1、Designation: D7503 10Standard Test Method forMeasuring the Exchange Complex and Cation ExchangeCapacity of Inorganic Fine-Grained Soils1This standard is issued under the fixed designation D7503; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes the procedures for measuringthe soluble and bound cations as well a
3、s the cation exchangecapacity (CEC) of fine-grained inorganic soils. Clay mineralsin fine-grained soils carry a negative surface charge that isbalanced by bound cations near the mineral surface. Thesebound cations can be exchanged by other cations in the porewater, which are referred to as soluble c
4、ations. The cationexchange capacity is a measure of the negative surface chargeon the mineral surface. The CEC generally is satisfied bycalcium (Ca), sodium (Na), magnesium (Mg), and potassium(K), although other cations may be present depending on theenvironment in which the soil exists. This test m
5、ethod wasdeveloped from concepts described previously in Lavkulich(1981) (1)2and Rhoades (1982) (2). In soils with appreciablegypsum or calcite, dissolution of these minerals will release Cain solution that may affect the measurement.1.2 In this test method, the soluble salts from the mineralsurface
6、 are washed off with de-ionized water and then theconcentration of soluble salts within the extract is measured.The bound cations of the clay are measured by using a solutioncontaining an index ion that forces the existing cations in thebound layer into solution. The total concentrations of boundand
7、 soluble cations in this solution are measured. The CEC ismeasured by displacing the index ion with another salt solutionand measuring the amount of the displaced index ion.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibili
8、ty of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.4 All observed and calculated values shall conform to theguide for significant digits and rounding established in PracticeD6026. The procedu
9、res in Practice D6026 that are used tospecify how data are collected, recorded, and calculated areregarded as the industry standard. In addition, they are repre-sentative of the significant digits that should generally beretained. The procedures do not consider material variation,purpose for obtaini
10、ng the data, special purpose studies, or anyconsiderations for the objectives of the user. Increasing orreducing the significant digits of reported data to be commen-surate with these considerations is common practice. Consid-eration of the significant digits to be used in analysis methodsfor engine
11、ering design is beyond the scope of this standard.1.5 The values stated in SI units are to be regarded as thestandard, unless other units are specifically given.2. Referenced Documents2.1 ASTM Standards:3D653 Terminology Relating to Soil, Rock, and ContainedFluidsD1193 Specification for Reagent Wate
12、rD2216 Test Methods for Laboratory Determination of Wa-ter (Moisture) Content of Soil and Rock by MassD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD6026 Practice for Using Significant Digits in
13、GeotechnicalDataE145 Specification for Gravity-Convection and Forced-Ventilation Ovens3. Terminology3.1 For definitions of other terms used in this standard, seeTerminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 acid wash, nthe process of initially rinsing equip-ment with tap
14、water, followed by a rinse with 10 % HNO3solution, and then finally rinsing 3 times with DI water.3.2.2 bound cations (BC), ncations that are adsorbed(bound) to mineral surfaces that may be exchanged.3.2.3 cation exchange capacity (CEC), nthe total negativecharge on mineral surface to be satisfied b
15、y bound cations.3.2.4 exchange complex, nthe collection of bound cationssatisfying the CEC.1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.04 on HydrologicProperties and Hydraulic Barriers.Current edition approved
16、July 1, 2010. Published August 2010.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume informat
17、ion, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.5 fine-grained soils, nany soil with more than 50 %passing the No. 200 US standard sieve.3.2.6 inorganic soils,
18、nany soil with a loss of ignition(LOI) less than 1 %.3.2.7 soluble cations (SC), ncations in the soil that are notbound to the mineral surface.4. Significance and Use4.1 Fine-grained soils are used in waste containment sys-tems as barriers to flow and contaminant transport. Liquidscontained by these
19、 barriers can contain ions that may interactwith the mineral surfaces in fine-grained soils.4.2 The liquid passing through the pores of fine-grained soilcan interact with the mineral surface, and affect the physicaland chemical characteristics of the soil. This method can beused as part of an evalua
