SILICA IN DRINKING WATER
Silica Concentration in Drinking Water
The role of silica in water treatment is crucial because it has a propensity to form scale deposits on surfaces it contacts. Water sources may have silica concentrations ranging from negligible amounts in surface water to greater than 100 ppm in certain groundwater supplies. In its colloidal form, silica consists of minute particles that remain suspended in the water. This discussion seeks to clarify the characteristics of silica and its appropriate management in potable water. Composed of silicon and oxygen (SiO2), silica is a tough, glassy mineral that can be found in substances such as sand, quartz, sandstone, and granite, as well as in the frameworks of diverse plants and animals. As the seventh most abundant element in the universe and the second most common on Earth after oxygen, it is widespread in the majority of water sources. Most natural water bodies contain dissolved silica, and many also contain colloidal silica. Its presence in solution can manifest as silicic acid or silicate ions, which are affected by the pH level. Silica is also found in certain foods, including cucumbers, oats, brown rice, wheat, strawberries, onions, avocados, and root vegetables. The Earth’s crust is made up of 80% to 90% silicates or silicon-based compounds, with water absorbing silica from sands, rocks, and minerals as impurities. Typically, natural waters hold between 5 to 25 mg/L of silica, while some areas have reported concentrations surpassing 100 mg/L. Silicates, which combine silicon and oxygen with metals such as aluminum, calcium, magnesium, iron, potassium, sodium, and others, are categorized as salts and are abundant in minerals like asbestos, mica, and talc. Colloids are tiny, suspended particles in a solution that cannot be removed by conventional filtration due to their small size and light weight, which prevents them from settling. These particles carry a charge, leading to repulsion among them and preventing aggregation. Colloids barely or slowly pass through membranes and have minimal effects on the solution’s freezing or boiling points or vapor pressure.
Silica Removal Techniques encompass:
- Filtration
- Chemical Precipitation
- Reverse Osmosis
- Strong Base and Ion Exchange
Conventional precipitation techniques are laborious and disorganized. For effective silica removal, a combination of Reverse Osmosis and ion exchange is frequently utilized. RO systems, while less efficient than ion exchange at removing silica, are adept at eliminating non-reactive forms of silica and additional contaminants that ion exchange fails to target.