Holm, V. C., Clark, Alfred, Preprints, Division of Petroleum Chemistry, 142nd Meeting, ACS, Sept. 9-14, 1962, p. A-45. Mills, G. A.. Heinemann, H.. Milliken, T. H.. Oblad. A. G., Ind.'Eng. Chem. 45, 134 (1953). Orlov, K. Y., Martynov, A. A., Izu. Akad. Nauk SSSR Ser. Khim. No. 5, 796-800 (1965). Orlov, K. Y., Martinov, A. A., Bulychev, V. P., Izu. Akad. Nauk, SSSR Ser. Khim. No. 5 , 792-6 (1965).
Pushkin, Y. M., Orlov, K. Y., Izv. Akad. Nauk SSSR Otdel. Khim. Nauk 1961, 657-63. Weisz, P. B., Swegler, E. W., Science 126, 31 (1957).
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RECEIVED for review July 10, 1968 ACCEPTED March 13, 1969 Division of Petroleum Chemistry, 155th Meeting, ACS, San Francisco, Calif., April 1968.
EFFECT OF CLAY CATION EXCHANGE ON FOUNDRY SAND CHARACTERISTICS THOMAS
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Ceramic Engineering Department, The University of Texas, Austin, Tex. 78712 A study was made of changes in foundry sand properties due to the exchangeable cation of a n illitic clay binder. Grundite, an illitic clay, was modified by an ion exchange process to convert the exchangeable cation to Na-, Ca2-, NHI', and Mg2- ion forms. Typical green foundry sand mixtures of sand, water, seacoal, and the processed clay were prepared and a series of standard room temperature foundry tests was made. The various ion forms of the Grundite produced significant differences in the green compressive strength, permeability, and stress-strain behavior of the foundry sand mixtures.
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AN effort to provide improved and uniform product properties, the modern clay industry uses a variety of processing steps, chemical additives, and blending techniques (Dohman et al., 1967; Hogue, 1966; Law, 1966; Mercade, 1967; Ovcharenko and Nichiporenko, 1963; Sheldon et al., 1966). This study discusses the modification of a clay by an ion exchange process and the effect of this modification on the clay as a foundry sand binder. It has been known for many years that some clays have exchangeable cations (Grim, 1953). Grimshaw (1958) and German (1964) commented on the modification of clay properties by the replacement of the exchangeable cation with another cation species. Most studies have used a salt exchange technique (Fox et al., 1961) in which the clay is brought in contact with a soluble salt solution of the desired cation. I n an early study, Lewis (1953) reported on the use of a synthetic ion exchange resin to replace the clay cation with another cation species. Eschenberg et al. (1956) prepared different ion forms of Grundite clay, using a synthetic resin column, and showed that the cation type in the processed clay influenced the physical properties of the clay. Grundite clay, an illitic clay originally identified with Grundy County, Illinois, finds some application as a foun-
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Present address, Clarkson College of Technology, Potsdam,
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dry sand binder where the clay comprises only a small percentage of the over-all mixture composition. For this reason, a study was undertaken to determine the influence of the clay cation type on the foundry sand properties. The Eschenberg column process was selected for scaleup because it would isolate effects due to the exchangeable cation from those due to the salt. Experimental
Ion-Exchange Column Preparation. Four-inch-diameter glass columns were hydraulically filled to a 28-inch depth with Nalcrite-HCR, a nuclear sulfonic acid resin (Nalco Chemical Co.). The columns were downflow-charged with 3N salt solutions a t 60 cc. per minute to prepare the Na', Caz-, NH,-, and Mg2- columns. The salt solutions used in the four columns were sodium chloride, calcium chloride, ammonium acetate, and magnesium perchlorate. After charging, the excess salt was removed by water washing. The columns were reclassified by water backflushing before the clay exchange was started. Clay Preparation. The Grundite clay analyzed 98% finer than 44 microns, The plus-44-micron fraction was composed of quartz, pyrite, and ligneous material. The clay was first prepared as a 30% clay-in-water suspension, using deionized water, and agitated in a rubber ball mill to obtain good separation of the clay particles. This was then diluted to a 1.5% suspension and screened through
a µn screen. The underflow was continuously agitated and fed to one of the columns a t 60-cc.-per-minute rate. The product from each column was concentrated to dryness a t 50" C. with air heaters and milled in a laboratory hammer mill to a si:ze comparable to the unprocessed clay. This clay procedure was followed for each cation type of clay prepared. A separate batch of clay was also scrubbed, screened, dried, and crushed for use as a check on the physical clay treatment and on the effect of the plus-44-micron fraction. Preparation of Foundry Sand Specimens. An Ottawa silica sand of A.F.S. fineness 81 (Standard Silica Corp.) was used throughout the study. Carbon in the form of Seacoal D (M. A. Bell Co.) was used as a 2 5 (dry basis) additive to duplicate typical foundry practice. Foundry sand mixtures were prepared using sand, carbon, various amounts of each ion type of processed clay, and various amounts of water. The moisture contents were determined by measured additions of deionized water to the dry mixture. A dry basis, selected as constant weight a t 50°C., was used so that careful material balances could be used for more accurate control of moisture throughout the tests. This provided a more suitable laboratory control of moisture content than the standard A.F.S. procedure. The sand mixtures were hand-mulled, and standard rammed specimens prepared. Foundry Tests. Compressive strength, permeability, hardness, deformation, and stress-strain tests were made on the moist sand samples with standard test equipment ( € 3 . W. Dietert Co.). Except for the determination of moisture content, the ,standard American Foundry