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ION EXCHANGE

ION EXCHANGE. Presentation Outline. Ion Exchange Reactions Unit Operations of Ion Exchange Sodium, Hydrogen Cycle and Regeneration Production of Pure Water Active or Exchange Zone Design of Ion Exchangers Quantity of Regenerant Wastewater Production. Ion Exchange Reactions.

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ION EXCHANGE

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  1. ION EXCHANGE

  2. Presentation Outline • Ion Exchange Reactions • Unit Operations of Ion Exchange • Sodium, Hydrogen Cycle and Regeneration • Production of Pure Water • Active or Exchange Zone • Design of Ion Exchangers • Quantity of Regenerant • Wastewater Production

  3. Ion Exchange Reactions • Ion Exchange is the displacement of ion by another • Ion Exchange is a reversible chemical reactions wherein an ion from solution is exchanged for a similarly charged ion attached to an immobile solid particles • The displaced ion moves into solution and the displacing ion becomes a part of the insoluble materials (Resin)

  4. Ion Exchange • Two types of ion exchange materials are used • The cation exchange material • The anion exchange material

  5. Ion Exchange

  6. Ion Exchange

  7. Ion Exchange • The insoluble part of the exchange materials is called the host • The cation exchange materials may be represented by • r : the number of active sites in the insoluble material • r n/m: the number of charged exchangeable particles attached to the host materials • -n: is the charge of the host • +m: is the charge of the exchangeable cation

  8. Ion Exchange Reactions • cation exchange reaction as well as the anion exchange reaction are as follows • Ion exchange reaction are governed by Equilibrium. For this reason, effluents from ion exchange processes never yield pure water

  9. Ion Exchange Reactions Displacement Series for Ion Exchange • Displacement series for ion exchange materials is shown in left side table • when an ion species high in table is in solution, it can displace ion species in the insoluble material below it in the table. • to remove any cation in solution, the displaceable cation must be the proton, and to remove any anion, the displaceable anion must be the hudroxyl ion.

  10. ION Exchange Reactions • Examples of exchange materials • Zeolites (Natural Material) • Synthetic resins • Synthetic resins are insoluble polymers • These polymers are either acidic or basic group, and they are called functional group

  11. Ion Exchange Reactions • These groups are capable of performing reversible exchange reactions with ions in solution • The total number of these groups determine the exchange capacity of the exchange material • The type of functional group determines ion selectivity • The exchanger may be regenerated by the reverse reactions (upon exhaustion)

  12. Unit Operation of Ion Exchange

  13. Unit Operation of Ion Exchange • In both units, the influent is introduced at the top of the vessel • the bed of ion exchanger materials would be inside the vessels • As the to be treated passes through, exchange of ions takes place • This exchange of ions is the chemical reaction of the unit process of ion exchange

  14. Sodium, Hydrogen cycle, And Regeneration • Sodium and Hydrogen are the logical choices for the exchangeable ions. • The cation exchange resin using sodium to remove the Ca+2 may be represented by the following reactions

  15. Sodium, Hydrogen Cycle, And Regeneration • As soon as the resin is exhausted, it may be regenerated • The resin is regenerated by using a concentration of NaCl of a bout 5 to 10%, thus, driving the reaction to the left • Operations where regeneration is done using NaCl, the cycle is called the Sodium Cycle • Operations where regeneration is done using acids (H2SO4), the cycle is called the Hydrogen Cycle

  16. Sodium, Hydrogen Cycle, And Regeneration • The following table shows approximate exchange capacities and regeneration requirements for ion exchangers

  17. Sodium, Hydrogen Cycle, And Regeneration

  18. Sodium, Hydrogen Cycle, And Regeneration • In order to determine the exchange capacities and regeneration requirements we have to do the following: • Perform an actual experiment • Obtain data form the manufacturer

  19. Sodium, Hydrogen Cycle, And Regeneration Table below shows some additional properties of exchangers

  20. Sodium, Hydrogen Cycle, And Regeneration • The strongly acidic (cation) exchangers readily remove cations from solutions • The weakly acidic exchangers have limited ability to remove certain cations • The strongly basic (anion) exchangers can readily remove all the anions • The weakly basic one remove mainly the anions of strong acid such as SO4-2 and Cl

  21. Production of “PURE WATER’’ • Theoretically, It would seem possible to produce pure water by combining the cation exchanger and the anion exchanger • The following equation for the hydrogen cycle is

  22. Production of “PURE WATER’’ • Letting the molar concentration of be • The corresponding concentration in geq / L is

  23. Productionof “PURE WATER’’ • Therefore, the total concentration in gram equivalents per liter of removable cations in solutions is the sum of all the cations. Thus, • As, [CatT]eq of cations is removed form solution, a corresponding number of equivalent concentrations of anions pair with the H+ ions displaced from the cation bed

  24. Production of “PURE WATER’’ • The total anions and the hydrogen ions displaced is expressed as follows • Practically, we may say that “ pure water” is produced and expressed as follows The units of ti are equivalents per mole

  25. Production of “PURE WATER’’ • Example: A wastewater contains the following ions: Calculate the total equivalents of cations and anions, assuming the volume of the wastewater is 450 m3.

