Ion exchange phenomena in clay minerals.pptx

Ion exchange

1. Ion Exchange

2. Ion exchange Clay minerals have the property of anions and cations and retain them in an exchangeable state. These ions are exchangeable for anions and cations in a solution. Retension and of K in fertilizrs depend on cation exchange between K salt and clay mineral. Tilth of soil is determined by the character of exchangeable ion.

3. Na replaced by Ca improve soil structure. An ideal soil – consist of 65 % Ca, 10% Mg, 5% K and 20 % H. Weathering process liberate alkali / alkaline earth – retain in secondary minerals based exchange reactions. Physical properties depend on exchangeable ions of clay. Plastic property vary with exchangeable Ca 2+ / Na + .

4. Cation exchange Thompson – first person to study CE. Base exchange – used to describe the reaction since H + ion believed to be involved in the exchange reaction. In 1845, Thompson – When soils are mixed with NH 3 , leached with water, ammonia fixed in soil.

5. CEC of clay minerals (C mol (P + )Kg -1 soil) Kaolinite 3 – 15 Halloysite 2 H2O 5 – 10 Halloysite 4H2O 40 – 50 Smectite 80 – 150 Illite 10 – 40 Vermiculite 100 – 150 Allophane 25 – 50 Chlorite 10 - 40 Sepiolite 3 - 15 Attapulgite Polygosilicate

6. All inorganic minerals have small CEC due to PH dependent change. Zeolite – CEC – 100 – 300 C mol (P + )Kg -1 soil Organic – CEC -150 – 500 C mol (P + )Kg -1 soil Causes of CEC Broken bonds – Ex. Kaolinite , Halloysite Isomorphic substitution – Ex. Smectite , Vermiculite Hydrogen of exposed OH – Ex. Kaolinite , Halloysite .

7. Replaceability of exchangeable cations Replacing power of ions Na + < K + < Ca 2+ < Mg 2+ < NH 4 + Replacement of Ca 2+ / Mg 2+ by NH 4 + in soil increased when the concentration of NH 4 + is high. Exchange reaction vary with complementary ions. Higher the vacancy greater is replacing power.

8. H is exception since it behaves like divalent of trivalent ion. Ions of same vacancy replacing power increase as the size of ion increase. Smaller ions held lightly than larger ions. Least hydrated ion have great replacing power. Li – Very small ion After hydration, replacing power of Li is reduced.

9. Fixation of cations K is common ion fixed and important phenomenon in soil fertility. Illite fix K between basal surface of the minerals - Fixation is high when saturated with Ca 2+ / Na + than H + / NH 4 + . Smectite / vermiculite fix K in basal plaenes between the unit layers. Loss K fixation as compared to Illite .

10. Anion exchange Replacement of OH ions (P adsorption by kaolinite ). Replacement of OH ions by fluorine in kaolinite . Anions viz., Po 4 , arsenate, borate have same size & geometry as Si tetrahedron – adsorbed by fitting on the edges of STH.

11. Anions viz., So 4 - , Cl - , No 3 - since their geometry does not fit with that of STH sheets cannot be adsorbed. Kaolinite CE is due to broken bonds CE = AE Smectite & Vermiculite CE – Mostly due to Isomorphous substitution. AE Only a small fraction of CEC. Illite , Chlorite, sepiolite , polygoskite minerals AEC < CEC.

12. Clay – mineral – Organic reactions Ex. HA – Protein – Clay Reduction in base exchange capacity by complexing clay with protein. Organic cations contain basic amino groups. Gelatin – clay complex – prepared by mixing alkaline suspension of gelatin and clay, acidifying to P H 2.6 with acetic acid.

13. Organic ions held by van der waals forces and columbic forces. Adsorbed proteins are resistant to microbial decomposition compared to free proteins. Protein – montmorillonite complezes – prepared by ion exchange – proteins adsorbed as cations. Adsorption of albumin & hemoglobin by ion exchange in montmorillonite

14. Enzyme hydrolysis is reduced by protein adsorption in clay. Active group – not accessible to enzyme Stability of amine – montmorillonite complex – depends on enzyme and amine used in the complex. Break down of organic complex depend on type of clay mineral. Carbohydrate – clay complex Resistant to microbial activity – more in montmorillonite & Attapulgite loss in Kaolinite & Illite .

15. Adsorption of Protein, enzymes & antibiotics. Protein – Montmorillonite – Mono / Poly layer complex. Mono layer complex – Low microbial decomposition. Poly layer complex – Extensive decomposition.

