LOGO Cation Exchange And It s Role On Soil Behavior Presented by Sh.Maghami Instructor : Dr.Nikoodel Autumn,1391
Contents Chapter 1) Introduction Deffinitions Why do soils have CEC Basics of Clay content & CEC Chapter 2) Clay Structure How do clays Have a CEC Isomorphous substitution Foundations and differences of Clays structures Some properties of clay minerals Chapter 3) Surface Properties Surface Properties Relations Chapter 4) Engineering Properties The physical properties affected by surface phenomenones
What expect you to know Cation Exchange How the soil properties could related to each other Cation Exchange & Cation Echange Capacity (CEC) How CEC effect on soil properties? What properties affected? Cation CEC Agents and what Is their relationship to soil What is the relation of surface properties of the soil Describing the clay structures and the differences between those.
Chapter 1 INTRODUCTION Definitions Cation Exchange Cation Exchange Capacity Why do soils have CEC
Definitions Soil colloids will attract and hold positively charged ions to their surface Replacement of one ion for another from solution Cation Exchange For every cation that is adsorbed, one goes back into soil solution Cation Exchange Capacity (CEC) In soil science the maximum quantity of total cations, of any class, that a soil is capable of holding, at a given ph value, available for exchange with the soil solution (meq+/100g)
Why do soils have CEC? The cation exchange capacity (CEC) of the soil is determined by the amount of clay and/or humus that is present. Clay & Humus : Cation warehouse or reservoir of the soil Sandy soils with very little OM Clay soils with high levels of OM Low CEC much greater capacity to hold cations. (negative soil particles attract the positive cations) Sand Clay Si 2 O 4 SiAlO 4 - No charge. Does not retain cations Negative charge. Attracts and retains cations
CLAY STRUCTURE How do clays Have a CEC Isomorphous substitution Foundations and differences of Clays structures 1:1 Clays 2:1 Clays Some properties of clay minerals
Why do clays have a CEC? If the mineral was pure silica and oxygen (Quartz), the particle would not have any charge. Figure 1 ) SiO 2 Structure
Isomorphous substitution However, clay minerals could contain aluminum as well as silica. They have a net negative charge because of : the substitution of silica (Si4+) by aluminum (Al3+) in the clay. This replacement of silica by aluminum in the clay mineral s structure is called isomorphous substitution, and the result is clays with negative surface charge Figure 2) Tetrahedron - SiO 4 Octahedron - Al(OH) 6
How clays are forming basically? Sharing of O or OH groups Sheets and unit layers (a) Tetrahedral sheet (b) Octahedral sheet Si Al Figure 3) Sheets Formation
How clays are forming basically? Exposed Oxygen Shared Oxygen Hydrogen Balance Oxygen Charge Si Al Figure 4) Clays unit structure
Clay Types A) 1:1 Type Minerals Mostly Kaolinite Si Al 7A o Si Al Hydrogen bonding between layers. This gives 1:1 type minerals a very rigid structure. Figure 5) 1:1 clays Well crystallized Low cation adsorption Little isomorphous substitution Larger particle size (0.1-5 m m) Fixed lattice type No interlayer activity No shrink-swell Only external surface
Clay Types B) 2:1 Type Minerals 1. Expanding lattice Smectite group Mostly Montmorillonite 18A o Si Al Si Freely expanding Water in interlayer Large shrink-swell Small size Poorly crystallized Large internal surface Isomorphous substitution Large cation adsorption Adsorbed cations in interlayer Ca Mg H2O Si Al Si Figure 6) 2:1 expanding clays
Clay Types 2. Non-expanding lattice Fine-grained micas or illite Some distribution of Al for Si in the tetrahedral layers leads to permanent net negative charge Al +3 and K + substitute for Si +4 (tetrahedral sheet) weathering at edges = release of K + very limited expansion medium cation adsorption limited internal surface properties between kaolinite and vermiculite 10A o K - - - - - - - Si Al - - - - - - - - K - K - K - K - K - K - Si Si Al - - - - - - - Si Figure 7) 2:1 non expanding clays
Clay Types Chlorites : Mg replace K + of illite Similar to illite Vermiculite : similar to Smectite more structured => limited expansion Rather large cation adsorption Figure 8) Clays comparison
