a. Nature: In water there exist many different suspended substances. These substances can be treated differently depending on their size:

  • d > 10-4 mm: use sedimentation and filtration method.
    • d < 10-4 mm: must combine mechanical methods with chemical methods. That is, adding substances that create adhesion and pulling suspended particles to settle => is called flocculation method in water treatment. To carry out this process, appropriate reactants are added to water: Al2(SO4)3; FeSO4; or FeCl3.

b. Consider the coagulant as aluminum alum:

  • Alum: put in water, they dissociate into Al 3+ ——-> Al(OH)3

Al 3+ + 3H2O  à Al(OH)3 + 3H+

  • The pH of water directly affects the hydrolysis process:
    • pH < 4.5 : no hydrolysis occurs.
    • pH = 5.5 – 7.5 : achieve the best.
    • pH > 7.5 : The flocculation effect is not good.
    • The appropriate water temperature is approx 20-40oC, the best 35-40oC.
  • In addition, other influencing factors such as: Ion composition, organic matter, dosage…

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