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![• SOM includes living and partially decayed (non-living) materials as well
as assemblages of biomolecules and transformation products of organic
residue decay known as humic substances.
• SOM contains many reactive sites ranging from potentially anionic
hydroxyls (R-OH) and carboxylic groups (R-COOH) to cationic
sulfhydryl (R-SH) and amino groups (R-NH2), as well as aromatic (-Ar-)
and aliphatic ([-CH2-]n) group.
• Variations in the abundance, surface area and chemical composition of
these three sorbents significantly influence the sorption characteristics
of a given soil (Johnston & Tombácz 2002).
3. Soil organic matter (SOM).
Sorbents
Source
https://www.nature.com/scitable/knowled
ge/library/introduction-to-the-sorption-of-
chemical-constituents](https://image.slidesharecdn.com/soilchemistry-200515153742/75/sorption-and-desorption-phenomenon-in-soil-9-2048.jpg)
![Nigeria Faraday F. 0. Orumwense, 1995
Materials and Method
Standard lead solution was prepared by dissolving about
160 mg of lead nitrate in 1000 𝑐𝑚3
deionised- distilled
water (lead concentration is 100 mg 𝑑𝑚−3
).
From the stock of standard lead solution prepared as
described above, the experimental solutions of desired
concentrations were prepared by appropriate dilutions
The pH of each solution was adjusted to the desired value
ranging from pH 3 to 9.5 with solutions of either 0.5 M
NaOH or HCl.
To follow the adsorption of lead by the clay, 1.0 g of kaolinite clay
was introduced into different test tubes containing 50 𝑐𝑚3
of
aqueous solutions of [Pb(NO3)2] of the desired concentrations and
pH.](https://image.slidesharecdn.com/soilchemistry-200515153742/75/sorption-and-desorption-phenomenon-in-soil-53-2048.jpg)
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Similar to sorption and desorption phenomenon in soil
sorption and desorption phenomenon in soil
- 1. PRESENTATION ON- SORPTION ANDDESORPTION PHENOMENON IN SOIL COURSE NO- SOILS-503 COURE TITLE- SOIL CHEMISTRY COURSE INCHARGE- Dr. T. Anajaih (Dept. Of soil science and agricultural chemistry ) PRESENTED BY- PUJA PRIYADARSINI NAIK RAM/19-97
- 2. • Sorption isa physical and chemical process by which one substance becomes attached to another. • Specific cases of sorption are – A. ABSORPTION B. ADSORPTION C. ION EXCHANGE Sorption Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 3. A. Absorption –The incorporation of a substance in one state into another of a different state (E.g. Liquid being absorbed by solid or gases being absorbed by a liquid) B. Adsorption -The physical adherence or bonding of ions and molecules onto the surface of another phase. (E.g. Reagents adsorbed to a solid catalyst surface) C. Ion exchange -An exchange of ions between two electrolytes or between an electrolyte solution and a complex. The reverse of sorption is desorption. Sorption https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 4. SORPTIVE: Ions ormolecules in solution that could potentially participate in a sorption reaction. SORBATE - the substance which is sorbed on the surface SORBENT - the substance on which surface the sorbate is sorbed Source- https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 5. Most relevant chemicalscan be grouped into three sorptive categories: (a) Anionic Sorptives • These are negatively charged • e.g., orthophosphate, PO4 3- (b) Cationic Sorptives • These are positively charged • e.g., the divalent cations Ca2+ and Pb2+ (c) Uncharged Organic Sorptives • it exhibits a range of polarities (non-polar to polar) based on the distribution of electrons across the molecule • e.g., the aromatic ring compound, benzene, C6H6, has uniform electron distribution and hence is non-polar • Sucrose, C12H22O11, has a non-uniform distribution of electrons and is highly polar. Sorptives Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 6. The major solidphase materials (sorbents) in soils are 1. Layer silicate clays, 2. Metal-(oxyhydr)oxides, and 3. Soil organic matter (SOM). Sorbents Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 7. • Layer silicateclays are primarily negatively charged because their stacks of aluminum-oxygen and silicon- oxygen sheets are often chemically substituted by ions of lower valance. • In many soils, they represent the largest source of negative charge. 