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Chemical Treatment

Chemical Treatment. Precipitation and Reduction/Oxidation (Section 9-4). Solubility and Equilibrium. A m B n (s)  mA n+ + nB m- K sp = [A n+ ] m [B m- ] n. Example: Solubility Equation. What concentration of calcium would be in solution at equilibrium with phosphate?.

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Chemical Treatment

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  1. Chemical Treatment Precipitation and Reduction/Oxidation (Section 9-4)

  2. Solubility and Equilibrium AmBn (s)  mAn+ + nBm- Ksp = [An+]m [Bm-]n

  3. Example: Solubility Equation What concentration of calcium would be in solution at equilibrium with phosphate?

  4. Activity – Team If 50.0 mg of carbonate and 50.0 mg of calcium are present in 1 L of water, what will be the final (equilibrium) concentration of calcium? (Remember that the solubility equation uses the final (equilibrium) concentration, i.e., after precipitation has occurred.)

  5. Precipitants and Solubility • Hydroxides • Sulfides • Carbonates • Sulfates • Chlorides

  6. Activity – Team Given a saturated solution of calcium carbonate, how many moles of calcium ion will remain in solution after the addition of 3.16 x 10-4 M Na2CO3 at 25 oC?

  7. Example: Precipitant Dose Simple System Given a solution with an aqueous silver concentration of 100 mg/L, determine the mass of sodium chloride that must be added to reduce the aqueous silver concentration to 1 mg/L. The total solution volume is 55 gals (208.2 L).

  8. Example: Precipitant Dose Complexation Consider a cadmium-containing wastewater. It is to be precipitated with hydroxide to a free cadmium concentration of 1 mg/L (8.896 x 10-6 M). Determine the required equilibrium pH and the total soluble-phase cadmium concentration.

  9. Example continued Soluble Cadmium Species Cd2+ + H2O  CdOH+ + H+ Ksp = 10-10.1 Cd2+ + 2H2O  Cd(OH)2 + 2H+ Ksp = 10-14.35 Cd2+ + 3H2O  Cd(OH)3- + 3H+ Ksp = 10-33.3 Cd2+ + 4H2O  Cd(OH)42- + 4H+ Ksp = 10-47.4 Cd(OH)2(s) + H+ Cd2+ + 2H2O Ksp = 10+13.65

  10. Coagulation/Flocculation/Settling Successful precipitation requires effective separation.

  11. Example: Jar Test

  12. Process

  13. Design of Precipitation Process

  14. Activity – Team A metal plating firm is installing a precipitation system to remove zinc. They plan to use a pH meter to control the feed of hydroxide solution to the mixing tank. What pH should the controller be set at to achieve a zinc effluent concentration of 0.80 mg/L?

  15. Redox Reactions

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