.3 32.7 9870 2350 15.9 Mean (μg metal / g sediment) Zn Pb Fe Mn Cu Metal Organics Iron and Manganese Oxides Carbonates and Surface Bound Metals Proposed Phase(s) Attacked (a) 1 hr; (b) heat to reduce volume; (c)16 hr (a) 30% H 2 O 2 ; (b) 30% H 2 O 2 ; (c) 1 M NH 4 OAc 3 16 hr 0.11 M Acetic Acid 1 16 hr 0.1 M NH 2 OH•HCl (pH 2) 2 Reaction Time Extraction Reagent Step Table 1: BCR Procedure Kinetic studies of the BCR three-step sequential extraction procedure on sediments from an Indiana lake reveal discrepancies in the release of Zn and Fe in the first step. This is attributed to a rise in pH resulting from carbonates in the sediment. Increasing the concentration of acetic acid used in the extraction improves the results for Zn; however the acid’s ability to dissolve amorphous iron oxides undermines the operationally defined phases identified by the procedure. Figure 1. Release of iron and zinc and the change in pH as a function of time during the Step 1 extraction. Figure 2. Release of manganese and the change in pH as a function of time during the Step 1 extraction. A kinetic study of Step 1 of the BCR procedure was conducted, with each time increment represented by a separate sample. As shown in Figure 1, as the pH of the suspension increases the levels of extracted zinc and iron decrease. This is contrasted by the more typical results shown for manganese in Figure 2. These results suggest that the BCR procedure may not be accurately evaluating the levels of iron and zinc in the first extraction due to their reprecipitation and/or readsorption. The large increase in pH seen in Figures 1 and 2 might be the result of a carbonate rich sediment. If there is enough acetic acid present to neutralize all the carbonates present, then the resulting solution should be acidic. If acetic acid is the limiting reagent, an increase in pH will result from the unreacted carbonates. The presence of carbonates beyond the amount that can be neutralized by the acetic acid in Step 1 will compromise both the Step 1 results and the level of metal extracted during Step 2. In order to verify this hypothesis, the upper limit on the level of carbonates in the sediment, reported as %CaCO 3 , was determined by repeatedly washing the sediment with 5% acetic acid until all carbonates were eliminated. The sediment was found to be 55.07% with a standard deviation of 0.74. The problematic nature of calcareous sediments has been briefly addressed in the literature. 4 To determine the extent to which the level of carbonate affects the extraction, a rudimentary model sediment was created, consisting of 3% of the synthetic iron oxide compound, various percentages of calcium carbonate and sand. This material was then extracted for 16 hours using Step 1 and analyzed for the amount of released iron. As Figure 3 demonstrates, the study confirms there is a decrease in the level of extractable metal as the level of carbonates and, consequentially, the pH increase. Figure 3. Level of extractable iron in samples with increasing levels of carbonates. Approaches to analyzing carbonate-rich samples include increasing the concentration of acetic acid or repeatedly extracting the sample until no carbonate remains. 5 Figure 4 shows the level of zinc released from the sediment after 16 hour extractions when using increasing concentrations of acetic acid. Higher concentrations of acetic acid more effectively release extractable zinc, which begins to level out around 0.5 M. This suggests that 0.5 M acetic acid is capable of completely neutralizing the carbonates in this sediment. For iron, Figure 5 shows that the level of iron released begins to increase rapidly at 0.5 M and does not level off, suggesting that the acetic acid is releasing iron in other phases. One possibility is that amorphous iron oxides in the sediment, which are known to be soluble in acetic acid, are dissolving. The effect of acetic acid concentration was further explored in a kinetic study by using 0.11 M and 0.5 M acetic acid. The choice of 0.5 M acetic acid was based on the results from Figures 4 and 5, which indicate that this concentration was capable of neutralizing all the carbonate in the sediment. The kinetic study of the release of iron, shown in Figure 6, demonstrates that when using 0.5 M acetic acid the amount of extracted iron rapidly increases to a steady state concentration, as opposed to the decrease seen when using 0.11 M acetic