1. Layer silicate clays Sorbents Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 8. • Metal-(oxyhydr)oxides arevariably charged because their surfaces become hydroxylated when exposed to water (Liu et al. 1998) and assume anionic, neutral, or cationic forms based on the degree of protonation (≡M-O-, ≡MOH or ≡MOH2 +, where ≡M represents a metal bound at the edge of a crystal structure), which varies as a function of solution pH. • Thus, these variably charged minerals adopt a net positive surface charge at low pH and a net negative surface charge at high pH (Qafoku et al. 2004 ). 2. Metal-(oxyhydr)oxides Sorbents Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 9. • SOM includesliving and partially decayed (non-living) materials as well as assemblages of biomolecules and transformation products of organic residue decay known as humic substances. • SOM contains many reactive sites ranging from potentially anionic hydroxyls (R-OH) and carboxylic groups (R-COOH) to cationic sulfhydryl (R-SH) and amino groups (R-NH2), as well as aromatic (-Ar-) and aliphatic ([-CH2-]n) group. • Variations in the abundance, surface area and chemical composition of these three sorbents significantly influence the sorption characteristics of a given soil (Johnston & Tombácz 2002). 3. Soil organic matter (SOM). Sorbents Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 10. Factors Affecting Sorption 1.Sorptive concentration 2. Sorptive and sorbent charge 3. Solution pH 4. Sorbate size Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 11. 1. Sorptive concentration •At low sorptive concentration, Le Chatelier's Principle of chemical equilibrium predicts that increasing (or decreasing) sorptive concentration will result in an increase (or decrease) in sorbate concentration. • For instance, adding fertilizer to a soil will increase the solution potassium (K+) concentration and subsequently increase the amount of K sorbed by the solid phase. • Conversely, as growing plants uptake K+ from the soil solution, this will drive desorption of the sorbate K+ from the soil. In this way, the soil serves as a nutrient reserve for plants and soil organisms. Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 12. • A commonmethod for assessing sorption characteristics of a soil is to measure the relationship between the equilibrium concentration of the sorptive and the sorbate across a range of sorptive concentrations while holding temperature and other parameters constant. • The resulting dataset is termed a sorption isotherm and is often used in a predictive fashion to describe sorption behavior. Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 13. 2. Sorptive andsorbent charge • For ionic sorption, the sign and magnitude of electrical charge on the sorptive and sorbent are important determinates of sorptive fate. • Anions will be attracted to positively charged sorbents and cations will be attracted to negatively charged sorbents. • Ionic sorptives are attracted to oppositely charged sorbents by long- range electrostatic forces. • For example, on negatively charged sorbents, these forces result in a preferential accumulation of cations relative to anions near the sorbent surface. • However, diffusive and dispersive forces act to homogenize this ion distribution such that the ratio of cations to anions decreases exponentially with distance from the sorbent until the bulk solution ion balance is obtained. Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 14. • A precisedescription of the resulting ion distribution is complex and remains incomplete, but is commonly approximated by concepts involving an inner layer of cations immediately adjacent to the sorbent surface, often termed the Stern layer and a diffuse collection of cations and anions, termed the diffuse layer which undergo diffusive exchange with the bulk solution. • Sorbates within the Stern layer that shed one or more of their surrounding water molecules (i.e., waters of hydration) and form direct ionic and/or covalent (electron sharing) bonds with the sorbent are considered inner-sphere adsorption complexes, while those ions retaining their hydration spheres and maintaining proximity to the surface solely through electrostatic interactions are considered outer-sphere adsorption complexes (Sposito 2004). Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 15. • To accommodatea negatively charged sorbent, cations accumulate closer to the surface than anions. • Inner-sphere and outer-sphere complexes occupy the first layer of sorbates, with the remainder of the sorbent charge balanced by preferential cation accumulation in the diffuse layer. Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of-
