Silicate

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 and 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.

Calcium silicate, also known as slag, is produced when molten iron is made from iron ore, silicon dioxide and calcium carbonate in a blast furnace. When this material is processed into a highly refined, re-purposed calcium silicate aggregate, it is used in the remediation of acid mine drainage (AMD) on active and passive mine sites.[8] Calcium silicate neutralizes active acidity in AMD systems by removing free hydrogen ions from the bulk solution, thereby increasing pH.

Silicate minerals can be thought of as three-dimensional arrays of oxygen atoms that contain void spaces (i.e., crystallographic sites) where various cations can enter.
Besides the tetrahedral (4-fold coordination) sites, 6-fold, 8-fold, and 12-fold sites are common.
A correlation exists between the size of a cation (a positively charged ion) and the type of site it can occupy: the larger the cation, the greater the coordination, because large cations have more surface area with which the oxygen atoms can make contact.
Tetrahedral sites are generally occupied by silicon and aluminum; 6-fold sites by aluminum, iron, titanium, magnesium, lithium, manganese, and sodium; 8-fold sites by sodium, calcium, and potassium; and 12-fold sites by potassium.
Elements of similar ionic size often substitute for one another. An aluminum ion, for example, is only slightly larger than a silicon ion, allowing substitution for silicon in both tetrahedral and 6-fold sites.