acid. Although not shown, a similar trend was observed for zinc. Although 0.5 M acetic acid is appropriate for this sediment, it will not be appropriate for all sediments. A concentration of acetic acid that is too small will not neutralize all of the carbonate and a concentration that is too high will attack the amorphous iron oxides. In either case, the distinction between the operationally defined phases is blurred if insufficient acetic acid is used. Figure 6. Kinetic study of sediment extraction by 0.11 M and 0.5 M acetic acid. Figure 5. Levels of iron extracted from a sediment after 16h vs. concentration of acetic acid used, plotted against the final pH of the solution. Figure 4. Levels of zinc extracted from a sediment after 16h vs. concentration of acetic acid used, plotted against the final pH of the solution. Higher concentrations of acetic acid are more effective at preventing the readsorption and/or reprecipitation of metals by neutralizing carbonates and maintaining a low pH. However, higher concentrations of acetic acid can also be detrimental to phase specificity. As Figure 5 demonstrates, the level of iron released does not level off when using higher concentrations of acetic acid. This indicates that the acetic acid could be attacking the iron oxides, which are presumed by the BCR to be maintained until Step 2. This was further explored by extracting a synthetic iron oxide compound for 16 hours with varying concentrations of both unbuffered acetic acid and acetic acid buffered to a pH of 4. As Figure 7 shows, buffering the acetic acid significantly decreases the release of iron. As shown in Figure 4, acetic acid buffered to a pH of 4 is equally effective in extracting zinc. These results suggests that buffering a higher concentration of acetic acid might allow for fully neutralizing carbonates while still maintaining the operationally defined phases. Figure 7. Extraction of an iron compound with unbuffered acetic acid and acetic acid buffered at a pH of 4, at varying concentrations. To understand the contrast between the effects of the buffered and unbuffered acetic acid on the release of iron, the role of pH was explored further. A mixture of sand and 3% of the synthetic iron compound was extracted for 16 hours with 0.11 M acetic acid buffered to various pH levels. Figure 8 shows the decreasing levels of iron extracted at higher pH levels. This indicates that iron oxides are more soluble at lower pH levels, an observation confirmed by the literature. 6 Figure 8. Extraction of an iron compound with 0.11M acetic acid buffered to varying pH levels. Continuation of this project will include further investigations into the optimization of the BCR procedure for carbonate rich sediments. This will be explored through the creation of model sediments incorporating, SiO 2 amorphous Fe(OH) 3 , FeOOH, CaCO 3 , FeCO 3 and spiked with trace metals such as Zn, Cu and Pb. 1. D’Amore, J; Al-Abed, S; spiking, K; Ryan, J. Journal of Environmental Quality. 2005, 34, 1707-1745. 2. Thomas, R; Ure, A.M.; Davidson, C.M.; Littlejohn, D. Analytica Chimica Acta. 1994, 286, 423-429. 3. Turner, A; Harvey, D. Unpublished Research, Summer 2005, DePauw University 4. Manouchehri, N; Besancon, S; Bermond, A. Analytica Chimica Acta, 2006, 559, 105- 112. 5. Cappuyns, V; Swennen, R; Verhulst, J. Soil & Sediment Contamination. 2006, 15, 169- 186. 6. Slavek, J; Pickering, W.F. Water, Air and Soil Pollution. 1986, 28, 151-162.
Transcript of FinalPoster · Title: FinalPoster.ppt Author: David Harvey Created Date: 9/13/2006 1:43:11 PM
Kelly Presutti and David HarveyKelly Presutti and David HarveyDepartment of Chemistry and Biochemistry Department of Chemistry and Biochemistry DePauw University DePauw University Greencastle, Indiana Greencastle, Indiana
AbstractAbstract
The utility of using a sequential extraction procedure toassess the level of hazardous trace metals in sedimentshas already been well evidenced.1 A simple digestion ofa sediment sample provides insufficient information asto the bioavailability of trace metals because they arecontained within different phases, or compartments,within the sediment that differ in reactivity. A sequential
Example of a Gel of our PCR product
KP would like to thank DePauw University, the Faculty DevelopmentCommittee, and Dr. David Harvey for making this project possible. Fundingfor the Varian 220FS atomic absorption spectrometer is from NSF Grant0125835.