- 16. 3. Solution pH •Solution pH can have a pronounced effect on sorption by influencing both the magnitude and sign of sorptive and sorbent charge. • As the solution pH increases, sorbent hydroxyl and carboxyl functional groups of metal-(oxyhydr)oxides and SOM deprontonate. • In turn, this increases negative charge density on the sorbent thus facilitating cation adsorption while decreasing anion adsorption. Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of- chemical-constituents
- 17. 4. Sorptive Size •Many isovalent series cations exhibit decreasing sorption affinity with decreasing ionic radius: Cs+ > Rb+ > K+ > Na+ > Li+ Ba2+ > Sr2+ > Ca2+ > Mg2+ Hg2+ > Cd2+ > Zn2+ • Ionic potential: defined as the charge over the radius (Z/r). • More is the (Z/r), more is the hydration energy of an ion, so more is the thickness of hydration shell • The more is the hydration, more is the effective distance between the colloidal charge sites to ions and lesser is the attraction. Source https://www.nature.com/scitable/knowled ge/library/introduction-to-the-sorption-of-
- 18. ADSORPTION IN SOIL •Adsorption is one of the reactions attributed to the surface chemistry of soil colloid. • The adsorption process deals with the adsorption of molecules or ions from the soil solution on the surfaces of the soil solids. • The material adsorbed is called- Adsorbate • The material on which adsorption occurs is called adsorbent. Source PRINCIPLES OF SOIL CHEMISTRY Fourth Edition Kim H. Tan
- 19. • The amountof material adsorbed per unit mass of the adsorbent depends largely upon the nature of the adsorbate and the adsorbent, also on the concentration of the adsorbate and temperature where, x is the amount of adsorbate adsorbed m mass of the adsorbent, C is the equilibrium concentration of the adsorbate T is the temperature 𝒙 𝒎 = 𝒇(𝐧𝐚𝐭𝐮𝐫𝐞 𝐨𝐟 𝐚𝐝𝐬𝐨𝐫𝐛𝐚𝐭𝐞 and adsorbent, C, T) ADSORPTION IN SOIL Source PRINCIPLES OF SOIL CHEMISTRY Fourth Edition Kim H. Tan
- 20. • if theconcentration of adsorbate is more on the colloidal surface as compared to its concentration in bulk phase. • The solute usually decreases surface tension. • If the concentration of the adsorbate is less on the colloidal surface than its concentration in bulk phase. • In this case, surface tension is increased. Bailey and White (1970) believe that perhaps the surface acidity of the adsorbent may play an important role in the rate and degree of negative or positive adsorption. The term surface acidity refers to the H+ ion concentration (acidity) in the interface. Positive Adsorption Negative Adsoption Source PRINCIPLES OF SOIL CHEMISTRY Fourth Edition
- 21. • • Specific Adsorption Non-specific Adsorption • Adsorption reactionrelated to covalent bonding of solutes by the adsorbents. • This type of adsorption is also called chemisorption by Schwertmann and Taylor (1977). • Adsorption reaction related to electrostatic bonding of solutes by clay is known as nonspecific adsorption. • Sposito (1989) refers specific adsorption to complexation of solutes by innersphere surfaces of clay minerals. • Nonspecific adsorption is related to complexation of solutes by outersphere surfaces of clay minerals. Source PRINCIPLES OF SOIL CHEMISTRY Fourth Edition Kim H. Tan
- 22. Adsorption Characteristics 1. SURFACEAREA • Adsorption is dependent not only on the surface charge, but also on the surface area. • The amount of material adsorbed is directly proportional to the specific surface. Clay minerals Surface area Kaolinite 7-30 m2/g Smectite, vermiculite 600-800 m2/g Illite 60-100m2/g Source PRINCIPLES OF SOIL CHEMISTRY Fourth Edition Kim H. Tan
- 23. 2. The surfacecharge density • It is defined as the number of charges per formula weight divided by the specific surface area: σo = e/S • Where, σo is the surface charge density , e is the number of charges per unit formula, and S is the specific surface (Fripiat, 1965). • Due to its small specific surface, the surface charge density of kaolinite may be larger than smectite; hence, kaolinite would be expected to have a larger adsorption capacity than smectite. • However, Bailey and White (1970) believe that the total charge is more important than the surface charge density in adsorption processes. Adsorption Characteristics Source PRINCIPLES OF SOIL CHEMISTRY Fourth Edition Kim H. Tan
