ASTM D4319-93
(Test Method)Standard Test Method for Distribution Ratios by the Short-Term Batch Method
Standard Test Method for Distribution Ratios by the Short-Term Batch Method
SCOPE
1.1 This test method covers the determination of distribution ratios of chemical species for site-specific geological media by a batch sorption technique. It is a short-term laboratory method primarily intended for ionic species subject to migration in granular porous material, and the application of the results to long-term field behavior is not known. Distribution ratios for radionuclides in selected geomedia are commonly determined for the purpose of assessing potential migratory behavior at waste repositories. This test method is also applicable to studies of intrusion waters and for parametric studies of the effects of variables and of mechanisms which determine the measured distribution ratios.
1.2 The values stated in acceptable metric units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety problems, 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.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 4319 – 93
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Distribution Ratios by the Short-Term Batch Method
This standard is issued under the fixed designation D 4319; 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 (e) 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
upon the chemistry of the fluid itself and upon the chemistry and geochemistry of other fluids and solid
phases with which it comes in contact. These geochemical interactions determine the relative rates at
which chemical species in the migrating fluid (such as ions) travel with respect to the advancing front
of water. Processes of potential importance in retarding the flow of chemical species in the migrating
fluid (movement of species at velocities less than the ground-water velocity) include ion exchange,
++ ++
adsorption, complex formation, precipitation (or coprecipitation, for example Ba and Ra
co-precipitating as the sulfate), oxidation-reduction reactions, and precipitate filtration. This test
method applies to situations in which only sorptive processes (adsorption and ion exchange) are
operable for the species of interest, however, and is restricted to granular porous media.
It is difficult to derive generalized equations to depict ion exchange-adsorption reactions in the
geological environment. Instead, a parameter known as the distribution coeffıcient (K ) has been used
d
to quantify certain of these sorption reactions for the purpose of modeling (usually, but not solely,
applied to ionic species). The distribution coefficient is used to assess the degree to which a chemical
species will be removed from solution as the fluid migrates through the geologic media; that is, the
distribution coefficient provides an indication of how rapidly an ion can move relative to the rate of
ground-water movement under the geochemical conditions tested.
This test method is for the laboratory determination of the distribution ratio (R ), which may be
d
used by qualified experts for estimating the value of the distribution coefficient 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 distribution ratio or degree of
partitioning between liquid and solid, under a certain set of laboratory conditions, for the species of
interest.
Justification for the distribution coefficient concept is generally acknowledged to be based on
expediency in modeling-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. Equilibrium implies that (1) a reaction can be described by an equation and the free energy
change of the reaction, within a specific system, is zero, and (2) any change in the equilibrium
conditions (T, P, concentration, etc.) will result in immediate reaction toward equilibrium (the concept
is based upon reversibility of reactions). Measured partitioning factors may include adsorption,
coprecipitation, and filtration processes that cannot be described easily by equations and, furthermore,
these solute removal mechanisms may not instantaneously respond to changes in prevailing
conditions. Validity of the distribution coefficient concept for a given set of geochemical conditions
should not be assumed initially, but rather should be determined for each situation.
This is a short-term test and the attainment of equilibrium in this laboratory test is not presumed,
although this may be so for certain systems (for example, strictly interlayer ion exchange reactions of
clays). Consistent with general usage, the result of this test could be referred to as “distribution
coefficient” or as “distribution ratio;” in the strictest sense, however, the term “distribution ratio” is
preferable in that the attainment of equilibrium is not implied.
D 4319
The distribution ratio (R ) for a specific chemical species may be defined as the ratio of the mass
d
sorbed onto a solid phase to the mass remaining in solution, which can be expressed as:
~mass of solute on the solid phase per unit mass of solid phase!
R 5 (1)
d
~mass of solute in solution per unit volume of the liquid phase!
The usual units of R are mL/g (obtained by dividing g solute/g solid by g solute/mL solution, using
d
concentrations obtained in accordance with this test method).
Major difficulties exist in the interpretation, application, and meaning of laboratory-determined
distribution ratio values relative to a real system of aqueous fluid migrating through geologic media.
Typically, only reactions between migrating solutions and solid phases are quantified. In general,
geochemical reactions that can result from interaction of the migrating fluid with another aqueous
phase of a differing chemistry have not been adequately considered (interactions with other liquids can
profoundly change the solution chemistry). Additionally, as noted above, the distribution coefficient or
K concept implies an equilibrium condition for given reactions, which may not realistically apply in
d
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. Thus, the distribution coefficient or K concept is only directly applicable to
d
problems involving contaminant migration in granular porous material.
Sorption phenomena are also strongly dependent upon the thermodynamic activity of the species of
interest in solution (chemical potential). Therefore, experiments performed using only one activity or
concentration of a particular chemical species may not be representative of actual in situ conditions
or of other conditions of primary interest. Similarly, unless experimental techniques consider all ionic
species anticipated to be present in a migrating solution, adequate attention is not directed to
competing ion and ion complexation effects, which may strongly influence the R for a particular
d
species.
