The cation exchange capacity of clay-size material extracted from soil with a low organic matter content is largely dependent on the kinds of clay minerals present. If the extracted clay is composed mostly of one kind of clay mineral, the exchange capacity will indicate what that mineral is. This paper reports on cation exchange capacity determinations made on the minus 2 micron clay-size range of selected samples of loess from the southwestern Iowa area

Davidson, D. T.

Sheeler, J. B.

English

University of Northern Iowa

Proceedings of the Iowa Academy of ScienceVolume 60 | Annual Issue Article 441953Cation Exchange Capacity of the Clay Fraction ofLoess in Southwestern IowaD. T. DavidsonIowa State CollegeJ. B. SheelerIowa State CollegeCopyright © Copyright 1953 by the Iowa Academy of Science, Inc.Follow this and additional works at: https://scholarworks.uni.edu/piasThis Research is brought to you for free and open access by UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academyof Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu.Recommended CitationDavidson, D. T. and Sheeler, J. B. (1953) "Cation Exchange Capacity of the Clay Fraction of Loess in Southwestern Iowa," Proceedingsof the Iowa Academy of Science: Vol. 60: No. 1 , Article 44.Available at: https://scholarworks.uni.edu/pias/vol60/iss1/44Cation Exchange Capacity of the Clay Fraction of Loess in Southwestern Iowa By D. T. DAVIDSON AND J.B. SHEELER The cation exchange capacity of clay-size material extracted from soil with a low organic matter content is largely dependent on the kinds of clay minerals present. If the extracted clay is com-posed mostly of one kind of clay mineral, the exchange capacity will indicate what that mineral is. This paper reports on cation exchange capacity determinations made on the minus 2 micron clay-size range of selected samples of loess from. the southwestern Iowa area shown in Figure 1. WHOLE LoEss SAMPLES The origin, distribution, and property variations of the Wiscon-Sy mbo ls Sioux City East Valley---Wall Council Bluffs N f • Wisconsin Loess Samples (Unditfere ntiatedl • Upper Wisconsin Loess Sample & Loveland Soi I and Loess Samples 20-2 Sample Numbers Arbitrary -----T' East Boundary Figure 1. Distribution of samrling locations in southwestern Iowa loess area. Symbols indicate age classification o loess sampled. 354 1Davidson and Sheeler: Cation Exchange Capacity of the Clay Fraction of Loess in SouthwePublished by UNI ScholarWorks, 19531953] CATION EXCHANGE CAPACITY OF LOESS 355 sin* loess which mantles much of the southwestern Iowa area shown in Figure 1 have been discussed in previous papers (I, 2, 3) . The minus 2 micron clay fractions used in the study reported in this paper were extracted from eleven samples of whole loess which were selected as representing the range in properties of the more than 150 loess samples that have been tested in the property varia-tion studies of the Iowa Engineering Experiment Station. Descriptive information of the locations from which the whole loess samples were taken are given in Table I, and the distribution of sampling locations is shown in Figure 1. Sample 55-1 is Upper Wisconsin or Cary-Mankato loess from the Pisgah road section identified by Rube ( 4) . The other Wisconsin age loess samples are undifferentiated because the buried (Brady) soil (6) which separates the upper and fower Wisconsin components was not present. The samples of Loveland soilt and of Loveland loess from the type section at Loveland, Pottawattamie County, were included in the study for comparative purposes. Table II gives some properties of the whole loess which are indicative of the cation exchange material in the samples. The Wis-consin loess samples are arranged in this table in the order of in-creasing clay content. The range in clay content of the Wiscon~in loess in southwestern Iowa is shown by these samples. Whether the type section Loveland samples used herein are representative of Loveland soil and loess exposed elsewhere in southwestern Iowa is not as yet known. The Loveland soil had a higher clay content than the underlying loess, and both Loveland samples had lower clay contents than some of the more plastic Wisconsin loes samples. Sample 26-2 is from the same location as sample 26-1 but was taken at a greater depth in the '"1isconsin loess section. Both samples contain practically the same amount of clay. However sample 26-2 is unoxidized and unleached, and sample 26-1 is oxidized and leached. Sample 26-2 was included in the study to determine what effect oxidation and leaching might have on the clay mineral present in the loess. This was the only unoxidized sample used in the study. The organic matter content of all samples was low, and for this reason the inorganic clay minerals are considered to be largely re-sponsible for cation exchange. Carbonate contents were variable, being relatively high for unleached samples taken near the major source areas of the loess (3). The distribution of carbonates m *Also referred to as Peorian loess in the geological literature. tSangamon soil profile on Loveland loess. 