- 24. 3. Adsorption reactionsare reversible and equilibrium reactions. • Sometimes an adsorption process results in chemical changes of the adsorbed material. • The changes are of such a nature that desorption is inhibited; hence, the process is neither reversible nor in equilibrium. This type of adsorption is called pseudo- adsorption. Adsorption Characteristics Source PRINCIPLES OF SOIL CHEMISTRY Fourth Edition Kim H. Tan
- 25. 4. Adsorption ischaracterized by a positive heat of adsorption, meaning that energy is released during the adsorption process. • The amount of heat produced because of adsorption of gas by solid surfaces can be expressed by the following equation (Gortner and Gortner, 1949): log h = log a + b log x in which h is the total heat released, x is the amount of gas adsorbed in cm3, and a and b are constants. Adsorption Characteristics Source PRINCIPLES OF SOIL CHEMISTRY Fourth Edition Kim H. Tan
- 26. 5. Temperature • Adsorptiongenerally decreases as temperature increases; in other words, adsorption is less at elevated temperatures. • This is caused by an increased kinetic energy of the molecules at higher temperature, which interferes with the concentrating process. Adsorption Characteristics Source PRINCIPLES OF SOIL CHEMISTRY Fourth Edition Kim H. Tan
- 27. FORCES OF ADSORPTION Forcesresponsible for adsorption reactions include (1)physical forces, (2)chemical forces, (3) hydrogen bonding (4)hydrophobic bonding, (5)electrostatic bonding, (6) coordination reactions, and (7) ligand exchange. Source PRINCIPLES OF SOIL CHEMISTRY Fourth Edition Kim H. Tan
- 28. Adsorption Isotherms • Thecapacity for a soil or mineral to adsorb a solute from solution can be determined by an experiment called a batch test. • In a batch test, a known mass of solid (S m) is mixed and allowed to equilibrate with a known volume of solution (V ) containing a known initial concentration of a solute (C i). • The solid and solution are then separated and the concentration (C ) of the solute remaining is measured. • The difference C i - C is the concentration of solute adsorbed.
- 29. • The massof solute adsorbed per mass of dry solid is given by where S m is the mass of the solid. • The test is repeated at constant temperature but varying values of C i. • A relationship between C and S can be graphed • . Such a graph is known as an isotherm and is usually non-linear. Adsorption Isotherms
- 31. • Adsorption isothermis a plot between the amount adsorbed per unit mass of the adsorbent and the equilibrium concentration of the adsorptive , at a constant temperature. • Various equations have been developed to predict precisely the shapes of the experimental adsorption isotherms between different adsorbates and adsorbents. • The most commonly used are due to Langmuir(1918), Freundlich(1926), Brunauer et al.,(1938) Adsorption Isotherms Source-ISSS
- 32. (1) Langmuir AdsorptionTheory • The basic theory of adsorption of gases on soilds is due to Langmuir. ASSUMPTION – • The surface of solid is made up of adsorption sites, each of which can adsorb one gas molecules. • All the adsortion sites are identical in their affinity for that gas molecule. • The presence of a gas molecules on one site does not affect the properties of the neighbouring sites. • The rate of adsorption is proportional to the number of adsorption sites and the pressure of the gas. The rate of desorption is proportional to the number of occupied sites. Source-ISSS
- 33. LINEAR EQUATION- 𝑪 𝑿 = 𝑪 𝑿𝒎 + 𝟏 𝑿𝒎𝑲 Where, C=concentration of the adsorbate at equilibrium. X =Amount adsorbed per unit mass of adsorbent at any instant Xm= maximum amount adsorbed per unit mass of the adsorbent as a monolayer K = Equilibrium constant (1) Langmuir Adsorption Theory Source-ISSS
- 34. USES • The useof langmuir equation provides a measure of the adsorption maximum(Xm) of soils. • It describes the nutrient (phosphate) retention process in soil, especially at higher adsorbate concentration. • From the value of Xm, the surface area (A)of soil or clay can be esimated , • A= 𝑋𝑚 𝑁∏𝑟² 𝑀 (1) Langmuir Adsorption Theory Source-ISSS