Table 1) Summary of Properties : Major Clay particles properties differences Size (um) Surface Area (m 2 /g) External Internal Interlayer Spacing (nm) Cation Sorption Kaolinite 0.1-5.0 10-50 - 0.7 5-15 Smectite <1.0 70-150 500-700 1.0-2.0 85-110 Vermiculite 0.1-5.0 50-100 450-600 1.0-1.4 100-120 Illite 0.1-2.0 50-100 5-100 1.0 15-40 Humus coatings - - - 100-300
What happens in soil R - H + R - H + R - H + + 4 Na + R - H + R - Na + R - Na + R - Na + + 4 H + R - Na + Figure 9) what happens in soil
Conclusion From the previous discussion, it is obvious that the amount and type of clay in the soil determines cation exchange capacity. Kaolinite Non Clays In addition, the type of clay also affects cation exchange capacity. There are three types of aluminosilicate clays in temperate region soils: Illite Montmorillonite CEC, Shrinkage & Swelling Figure 10) CEC comparison
How tight an ion is held. 1) Ion s hydrated radius Smaller radius = tighter hold 2) Magnitude of ion s charge Higher charge = tighter hold Al3+ > Ca2+ > Mg2+ > K+, NH4 + > Na+ > Li+ How likely an ion species is to be adsorbed is determined by its concentration in the soil solution Higher concentration = more adsorption High concentration of one ion species relative to another ion species can supersede the effect of radius and charge
Chapter 3 SURFACE PROPERTIES Surface Properties Relations
Surface Properties Relations There are some important correlations between some surface properties of soil,that have to be obvious. This Properties are :
1 m Reason of differences Montmorillonite Area : 18 m2 Area : 6 m2 Figure 11)
CEC & SSA Relationship Many researchers (e.g., Farrar and Coleman 1967; De Kimpe et al. 1979; Cihacek and Bremner 1979; Newman 1983; Tiller and Smith 1990) have found : Surface Area to relate closely to Cation Exchange Capacity of soils. The surface activity of a clayey soil can be described in part by its CEC or by its Specific Surface Area (Locat et al. 1984). Gill and Reaves (1957) presented SSA versus CEC with a correlation coefficient of r 2 = 0.95, which is similar to Mortland s (1954) and Reeve s et al. (1954) findings. Farrar and Coleman (1967) presented results for 19 British Clays, which show a relatively linear correlation between CEC and SSA. All of these equations can be found in Table 2.
Table 2) Equations between CEC and SSA Correlation Equations for Relationships Between CEC and Surface Area. CEC=0.15SA-1.99 Southestern US Clay Gill and Reaves (1957) CEC=0.28SA+2 British Clay Soils Farrar and Coleman (1967) CEC=0.12SA+3.23 Israel soils Banin and Amiel (1970) CEC=0.14SA+3.6 Osaka Bay Clay Tanaka (1999)
Figure 12) SSA versus CEC Correlation Between Between CEC CEC and and SSA SSA for Clay for Osaka Soils of Bay Israel. Clay. (after Banin (after and Tanaka Amiel 1999) 1970)
Figure 13) CF versus CEC Relationship Between between Cation Surface Exchange Area Capacity and Clay and Fraction Clay Fraction. for Sensitive Canadian (after Davidson Clays. (after et al. Locat 1952) et al. 1984)
Total surface area of different clays According to this chart it is expected to cation exchange capacity have an increasing trend from montmorillonit to kaolinite. External; Kaolinite; Internal; Kaolinite; 0 50 Internal; Illite; 600 External; Illite; 100 Internal; Montmorillonite; 700 External; Montmorillonite; 150 Figure 16) Surface area of clays Internal External M2/g
Figure 14) Cation activity chart Cation Activity Chart (after Kolbuszewski et al. 1965)
Chapter 4 ENGINEERING PROPERTIES How the surface properties affect on soil physical properties
Introduction Many properties of the fine-grained soils are attributed to cation exchange, which is a surface phenomenon. By replacing the existing cations in the exchange complex, several improvements can be effected in the soil properties. These beneficial changes are in the form of reduction in plasticity, increase in the strength, and reduction in the compressibility. Figure 11) Lime Stabilization The addition of lime to a soil supplies an excess of calcium ions, and cation exchange can take place with divalent calcium, Ca+2 replacing all other monovalent cations. The base exchange phenomenon has been used by several investigators to explain the effects of chemical stabilization. (K. Mathew 1997)
