Sodium Silicate

Sodium silicate is a generic name for chemical compounds with the formula Na_2xSiO_2+x or (Na₂O)_x·SiO₂, such as sodium metasilicate Na₂SiO₃, sodiumorthosilicate Na₄SiO₄, and sodium pyrosilicate Na₆Si₂O₇. 

The main applications of sodium silicates are in detergents, paper, water treatment, and construction materials.

Adhesive

The largest application of sodium silicate solutions is a cement for producing cardboard.^[1] When used as a paper cement, the tendency is for the sodium silicate joint eventually to crack within a few years, at which point it no longer holds the paper surfaces cemented together.

Drilling fluids

Sodium silicate is frequently used in drilling fluids to stabilize borehole walls and to avoid the collapse of bore walls. It is particularly useful when drill holes pass through argillaceousformations containing swelling clay minerals such as smectite or montmorillonite.

Concrete and general masonry treatment

Concrete treated with a sodium silicate solution helps to reduce porosity in most masonry products such as concrete, stucco, and plasters. This effect aids in reducing water penetration, but has no known effect on reducing water vapor transmission and emission^[21]. A chemical reaction occurs with the excess Ca(OH)₂ (portlandite) present in the concrete that permanently binds the silicates with the surface, making them far more durable and water repellent. This treatment generally is applied only after the initial cure has taken place (7 days or so depending on conditions). These coatings are known as silicate mineral paint.

Detergent auxiliaries

It is used in detergent auxiliaries such as complex sodium disilicate and modified sodium disilicate. The detergent granules gain their ruggedness from a coating of silicates.^[1]

Water treatment

Sodium silicate is used as an alum coagulant and an iron flocculant in wastewater treatment plants. Sodium silicate binds to colloidal molecules, creating larger aggregates that sink to the bottom of the water column. The microscopic negatively charged particles suspended in water interact with sodium silicate. Their electrical double layer collapses due to the increase of ionic strength caused by the addition of sodium silicate (doubly negatively charged anion accompanied by two sodium cations) and they subsequently aggregate. This process is called coagulation.^[1]