- 35. (1) Langmuir AdsorptionTheory LIMITATION • Normally, the langmuir equation is not used to calculate the surface area of solids because it does not define total adsorption process but covers only a certain fraction of adsorption site. • This isotherm refers to gaseous adsorption on non-ionic solid,while adsorption in soil is essentially an ionic process. • The soils are mixture of inorganic and organic substances with each substances reacting towards competing cations differently. Means, soil exchangers are essentially polyfunctional ion exchangers. • It does not take consideration the competition between the cationic species NOTES-Langmuir isotherm is for monolayer adsorption, but more than a monolayer of adsorbed molecules can formed at higher pressure. Source-ISSS
- 36. (2) The Freundlichisotherm • This is one of the most widely adsoption equations to describe the experimental data on adsorption of ionic or molecular species in soil. • It implies that the bonding energy of the adsorbate on a given adsorbent decreases with the fractional coverage of surface area of the adsorbent. • It does not predict any adsorption maximum. Source-ISSS
- 37. • Expressed byequation – Where, S=amount adsorbed per unit mass of adsorbent C= equilibrium concentration of the adsorbate K =partition coefficient and n 1 The linear form of this equation- n KCS (2) The Freundlich isotherm Log x = log K + n log C Source-ISSS
- 38. C (mg L -1 ) 010 20 30 40 S(mgg -1 ) 0 10 20 30 40 50 60 S = 1.5C 1.0 S = 5.0C 0.5 FREUNDLICH ISOTHERMS • When n < 1, the plot is concave with respect to the X- axis. When n = 1, the plot is linear. In this case, K is called the distribution coefficient (Kd ). (2) The Freundlich isotherm • The partition coefficient K is a measure of the degree to which a adsorbate partitions between the surface and the solution. The higher the value of K, the greater affinity the adsorbate has for the surface Source-ISSS
- 39. (3)Brunauer, Emmett, Teller(BET) Adsorption isotherm • This theory extends Langmuir derivations to obtain an equation for multilayer adsorption. ASSUMPTION – • Heat of adsorption in the second, third,…nth layers are the same as the heat of adsorption in the monolayer, i.e., heat of liquification or condensation of the gas • If the adsorption take place on a free surface then at p˚(saturation pressure of the gas), an infinity number of layers can be built up on the adsorbent. Source-ISSS
- 40. (3)Brunauer, Emmett, Teller(BET) Adsorption isotherm • The BET equation used to define multiple layer adsorption at any equilibrium pressure, p, LINEAR EQUATION – • Where, v=volume of gas adsorbed per unit mass of adsorbent Vm=volume of gas required for monolayer on the entire adsorbent surface of unit mass C’ =constant at a given temp 𝑝 𝑣(𝑝˚−𝑝) = 𝐶′−1 𝑝 𝑉𝑚𝐶′ 𝑝˚ + 1 𝑉𝑚𝐶′ Source-ISSS
- 41. (3)Brunauer, Emmett, Teller(BET) Adsorption isotherm • ADVANTAGES- I. It describes the multilayer adsorption. II. It yields the volume of gas required for a monolayer. III. It can be used to calculate the surface area of the soil. Source-ISSS
- 42. (3)Brunauer, Emmett, Teller(BET) Adsorption isotherm • Surface area can be calculated by multiplying Vm with the cross-sectional area of the adsorbate molecules. • To determined the surface area of soils and minerals, adsorbate molecules such as nitrogen, ethane, water, ammonia or other gases may be used. • Nitrogen is a weakly adsorbed molecules, may not penetrate in to all the interlayer surfaces, but use of strongly adsorbed molecules, like ammonia, which penetrate in to the internal surface also, leads to the measured surface area close to the total surface area. Source-ISSS
- 43. IONS EXCHAGE 1. Cationexchange 2. Anion exchange Cation exchange capacity- The capacity of the solids(clay) to adsorb and exchange cations is called as CEC. Or the total of the exchangeable cations that can be adsorbed by a soil colloidal surface Anion exchange capacity- The total amount of anions held exchangeably by a unit mass of soil, is termed as AEC Source-ISSS
- 44. THE SPECIFIC ADSORPTIONOF COPPER BY SOILS • Very small amounts of solution-plus-exchangeable copper are present in soil and it has been suggested that these forms of copper are in equilibrium with specifically adsorbed forms which constitute the bulk of the ‘available’ copper reserves (McLaren and Crawford, 1973). • In their paper, they examine the relative importance of different types of adsorbing surfaces in soils in relation to the adsorption of copper. R. G. McLaren and D. V. Crawford,1973