16. Quantitative determination of clay minerals an important index in geological survey, agricultural production, and environmental assessment Reliable methods X-ray powder diffractometry Differential thermal analysis (DTA) Infrared analysis (IR)

17. X-ray diffraction analysis Based on the relation between diffracted intensity and concentration of clay mineral. The contents of clay minerals are calculated by comparison with intensities yielded by standard samples with known components . Consequently, this method is semi-quantitative

18. X-ray diffraction analysis The analytical uncertainties can be influenced by many factors, such as the choice of standard sample sample preparation technique interference due to other minerals present in the sample.

19. X-ray diffraction analysis This method determine the relative amounts of clay minerals in soil samples As it is more difficult to quantify non-clay minerals in soil high precision result is not possible.

20. Other methods Amount of clay minerals quantified based on their molecular formulae Mass balance equations

21. CEC % vermiculite = CEC(Ca/Mg) – CEC(K/NH 4 ) 154 X 100 % Montmorillionite = CEC (K/NH 4 ) – (5+105 amor ) 105 X 100

22. Determination of CM Mica determination by HF-HClO 4 dissolution analysis Amorphous Material by NaOH Selective Dissolution Analysis The kaolinite plus halloysite contents are based on the SiO2 and Al203

23. Determination of CM When the Si02/Al2O3 a molar ratio is lower than 2, indicates the existence of free alumina or dissolved interlayer aluminum kaolinite plus halloysite content is based on the dissolved silica by the equation % Kaolinite + halloysite = % SiO2 / 46.5 x 100

24. Determination of CM amounts of SiO2 and Al2O 3 which dissolved at ll0 ο C are subtracted from those dissolved at 525 ο C to obtain the Si02 and the AI2O3

25. Determination of CM When the SiO2/AI2O3 molar ratio is higher than 3 indicates that some 2:1 layer silicates such as nontronitic montmorillonite dissolved kaolinite plus halloysite content is calculated on the basis of the dissolved alumina by the equation

26. Determination of CM % Kaolinite + halloysite = % Al2O3 / 39.5 x 100

27. Determination of CM Chlorite by Thermal Gravimetric Analysis % Chlorite = A-B /0.14 + (% FeO ) x 0.79 A is the ignition loss in per cent (300 to 950 ο C )

28. Determination of CM % FeO is the percentage of ferrous oxide present, determined by HF-H2SO 4 dissolution of the sample & titration with standard 0.1 N K2Cr207 solution

29. Determination of CM B is per cent water allocated to the minerals present other than chlorite, based on their content of hydroxyl water above 300 ο C in K saturated samples

30. Methods of identification (principles) X-ray diffraction (XRD) technique Minerals made up of regularly repeating unit cells Each unit cell have dimensions of a, b, and c along the three coordinate directions x, y, and z. In clay minerals, c spacing , dimension of the unit cell across the thickness of the layer c spacing varies from mineral to mineral 

31. X-ray diffraction (XRD) technique The other two dimensions ( a&b ) remain more or less constant among different clay minerals.

32. Differential Thermal Analysis DTA consists of heating a test sample and a thermally inert substance simultaneously at a constant rate of about 10°C/min Continuously measuring difference in temperature between the sample and the inert material Alumina and silicon carbide are commonly used as the thermally inert reference materials.

33. Differential Thermal Analysis The results of DTA are presented in the form of a thermogram Plotting of the temperature (T) on the x-axis and the difference in temperature between the sample and the inert material (ΔT) on the y-axis.

34. Transmission Electron Microscopy The transmission electron microscope was the first type of electron microscope developed Similar to light transmission microscope except that a focused beam of electrons is used instead of light to observe the specimen

35. Scanning electron microscope  One of the most versatile instruments available for the examination and analysis of: microstructure morphology chemical composition characterization of soils / other materials.

36. Scanning electron microscope  Zworykin et al. first described a true SEM in 1942 with a resolving power of 50 nm. Modern SEMs can have resolving power better than 1 nm

37. Infrared Spectroscopy It involves the absorption measurement of different IR frequencies by a sample positioned in the path of an IR beam.

38. Infrared Spectroscopy IR spectroscopy deals with the infrared region of the electromagnetic spectrum with a longer wave­length and lower frequency than visible light.

39. Infrared Spectroscopy Infrared radiation : electromagnetic spectrum having wave numbers from 13000 to 10 cm –1 or wavelengths from 0.78 to 1000 µm. It is bound by the red end of the visible region at high frequencies and the microwave region at low frequencies.

40. Infrared Spectroscopy The IR region is commonly divided into three smaller areas: near IR, mid IR, and far IR. For IR spectroscopy, the most frequently used is the mid IR region having wave number between 4000 and 400 cm –1  (or wave length between 2.5 and 25 µm).

41. Infrared Spectroscopy IR absorption positions are presented as either wave numbers or wave lengths. Wave number defines the number of waves per unit length usually expressed as number per cm (cm –1 ).