2Proceedings of the Iowa Academy of Science, Vol. 60 [1953], No. 1, Art. 44https://scholarworks.uni.edu/pias/vol60/iss1/44Table 1 Loess Sampling Locations in Southwestern Iowa. Sample No. Material 55-1 Loess 20-2 61-2 26-1 26-2 29-1 36-1 431/:!-l 46-1 49-3 Soil" 49-4 Loess Age classification Upper Wisconsinh Wisconsin (Undifferentiated) " Loveland Sampling depthc (ft.) 21/:l-31/:l 39-40 17-18 4-5 10-11 5-6 51/:l-61/:l 5-6 5-6 55d 65• Location County Section Harrison SW/c,S-8 Harrison S-15' Ida NWI,4,,S-9 Shelby SE%,,S-21 Audubon NW I c,SW%,,S-13 Montgomery SE%,,NE%,,S-14 Fremont NW/c,S-36 Page NW%,,S-30 Pottawattamie SE/ c,NW%,,S-3" "Sangamon soil profile on Loveland Loess. bAlso called Cary-Mankato loess and Bignell loess. Sampled from Pisgah road section (4). 'Measurements are from earth's surface. dSampled from about middle of 10 ± ft. Sangamon soil profile. "Sampled in Loveland loess about 3 ft. above slump. 'Sampled from bluff behind third ward school in city of Missouri Valley. •Sampled from type section of Loveland loess at northeast edge of town of Lon· land (:;I. CJ> "' °' Town-ship Range Soil North West series -0 81 44 Hamburg ~ > 78 43 Hamburg > ll 87 40 Monona > Cl 81 40 Monona trl s:: -< 78 36 Marshall 0 "'i 72 38 Marshall [J) 68 40 Marshall ll -67 37 Marshall trl z 77 44 Hamburg ll trl 3Davidson and Sheeler: Cation Exchange Capacity of the Clay Fraction of Loess in SouthwePublished by UNI ScholarWorks, 1953..... '° <.n w ~ Table 2 Some Properties of Whole Loess Samples. Sample Textural Composition• Pl as· CJ Organic Cat. Ex. ticity B.P.R.b > ..., Age Sand Silt Clay(%) matter Carbonates Cap Index Classifi--0 No. Classification (%) (%) -5µ -2µ (%) (%CaCO,) Oxidation pH ( m.e./lOOg) (%) cation z trl Upper >< 13.4 0.24 11.0 Oxidized CJ 55-1 Wisconsin 4.0 82.6 12.0 8.4 11.2 2.3 A-4(8) ::i:: Wisconsin > 20-2 ( U ndiff eren tiated) 1.4 78.8 19.8 16.0 0.17 10.2 Oxidized 8.7 13.4 6.2 A-4(8) z 0 61-2 5.2 70.8 24.0 19.8 0.15 11.5 Oxidized 8.3 14.2 10.8 A-6(8) trl 26-1 2.0 70.6 27.4 22.4 0.18 1.4 Oxidized 7.0 18.2 12.5 A-6(9) CJ > 26-2 0.9 69.8 29.3 23.1 0.17 8.7 Unoxidized 8.3 17.9 17.8 A-6(9) "ti > 29-1 1.0 67.9 31.1 25.0 0.25 2.9 Oxidized 8.3 19.5 18.0 A-6(11) ll -36-1 0.8 63.2 36.0 28.9 0.21 1.8 Oxidized 6.7 21.0 20.7 A-7-6(13) ..., >< 4311:!-l 0.4 60.2 39.4 33.0 0.37 0.5 Oxidized 6.7 24.4 33.4 A-7-6(18) 0 46-1 0.8 55.7 43.5 36.2 0.30 1.5 Oxidized 6.3 22.6 32.7 A-7-6(19) "'l t'"' 49-3 Loveland (soil) 2.7 61.1 36.2 31.4 0.19 1.3 Oxidized 8.2 22.7 24.6 A-7-6(15) 0 Loveland 5.3 65.9 28.8 24.6 0.11 7.0 Oxidized 8.2 16.6 15.3 A-6(10) trl 49-4 [fJ [fJ "Sand-2.0 to 0.05 mm., silt-0.05 to 0.005 mm. One micron equals 0.001 mm. •Bureau of Public Roads Soil Classification System. Also ref erred to as the Highway Research Board System or the American Association of State Highway Officials (AASHO) System (7). w <.n -.J 4Proceedings of the Iowa Academy of Science, Vol. 60 [1953], No. 1, Art. 44https://scholarworks.uni.edu/pias/vol60/iss1/44358 IOWA ACADEMY OF SCIENCE [Vol. 60 the different particle-size fractions of the loess has not as yet been determined. The pH values varied from 6. 7 to 8. 7 or from near neutral to alkaline. The variations in whole loess cation exchange capacity, in plasticity index, and in B.P.R. classification are mainly due to the variation in clay content (2). CLAY FRACTION The minus 2 micron portions of the whole loess samples were used for the exchange capacity determinations because practically all of the cation exchange material, the clay minerals, occur in this particle-size range. Complete separation of the clay minerals from other substances such as quartz and carbonates is difficult, but only very small amounts of such substances are commonly found in the minus 2 micron soil fraction. The separation of the minus 2 micron clay material from