SILICA IN DRINKING WATER

Many water supplies contain silica. This is not surprising since silicon is the second most abundant chemical element in the earth.

Silica. (silicon dioxide) A compound of silicon and oxygen (Si02). It is a hard, glassy mineral substance which occurs in a variety of forms such as sand, quartz, sandstone, and granite. It also is found in the skeletal parts of various animals and plants.

Silicon. (Si) One of the nonmetallic elements in abundant supply as part of various compounds in the crust of the earth.

The solid crust of the earth contains 80% to 90% silicates or other compounds of silicon. Water passing through or over the earth dissolves silica from sands, rocks and minerals as one of the impurities it collects.

Silicates. Compounds which contain silicon and oxygen in combination with such metals as aluminum, calcium, magnesium, iron, potassium, sodium and others. Silicates are classed as salts. Silicates are widely distributed in such minerals as asbestos, mica, talc, lava, etc.

Colloids. Extremely small solid particles suspended in a solution such as water. The weight of the individual particle is so low that a true colloid will not settle out, even after standing for an indefinite period. Colloidal particles are thought to have a charge which causes the particles to repel each other, and prevent their agglomeration into larger particles. A colloid diffuses very slowly or not at all through a membrane, and has little, if any, effect upon the freezing point, boiling point, or vapor pressure of the solution.

The silica content of water ranges from a few parts per million in surface supplies to well over 100 ppm in certain well waters.

In its colloidal form it consists of very fine particles in suspension. These can usually be removed by coagulation and settling or filtering.