20、tion of these interactions.NOTE 1The quality of the result produced by this standard depends onthe competence of the personnel performing the test and the suitability ofthe equipment and facilities used. Agencies that meet the criteria ofPractice D3740 are generally considered capable of competent a
21、ndobjective testing, sampling, inspection, etc. Users of this standard arecautioned that compliance with Practice D3740 does not in itself ensurereliable results. Reliable results depend on many factors. Practice D3740provides a means of evaluating some of these factors.5. Apparatus5.1 Drying Oven,
22、capable of maintaining a uniform tem-perature of 105 6 5 C that meets the requirements ofSpecification E145.5.2 No. 10 U.S. Standard Sieve5.3 Desiccator, containing silica gel.5.4 Laboratory Balance, 20 g capacity, 60.001 g accuracyand precision.5.5 Weighing Paper, or small weighing dish.5.6 End Ove
23、r End Shaker, capable of 30 rpm.5.7 Capped Containers should tightly fit in the end over endshaker holding compartment with capacities larger than 40 mL.5.8 500 mL Filtering Flask, connectable to low-pressurevacuum line, acid washed (See Fig. 1).5.9 Flexible Tubing, appropriate size to connect filte
24、ringflask to the low-pressure vacuum line (See Fig. 1).5.10 Buchner Funnel, 55 mm or 90 mm diameter, acidwashed (See Fig. 1).5.11 Wash Bottle, for dispensing solutions, new or acidwashed.5.12 Graduated Cylinder, for measuring solution portions,acid washed.FIG. 1 Experimental Setup for Vacuum Filtrat
25、ionD7503 1025.13 2.5 m Ashless Filter Paper that covers the surface ofBuchner funnel.5.14 250 mL Volumetric Flasks, class A flask for precisionand accuracy.6. Reagents6.1 Reagent Water:Use only ASTM Type II water as defined in SpecificationD1193.6.2 Ammonium Acetate, 1M:Dissolve 77.08 g of 99.9 % pu
26、re NH4OAc in Type II DIwater (See Specification D1193) and fill to volume in a 1000mL volumetric flask. Adjust the pH of the solution to 7 withammonium hydroxide or acetic acid. Approximately 1 L ofNH4OAc is needed per 6 samples.6.3 Isopropanol:Reagent grade.6.4 Potassium Chloride, 1M:Dissolve 74.6
27、g of 99 % pure KCl in Type II DI water and fillto volume in a 1000 mL volumetric flask. Approximately 1 Lof KCl is needed per 6 samples.6.5 Ammonium Sulfate:Dry 238 mg of ACS Certified (NH4)2SO4for4hat40C.Make a 200 mg/L stock solution by dissolving the driedcompound in 100 mL of Type II DI water an
28、d fill to volume ina 250 mL volumetric flask. Prepare calibration standards bydiluting the stock solution into concentrations of 10, 20, 40, 50,and 80 mg/L.6.6 Ca, Mg, K, and Na:Use ICP-grade or AA-grade element standards in an HNO3matrix to prepare quality control spikes in a NH4OAc matrix.7. Hazar
29、ds7.1 This standard does not address all of the safety concernsassociated with its use. The user of this standard is responsiblefor implementing proper safety precautions and should beaware of any possible health concerns and risks related with thematerials and chemicals used while following this st
30、andard.8. Determination of Required Air-Dried Mass of Soil forAnalysis8.1 Air-dry approximately 30 g of soil (12 g of solid isrequired for testing) according to the procedures described inTest Methods D2216.8.2 Oven-dry at least2goftheair-dry soil to determine thewater content following Test Methods
31、 D2216.8.3 Determine total mass of air-dry soil needed to have 2 gof soil solids for determination of soluble cations.8.4 Determine total mass of air-dry soil needed to have 10 gof soil solids for determination of bound cations.8.5 Use the oven-dry weight (2 or 10 g) of the soil for allcalculations.
32、NOTE 2Oven-dried soils should not be used for determining CEC,soluble cations, or bound cations because gypsum (CaSO42H2O) istransformed to plaster of paris (CaSO412 H2O) at high temperatures, andplaster of paris is more soluble in water than gypsum.9. Determination of Soluble Cations9.1 Use only ai
33、r-dry soil that passes the No. 10 US StandardSieve.9.2 Add mass of air-dry soil corresponding to 2 g of soilsolids and 100 mL of Type II DI water to a covered containerthat fits tightly into the shaker.9.3 Place the containers in an end-over-end shaker andshake for1hat30rpm.9.4 Vacuum filter the mix
34、ture in each container using 2.5 mashless filter paper.9.5 Transfer the extract to a 100 mL acid washed volumetricflask, preserve with 1 mL HNO3, and fill to volume.9.6 Analyze each extract for cation concentration (in mg/L)using inductively coupled plasma spectrometry, atomic absorp-tion, or anothe