Evaluating the Appropriateness of the BCR Procedure for Calcareous SedimentsEvaluating the Appropriateness of the BCR Procedure for Calcareous Sediments
IntroductionIntroductionVarying the Concentration of Acetic AcidVarying the Concentration of Acetic Acid
Kinetics Using 0.11 M & 0.5 M Acetic AcidKinetics Using 0.11 M & 0.5 M Acetic Acid
Effect of CarbonatesEffect of Carbonates
Calcareous SamplesCalcareous Samples
Kinetic InvestigationKinetic Investigation
Buffered vs. Unbuffered Acetic AcidBuffered vs. Unbuffered Acetic Acid
The Role of pHThe Role of pH
Future WorkFuture Work
ReferencesReferences
AcknowledgementsAcknowledgements
ProcedureProcedure
extraction, however, provides a method for determining the speciation of tracemetals, allowing one to predict the natural conditions under which the metalsmight be released. One should also be aware, however, of the difficulties inherentwith this type of procedure, in which the sediment phases are operationallydefined by the reagents that are used . A sequential extraction proceduredetermined to be sufficiently consistent was recently developed by the EuropeanCommission. This procedure, referred to as the BCR, involves extraction by threereagents, each assigned to attack a particular operational phase of the sediment.2The sediment phases identified by the BCR are carbonates, iron and manganeseoxides, and organics, attacked by Step 1, 2, and 3 respectively.
The literature includes few investigations into the kinetic aspects of sequentialextractions. Previous work in our lab concerning the release of trace metals froman Indiana lake sediment over time, however, revealed an unexpected trend.3 Withany extraction, it is expected that the concentration of released metal willgradually increase over time until it reaches a steady-state. This was observed inthe Step 1 extraction of manganese. In the Step 1 extraction of zinc and iron,however, an initial increase in concentration was seen, followed by a decrease inconcentration that eventually leveled off. This decrease in concentration over timesuggests that a significant amount of the zinc and iron reentered the sediment.This observation was further explored by reversing the order of Steps 1 and 2. Themajority of released manganese occurred in the first extraction, regardless ofwhether acetic acid or hydroxylamine was used. Iron again behaved unexpectedly.When Step 1 was performed first, very little iron was released by the acetic acid.When performing Step 2 first, however, the acetic acid extraction released asignificantly larger amount of iron. Thus, performing Step 2 first appeared tofacilitate the release of iron in Step 1. This research project sought to furtherexplore and attempt to explain these observations, specifically regarding theappropriateness of the BCR for calcareous sediments.
Sediment was obtained from core samples collected from Lake Tippecanoe andLake Wawasee in northern Indiana. The samples, of depths ranging from thesediment-solution interface to 50 centimeters, were dried, ground and combinedto create a single sample. The homogeneity of the sediment was evaluated by a16 hour extraction with 0.5 M HCl (n = 5). The results, shown in Table 2,verified that the sample was sufficiently homogeneous for our purposes, withrelative standard deviations of less than 10%.
In some studies, the concentrations of trace metals were increased by spiking thesediment. This was done by equilibrating the sediment overnight with a solutioncontaining the dissolved metal ions. Model sediments were created using an ironoxide compound synthesized by adding KOH to a solution of Fe(NO3)3 and agingthe solution at 60º for 24 hours. The compound was tentatively identified asgoethite on the basis of its color.