- 45. Materials and Method •Twenty-four different topsoil samples (air dried) were used in these studies. • They were selected to include ranges of pH, organic matter, free oxides, clay, and total copper contents since these properties were expected to exert the greatest influence on the behaviour of copper in soils. • As well as different soil constituents like A. Organic matter B. Clay minerals C. Soil oxide material i. Concretionary material (ferro-manganese concretions) ii. Iron oxide iii. Manganese oxide R. G. McLaren and D. V. Crawford,1973
- 46. Materials and Method 1gram samples of soil were equilibrated with 200 ml solution(known amount of copper and 0.05M CaCl2) at 30˚C in 250 ml centrifuge bottle After 24 hours, the samples were then centrifuged The supernatant liquid analyzed for copper by atomic absorption spectrophotometry Copper adsorbed was calculated from the initial and final copper concentrations in the solution R. G. McLaren and D. V. Crawford,1973
- 47. Results and Discussion experimentsshowed that pH had a considerable effect on the amount of copper adsorbed by soils and individual soil constituents Adsorption maxima for soil constituents followed the order manganese oxides > organic matter > iron oxides > clay minerals, R. G. McLaren and D. V. Crawford,1973
- 48. Results and Discussion Inorder to compare satisfactorily different materials, adsorption was studied in single pH A pH of 5.5 was selected because most types of soil surface showed considerable adsorption of copper at this pH from a solution of concentration 5 μg Cu 𝒎𝒍−𝟏 R. G. McLaren and D. V. Crawford,1973
- 49. Results and Discussion Where x=the amount of copper adsorbed by unit weight of soil c = equilibrium copper concentration in solution a = the Langmuir adsorption maximum b = the Langmuir ‘bonding term’-related to bonding energy Replotting the data in accordance with the Langmuir adsorption equation produced linear graphs, indicating satisfactory agreement with this theoretically derived equation 𝒄 𝒙 = 𝟏 𝒂𝒃 + 𝒄 𝒂 R. G. McLaren and D. V. Crawford,1973
- 50. Results and Discussion Atlow solution concentrations of copper, specific adsorption appears to exceed non- specific adsorption R. G. McLaren and D. V. Crawford,1973
- 51. Conclusion • Soils werefound to have specific adsorption maxima at pH 5.5 of between 340 and 5780 μg 𝒈−𝟏 , and a multiple regression analysis revealed that organic matter and free manganese oxides were the dominant constituents contributing towards specific adsorption. • Adsorption maxima for soil constituents followed the order manganese oxides > organic matter > iron oxides > clay minerals. • Clay minerals and free iron oxides show only weak specific adsorption of copper. • The link between the amount of solution-plus-exchangeable copper and the pool of specifically adsorbed copper ,commonly associated with soil organic fraction, has been well established in certain condition. R. G. McLaren and D. V. Crawford,1973
- 52. Removal of Leadfrom Water by Adsorption on a Kaolinite Clay • The possible use of kaolinite clay from Nigeria as an adsorbent for the removal of lead from water was investigated. • Studies were carried out as a function of contact times, concentrations, temperatures and pH. • The kinetics of adsorption as well as adsorption isotherms at different temperatures were equally studied. Nigeria Faraday F. 0. Orumwense, 1995
- 53. Nigeria Faraday F.0. Orumwense, 1995 Materials and Method Standard lead solution was prepared by dissolving about 160 mg of lead nitrate in 1000 𝑐𝑚3 deionised- distilled water (lead concentration is 100 mg 𝑑𝑚−3 ). From the stock of standard lead solution prepared as described above, the experimental solutions of desired concentrations were prepared by appropriate dilutions The pH of each solution was adjusted to the desired value ranging from pH 3 to 9.5 with solutions of either 0.5 M NaOH or HCl. To follow the adsorption of lead by the clay, 1.0 g of kaolinite clay was introduced into different test tubes containing 50 𝑐𝑚3 of aqueous solutions of [Pb(NO3)2] of the desired concentrations and pH.
