Overview
Sodium metasilicate is a type of silicic acid salt and is classified as an inorganic salt products, and its molecular formula is Na2SiO3•nH2O. It is a non-toxic, odorless and harmless white powder or crystalline particle. It is soluble in water, but not in alcohols or acids. Its aqueous solution is alkaline and is capable of hygroscopy and deliquescence when in contact with air. It has purifying, emulsifying, dispersing, moistening, permeating and PH buffering abilities. Sodium metasilicate is a low molecular weight crystal that results from the heat reaction between foaming alkaline and caustic soda water. Products include anhydrous, pentahydrate and nonahydrate compounds.
Among inorganic electrolytes, sodium metasilicate’s active alkalinity and PH buffering index is the highest. It has strong moistening, emulsifying and saponifying effect on fats. It is excellent at eliminating, dispersing and suspending impurities, and it can prevent impurities from recollecting. It has strong cleansing, buffering and neutralizing abilities, can emulsify fats and oils, is an anti-flocculant for inorganic matter, protects metals from erosion, can replace sodium tripolyphosphate in producing detergents and metal cleansing agents, thus reducing the environmental pollution of sodium tripolyphosphate.
Sodium metasilicate is widely used in laundry detergent, ceramics, plating, textiles, printing, papermaking, concrete, cement, fireproof materials, oils, leather processing, and many other industrial fields. Currently, the industries that use it the most are: ceramics, industrial cleaning, laundry detergent, concrete, printing, papermaking, cement, oil mining, etc.
Identifying tests
Dissolve a 200mg sample in 10ml water and dispense a drop of this liquid onto a color palette. Add 1 drop of 4mol/L sodium hydroxide and one drop of a solution of 0.5g of ammonium molybdate in 10ml water. Then add 3ml sulfuric acid, and it should turn dark yellow to indicate the presence of silicate. Dip a nichrome wire into the test solution of experiment 1 and place it in a flame; it should turn bright yellow to indicate the presence of sodium.
Content Analysis
Take a 1g sample of silica, place it in a beaker, use 5ml hydrochloric acid to acidify it, and evaporate on a steam bath until dry. Then add another 5ml hydrochloric acid and repeat the steps once. Mix the remainder with 1ml hydrochloric acid and 2ml water, hydrolyze into a soluble salt on the steam bath, and strain through a quantitative analysis filter paper. After rinsing with hot water, move to a platinum crucible and dry for 1h at 105℃, and use a lower temperature to carbonize. Then burn at 1000℃ until it maintains a constant weight. Use a few drops of water to moisten the remainder, and then add 15ml hydrofluoric acid and 5 drops of 1:3 sulfuric acid. After removing the acid on a hot plate, burn at 1000℃ until it maintains a constant weight.
Toxicity
Corrosive; do not contact with eyes, skin or clothes, and do not inhale its vapor.
GRAS(GMP；FDA，§184.1769a，2000).
Chemical Properties
The metasilicates are highly water soluble, but insoluble in
alcohol, acid, and salt solutions. Solutions of sodium metasilicate,
when heated or acidified, are hydrolyzed to free sodium
ions and silicic acid. In moist air, they are corrosive to metals,
including zinc, aluminum, tin, and lead, forming hydrogen
gas. They are all strong bases reacting violently with acid.
Chemical Properties
White, granular powder. Soluble in
water; p H of 1% solution 12.7. Noncombustible.
Uses
The various hydrates of sodium metasilicate are used in soap,
detergent, and bath/washing products. They also have a
major use as a builder (a material that enhances or maintains
the cleaning efficiency of the surfactant, principally by
inactivating water hardness) in soaps and detergents. They
are also used as an anticorrosion agent in boiler-water feeds.
Uses
Laundry, dairy, and metal cleaning; floor clean-
ing; base for detergent formulations; bleaching aid;
deinking paper. Also available as the pentahydrate
whose properties are mp 72.2C, total Na
2
O content
29.3%, total Na
2
O in active form 27.8%, d 1.75 or
55 lb/cu ft.
Uses
Sodium Metasilicate is an antibacterial pharmaceutical compound containing Sodium Hydrogen Carbonate.
Definition
A crystalline silicate.
Hazard
Toxic by ingestion, protective clothing
required.
Flammability and Explosibility
Not classified
Safety Profile
Poison by ingestion and intraperitoneal routes. A caustic material whch is a severe eye, sktn, and mucous membrane irritant. Experimental reproductive effects. Ingestion causes gastrointestinal tract upset. Violent reaction with F2. When heated to decomposition it emits toxic fumes of Na2O. Used in cosmetics. See also SILICATES.
Synthesis
Crystalline sodium metasilicate is produced via solid-state reaction by calcining stoichiometric mixtures of silica (from commercial sand or rice husk ash) with sodium bicarbonate, sodium carbonate, or sodium hydroxide at temperatures ranging from 900 to 1400 ºC[1][2][3]. Alternatively, the compound is synthesized through precipitation from aqueous solutions of tetraethyl orthosilicate and sodium hydroxide, or by autoclaving silica and sodium hydroxide at 180–240 ºC under pressure[1][3]. Hydrated forms (Na2SiO3·5H2O, Na2SiO3·6H2O, Na2SiO3·8H2O) and anhydrous sodium metasilicate are obtained by controlling the drying modulus of the liquor, with anhydrous product specifically gained by drying at 120 ºC[2].
Purification Methods
Crystallise it from aqueous 5% NaOH solution. [Schwartz Z Anorg Allgem Chem 126 62 1923.]
References
[1] Tejeda-Ochoa et al. Revista Mexicana de Ingeniería Química Vol. 18, No. 2 (2019) 581-588.
[2]Liu, X., Li, Z., Chen, H., Yang, L., Tian, Y., & Wang, Z. (2015). Rice husk ash as a renewable source for synthesis of sodium metasilicate crystal and its characterization. Research on Chemical Intermediates, 42(4), 3887–3903.
https://doi.org/10.1007/s11164-015-2251-7 [3]Rodríguez, M. T., & Pfeiffer, H. (2008). Sodium metasilicate (Na2SiO3): A thermo-kinetic analysis of its CO2 chemical sorption. Thermochimica Acta, 473(1-2), 92–95.
https://doi.org/10.1016/j.tca.2008.04.022