All extractions were performed using the standard BCR ratio of 25 mg solid to1 mL of the extraction reagent. The sediment and solution were shaken inpolyurethane bottles using a shaker table, and then gravity filtered. The filtratewas analyzed using a Varian model 220FS atomic absorption spectrometer withan air/acetylene flame.
Table 2: Average Concentrations of Trace Metals in Sediment
4.18%6.39%7.86%4.85%5.30%relative standard deviation
2.102.097761140.844standard deviation
50.332.79870235015.9Mean (µg metal / g sediment)ZnPbFeMnCuMetal
Organics
Iron and Manganese Oxides
Carbonates and SurfaceBound Metals
Proposed Phase(s) Attacked
(a) 1 hr; (b) heat toreduce volume;(c)16 hr
(a) 30% H2O2; (b) 30%H2O2; (c) 1 M NH4OAc
3
16 hr0.11 M Acetic Acid1
16 hr0.1 M NH2OH•HCl (pH 2)2
Reaction TimeExtraction ReagentStep
Table 1: BCR Procedure
Kinetic studies of the BCR three-step sequential extraction procedure onsediments from an Indiana lake reveal discrepancies in the release of Zn and Fe inthe first step. This is attributed to a rise in pH resulting from carbonates in thesediment. Increasing the concentration of acetic acid used in the extractionimproves the results for Zn; however the acid’s ability to dissolve amorphous ironoxides undermines the operationally defined phases identified by the procedure.
Figure 1. Release of iron and zinc and the change in pH as a function of timeduring the Step 1 extraction.
Figure 2. Release of manganese and the change in pH as a function of time duringthe Step 1 extraction.
A kinetic study of Step 1 of the BCR procedure was conducted, with each time incrementrepresented by a separate sample. As shown in Figure 1, as the pH of the suspensionincreases the levels of extracted zinc and iron decrease. This is contrasted by the moretypical results shown for manganese in Figure 2. These results suggest that the BCRprocedure may not be accurately evaluating the levels of iron and zinc in the firstextraction due to their reprecipitation and/or readsorption.
The large increase in pH seen in Figures 1 and 2 might be the result of a carbonate richsediment. If there is enough acetic acid present to neutralize all the carbonates present, thenthe resulting solution should be acidic. If acetic acid is the limiting reagent, an increase in pHwill result from the unreacted carbonates. The presence of carbonates beyond the amount thatcan be neutralized by the acetic acid in Step 1 will compromise both the Step 1 results and thelevel of metal extracted during Step 2. In order to verify this hypothesis, the upper limit onthe level of carbonates in the sediment, reported as %CaCO3, was determined by repeatedlywashing the sediment with 5% acetic acid until all carbonates were eliminated. The sedimentwas found to be 55.07% with a standard deviation of 0.74.
The problematic nature of calcareous sediments has been briefly addressed in theliterature.4 To determine the extent to which the level of carbonate affects the extraction,a rudimentary model sediment was created, consisting of 3% of the synthetic iron oxidecompound, various percentages of calcium carbonate and sand. This material was thenextracted for 16 hours using Step 1 and analyzed for the amount of released iron. AsFigure 3 demonstrates, the study confirms there is a decrease in the level of extractablemetal as the level of carbonates and, consequentially, the pH increase.
Figure 3. Level of extractable iron in samples with increasing levels of carbonates.
Approaches to analyzing carbonate-rich samples include increasing theconcentration of acetic acid or repeatedly extracting the sample until no carbonateremains.5 Figure 4 shows the level of zinc released from the sediment after 16 hourextractions when using increasing concentrations of acetic acid. Higherconcentrations of acetic acid more effectively release extractable zinc, which beginsto level out around 0.5 M. This suggests that 0.5 M acetic acid is capable ofcompletely neutralizing the carbonates in this sediment. For iron, Figure 5 showsthat the level of iron released begins to increase rapidly at 0.5 M and does not leveloff, suggesting that the acetic acid is releasing iron in other phases. One possibilityis that amorphous iron oxides in the sediment, which are known to be soluble inacetic acid, are dissolving.
