The Total Silica content found in water is primarily divided into two main types: Reactive Silica and Unreactive Silica. This classification is crucial for understanding water chemistry and treatment processes.
Understanding Total Silica in Water
Water naturally dissolves minerals from the environment, and silica (silicon dioxide) is one such common component. The way silica exists in water varies, influencing how it can be measured and removed.
The Two Main Types of Silica
According to the provided reference, the total silica in water is composed of:
1. Reactive Silica
- Description: This type of silica is dissolved in the water and exists in simpler forms, such as silicates like SiO₄⁴⁻ or silicic acid (H₄SiO₄).
- Characteristics:
- Dissolved in water.
- Slightly ionized.
- Has not been polymerized into long chains.
- Significance: Reactive silica is the form that readily reacts with chemicals used in standard water analysis methods. More importantly, it is the form that is targeted and effectively removed by advanced water treatment processes like reverse osmosis (RO) and ion exchange. As the reference states, this is the form that "RO and ion exchange chemists hope for" because it is amenable to removal by these methods.
2. Unreactive Silica
- Description: This type includes silica that is not in the simple, dissolved silicate or silicic acid form. It is often present as colloidal particles (very small suspended particles) or larger polymerized chains of silica molecules.
- Characteristics:
- May be suspended (colloidal) or in complex polymerized forms.
- Does not readily react in standard "reactive" silica tests.
- Significance: Unreactive silica is more difficult to measure accurately using standard tests and is also more challenging to remove with typical water treatment methods like RO or ion exchange, which are designed primarily for dissolved substances. Special pretreatment steps, such as filtration or coagulation, may be required to remove unreactive silica before other processes.
Summary Table
| Type | State in Water | Reactivity in Tests | Treatability (RO/Ion Exchange) | Typical Form(s) |
|---|---|---|---|---|
| Reactive Silica | Dissolved | High | Good | Silicates (e.g., SiO₄⁴⁻), Silicic Acid (H₄SiO₄) |
| Unreactive Silica | Colloidal or Polymerized Chains | Low | Poor | Colloidal silica, Polysilicates |
Understanding the distinction between reactive and unreactive silica is essential for designing effective water treatment strategies, especially when aiming to achieve high-purity water for industrial or specific domestic uses.
