1、Designation: D7503 18Standard 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. Scope*1.1 This test method describes the procedures for measuringthe soluble and bound cations as well
3、as 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
4、cations. 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
5、method 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 mineralsurfac
6、e 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 boundan
7、d 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 theresponsibil
8、ity of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 All observed and calculated values shall conform to theguide for significant digits and rounding established in PracticeD
9、6026. The procedures 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,pu
10、rpose for obtaining 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
11、methodsfor engineering design is beyond the scope of this standard.1.5 UnitsThe values stated in SI units are to be regardedas standard. No other units of measurement are included in thisstandard. Reporting of test results in units other than SI shallnot be regarded as nonconformance with this test
12、method.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarr
13、iers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3D653 Terminology Relating to Soil, Rock, and ContainedFluidsD1193 Specification for Reagent WaterD2216 Test Methods for Laboratory Determination of Water(Moisture) Content of Soil and Rock by MassD3740 Practice for Minimum Requ
14、irements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD4753 Guide for Evaluating, Selecting, and Specifying Bal-ances and Standard Masses for Use in Soil, Rock, andConstruction Materials TestingD6026 Practice for Using Significant Dig
15、its in GeotechnicalDataE145 Specification for Gravity-Convection and Forced-Ventilation Ovens1This 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 approve
16、d March 1, 2018. Published March 2018. Originallyapporved in 2010. Last previous edition approved in 2010 as D750310. DOI:10.1520/D750318.2The 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
17、, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700
18、, 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 International Standards, Guides and Recommendations issued by the Wor
19、ld Trade Organization Technical Barriers to Trade (TBT) Committee.13. 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 water, followed by
20、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 by bound cations.3.2
21、.4 exchange complex, nthe collection of bound cationssatisfying the CEC.3.2.5 fine-grained soils, nany soil with more than 50 %passing the sieve having an opening size of 0.075 mm.3.2.6 inorganic soils, nany soil with a loss of ignition(LOI) less than 1 %.3.2.7 soluble cations (SC), ncations in the
22、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 barriers can contain ions that may interactwith the mineral surfaces in fine-grained soils.4.2 T
23、he 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 evaluation of these interactions.NOTE 1The quality of the result produced by this standard depends onth
24、e 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 andobjective testing, sampling, inspection, etc. Users of this standard arecautioned that complian
25、ce 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, capable of maintaining a uniform tem-perature of 105 6 5 C that meets the requirements ofSpecific
26、ation E145.5.2 Sieve having an opening of 2.00 mm.5.3 Desiccator, containing silica gel.5.4 Laboratory Balance, 20 g capacity, 60.001 g accuracyand precision selected in accordance with Guide D4753.5.5 Weighing Paper, or small weighing dish.5.6 End Over End Shaker, capable of 30 rpm.5.7 Capped Conta
27、iners 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 filteringflask to the low-pressure vacuum line (See F
28、ig. 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.5.13 2.5 m Ashless Filter Paper that covers the surface ofBuchner funnel.5.14 250 mL Volumet
29、ric Flasks, class A flask for precisionand accuracy.6. Reagents6.1 Reagent WaterUse only ASTM Type II water asdefined in Specification D1193.6.2 Ammonium Acetate, 1MDissolve 77.08 g of 99.9 %pure NH4OAc in Type II DI water (See Specification D1193)and fill to volume in a 1000 mL volumetric flask.Adj
30、ust the pHof the solution to 7 with ammonium hydroxide or acetic acid.Approximately 1 L of NH4OAc is needed per 6 samples.6.3 IsopropanolReagent grade.6.4 Potassium Chloride, 1MDissolve 74.6 g of 99 % pureKCl in Type II DI water and fill to volume in a 1000 mLvolumetric flask. Approximately 1 L of K
31、Cl is needed per 6samples.6.5 Ammonium SulfateDry 238 mg of ACS Certified(NH4)2SO4for4hat40C.Make a 200 mg/L stock solutionby dissolving the dried compound in 100 mL of Type II DIwater and fill to volume in a 250 mL volumetric flask. Preparecalibration standards by diluting the stock solution into c
32、on-centrations of 10, 20, 40, 50, and 80 mg/L.6.6 Ca, Mg, K, and NaUse ICP-grade or AA-gradeelement standards in an HNO3matrix to prepare quality controlspikes in a NH4OAc matrix.7. Hazards7.1 This standard does not address all of the safety concernsassociated with its use. The user of this standard
33、 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 standard.8. Determination of Required Air-Dried Mass of Soil forAnalysis8.1 Air-dry approximately 30 g of soil (12
34、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 D2216.8.3 Determine total mass of air-dry soil needed to have 2 gof soil solids for determination of soluble cat
35、ions.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.D7503 182NOTE 2Oven-dried soils should not be used for determining CEC,soluble cations, or bound cations because
36、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 air-dry soil that passes the sieve having anopening size of 2.00 mm.9.2 Add mass of air-dry soil correspon
37、ding to2gofsoilsolids 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 mixture in each container using 2.5 mashless filter paper.9.5 Transfer the extract to a 100 mL a
38、cid 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, atomicabsorption, or another suitable method.NOTE 3Low solid to liquid ratios can result in peptization andhydrolysis in s
39、ome 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 sieve having anopening size of 2.00 mm.10.2 Prepare a blank sample for analysis by placing 100 mLof DI water in a covered con
40、tainer.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 of1MNH4OAc into 100 mL coveredcontainer (use a container which tightly fits into the en
41、d 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 h shake the container with the mixture for 15min at 30 rpm in the end over end
42、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).FIG. 1 Experimental Setup for Vacuum FiltrationD7503 18310.8 Transfer the contents of the sh
43、aken 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 each 30 mL portion slowly
44、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 be used for determining
45、the cationexchange capacity (CEC).10.13 Rinse the 250 mL volumetric flask with 1 MNH4OAc.10.14 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 volumewith NH4OAc.10.15 Analyze the catio
46、n 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 exchangeable acidity.11. Determination of
47、 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 the soil to dry when suction is a
48、pplied.11.4 Wash the soil with three 40 mL portions of isopropa-nol. Allow each 40 mL portion to drain before adding the nextportion. Washing with isopropanol removes residual NH4OAc.11.5 Turn off the suction to the filtering flask when freeliquid is no longer visible.11.6 Separate the Buchner funne
49、l 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 suction 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