The effect of acetic acid concentration was further explored in a kinetic study byusing 0.11 M and 0.5 M acetic acid. The choice of 0.5 M acetic acid was based onthe results from Figures 4 and 5, which indicate that this concentration wascapable of neutralizing all the carbonate in the sediment. The kinetic study of therelease of iron, shown in Figure 6, demonstrates that when using 0.5 M aceticacid the amount of extracted iron rapidly increases to a steady state concentration,as opposed to the decrease seen when using 0.11 M acetic acid. Although notshown, a similar trend was observed for zinc. Although 0.5 M acetic acid isappropriate for this sediment, it will not be appropriate for all sediments. Aconcentration of acetic acid that is too small will not neutralize all of thecarbonate and a concentration that is too high will attack the amorphous ironoxides. In either case, the distinction between the operationally defined phases isblurred if insufficient acetic acid is used.
Figure 6. Kinetic study of sediment extraction by 0.11 M and 0.5 M acetic acid.
Figure 5. Levels of iron extracted from a sediment after 16h vs. concentration ofacetic acid used, plotted against the final pH of the solution.
Figure 4. Levels of zinc extracted from a sediment after 16h vs. concentration ofacetic acid used, plotted against the final pH of the solution.
Higher concentrations of acetic acid are more effective at preventing the readsorptionand/or reprecipitation of metals by neutralizing carbonates and maintaining a low pH.However, higher concentrations of acetic acid can also be detrimental to phase specificity.As Figure 5 demonstrates, the level of iron released does not level off when using higherconcentrations of acetic acid. This indicates that the acetic acid could be attacking the ironoxides, which are presumed by the BCR to be maintained until Step 2. This was furtherexplored by extracting a synthetic iron oxide compound for 16 hours with varyingconcentrations of both unbuffered acetic acid and acetic acid buffered to a pH of 4. AsFigure 7 shows, buffering the acetic acid significantly decreases the release of iron. Asshown in Figure 4, acetic acid buffered to a pH of 4 is equally effective in extracting zinc.These results suggests that buffering a higher concentration of acetic acid might allow forfully neutralizing carbonates while still maintaining the operationally defined phases.
Figure 7. Extraction of an iron compound with unbuffered acetic acid and aceticacid buffered at a pH of 4, at varying concentrations.
To understand the contrast between the effects of the buffered and unbuffered acetic acidon the release of iron, the role of pH was explored further. A mixture of sand and 3% ofthe synthetic iron compound was extracted for 16 hours with 0.11 M acetic acid bufferedto various pH levels. Figure 8 shows the decreasing levels of iron extracted at higher pHlevels. This indicates that iron oxides are more soluble at lower pH levels, an observationconfirmed by the literature.6
Figure 8. Extraction of an iron compound with 0.11M acetic acid buffered tovarying pH levels.
Continuation of this project will include further investigations into the optimization of theBCR procedure for carbonate rich sediments. This will be explored through the creation ofmodel sediments incorporating, SiO2 amorphous Fe(OH)3, FeOOH, CaCO3, FeCO3 andspiked with trace metals such as Zn, Cu and Pb.
1. D’Amore, J; Al-Abed, S; spiking, K; Ryan, J. Journal of Environmental Quality. 2005,34, 1707-1745.
2. Thomas, R; Ure, A.M.; Davidson, C.M.; Littlejohn, D. Analytica Chimica Acta. 1994,286, 423-429.
3. Turner, A; Harvey, D. Unpublished Research, Summer 2005, DePauw University4. Manouchehri, N; Besancon, S; Bermond, A. Analytica Chimica Acta, 2006, 559, 105-
112.5. Cappuyns, V; Swennen, R; Verhulst, J. Soil & Sediment Contamination. 2006, 15, 169-
186.6. Slavek, J; Pickering, W.F. Water, Air and Soil Pollution. 1986, 28, 151-162.