the whole loess was by means of a sedimentation procedure which is the subject of another paper now in preparation. In this procedure neither the whole loess nor the separated clay was given hydro-chloric acid or hydrogen peroxide treatments. When a deflocculat-ing agent was needed to prevent flocculation, 0.1 N sodium hydrox-ide was used. DETERMINATION OF CATION EXCHANGE CAPACITY Cation exchange capacity can be determined by a number of methods, most of which involve leaching the soil sample with a salt solution containing known cations followed by analysis either of the resulting soil or of the solution for the amount of cations ex-changed. Because of solubility and decomposition effects Kelly and Brown (8) recommended the determination of the cations ab-sorbed by the soil rather than of the amount of cations that are brought into solution from the soil. The cation exchange capacity of a soil denotes the total amount of cations that can be exchanged under a given set of conditions and not necessarily the amount that could be exchanged under other conditions. The determination is particularly sensitive to the pH of the salt solution; the common practice is to use a neutral (pH = 7) solution. Neutral normal ammonium acetate has been found to be a salt solution especially well adapted to the exchange capacity determination (9). With this solution the exchange ca-pacity of inorganic soils can be determined with reasonable accur-acy even when the soil contains soluble salts and calcium carbonate. Test methods used in determining cation exchange capacities of whole Wisconsin loess samples have been previously presented by 5Davidson and Sheeler: Cation Exchange Capacity of the Clay Fraction of Loess in SouthwePublished by UNI ScholarWorks, 19531953] CATION EXCHANGE CAPACITY OF LOESS 359 the authors (2). A step-by-step summary of the procedure used in the present study is as follows: I. Weigh out about one gram (accurate to 1 mg) of representative air-dry clay and place in a 300 ml centrifuge bottle. (A similar sample should be weighed out for the hygroscopic moisture determination needed to convert air-dry weight to oven-dry weight.) 2. Add IO g of fine Ottawa sand to the clay in the centrifuge bottle. (Ottawa sand is inert and increases the permeability for the purpose of filtration in Step 7.) 3. Add 250 ml of neutral normal ammonium acetate to the contents of the cen-trifuge bottle and shake for 3 min. (Higher normalities and increased shak-ing times were experimented with hut did not significantly affect results.) 4. Centrifuge at 2000 RPM for IO min. 5. Decant the clear supernatant liquid. 6. Repeat Step 3. 7. Filter the contents of the centrifuge bottle with a Buchner funnel con-taining two fine filter papers. 8. Wash the material retained on the filter paper with 150 ml of neutral 70 percent (by volume) methyl alcohol to remove the excess ammonium acetate trapped in void spaces. 9. Determine the amount of ammonia held in the exchange positions of the clay by a modified Kjeldahl nitrogen determination (2). 10. Calculate the cation exchange capacity in milliequivalents per IOO g of oven-dry clay ( 2). CATION EXCHANGE CAPACITIES Cation exchange capacities of minus 2 micron clay fractions are given in Table III. Since the clay minerals are the primary seat of cation exchange, the uniformity of the exchange capacity data Table 3 Cation Exchange Capacities of Minus 2 Micron Clay Fractions Sample no. 55-1 20-2 61-2 26-1 26-2 29-1 36-1 43112-1 46-1 49-3 49-4 Material Loess Soil Loess Age Classification Upper Wisconsin Wisconsin (Undifferentiated) Loveland "Values reported are the average of two determinations. Cation Exchange Capacity• (m.e./IOOg) 59.3 58.6 52.5 62.8 59.0 62.2 63.1 59.9 57.4 63.4 54.4 6Proceedings of the Iowa Academy of Science, Vol. 60 [1953], No. 1, Art. 44https://scholarworks.uni.edu/pias/vol60/iss1/44360 IOWA ACADEMY OF SCIENCE [Vol. 60 indicates that there is little variation in the kinds of clay minerals in the Wisconsin Loess. The data further indicates that there is little difference between the clay fractions of the Wisconsin loess and the Loveland Loess. The results of differential thermal analy-ses on whole loess samples ( 3) substantiate this interpretation. Slight variations in the cation exchange capacity values in Table III may or may not be significant. Further studies are in progress to determine whether they are due to experimental factors or to slight variations in mineral composition. The clay fractions extracted from soils are rarely composed of a single kind of clay mineral but usually contain two or more mixed with other substances from which complete separation is difficult. The exchange capacity of the minus 2 micron particle-size range for this reason can at best be used only to estimate roughly the pre-dominant kind of clay mineral present. The estimation can be made by comparing the determined value with the exchange ca-pacities of comparatively pure clay minerals. Grim ( 10) gives cation exchange capacities of the common clay minerals as: Montmorillonite ................................ 