Silicon or Silica: what is it and what is its Relation with Water
Silicon, also called silica in its mineral form, is the second most abundant element on earth and represents about 59% of the earth's crust.

Before going any further, it is important to specify that silicon, with the symbol Si, is not present in its pure form in nature. It is most often found in its mineral form: silica & silicates. In the water treatment industry, it is usually silica that is problematic.

Silica is composed of the two most common elements on earth, silicon and oxygen. On earth, SiO2 (silica) is found in many forms. The three most common forms of silica are quartz, tridymite and cristobalite.


Silica and Water

Because of its abundance in the environment, silicon is found in virtually all waters on earth. In its most common form in water, silica (SiO2), concentrations generally vary greatly, from 20 mg/L to over 1000 mg/L, depending on the source of the water. Brackish waters generally have high concentrations of silicon or its derivatives.


When silicon derivatives are added to water, it is usually as a conditioner, detergent or corrosion inhibitor. Whether added for a specific use or naturally occurring in water, silica can cause problems for some industrial equipment.


In the presence of water at high temperatures or under high pressure, silica can cause deposits. This is why in applications such as water for industrial boilers, the presence of silica can be risky for the safety and efficiency of equipment. To avoid the formation of silica deposits, which are characterized by a glassy appearance, silica levels should be below 0.005 mg/L.

What are BOD and COD?
These terms refer to biological oxygen demand and chemical oxygen demand.