Diagram 1: Atterberg Limits 2: Dispersion 3: Hydraulic conductivity Following previous session,some soil engineering properties changes that found to be related,directly or not,with Cation Exchange process are discussed 4: Swelling Potential 5: Compressibility 6: Consoildation
LL% 1 : Atterberg Limits Sridharan et al. (1975) tested seven natural soils containing montmorillonite as the dominant clay mineral and showed the relationship between the Atterberg limits and Clay Fraction (CF), SSA and CEC. The Liquid Limit versus CEC shows somewhat of a linear trend, as indicated in Figure 19. CEC Figure 15) CEC versus LL% (Sridharan et al.1975)
Figure 16) LL versus CEC Relationship Between Cation Exchange Capacity and Liquid Limit. (after Davidson et al. 1952)
Figure 17) PL versus CEC This Slide Removed For More Reviews
Figure 18) IP versus CEC Relationship Between Cation Exchange Capacity and Plasticity Index (after Davidson et al. 1952)
Figure 19) SL versus CEC Relationship Between Cation Exchange Capacity and Shrinkage Limit. (after Davidson et al. 1952)
Shrinkage Limit The shrinkage of clay soils is often said to depend not only on the amount of clay, but also on its nature (Greene-Kelly 1974). Montmorillonitic soils = high water adsorption = high shrinkage (Smith 1959) optimum clay content (Sridharan 1998). Clay % 30 and 50 %.
Table 3) Equations between PL, LL & SA The Plastic and Liquid limit has been highly correlated with CEC and Specific Surface Area (Smith et al. 1985; Gill and Reaves 1957; Farrar and Coleman 1967; Odell et al. 1960), as seen in Table 3. Correlation Equations for Relationships Between PL,LL,and SA CEC=0.55LL-12.2 British Clay Soils Farrar and Coleman (1967) CEC=1.74LL-38.15 Clays from Israel Smith et al. (1985) CEC=3.57PL-61.3 Clays from Israel Smith et al. (1985) PL=0.43SA ext. +16.95 African/Georgia/Missoury Hammel et al. (1983) PL=0.064SA+16.60 Clays from Israel Smith et al. (1985)
2: Dispersion Surface area may also play a significant role in controlling the behavior of dispersive clays through surface charge properties (e.g., Heinzen et al. 1977; Harmse et al. 1988; Sridharan et al. 1992; Bell et al. 1994). Sodic soils are typically highly dispersive. Sodic soils have a high concentration of exchangeable Na +,therefore much of the negative charge on the clay is neutralized by Na +, creating a thick layer of positive charge that may prevent clay particles from flocculating. - - - - - - - - - - 2+ 2+ 2+ 2+ 2+ 2+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
3: Hydraulic conductivity A laboratory study of the hydraulic conductivity (HC) of a marine clay with monovalent, divalent and trivalent cations revealed large differences in HC. RAO et all 1995 suggests that HC is significantly affected by the valency and size of the adsorbed cations. An increase in the valency of the adsorbed cations For a constant valency An increase in the hydrated radius of the adsorbed cations Higher HC Lower HC As per Ahmed et al (1969) and Quirk and Schofield (1955) HC is related to exchangeable cations in the following order Ca = Mg > K > Na
4: Swelling Potential The more montmorillonite in the mixture, the more internal surface and the surface area. As the surface area increases, the swelling potential increases De Bruyn et al. (1957) presented results and a classification of various soils using Specific Surface Area and moisture contents. His criteria state that soils with : TSSA < 70 m 2 /g & w % < 3% non-expansive (good). TSSA > 300 m 2 /g & w % > 10% expansive (bad).
Swelling Figure 21) Swelling versus SSA Specific Surface Area (De Bruyn et al,1957)
5: Compressibility It has been established that the thickness of the double layer is sensitive to changes in cations present on the surface (Van Olphen 1963). The divalent and trivalent cations in the adsorbed complex of clayey soil are known to reduce the thickness of the diffuse double layer by one-half and one-third. respectively (Mitchell 1976) An increase in valency leads to a reduction in compressibility, and at a constant valency an increase in the hydrated radii of the adsorbed cations resulted in an increase in compressibility. Further, it has been found that preconsolidation pressure increases with valency of the cations.(k. Mathew 1997).