Society test procedures were used. Chemical Tests. The total cation exchange capacity and the individual cation concentrations were determined by procedures similar to those reported earlier (Eschenberg et al., 1956). A clay sainple was mixed with 3N ammonium acetate, centrifuged, and decanted. This was done four times and the supernatant liquid analyzed for the individual cations of interest in a spectrophotometer. The centrifuged clay cake was washed with an 80% alcohol-in-water solution until it was acetate-free and then distilled in a Kjeldahl apparatus with NaOH. The distillate was neutralized with HC1 and then titrated with NaOH. The total cation exch.ange capacity was calculated from the data of this procedure. The "4content of the ammonium Grundite clay was determined by the same method as the total cation exchange capacity, beginning a t the point of alcohol washing. Results and Discussioin
The compressive strength of the moist foundry sand mixtures is shown in Figure 1. The data illustrated are averages of 20 test runs. The reproducibility of the green compressive strength results was good, with standard deviations typically in the range of 7% for the 5% clay clay mixtures. I n the region mixtures and 2% for the of most interest ( 2 to moisture), the clay cation exchange can result in significant increases in compressive strength, even though the amount of clay is very small. The sodium and magnesium types of ion-exchanged clay, for example, result in a 50% increase in strength when only 10"'; clay is used in the mixture. The green com-
Figure 1. Compressive strength of foundry sand mixtures Ottawa sand-Grundite cloy-2%
seacoal-water
pressive strength of the untreated clay, whose exchangeable cations are principally calcium and magnesium, does not fall between the ion-exchanged calcium and magnesium clay. This might be due to factors in the processing such as the hammer milling or the 50'C. drying. However, some clay was processed in a manner similar to the exchanged clay except for the ion exchange itself. This clay gave results that agreed with the untreated clay. pH was measured on all the clay mixtures, but there was no significant pH difference between the various ion forms and the untreated clay. Typical stress-strain curves (Figures 2 , 3, and 4) for mixtures containing 5% clay and 1% water, 1 0 5 clay and 2 c ~water, and 1570 clay and 3% water clearly show the improved strength and deformation characteristics of the ion-exchanged clay. The reproducibility of the deformation data was poor, with standard deviations as
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Figure 2 . Stress-strain curves for foundry sand mixtures containing 5 % clay a n d 1% water VOL. 8 N O . 2 JUNE 1 9 6 9
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Figure 3. Stress-strain curves for foundry sand mixtures containing 10% clay and 2% water
high as 50% for some mixtures. However, the data illustrated are the most representative of the 20 values taken for each mixture. The results of the hardness tests (not illustrated) showed about the same effect as the compressive strength test, but did not have as high reproducibility. This is interesting because of the widespread use of the simple hardness test in foundry practice. There was a slight decrease in permeability when the Na+, Ca2+,and Mg2+ ion-exchanged clays were used and a slight increase with the "4clay over the untreated clay mixture. These were small, insignificant differences of the order of 5% or less. Maximum permeability for all the mixtures was encountered with moisture contents in the 2 to 4% range. The total cation exchange capacity of the minus-44micron Grundite used in this work was 25.6 meq. per 100 grams of clay. As expected, this is less than the 28.6 meq. per 100 grams reported for the minus-5-micron fraction (Eschenberg et al., 1956). The efficiency of the column exchange process for each ion type of the minus-44-micron clay fraction was: Ion type Efficiency, 7c
Ka56.8
Ca257.9
NHa60.2
Mg" 60.1
These are less than the average 80% efficiency reported by Eschenberg et al. (1956) for a laboratory-scale study of a similar process. The low efficiencies are probably due to the coating of the resin particles by the clay. Even though the exchange capacity of the clay processed in a column corresponded to only one fifth of the resin column exchange capacity, the clay tended to accumulate as a coating on the resin particles and reduce the contact between the resin and the clay slurry. Higher efficiencies might be obtained by using an agitated resin tank or by periodic flushing or pulsing of the resin bed with water.
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Figure 4. Stress-strain curves for foundry sand mixtures containing 15% clay and 3% water
This demonstration of the effect of very small additions of ion-exchanged clay on foundry sand mixtures suggests that improved product specifications might be obtained in other applications, such as the storage of radioactive wastes as vitrified solids. Literature Cited
Dohman, E. J., Shaler, R. G., Rinehimer, W. A. (to American Tansul Co.), U. S. Patent 3,298,849 (Jan. 17, 1967). Eschenberg, R. L., Stone, R. L., Weiss, E. J., J . Am. Ceram. Soc. 39, 398 (1956). Fox, H. A., Jr., Kerr, G. T., Zimmerman, R. H . (to AMP, Inc.), U. S.Patent 3,012,050 (Dec. 5, 1961). German, W. L., Ceramics 15, 16 (1964). Grim, R. E., "Clay Mineralogy," McGraw-Hill, New York, 1953. Grimshaw, R. W., Trans. Brit. Ceram. SOC.57, 340 (1958). Hogue, C. H., Brick Clay Record 149, 34 (1966). Law, J. P., Ph.D. thesis, Texas A & M, College Station, Tex., 1966. Lewis, D. R., Znd. Eng. Chem. 45, 1782 (1953). Mercade, V. (to Minerals and Chemicals Philipp Corp.), U. S. Patent 3,337,048 (Aug. 22, 1967). Ovcharenko, F. D., Yichiporenko, S. P., Zh. Vses. Khim. Obshchestua im. D . I . Mendeleeva 8, 171 (1963). Sheldon, F. R., Kibbell, W. H., Jr., Kressbach, J. E. (to FMC Corp.), U. S. Patent 3,290,161 (Dec. 6, 1966). RECEIVED for review July 17, 1968 ACCEPTED February 3, 1969