35、r suitable method.NOTE 3Low solid to liquid ratios can result in peptization andhydrolysis in some cases. If these reactions are of concern a lower solid toliquid ratio such as 1:2 can be used.10. Determination of Bound Cations10.1 Use only air-dry soil that passes the No. 10 USStandard Sieve.10.2 P
36、repare a blank sample for analysis by placing 100 mLof DI water in a covered container.10.3 Prepare quality control samples for analysis by creat-ing a duplicate and a spike and place in a covered container.Add determined mass of air-dried soil corresponding to 10.0 gof soil solids and 40 mL of1MNH4
37、OAc into 100 mL coveredcontainer (use a container which tightly fits into the end overend shaker).10.4 Shake the covered containers for 5 min in an end overend shaker at 30 rpm. Agitate the container to rinse theparticles from the side of the container and let the mixturestand for 24 h.10.5 After 24
38、 h shake the container with the mixture for 15min at 30 rpm in the end over end shaker.10.6 Rinse the 500 mL filtering flask and Buchner funnelwith NH4OAc.10.7 Place the Buchner funnel over the 500 mL filteringflask and line the Buchner funnel with 2.5 m ashless filterpaper (See Fig. 1).10.8 Transfe
39、r the contents of the shaken container to theBuchner funnel.10.9 Rinse the container and cap into the Buchner funnelusing a squirt bottle containing1MNH4OAc.10.10 Apply low suction to the filtering flask (10 kPa).10.11 Wash the soil in the Buchner funnel with four 30 mLportions of 1 M NH4OAc. Add ea
40、ch 30 mL portion slowly andallow the entire 30 mL portion to drain before adding the next30 mL portion. Do not allow the soil to dry between additionsof NH4OAc.10.12 Turn the suction off to the filtering flask after the lastwashing. Leave the NH4OAc washed soil in the Buchnerfunnel; this soil is to
41、be used for determining the cationexchange capacity (CEC).10.13 Rinse the 250 mL volumetric flask with 1 MNH4OAc.D7503 10310.14 Transfer the filtered aqueous solution into the 250 mLvolumetric flask. Preserve the solution to pH of 2 withICP-grade nitric acid and fill the volumetric flask to volumewi
42、th NH4OAc.10.15 Analyze the cation concentration (in mg/L) in theaqueous solution using inductively coupled plasma spectrom-etry or atomic absorption.NOTE 4Typically Na, Ca, Mg, and K cations satisfy the majority ofthe CEC. The user may analyze for other cations of concern, which mayinclude exchange
43、able acidity.11. Determination of the Cation Exchange Capacity11.1 Rinse an acid washed 500 mL filtering flask withisopropanol.11.2 Place the Buchner funnel with the1MNH4OAcwashed sample onto the 500 mL filtering flask (See Fig. 1).11.3 Apply low suction (10 kPa) to the filtering flask. Donot allow
44、the soil to dry when suction is applied.11.4 Wash the soil with three 40 mL portions of isopro-panol. Allow each 40 mL portion to drain before adding thenext portion. Washing with isopropanol removes residualNH4OAc.11.5 Turn off the suction to the filtering flask when freeliquid is no longer visible
45、.11.6 Separate the Buchner funnel from the filtering flask.Discard the isopropanol collected in the 500 mL filtering flaskand rinse the flask with Type II DI water three times.11.7 Return the Buchner funnel containing the isopropanolwashed soil to the rinsed filtering flask (See Fig. 1).11.8 Apply s
46、uction to the filtering flask and wash the soilwith four 50 mL portions of 1 M KCl solution. Allow eachportion of the 1 M KCl solution to drain before adding the nextportion. Do not allow the soil to dry between additions of KClsolution.11.9 Rinse a 250 mL volumetric flask with 1 M KCl.11.10 Transfe
47、r the extract into the 250 mL volumetric flask.Rinse the filtering flask with Type II DI water and transfer thecontents into the volumetric flask.11.11 Fill the volumetric flask to volume with water.11.12 Analyze the KCl extract for nitrogen concentration(mg/L) using a spectrophotometer.12. Calculat
48、ions12.1 Calculate the concentration of soluble cations as fol-lows:S 5 C 30.100LMog!3 1000gkgwhere:S = concentration of soluble cations (cmol+/kg) in thesoil,C = concentration of cations (cmol+/L) in the DI waterextract from 9.6, andMo= oven-dry mass of soil.12.2 Calculate the concentration of boun
49、d cations as fol-lows:M15 C 30.25LMog!3 1000gkg Swhere:M+= concentration of adsorbed cation (cmol+/kg) in soil,andC = concentration of cation (cmol+/L) in the NH4OAcextract from 10.15.12.3 Calculate the cation exchange capacity as follows:CEC 5 N 31cmol1140mg30.25LMog!3 1000gkgwhere:CEC = concentration of cation exchange capacity (cmol+/kg), andN = concentration of nitrogen (mg/L) from 11.12.13. Report13.1 Report the following information:13.1.1 Source and description of the soil.13.1.2 Source and description of all chemicals used to makemixtures and solutions
