ASTM C1733-10
(Test Method)Standard Test Method for Distribution Coefficients of Inorganic Species by the Batch Method
Standard Test Method for Distribution Coefficients of Inorganic Species by the Batch Method
SIGNIFICANCE AND USE
The distribution coefficient, Kd, is an experimentally determined ratio quantifying the distribution of a chemical species between a given fluid and geomedium sample under certain conditions, including the attainment of constant aqueous concentrations of the species of interest. The Kd concept is used in mass transport modeling, for example, to assess the degree to which the movement of a species will be delayed by interactions with the geomedium as the solution migrates through the geosphere under a given set of underground geochemical conditions (pH, temperature, ionic strength, etc.). The retardation factor (Rf) is the ratio of the velocity of the groundwater divided by the velocity of the contaminant, which can be expressed as:
SCOPE
1.1 This test method covers the determination of distribution coefficients of chemical species to quantify uptake onto solid materials by a batch sorption technique. It is a laboratory method primarily intended to assess sorption of dissolved ionic species subject to migration through pores and interstices of site specific geomedia. It may also be applied to other materials such as manufactured adsorption media and construction materials. Application of the results to long-term field behavior is not addressed in this method. Distribution coefficients for radionuclides in selected geomedia are commonly determined for the purpose of assessing potential migratory behavior of contaminants in the subsurface of contaminated sites and waste disposal facilities. This test method is also applicable to studies for parametric studies of the variables and mechanisms which contribute to the measured distribution coefficient.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: C1733 − 10
Standard Test Method for
Distribution Coefficients of Inorganic Species by the Batch
Method
This standard is issued under the fixed designation C1733; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
As an aqueous fluid migrates through geologic media, certain reactions occur that are dependent
uponthechemistryofthefluiditselfanduponthechemistryandgeochemistryofotherfluidsandsolid
phaseswithwhichitcomesincontact.Thesegeochemicalinteractionsaffecttherelativeratesatwhich
chemical species in the migrating fluid (such as ions) travel with respect to the advancing front of
water.Processesofpotentialimportanceinretardingthetransportofchemicalspeciesinthemigrating
fluid (movement of species at velocities less than the ground-water velocity) include ion exchange,
2+ 2+
adsorption, complex formation, precipitation (or coprecipitation, for example Ba and Ra
co-precipitating as the sulfate), oxidation-reduction reactions, and precipitate filtration. Partitioning
may be caused by processes that include adsorption, precipitation, and coprecipitation that cannot be
described easily by equations and, furthermore, these solute removal mechanisms may not instanta-
neously respond to changes in prevailing conditions and may not be entirely reversible.
An empirical ratio known as the distribution coeffıcient (K ) is defined as:
d
Mass of solute on the solid phase per unit mass of solid phase
K 5
d
Mass of solute in solution per unit volume of the liquid phase
and has been used to quantify the collective effects of these processes for the purpose of modeling (usually, but not solely,
appliedtoionicspecies).Thedistributioncoefficientisusedtoassessthedegreetowhichachemicalspecieswillberemovedfrom
solution(permanentlyortemporarily)asthefluidmigratesthroughthegeologicmedium;thatis,thedistributioncoefficientisused
to calculate the retardation factor that quantifies how rapidly an ion can move relative to the rate of ground-water movement.
This test method is for the laboratory determination of the distribution coefficient (K ), which may be used by qualified experts
d
for estimating the retardation of contaminants for given underground geochemical conditions based on a knowledge and
understanding of important site-specific factors. It is beyond the scope of this test method to define the expert qualifications
required, or to justify the application of laboratory data for modeling or predictive purposes. Rather, this test method is considered
as simply a measurement technique for determining the degree of partitioning between liquid and solid, under a certain set of
conditions, for the species of interest.
Justificationforthedistributioncoefficientconceptisgenerallyacknowledgedtobebasedonexpediencyinmodeling-averaging
the effects of attenuation reactions. In reference to partitioning in soils, equilibrium is assumed although it is known that this may
not be a valid assumption in many cases.
The distribution coefficient (K ) for a specific chemical species may be defined as the ratio of the mass sorbed per unit of solid
d
phase to the mass remaining per unit of solution, as expressed in the above equation. The usual units of K are mL/g (obtained
d
by dividing g solute/g solid by g solute/mL solution, using concentrations obtained in accordance with this test method).