  26. Production of “PURE WATER’’ • Solution: a Equiv. mass b120/58 = 2.069

  27. Production of “PURE WATER’’ • Solution (Cont’d) • Total equivalents of cations = 2.395(450) = 1077.75 Ans • Total equivalents of cations = 2.069(450) = 931.05 Ans

  28. Active or Exchange Zone • Active zone is a segment of exchanger bed engaged in exchanging ions

  29. Active or Exchange Zone Where: = length of active zone = total volume of water or wastewater treated at complete exhaustion of bed = volume treated at breakthrough = influent concentration to = total volume treated at time

  30. Active or Exchange Zone (Cont’d) = total volume treated at time = concentration of solute at effluent of at time = concentration of solute at effluent of at time = surficial area of exchanger bed

  31. Active or Exchange Zone • Active zone at various times during adsorption and the breakthrough curve

  32. Active or Exchange Zone • Example 2: A breakthrough experiment is conducted for a wastewater producing the results below. Determine the length of the active zone. The diameter of the column used is 2.5 cm. and the packed density of the bed is 750 kg/m3. is equal to 2.2 meq/L. And • The experiments results are tabulated on the next slide

  33. Active or Exchange Zone

  34. Active or Exchange Zone Solution:

  35. Active or Exchange Zone

  36. Active or Exchange Zone Therefore, = 1.2 mm

  37. Design of Ion Exchangers • Designs of ion exchangers should include the following: • Quantity of exchange materials • Quantity of regenerant

  38. Quantity of Exchange Materials • The amount of exchange bed materials required can be determined by the calculating the amount of displacing ions in solution to be removed • The equivalents of ion displaced from the bed is equal to the equivalents of displacing ion in solution • The mass of bed materials CatTBedMass in kilograms is

  39. Quantity of Exchange Materials Q is the m3/d of flow and tint is the interval of regeneration in hours

  40. Quantity of Exchange Materials • By analogy, the mass bed materials for the anion exchanger in Kiograms is:

  41. Quantity of Exchange Materials • The volume in m3 for CatBedVol

  42. Quantity of Exchange Materials • the volume in m3 For AnionTBedVol • The percentage of swell of the exchanger bed is a very important property • It determines the final size of the tank into which the material is to be put • This value can be obtained through • Experiments • from the manufacturer

  43. Quantity of Exchange Materials • Example: Using a bed exchanger, 75 m3 of water per day is to be treated for hardness removal between regenerations having intervals of 8 h. the raw water contains 400 mg/L of hardness as CaCO3. The exchanger is a resin of exchange capacity of 1412.8 geq/m3. Assume that the packed density of the resin is 720 kg/m3. Calculate the mass of exchanger material to be used and the resulting volume when the exchanger is put into operation.

  44. Quantity of Exchange Materials • Solution: Assume cation exchanger: Also, assume that all of the cations are removed

  45. Quantity of Exchange Materials Therefore, Assume swell= 0.8

  46. Quantity of Regenerant • The Kilogram equivalents of regenerant, CatRegenerant, used to regenerate cation exchangers is • The Kilograme equivalents of regenerant, Anion Regenerant, used to regenerate anion exchange is

  47. Quantity of Regenerant • Example: Using a bed exchanger, 75 m3 of water per day is to be treated for hardness removal between regeneration having intervals of 8 hours. The raw water contains 80 mg/L of Ca+2 and 15 mg/L of Mg2+. The exchanger is a resin of exchange capacity of 1412.8 geq/m3. Assume that the packed density of the resin is 720 kg/m3. Calculate the kilograms of sodium chloride regenerant required assuming R = 2 and that all of the cations were removed

  48. Quantity of Regenerant • Solution: Therefore,

  49. Wastewater Production • In the operation of ion exchangers, wastewater are produced. These come form: • Solvent water (used to dissolve the regenerant) • Backwash and rinse requirements

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