Figure 22)C c versus SSA (De Bruyn et al,1957)
References : AMY B. CERATO ;2003 ; INFLUENCE OF SPECIFIC SURFACE AREA ON GEOTECHNICAL CHARACTERISTICS OF FINE- GRAINED SOILS. Paul K. Mathew and S. Narasimha Rao ; 1997 ; EFFECT OF LIME ON CATION EXCHANGE CAPACITY OF MARINE CLAY. Paul K. Mathew and S. Narasimha Raoz ;1997 ; INFLUENCE OF CATIONS ON COMPRESSIBILITY BEHAVIOR OF A MARINE CLAY S. NARASIMHA RAO AND PAUL K. MATHEW ;1999 ; EFFECTS OF EXCHANGEABLE CATIONS ON HYDRAULIC CONDUCTIVITY OF A MARINE CLAY. Paul K. Mathew! and S. Narasimha Rao2 ;1997 ; EFFECT OF LIME ON CATION EXCHANGE CAPACITY OF MARINE CLAY. EWA T. STI~PKOWSKA ;1989 ; Aspects of the Clay/ Electrolyte/ Water System with Special Reference to the Geotechnical Properties of Clays. Sridharan, A. and Rao, G.V. 1975. Mechanisms Controlling the Liquid Limits of Clays. Locat, J. Lefebvre, G, and Ballivy, G., 1984. Mineralogy, Chemistry, and Physical Property Interrelationships of Some Sensitive Clays from Eastern Canada. SHAINBERG, N. ALPEROVITCH, AND R. KEREN; 1988 ; EFFECT OF MAGNESIUM ON THE HYDRAULIC CONDUCTIVITY OF Na- SMECTITE-SAND MIXTURES Uehara, G. 1982. Soil Science for the Tropics. Manja Kurecic and Majda Sfiligoj Smole ;2012 ; Polymer Nanocomposite Hydrogels for Water Purification. Angelo Vaccari ;1998 ; Preparation and catalytic properties of cationic and anionic clays. College of Agriculture and Life Sciences,Cornell University ; 2007 ; Cation Exchange Capacity Greene-Kelly, R. 1974. Shrinkage of Clay Soils: A Statistical Correlation with Other Soil Properties. Smith R.M. 1959. Some Structural Relationships of Texas Blackland Soils with Special Attention to Shrinkage and Swelling. Sridharan, A. and Prakash, K. 1998. Mechanism Controlling the Shrinkage Limit of Soils. Sridharan, A., and Nagaraj, H.B. 2000. Compressibility Behaviour of Remoulded, Fine-Grained Soils and Correlation With Index Properties. Smith, C.W., Hadas, A., Dan, J., and Koyumdjisky, H., 1985. Shrinkage and Atterberg Limits Relation to Other Properties of Principle Soil Types in Israel. Grabowska-Olszewska, B. 1970. Physical Properties of Clay Soils as a Function of Their Specific Surface. Heinzen, R.T. and Arulanandan, K., 1977. Factors Influencing Dispersive Clays and Methods of Identification. Tanaka, H. and Locat J. 1999. A Microstructural Investigation of Osaka Bay Clay. Banin, A., and Amiel, A. 1970. A Correlative Study of The Chemical and Physical Properties of a Group of Natural Soils of Israel. Kolbuszewski, J., Birch, N., and Shojobi, J.O. (1965) Keuper Marl Research. Davidson, D.T. and Sheeler, J.B., 1952. Clay Fraction in Engineering Soils: Influence of Amount on Properties. Işık Yilmaz, Berrin Civelekoglu ;2009; Gypsum: An additive for stabilization of swelling clay soils. Yeliz Yukselen-Aksoy a,, Abidin Kaya ;2010 ; Method dependency of relationships between specific surface area and soil physicochemical properties
LOGO Engineering Geology Department, Tarbiat Modares University,Tehran Iran. Shahram.maghami@modares.ac.ir