Definition - What does Activated Silica mean?
Activated silica is a substance or material usually formed from the reaction of a dilute silicate solution with a dilute acid. Activated silica is frequently useful as a coagulation aid in water treatment.
Its use has become standard practice in many municipal and industrial water purification plants. The addition of activated silica broadens the pH range at which good flocculation is obtained, and considerably reduces the dosage of aluminum sulfate.
Corrosionpedia explains Activated Silica
Coagulation and flocculation is the most common method in potable water treatment to remove particulate and soluble impurities. These impurities may be mineral or organic in origin. The polymerized silica or the colloidal silica used in water purification to aid coagulation of colloidal matters is called activated silica. The activated silica is prepared from sodium silicate by activation with such chemicals as:
- Sulfuric acid
- Ammonium sulfate
- Carbon dioxide
- Aluminum sulfate
The activation reaction is believed to be the neutralization of sodium silicate, leading to polymerization of silicate ions. The process acidifies the silicate and uses caustic material to raise the pH to less than 12 to stabilize the activated silica.
The applications of activated silica depend mainly on the size, charge and shape of the polymer. The size of the activated silica polymer can be varied over a wide range by controlling the aging time. The charge of the polymer may be varied by changing the pH or by forming the polymer in the presence of ions and molecules that are adsorbed. This changes the chemical/physical properties of the polymer. A larger amount of activated silica is required at a lower pH value to produce good coagulation of aluminum hydroxide.