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Sodium
silicates are economical, effective, and environmentally benign chemicals that
have been used in water treatment for more than 70 years. Silicates are used in
water treatment for corrosion inhibition, iron and manganese control, and as a
coagulant aid.
Corrosion Inhibition
Sodium silicate can be used as a
corrosion inhibitor in potable and industrial water. Sodium silicate inhibits
corrosion by forming a protective film on metal surfaces that isolates the metal
from further corrosive attack. Because soluble silicates are alkaline, moreover,
they bring the further benefit of increasing the pH of water. Sodium silicate
can be used to inhibit corrosion of cast iron pipes, service lines, and
fixtures—to protect the infrastructure and to help water utilities meet the
requirements of the lead/copper rule. Selection of silicate for this application
depends on the pH and alkalinity of the untreated water. (Refer to our Water Treatment Bulletins for further information.)
Iron and Manganese Control
Sodium
silicate can be used as a sequestrant to prevent colored water in the
distribution system from iron and manganese in groundwater. N® Sodium
Silicate is typically used for this application, although more alkaline
silicates can be used for more acidic water sources. Sodium hypochlorite is
added at the well site to oxidize the iron. Adding sodium silicate immediately
afterward holds the oxidized iron in a colloidal suspension. Manganese is
suspended or is adsorbed onto the iron. Dosage varies case-by-case, according to
the amount of iron and manganese in the water, water hardness, and detention
time in the system. Dosage is best determined by a jar test on site.
Coagulant Aid
Activated silica can be used as a
secondary coagulant, along with a primary coagulant such as alum or ferric
chloride, to improve the performance of water systems. Activated Silica is
formed on site by partially neutralizing N Sodium Silicate on site, then
diluting to a feed solution concentration of about 1% SiO2. Activated
silica creates a heavier denser floc that settles faster. It thereby reduces the
turbidity of the water entering the filters and allows longer filter runs.
PQ Technical Service Group can support these applications by running jar
tests on-site and by coordinating and overseeing plant trials.
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