Major difficulties exist in the interpretation, application, and meaning of laboratory-determined distribution coefficient values
relativetoarealsystemofaqueousfluidmigratingthroughgeologicmedia (1) .Thedistributioncoefficientor K conceptisbased
d
on an equilibrium condition for given reactions, which may not be attained in the natural situation because of the time-dependence
or kinetics of specific reactions involved. Also, migrating solutions always follow the more permeable paths of least resistance,
such as joints and fractures, and larger sediment grain zones.This tends to allow less time for reactions to occur and less sediment
surface exposure to the migrating solution, and may preclude the attainment of local chemical equilibrium.
Sorption phenomena also can be strongly dependent upon the concentration of the species of interest in solution. Therefore,
experiments performed using only one concentration of a particular chemical species may not be representative of actual in situ
conditions or of other conditions of primary interest. Similarly, experimental techniques should consider all ionic species
anticipated to be present in a migrating solution, in order to address competing ion and ion complexation effects, which may
strongly influence the sorption of a particular species.
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C1733 − 10
Sorption can be strongly controlled, by pH. Therefore, in situ pH, especially of groundwater, should be considered in
determinations of K . Values of pH must be determined, preferably in the field when materials are sampled and must be carefully
d
determined in the laboratory procedure. Other in situ conditions (for example, ionic strength, anoxic conditions, or temperature)
could likewise have considerable effect on the K and need to be considered for each situation.
d
Site-specific materials must be used in the measurement of K . This is because the determined K values are dependent upon
d d
rock and soil properties such as the mineralogy (surface charge and energy), particle size distribution (surface area), and biological
conditions (for example, bacterial growth and organic matter). Special precautions may be necessary to assure that the site-specific
materials are not significantly changed prior to laboratory testing.This may require refrigeration or freezing of both soil and water
samples. Chemical means of preservation (such as addition of acid to groundwater) will cause changes in sample chemistry and
must be avoided.
The choice of fluid composition for the test may be difficult for certain contaminant transport studies. In field situations, the
contaminant solution moves from the source through the porous medium.As it moves, it displaces the original ground water, with
some mixing caused by dispersion. If the contaminant of interest has a K of any significant magnitude, the front of the zone
d
containing this contaminant will be considerably retarded. This means that the granular medium encountered by the contaminant
has had many pore volumes of the contaminant source water pass through it. The exchange sites achieve a different population
status and this new population status can control the partitioning that occurs when the retarded contaminant reaches the point of
interest.Itisrecommendedthatgroundwaterrepresentativeofthetestzone(butcontainingaddedtracers)beusedascontactliquid
in this test; concentrations of potential contaminants of interest used in the contact liquid should be judiciously chosen. For studies
of interactions with intrusion waters, the site-specific ground water may be substituted by liquids of other compositions.
Thedistributioncoefficientforagivenchemicalspeciesgenerallyassumesadifferentvaluewhenconditionsarealtered.Clearly,
a very thorough understanding of the site-specific conditions that determine their values is required if one is to confidently apply
the K concept to migration evaluation and prediction.
d
The most convenient method of determining K is probably the batch method (this test method), in which concentrations of the
d
chemical species in solid and liquid phases, which are in contact with one another, are measured. Other methods include dynamic
column flow-through methods using continuous input of tracer or pulsed input. In the field, a dual tracer test can be conducted
using a conservative (nonsorbing) tracer and one that does sorb; from the difference in travel times of the two tracers, K can be
d
calculated.
In summary, the distribution coefficient, K , is affected by many variables, some of which may not be adequately controlled or
d
measuredbythebatchmethoddetermination.Theapplicationofexperimentallydetermined K valuesforpredictivepurposesmust
d
bedonejudiciouslybyqualifiedexpertswithaknowledgeandunderstandingoftheimportantsite-specificfactors.However,when
properlycombinedwithknowledgeofthebehaviorofchemicalspeciesundervaryingphysicochemicalconditionsofthegeomedia
and the migrating fluid, distribution coefficients can be used for assessing the rate of migration of chemical species through a
saturated geomedium.
This test method is under the jurisdiction of ASTM Committee C26 on Nuclear Fuel Cycle and is the direct responsibility of Subcommittee C26.13 on Spent Fuel and
High Level Waste.
Current edition approved Oct. 1, 2010. Published October 2010. DOI: 10.1520/C1733–10.
The boldface numbers in parentheses refer to a list of references at the end of this standard.
