Silicic acid is a very weak acid. It is the compound of silicon, oxygen and hydrogen. Silicon is not found in free form in the nature. Mostly it is found in the nature in oxide form. Usually, oxides of silicon are very little soluble in the water whereas the others silicon compounds are insoluble in water. The solubility of silicon dioxide creates silicic acid. Little amount of silicic acid is not harmful to our health; rather it is benefits to our health. On the other hand it is responsible for scaling in boiler. It is also known as ortho silicic acid. The chemical formula of silicic acid is H4SiO4 or Si(OH)4. It makes colloidal system in the water.
Silicic acid solubility in water
Silicon dioxide dissolved in water very slowly. One molecule silicon dioxide absorbed two molecules water and makes one molecule silicic acid in water. Conversely, silicic acid is an unstable compound in water medium, it breaks and creates silicon dioxide and water. So both the compound makes and equilibrium condition which is as follow:
SiO2(s) + 2H2O(l) ↔ H4SiO4(aq)
It has a water solubility of 0.12 g/l. The solubility will depend on temperature and pH. It increases with the increased temperature and pH. The ionic condition of the silicic acid is as below:
H4SiO4(aq) ↔ H3SiO4– + H+
Silicic acid benefits
Silicic acid plays an important rule for our body. It removes toxic aluminium from our body through the urine which is responsible for Alzheimer’s disease. Moreover, the deficiency of silicon may leads to pale and wrinkle skin, brittle nails and hair. In addition, it also improves bone formation, joint health, preserve dental health, and stimulate digestion. So we should drink silicic acid containing water.
Disadvantage of silicic acid in water
The plant which produces steam for many purposes, are unsafe to use silicic containing water. It is responsible for many boiler disturbances. It can create scaling in boiler and its tubes. Therefore the boiler performance and boiler life will be reduced due to scaling. We will get poor heat transfer. To get sufficient steam, we over heat the boiler tube. Hence the effectiveness of the boiler will be decreased and the fuel and maintenance cost will be increased.
Removal of silicic acid from water
Silicic acid can be removed from the water by many ways. But these methods cannot remove the silica completely; they can just reduce the amount of this element. Using trivalent ions like iron or aluminum will brings better result than divalent or monovalent metal ions. Sodium aluminate is one of the effective methods to eliminate silicic acid. Aluminium hydroxide is another process to reduce silicic acid. The effectiveness of these processes depends on pH value; the effective pH value is 7.0 to 9.0. More over it is also depends on the ratio of (Ca+mg):Na.
Although the silicic acid in drinking water is good for health, it is not good for boiler water. So when you use silicic acid containing water as drinking purpose, it need not to remove them; but when you use them as boiler purpose, you must remove them before using.