Free Flowing Salts and Desiccants
Calcium silicate (CaSiO3), a commonly used anti-caking agent, added to e.g. table salt, absorbs both water and oil. This white powder has the incredible ability to absorb liquids and still remain a flee-flowing powder. In general, calcium silicate absorbs 1 to 2.5 times its weight of liquids. For water, its total absorption power is estimated as 600%, that is, absorbing 600 times its weight of water.
Desiccants – Silica Gel
A desiccant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its local vicinity in a moderately well-sealed container. Some commonly used desiccants are: silica gel, activated charcoal, calcium sulfate, calcium chloride, montmorillonite clay, and molecular sieves such as Zeolites. These desiccants remove water by a variety of physical and chemical methods: adsorption, a process whereby a layer or layers of water molecules adhere to the surface of the desiccant; capillary condensation, a procedure whereby the small pores of the desiccant become filled with water; and chemical action, a procedure whereby the desiccant undergoes a chemical reaction with water.
Montmorillonite clay is a naturally occurring adsorbent that swells to several times its original volume when water adsorption occurs.
The most commonly used desiccant is silica gel (SiO2. H20), an amorphous form of silica manufactured from sodium silicate and sulphuric acid. The porous nature of silica gel forms a vast surface area that attracts and holds water by both adsorption and capillary condensation, allowing silica gel to adsorb about 40% of its weight in water. Zeolites or “molecular sieves” are rigid, hydrated crystalline aluminosilicate minerals that contain alkali and alkaline earth metals. Zeolites possess a three-dimensional crystal lattice structure that forms surface pores of uniform diameter and contain numerous regular internal cavities and channels. Water molecules are readily incorporated within the pores and cavities.