60-100 m.e./lOOg Attapulgite ......................................... 25-30 Illite .................................................... 20-40 Kaolinite ............................................ 3 -15 Halloysite ........................................... 6 -10 A comparison of the data in Table III with Grim's values indi-cates that the loess clay fractions contain a predominance of mont-morillonite group minerals. Differential thermal curves for samples of whole loess from southwestern Iowa have indicated the presence of illite ( 3) . This mineral is often associated with montmorillonite in soils, and its presence would tend to lower the exchange capacity (9). According to Jackson et al ( 11), montomorillonite can develop from illite by weathering, which may be the reason why the Love-land soil has a higher exchange capacity than the loess on which it developed. The same explanation may apply to the difference in the exchange capacities of samples 26-1 and 26-2. The oxidized and leached sample ( 26-1) had a slightly higher exchange capacity than the unoxidized and unleached sample (26-2). ACKNOWLEDGMENT The subject matter of this paper was obtained as part of the re-search being done under Project 283-S of the Iowa Engineering Experiment Station of Iowa State College. This project, entitled "The Loess and Glacial Till Materials of Iowa; An Investigation of 7Davidson and Sheeler: Cation Exchange Capacity of the Clay Fraction of Loess in SouthwePublished by UNI ScholarWorks, 19531953] CATION EXCHANGE CAPACITY OF LOESS 361 Their Physicial and Chemical Properties and Techniques for pro-cessing Them to Increase Their All-Weather Stability for Road Construction" is being carried on under contract with the Iowa State Highway Commission and under the sponsorship of the Iowa Highway Research Board. It is supported by funds supplied by the Commission and the U. S. Bureau of Public Roads. References Cited 1. Davidson, D. T. and Sheeler, J. B. 1951. Studies of the clay fraction in engineering soils: III Influence of amount of clay on engineering prop-erties. Proc. Hwy. Res. Bd. 31 :558-563. 2. Davidson, D. T. and Sheeler, J. B. 1952. Cation exchange capacity of loess and its relation to engineering properties. Symposium on Exchange Phe· nomena in Soils, Am. Soc. Testing Mat. Special Tech. Pub. 142. pp. 1-19 3. Davidson, D. T. and Handy, R. L. 1952. Property variations in the Peorian loess of southwestern Iowa. Proc. Iowa Acad. Sci. 59 :248-265. 4. Ruhe, R. V. 1949. A Bignell (?) loess section in western Iowa. Proc. Iowa Acad. Sci. 56 :229-231. 5. Kay, George F. et al. 1944. The Pleistocene geology of Iowa. Spec. Rpt., Iowa Geologic Survey. 6. Ruhe, R. V. 1952. Classification of the Wisconsin glacial stage. J our. Geo!. 60 :398-401. 7. American Association of State Highway Officials. 1950. Standard specifi-cations for highway materials and methods of sampling and testing, Part I. Specifications: The Association, Washington 25, D. C. 8. Kelly, W. P. and Brown, S. M. 1924. Replaceable bases in soils. California Agr. Exp. Sta. Tech Paper. 15: 1-39. 9. Kelly, W. P. 1948. Cation Exchange in Soils. Reinhold Publishing Corp., New York, N. Y. IO. Grim, R. E. 1942. Modern concepts of clay materials. lour. Geo!. 50 :225-275. 11. Jackson et al. 1948. Weathering sequence of clay-size minerals in soils. and sediments. lour. Phys. and Colloid Chem. 52 :1237-1260. IowA ENGINEERING EXPERIMENT STATION IowA STATE COLLEGE AMES, IowA 8Proceedings of the Iowa Academy of Science, Vol. 60 [1953], No. 1, Art. 44https://scholarworks.uni.edu/pias/vol60/iss1/44

Cation Exchange Capacity of the Clay Fraction of Loess in Southwestern Iowa

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Cation Exchange Capacity of the Clay Fraction of Loess in Southwestern Iowa

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