Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community for help and clear up your study doubts
Discover the best universities in your country according to Docsity users
Free resources
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
The parameter known as the partition (or distribution) coefficient (Kd) is one of the most important parameters used in estimating the migration potential of ...
Typology: Schemes and Mind Maps
1 / 341
This page cannot be seen from the preview
Don't miss anything!
United States Office of Air and Radiation EPA 402-R-99-004B Environmental Protection August 1999 Agency
Office of Radiation and Indoor Air Office of Solid Waste and Emergency Response U.S. Environmental Protection Agency Washington, DC 20460
Office of Environmental Restoration U.S. Department of Energy Washington, DC 20585
Understanding the long-term behavior of contaminants in the subsurface is becoming increasingly more important as the nation addresses groundwater contamination. Groundwater contamination is a national concern as about 50 percent of the United States population receives its drinking water from groundwater. It is the goal of the Environmental Protection Agency (EPA) to prevent adverse effects to human health and the environment and to protect the environmental integrity of the nation’s groundwater.
Once groundwater is contaminated, it is important to understand how the contaminant moves in the subsurface environment. Proper understanding of the contaminant fate and transport is necessary in order to characterize the risks associated with the contamination and to develop, when necessary, emergency or remedial action plans. The parameter known as the partition (or distribution) coefficient (Kd) is one of the most important parameters used in estimating the migration potential of contaminants present in aqueous solutions in contact with surface, subsurface and suspended solids.
This two-volume report describes: (1) the conceptualization, measurement, and use of the partition coefficient parameter; and (2) the geochemical aqueous solution and sorbent properties that are most important in controlling adsorption/retardation behavior of selected contaminants. Volume I of this document focuses on providing EPA and other environmental remediation professionals with a reasoned and documented discussion of the major issues related to the selection and measurement of the partition coefficient for a select group of contaminants. The selected contaminants investigated in this two-volume document include: chromium, cadmium, cesium, lead, plutonium, radon, strontium, thorium, tritium (^3 H), and uranium. This two-volume report also addresses a void that has existed on this subject in both this Agency and in the user community.
It is important to note that soil scientists and geochemists knowledgeable of sorption processes in natural environments have long known that generic or default partition coefficient values found in the literature can result in significant errors when used to predict the absolute impacts of contaminant migration or site-remediation options. Accordingly, one of the major recommendations of this report is that for site-specific calculations, partition coefficient values measured at site-specific conditions are absolutely essential.
For those cases when the partition coefficient parameter is not or cannot be measured, Volume II of this document: (1) provides a “thumb-nail sketch” of the key geochemical processes affecting the sorption of the selected contaminants; (2) provides references to related key experimental and review articles for further reading; (3) identifies the important aqueous- and solid-phase parameters controlling the sorption of these contaminants in the subsurface environment under oxidizing conditions; and (4) identifies, when possible, minimum and maximum conservative partition coefficient values for each contaminant as a function of the key geochemical processes affecting their sorption.
iii
This publication is the result of a cooperative effort between the EPA Office of Radiation and Indoor Air, Office of Solid Waste and Emergency Response, and the Department of Energy Office of Environmental Restoration (EM-40). In addition, this publication is produced as part of ORIA’s long-term strategic plan to assist in the remediation of contaminated sites. It is published and made available to assist all environmental remediation professionals in the cleanup of groundwater sources all over the United States.