- 54. Nigeria Faraday F.0. Orumwense, 1995 The stoppered test tubes were agitated in a thermostat shaker bath at 25°C for different time intervals. The speed of agitation was kept constant for each run throughout the experiment to ensure equal mixing. After different periods of time, the adsorbates were separated by filtration using filter paper and the supernatant liquid was analysed using the atomic absorption spectrophotometer for residual lead content. Materials and Method
- 55. Nigeria Faraday F.0. Orumwense, 1995 Results and Discussion • Figure shows the variation of the amount of lead adsorbed as a function of time. • It may be observed from the figure that the amount of lead adsorbed increases with time and the concentration of lead and then attains a constant value after 120 mins
- 56. Results and Discussion Langmuirequation has been used to determine the equilibrium distribution of lead at the solid- liquid interface and its given by: Where, C= equilibrium concentration of lead in solution, q=the amount of lead adsorbed at equilibrium (mg g-') Qo and b are the Langmuir constants showing the adsorption capacity of the adsorbent and energy of the adsorption process, respectively. It is clear from Table and Fig that the adsorption capacity of the clay for the removal of lead increases with an increase in temperature of the solution, that is, the equilibrium amount of lead adsorbed decreases with an increase in temperature 𝐶𝑒 𝑞𝑒 = 1 𝑄°𝑏 + 𝐶𝑒 𝑄° Nigeria Faraday F. 0. Orumwense, 1995
- 57. Nigeria Faraday F.0. Orumwense, 1995 Results and Discussion • The pH of the aqueous solution is an important variable which controls the adsorption of the metal at the clay-water interfaces. • Hence, the adsorption of lead on the clay was examined from solution at different pH values covering a range of 3 to 9.5. • The results are presented in figure, which reveals that the adsorption of lead decreases from 9.30 mg g-' (93%) to 8.20 mg g-' (82%) with an increase in the pH of the solution
- 58. Nigeria Faraday F.0. Orumwense, 1995 On the basis of the above results and discussion, the following conclusions can be drawn. 1. The adsorption process does exhibit a Langmuir type behaviour which is affected by temperature. 2. The presence of a negative charge on the silica surface sites of the adsorbent is responsible for the adsorption of lead. 3. Lead removal is favoured by low concentration, high temperature and acidic pH. 4. The high lead adsorption capacity of the clay at high temperature is suggestive of an endothermic reaction. The +∆H value at high temperature (40°C) further confirms that the adsorption process is endothermic, which is an indication of the existence of a strong interaction between adsorbate and adsorbent. 5. The results obtained show that the kaolinitic clay is a good adsorbing medium for lead ions. Conclusion
Editor's Notes
- #4 desorption: The release of ions or molecules from solids into solution.
- #23 The 1:1 layer lattice minerals are known to exhibit low surface areas. The surface area of kaolinite is estimated to be 7 to 30 m2/g. This low surface area, together with its low cation exchange capacity, are the reasons for a low adsorption capacity of kaolinite minerals. On the other hand, smectite and vermiculite, with surface areas ranging from 600 to 800 m2/g and high cation exchange capacities, are expected to have high adsorption capacities. The adsorption capacity of illite (surface area = 60 to 100 m2/g) is intermediate between kaolinite and smectite.