1. Scope 1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
1.1 This test method covers the determination of distribu-
standard.
tion coefficients of chemical species to quantify uptake onto
1.3 This standard does not purport to address all of the
solid materials by a batch sorption technique. It is a laboratory
safety concerns, if any, associated with its use. It is the
methodprimarilyintendedtoassesssorptionofdissolvedionic
responsibility of the user of this standard to establish appro-
species subject to migration through pores and interstices of
priate safety and health practices and determine the applica-
sitespecificgeomedia.Itmayalsobeappliedtoothermaterials
bility of regulatory limitations prior to use.
such as manufactured adsorption media and construction
materials.Application of the results to long-term field behavior
2. Referenced Documents
is not addressed in this method. Distribution coefficients for
2.1 ASTM Standards:
radionuclides in selected geomedia are commonly determined
for the purpose of assessing potential migratory behavior of
contaminantsinthesubsurfaceofcontaminatedsitesandwaste
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
disposalfacilities.Thistestmethodisalsoapplicabletostudies
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
for parametric studies of the variables and mechanisms which
Standards volume information, refer to the standard’s Document Summary page on
contribute to the measured distribution coefficient. the ASTM website.
C1733 − 10
D422 Test Method for Particle-SizeAnalysis of Soils (With- where:
drawn 2016)
ρ = bulk density of the porous medium (mass/length ) and
b
D1293 Test Methods for pH of Water
D2216 Test Methods for Laboratory Determination ofWater
η = effective porosity of the medium (unitless) expressed as
e
(Moisture) Content of Soil and Rock by Mass
a decimal.
D2488 Practice for Description and Identification of Soils
4.2 Because of the sensitivity of K to site specific condi-
d
(Visual-Manual Procedure)
tions and materials, the use of literature derived K values is
d
D3370 Practices for Sampling Water from Closed Conduits
strongly discouraged. For applications other than transport
D4319 Test Method for Distribution Ratios by the Short-
modeling, batch K measurements also may be used, for
d
Term Batch Method (Withdrawn 2007)
example, for parametric studies of the effects of changing
D4448 Guide for Sampling Ground-Water MonitoringWells
chemical conditions and of mechanisms related to the interac-
D5730 Guide for Site Characterization for Environmental
tions of fluids with geomedia.
Purposes With Emphasis on Soil, Rock, the Vadose Zone
and Groundwater (Withdrawn 2013)
5. Apparatus
5.1 Laboratory Ware (plastic bottles, centrifuge tubes, open
3. Terminology
dishes, pipettes) cleaned in a manner consistent with the
3.1 Definitions of Terms Specific to This Standard:
analyses to be performed and the required precision. Where
3.1.1 distribution coeffıcient, K,n—the concentration of a
d
plateout may have significant effect on the measurement,
species sorbed on a solid material, divided by its concentration
certain porous plastics should be avoided and the use of FEP
in solution in contact with the solid, under constant concentra-
TFE-fluorocarbon containers is recommended.
tion conditions, as follows:
5.2 Centrifuge, capable of attaining 1400 g, or filtering
Mass of solute on the solid phase per unit mass of solid phase
K 5
apparatus.
d
Mass of solute in solution per unit volume of the liquid phase
5.3 Filters, filtration apparatus, including syringe filters,
(1)
capable of removing particles of ≥0.45 micrometers. Filter
3.1.1.1 Discussion—By constant concentration conditions,
media should be selected to not sorb species of interest under
it is meant that the K values obtained for samples exposed to
d
theexperimentconditions.Sorptionhasbeenobservedonfilter
the contact liquid for two different time periods (at least one
media composed of certain materials (3).
day apart), other conditions remaining constant, shall differ by
not more than the expected precision for this test method. It is
5.4 Laboratory Shaker/Rotator, ultrasonic cleaner (op-
convenienttoexpress K inunitsofmL(orcm )ofsolutionper
d tional).
gram of geomedia.
5.5 Environmental Monitoring Instruments, a pH meter,
3.1.2 species, n—specific form of an element defined as to
conductance meter, and thermometer.
isotopic composition, electronic or oxidation state, complex or
5.6 Analytical Balance capable of measuring to 0.01g.
molecular structure, or combinations thereof (2).
5.7 Appropriate Equipment, necessary to replicate in situ
3.1.3 tracer, n—an identifiable substance, such as a dye or
conditions within the laboratory apparatus.
radioactive isotope, that can be followed through the course of
a mechanical, chemical, or biological process.
5.8 Analytical Instrumentation, appropriate for determina-
tion of the concentration of major constituents (cations and
4. Significance and Use
anions) and of the species of interest (for which K is being
d
determined) in the contact solutions (and, optionally, in the
4.1 The distribution coefficient, K , is an experimentally
d
geomedia samples).
determined ratio quantifying the distribution of a chemical
species between a given fluid and geomedium sample under
6. Sampling
certain conditions, including the attainment of constant aque-
ous concentrations of the species of interest. The K concept is
d 6.1 The samples of soil, rock, or sediment shall be consid-
used in m
...
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