Stephen D. Page, Director Office of Radiation and Indoor Air
iv
Send all comments/updates to:
U.S. Environmental Protection Agency Office of Radiation and Indoor Air Attention: Understanding Variation in Partition (Kd) Values 401 M Street, SW (6602J) Washington, DC 20460
or
radiation.questions@epa.gov
vi
This two-volume report describes the conceptualization, measurement, and use of the partition (or distribution) coefficient, Kd, parameter, and the geochemical aqueous solution and sorbent properties that are most important in controlling adsorption/retardation behavior of selected contaminants. The report is provided for technical staff from EPA and other organizations who are responsible for prioritizing site remediation and waste management decisions. Volume I discusses the technical issues associated with the measurement of Kd values and its use in formulating the retardation factor, Rf. The Kd concept and methods for measurement of Kd values are discussed in detail in Volume I. Particular attention is directed at providing an understanding of: (1) the use of Kd values in formulating Rf, (2) the difference between the original thermodynamic Kd parameter derived from ion-exchange literature and its “empiricized” use in contaminant transport codes, and (3) the explicit and implicit assumptions underlying the use of the Kd parameter in contaminant transport codes. A conceptual overview of chemical reaction models and their use in addressing technical defensibility issues associated with data from Kd studies is presented. The capabilities of EPA’s geochemical reaction model MINTEQA2 and its different conceptual adsorption models are also reviewed. Volume II provides a “thumb-nail sketch” of the key geochemical processes affecting the sorption of selected inorganic contaminants, and a summary of Kd values given in the literature for these contaminants under oxidizing conditions. The contaminants chosen for the first phase of this project include chromium, cadmium, cesium, lead, plutonium, radon, strontium, thorium, tritium (^3 H), and uranium. Important aqueous speciation, (co)precipitation/dissolution, and adsorption reactions are discussed for each contaminant. References to related key experimental and review articles for further reading are also listed.
vii
- Magnesium, and Sulfide Concentrations, and Redox Conditions 5. Page
Figure 5.1. Calculated distribution of cadmium aqueous species as a function of pH for the water composition in Table 5.1............................... 5.
Figure 5.2. Calculated distribution of lead aqueous species as a function of pH for the water composition listed in Table 5.1...................... 5.
Figure 5.3. Calculated distribution of plutonium aqueous species as a function of pH for the water composition in Table 5.1........................... 5.
Figure 5.4. Calculated distribution of thorium hydrolytic species as a function of pH... 5.
Figure 5.5. Calculated distribution of thorium aqueous species as a function of pH for the water composition in Table 5.1........................... 5.
Figure 5.6a. Calculated distribution of U(VI) hydrolytic species as a function of pH at 0.1 :g/l total dissolved U(VI)................................ 5.
Figure 5.6b. Calculated distribution of U(VI) hydrolytic species as a function of pH at 1,000 :g/l total dissolved U(VI)................................. 5.
Figure 5.7. Calculated distribution of U(VI) aqueous species as a function of pH for the water composition in Table 5.1.............................. 5.
Figure C.1. Relation between cadmium Kd values and pH in soils................... C.
Figure D.1. Relation between cesium Kd values and CEC......................... D.
Figure D.2. Relation between CEC and clay content............................. D.
Figure D.3. Kd values calculated from an overall literature Fruendlich equation for cesium (Equation D.2).......................................... D.
Figure D.4. Generalized cesium Freundlich equation (Equation D.3) derived from the literature.............................................. D.
Figure D.5. Cesium Kd values calculated from generalized Fruendlich equation (Equations D.3 and D.4) derived from the literature................... D.
xiii
Page
Table 5.1. Estimated mean composition of river water of the world from Hem (1985)...... 5.
Table 5.2. Concentrations of contaminants used in the aqueous species distribution calculations.............................................. 5.
Table 5.3. Cadmium aqueous species included in the speciation calculations............. 5.
Table 5.4. Estimated range of Kd values for cadmium as a function of pH............... 5.
Table 5.5. Estimated range of Kd values (ml/g) for cesium based on CEC or clay content for systems containing <5 percent mica-like minerals in clay-size fraction and <10-9^ M aqueous cesium......................... 5.
Table 5.6. Estimated range of Kd values (ml/g) for cesium based on CEC or clay content for systems containing >5 percent mica-like minerals in clay-size fraction and <10-9^ M aqueous cesium......................... 5.
Table 5.7. Estimated range of Kd values for chromium (VI) as a function of soil pH, extractable iron content, and soluble sulfate............................. 5.
Table 5.8. Lead aqueous species included in the speciation calculations............... 5.
Table 5.9. Estimated range of Kd values for lead as a function of soil pH, and equilibrium lead concentrations....................................... 5.