Many “sorption” ion complexation effects are strongly influenced, if not controlled, by conditions
of pH and Eh. Therefore, in situ conditions of pH and redox potential should be considered in
determinations of R . To the extent possible, these pH and Eh conditions should be determined for field
d
locations and must be approximated (for transition elements) in the laboratory procedure.
Other in situ conditions (for example, ionic strength, anoxic conditions, or temperature) could
likewise have considerable effect on the R and need to be considered for each situation. Additionally,
d
site-specific materials must be used in the measurement of R . This is because the determined R
d d
values are dependent upon 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.
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 an R of any significant magnitude, the front of the zone containing
d
this containment will be considerably retarded. This means that the porous 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. It is recommended
that ground water representative of the test zone be used as contact liquid 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.
The distribution ratio for a given chemical species generally assumes a different value when any of
the above conditions are altered. Clearly, a very thorough understanding of distribution coefficients
and the site-specific conditions that determine their values is required if one is to confidently apply the
K concept (and the measured R values) to migration evaluation and prediction.
d d
The adoption of a standard method for determining distribution ratios, R , especially applicable for
d
ionic species, is important in that it will provide a common basis for comparison of experimental
results (particularly for near-similar conditions).
The most convenient method of determining R is probably the batch method (this test method), in
d
which concentrations of the chemical species in solid and liquid phases, which are in contact with one
D 4319
another, are measured with time. Other methods include the dynamic test or column flow-through
method using (1) continuous input and (2) pulsed input, the in situ dual tracer test, and the thin-layer
chromatography (TLC) test.
In summary, this distribution ratio, R , is affected by many variables, all of which may not be
d
adequately controlled or measured by the batch method determination. The application of experimen-
tally determined R values for predictive purposes (assuming a functional relationship such as
d
R 5 K ) must be done judiciously by qualified experts with a knowledge and understanding of the
d d
important site-specific factors. However, when properly combined with knowledge of the behavior of
chemical species under varying physicochemical conditions of the geomedia and the migrating fluid,
distribution coefficients (ratios) can be used for assessing the rate of migration of chemical species
through a saturated geomedium.
1. Scope such an assumption can only be determined by informed
experts making a judgment (albeit uncertain) based on a
1.1 This test method covers the determination of distribu-
detailed study of the specific site.
tion ratios of chemical species for site-specific geological
3.1.2 distribution ratio, R —the ratio of the concentration
media by a batch sorption technique. It is a short-term d
of the species sorbed on the soil or other geomedia, divided by
laboratory method primarily intended for ionic species subject
its concentration in solution under steady-state conditions, as
to migration in granular porous material, and the application of
follows:
the results to long-term field behavior is not known. Distribu-
tion ratios for radionuclides in selected geomedia are com- ~mass of solute on the solid phase per unit mass of solid phase!
R 5
d
~mass of solute in solution per unit volume of the liquid phase!
monly determined for the purpose of assessing potential
(2)
migratory behavior at waste repositories. This test method is
by steady-state conditions it is meant that the R values
also applicable to studies of intrusion waters and for parametric
d
studies of the effects of variables and of mechanisms which obtained for three different samples exposed to the contact
liquid for periods ranging from 3 to at least 14 days, other
determine the measured distribution ratios.
1.2 The values stated in acceptable metric units are to be conditions remaining constant, shall differ by not more than the
expected precision for this test method.
regarded as the standard.
1.3 This standard does not purport to address all of the The dimensions of the expression for R reduce to cubic
d
length per mass (L /M). It is convenient to express R in units
safety problems, if any, associated with its use. It is the
d
responsibility of the user of this standard to establish appro- of millilitres (or cubic centimetres) of solution per gram of
priate safety and health practices and determine the applica- geomedia.
bility of regulatory limitations prior to use. 3.1.3 species—a distinct chemical entity (such as an ion) in
which the constituent atoms are in specified oxidation states.
2. Referenced Documents
4. Significance and Use
2.1 ASTM Standards:
D 422 Test Method for Particle-Size Analysis of Soils
4.1 The distribution ratio, R , is an experimentally deter-
d
D 2217 Practice for Wet Preparation of Soil Samples for
mined parameter representing the distribution of a chemical
Particle-Size Analysis and Determination of Soil Con-
species between a given fluid and a geomedium sample under
stants
certain conditions, including the attainment of a steady state.
D 2488 Practice for Description and Identification of Soils
Based on a knowledge and understanding of the important
(Visual-Manual Procedure)
site-specific factors, R values may be used by qualified experts
d
D 3370 Practices for Sampling Water
for estimating the value of the distribution coefficient, K , for
d
a given set of underground geochemical conditions. The K
d
3. Terminology
concept is used in mass transport modeling, for example, to
3.1 Definitions of Terms Specific to This Standard: assess the degree to which an ionic species will be removed
3.1.1 distribution coeffıcient, K —is identically defined as
from solution as the solution migrates through the geosphere.
d
R for equilibrium conditions and for ion exchange-adsorption For applications other than transport modeling, batch R
d
d
reactions only. To apply R values to field situations, an
measurements also may be used, for example, for parametric
d
assumption such that R 5 K is necessary. The validity of studies of the effects of variables and of mechanisms related to
d d
the interactions of fluids with geomedia.
This test method is u
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.