What Is A Typical Concentration for Silica (Sio2) or Silicates in Fresh Surface and Groundwater Supplies on Earth? - Page 2

Silica (SiO2) is an oxide of silicon, and is present in almost all minerals: It is found in surface and well water in the range of 1 - 100 mg/i. Silica is considered to be colloidal in nature because of the way it reacts with adsorbents. A colloid is a gelatinous substance made up of non­diffusible particles that remain suspended in a fluid medium. Silica is objectionable in cooling tower makeup and boiler feed water. Silica evaporates in a boiler at high temperatures and then redeposits on the turbine blades. These deposits must be periodically removed or damage to the turbine will occur. Silica is not listed in the Primary or the Secondary Drinking Water Standards issued by the US EPA.

Where does Silica come from?

The solid crust of the earth contains 80 to 90 compounds of silicon such as silica or silicon dioxide. Most silicate salts are only slightly soluble in water and are widely distributed in nature. Minerals such as asbestos, mica, talc, lava, etc. contain silicates.

Silicate is a common contaminant in most waters because of the many natural deposits that dissolve in water over time. Natural physical and chemical weathering processes also produce many extremely small particles or colloids of silicate materials. In the water, all sorts of algae require phosphorous and nitrogen as nutrients; but only diatoms (a type of algae) also require silicate for growth. Increased silicate concentration causes increased production in the “trophic levels” of the food chain. This directly relates to the increased zooplankton biomass and increased fish biomass.

Outside of the water, sodium silicates are used in several raw materials for making silica gel. Some examples of materials using silica are pottery, stoneware, fireproofing paper, wood, cement, fixing pigments in paintings, cloth printing and for preserving eggs.

Increased silicate concentrations will affect the water ecosystem and the possibilities for use of the water system by humans. In water treatment, we are concerned with silica because of its capacity to form scale deposits on surfaces it comes in contact with. In its colloidal form it consists of very fine particles in suspension. The current removal processes of silica are filtration, chemical precipitation, reverse osmosis, and strong base and ion exchange.