Table 5.10. Plutonium aqueous species included in the speciation calculations.......... 5.
Table 5.11. Estimated range of Kd values for plutonium as a function of the soluble carbonate and soil clay content values................................. 5.
Table 5.12. Strontium aqueous species included in the speciation calculations........... 5.
Table 5.13. Look-up table for estimated range of Kd values for strontium based on CEC (meq/100 g), clay content (wt.%), and pH.......................... 5.
Table 5.14. Thorium aqueous species included in the speciation calculations........... 5.
Table 5.15. Look-up table for thorium Kd values (ml/g) based on pH and dissolved thorium concentrations.................................... 5.
xv
Table 5.16. Uranium(VI) aqueous species included in the speciation calculations......... 5.
Table 5.17. Look-up table for estimated range of Kd values for uranium based on pH..... 5.
Table 5.18. Selected chemical and transport properties of the contaminants............. 5.
Table 5.19. Distribution of dominant contaminant species at 3 pH values for an oxidizing water described in Tables 5.1 and 5.2............... 5.
Table 5.20. Some of the more important aqueous- and solid-phase parameters affecting contaminant sorption...................................... 5.
Table C.1. Descriptive statistics of the cadmium Kd data set for soils................... C.
Table C.2. Correlation coefficients (r) of the cadmium Kd data set for soils.............. C.
Table C.3. Look-up table for estimated range of Kd values for cadmium based on pH...... C.
Table C.4. Cadmium Kd data set for soils......................................... C.
Table D.1. Descriptive statistics of cesium Kd data set including soil and pure mineral phases.......................................... D.
Table D.2. Descriptive statistics of data set including soils only....................... D.
Table D.3. Correlation coefficients (r) of the cesium Kd value data set that included soils and pure mineral phases.................................. D.
Table D.4. Correlation coefficients (r) of the soil-only data set........................ D.
Table D.5. Effect of mineralogy on cesium exchange................................ D.
Table D.6 Cesium Kd values measured on mica (Fithian illite) via adsorption and desorption experiments.......................................... D.
Table D.7. Approximate upper limits of linear range of adsorption isotherms on various solid phases................................................ D.
Table D.8. Fruendlich equations identified in literature for cesium.................... D.
Table D.9. Descriptive statistics of the cesium Freundlich equations (Table D.8) reported in the literature............................................. D.
Table D.10. Estimated range of Kd values (ml/g) for cesium based on CEC
xvi
Table H.4. Look-up table for estimated range of Kd values for strontium based on CEC and pH.................................................... H.
Table H.5. Look-up table for estimated range of Kd values for strontium based on clay content and pH................................................ H.
Table H.6. Calculations of clay content using regression equations containing CEC as a independent variable........................................ H.
Table H.7. Strontium Kd data set for soils........................................ H.
Table H.8. Strontium Kd data set for pure mineral phases and soils................... H.
Table I.1. Descriptive statistics of thorium Kd value data set presented in Section I.3....... I.
Table I.2. Correlation coefficients (r) of the thorium Kd value data set presented in Section I.3....................................................... I.
Table I.3. Calculated aqueous speciation of thorium as a function of pH................. I.
Table I.4. Regression coefficient and their statistics relating thorium Kd values and pH..... I.
Table I.5. Look-up table for thorium Kd values (ml/g) based on pH and dissolved thorium concentrations....................................... I.
Table I.6. Data set containing thorium Kd values................................... I.
Table J.1. Uranium Kd values (ml/g) listed by Warnecke et al. (1994, Table 1).......... J.
Table J.2. Uranium Kd values listed by McKinley and Scholtis (1993, Tables 1, 2, and 4) from sorption databases used by different international organizations for performance assessments of repositories for radioactive wastes.............. J.
xviii
Table J.3. Geometric mean uranium Kd values derived by Thibault et al. (1990) for sand, loam, clay, and organic soil types........................ J.
Table J.4. Look-up table for estimated range of Kd values for uranium based on pH....... J.
Table J.5. Uranium Kd values selected from literature for development of look-up table.................................................... J.
xix