- #28 1.The most important physical force is the van der Waals force. This force is a result of short-range dipole–dipole interactions. Its role is only of importance at close distances, because this type of force decreases rapidly with distance. Because van der Waals forces decay rapidly with distance from the colloidal surface, their effect on adsorption is greatest for ions in close contact with the colloid surface. The less intimate the contact between the solute and the colloid surface, the smaller is the rate of adsorption. Hence, the small and spherically shaped ions will be in closer contact with the surface than the larger ions. 2.3. the bond by which a hydrogen atom acts as the connecting linkage is called a hydrogen bond. It is believed that hydrogen bonding is related to protonation. Whereas protonation involves a full charge transfer from the electron donor (base) to the electron acceptor (acid), hydrogen bonding is a partial charge transfer (Hadzi et al., 1968) 4.This type of bonding is associated with adsorption of nonpolar compounds 5. Another type of force in adsorption is electrostatic attraction of substances, which is the result of the electrical charge on the colloid surface. This is the reason for (1) adsorption of water, (2) adsorption of cations, which leads to cation exchange reactions, and (3) adsorption of organic compounds. 6. The reaction involves coordinate covalent bonding. The latter occurs when the ligand donates electron pairs to a metal ion, usually a transition metal. 7. This entails the replacement of a ligand by an adsorbate molecule. The adsorbate must have a stronger chelation capacity than the ligand.
- #36 The amount of cations o the adsorbed phase is governed only by the cocnetration of that cation and not the function of the competing cations.
- #39 . The graph above shows how K and n affect the shape of the Freundlich isotherm. The higher K, the steeper the initial slope of the isotherm. The smaller the value of n, the greater the deviation from linearity (the more concave the isotherm becomes with respect to the C axis. The case where n = 1 does not fit the adsorption of most inorganic solutes. However, a Freundlich isotherm with n = 1 is often used successfully to describe the sorption of hydrophobic organic compounds (e.g., carbon tetrachloride).
- #47 1 gram samples of soil were equilibrated with 200 ml solution(known amount of copper and 0.05M CaCl2) at 30˚C in 250 ml centrifuge bottle After 24 hours, the samples were then centrifuged the supernatant liquid analysed for copper by atomic absorption s ectrophotometry Copper adsorbed was calculated from the initial and final copper concentrations in the solution
- #54 Standard lead solution was prepared by dissolving about 160 mg of lead nitrate in 1000 cm3 deionised- distilled water (lead concentration is 100 mg dmP3). Lead nitrate [Pb(NO,),] was selected because it is one of the few lead salts freely soluble in water, but contrary to the behaviour of most nitrates, it is incompletely dis- sociated in solution, and therefore it is possible to find the species PbNO: in the s~lution.'~*'~ From the stock of standard lead solution prepared as described above, the experimental solutions of desired concentrations were prepared by appropriate dilutions. The pH of each solution was adjusted to the desired value ranging from pH 3 to 9.5 with solutions of either 0-5 M NaOH or HCl. All chemicals were of analytical grade. To follow the adsorption of lead by the clay, 1.0 g of Giru clay was introduced into different test tubes con- taining 50 cm3 of aqueous solutions of [Pb(NO,),] of the desired concentrations and pH. The stoppered test tubes were agitated in a thermostat shaker bath at 25°C for different time intervals. The speed of agitation was kept constant for each run throughout the experiment to ensure equal mixing. After different periods of time, the adsorbates were separated by filtration using filter paper and the supernatant liquid was analysed using the atomic absorption spectrophotometer for residual lead content.
- #55 The stoppered test tubes were agitated in a thermostat shaker bath at 25°C for different time intervals. The speed of agitation was kept constant for each run throughout the experiment to ensure equal mixing. After different periods of time, the adsorbates were separated by filtration using filter paper and the supernatant liquid was analysed using the atomic absorption spectrophotometer for residual lead content.
- #57 𝐶𝑒 𝑞𝑒 = 1 𝑄°𝑏 + 𝐶𝑒 𝑄° Figure 5, which is a plot of CJq, us. C, produces straight lines at the three different temperatures investi- gated which is an indication of the applicability of the Langmuir isotherm for the system under consideration. The Qo and b values presented in Table 2 were calcu- lated from the slopes and intercepts of the plots.
- #60 Thank you