Calcium silicate

Calcium silicate (often referred to by its shortened trade name Cal-Sil or Calsil) is the chemical compound Ca₂SiO₄, also known as calcium orthosilicate and sometimes formulated 2CaO.SiO₂. It is one of group of compounds obtained by reacting calcium oxide and silica in various ratios^[1] e.g. 3CaO.SiO₂, Ca₃SiO₅; 2CaO.SiO₂, Ca₂SiO₄; 3CaO.2SiO₂, Ca₃Si₂O₇ and CaO.SiO₂, CaSiO₃. Calcium orthosilicate is a white powder with a low bulk density and high physical water absorption. It is used as an anti-caking agent and an antacid. A white free-flowing powder derived from limestone and diatomaceous earth, calcium silicate has no known adverse effects to health. It is used in roads, insulation, bricks, roof tiles, table salt^[2] and occurs in cements, where it is known as belite (or in cement chemist notation C₂S).

Calcium silicate passive fire protection board being clad around steel structure in order to achieve a fire-resistance rating.

High temperature insulation

Calcium silicate is commonly used as a safe alternative to asbestos for high temperature insulation materials. Industrial grade piping and equipment insulation is often fabricated from calcium silicate. Its fabrication is a routine part of the curriculum for insulation apprentices. Calcium silicate competes in these realms against rockwool as well as proprietary insulation solids, such as perlite mixture and vermiculite bonded with sodium silicate. Although it is popularly considered an asbestos substitute, early uses of calcium silicate for insulation still made use of asbestos fibers.

Passive fire protection

One of the most successful materials in fireproofing in Europe is calcium silicate. Where North Americans use spray fireproofing plasters, Europeans are more likely to use cladding made of calcium silicate. Calcium silicate is easily damaged by water. Therefore, silicone treated sheets are available to fabricators to mitigate potential harm from high humidity or general presence of water. Fabricators and installers of calcium silicate in passive fire protection often also install firestops.

Acid mine drainage remediation

Calcium silicate is also a constituent of the slag that is produced when molten iron is made from iron ore and calcium carbonate in a blast furnace. When this material is processed into a highly refined, repurposed calcium silicate aggregate, it is used in the remediation of acid mine drainage (AMD) on active and passive mine sites.^[3] Calcium silicate neutralizes active acidity in AMD systems by removing free hydrogen ions from the bulk solution, thereby increasing pH. As its silicate anion captures H⁺ ions (raising the pH), it forms monosilicic acid (H₄SiO₄), a neutral solute. Monosilicic acid remains in the bulk solution to play other important roles in correcting the adverse effects of acidic conditions. As opposed to limestone (a popular remediation material),^[4] calcium silicate effectively precipitates heavy metals and does not armor over, prolonging its effectiveness in AMD systems.^[3]^[5]

As a product of sealants

When sodium silicate is applied as a sealant to cured concrete or the shells of fresh eggs, it chemically reacts with calcium hydroxide or carbonate to form calcium silicate hydrate, sealing pores with a relatively impermeable material.

References

^ H F W Taylor, Cement Chemistry, Academic Press, 1990, ISBN 0-12-683900-X, p 33-34
^www.mortonsalt.com/faqs/food_salt_faq.html
^ ^a ^bZiemkiewicz, Paul. "The Use of Steel Slag in Acid Mine Drainage Treatment and Control". Retrieved 25 April 2011.
^Skousen, Jeff. "Chemicals". Overview of Acid Mine Drainage Treatment with Chemicals. West Virginia University Extension Service. Retrieved 29 March 2011.
^Hammarstrom, Jane M.; Philip L. Sibrell; Harvey E. Belkin. "Characterization of limestone reacted with acid-mine drainage". Applied Geochemistry (18): p.1710–1714. Retrieved 30 March 2011.