1、Designation:C173317Standard Test Method forDistribution Coefficients of Inorganic Species by the BatchMethod1This standard is issued under the fixed designation C1733;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last r
2、evision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONAs an aqueous fluid migrates through geologic media or contacts an engineered material,certainreactions occur that are dependent
3、 upon the chemistry of the fluid itself and upon the chemistry andgeochemistry of other fluids and solid phases with which it comes in contact.These chemical andgeochemical interactions affect the relative rates at which chemical species in the migrating fluid(suchas ions)travel with respect to the
4、advancing front of water.Processes of potential importance inretarding the transport of chemical species in the migrating fluid(movement of species at velocitiesless than the ground-water velocity)include ion exchange,adsorption,complex formation,precipi-tation(or coprecipitation,for example Ba2+and
5、 Ra2+co-precipitating as a sulfate),redox 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,thesesolute removal mechanisms may not instantaneously respond
6、 to changes in prevailing conditions andmay not be entirely reversible.An empirical ratio known as the distribution coeffcient(Kd)is defined as:Kd5Mass of solute on the solid phase per unit mass of solid phaseMass of solute in solution per unit volume of the liquid phaseand has been used to quantify
7、 the collective effects of these processes for the purpose of modeling(usually,but not solely,applied to ionic species).Kdis used to assess the degree to which a chemical species will be removed from solution(permanentlyor temporarily)as the fluid migrates through the geologic medium or contacts a s
8、olid material;that is,Kdis used to calculate theretardation 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 Kd,which may be used by qualified experts for estimating theretardation of contamin
9、ants for given underground geochemical conditions based on a knowledge and understanding of importantsite-specific factors.It is beyond the scope of this test method to define the expert qualifications required,or to justify theapplication of laboratory data for modeling or predictive purposes.Rathe
10、r,this test method is considered as simply a measurementtechnique for determining the degree of partitioning between liquid and solid,under a certain set of conditions,for the species ofinterest.Justification for the Kdconcept is generally acknowledged to be based on expediency in modeling-averaging
11、 the effects ofattenuation reactions.In reference to partitioning in soils,equilibrium is assumed although it is known that this may not be a validassumption in many cases.The Kdfor a specific chemical species may be defined as the ratio of the mass sorbed per unit of solid phase to the massremainin
12、g per unit of solution,as expressed in the above equation.The usual units of Kdare mL/g(obtained by dividing g solute/gsolid 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
13、-determined Kdvalues relative to a realsystem of aqueous fluid migrating through geologic media(1)2.The Kdconcept is based on an equilibrium condition for givenreactions,which may not be attained in the natural situation because of the time-dependence or kinetics of specific reactionsinvolved.Also,m
14、igrating solutions always follow the more permeable paths of least resistance,such as joints and fractures,andlarger sediment grain zones.This tends to allow less time for reactions to occur and less sediment surface exposure to the migratingsolution,and may preclude the attainment of local chemical
15、 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 situconditions or of other conditions of p
16、rimary interest.Similarly,experimental techniques should consider all ionic speciesanticipated to be present in a migrating solution,in order to address competing ion and ion complexation effects,which mayCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of Inter
