Silica Saturation Calculator

Calculator Inputs

Temperature (°C)

Used to estimate amorphous silica solubility.

Silica concentration

Enter measured dissolved silica.

Silica basis mg/L as SiO2 mg/L as Si

The calculator converts to a common basis.

pH (optional)

Higher pH can increase silica solubility.

Solubility correction factor

Use to approximate salinity/pH effects (default 1.00).

System notes (optional)

Included in exports for traceability.

Calculate Reset

Example Data Table

Examples are illustrative and assume the correction factor shown.

Formula Used

• SR < 1 indicates undersaturation (lower scaling potential).
• SR ≈ 1 indicates near equilibrium.
• SR > 1 indicates supersaturation (higher scaling potential).

How to Use This Calculator

1. Measure dissolved silica and note whether your lab reports SiO2 or Si.
2. Enter temperature at the point where scaling is a concern.
3. Optionally enter pH; if pH is high, consider a correction factor.
4. Use correction_factor to approximate salinity or process effects.
5. Click Calculate to see SR, SI, and a risk label.
6. Download CSV or PDF to share results and assumptions.

Silica scaling risk in real systems

Silica can polymerize and deposit as glassy scale on heat-transfer surfaces and membranes. Many operators treat SR near 1.00 as a practical trigger because small shifts in temperature, concentration, or chemistry can push water into supersaturation. In high-recovery systems, a 10–20% rise in dissolved silica is common across stages, so monitoring both feed and concentrate matters. Even thin deposits can reduce heat exchange and increase differential pressure, raising energy cost.

Why temperature drives solubility

Silica solubility increases strongly with temperature, so the same silica level may be safe in cold feedwater yet risky after heating. The calculator estimates an equilibrium solubility (Ceq) in mg/L as SiO2 using a temperature-based relationship. It then compares measured silica to Ceq to produce a saturation ratio and index that are easy to trend over time. Always enter temperature at the location where scale forms, not just at sampling.

Interpreting SR and SI outputs

SR is the measured silica divided by adjusted solubility. SR below 1.00 indicates undersaturation, while SR above 1.00 indicates supersaturation. SI is log10(SR), so SI of 0.00 is equilibrium, SI of 0.10 corresponds to about 26% supersaturation, and SI of −0.10 corresponds to about 21% undersaturation. Use these numbers for alarms and dashboards, and review variability before changing setpoints.

Using correction factors and pH context

Process water is rarely pure; ionic strength and pH can shift apparent solubility. The correction factor lets you apply a documented adjustment based on plant history, lab work, or vendor guidance. For example, if observed scaling begins when SR reaches 0.95, using a 1.05 factor can align the model with real performance and reduce false positives. Record the reason for each factor change to preserve comparability across months.

Operational actions when supersaturated

When SR exceeds 1.00, consider lowering recovery, blending lower-silica water, increasing antiscalant dosing, reducing heat flux, or adding pretreatment such as softening or adsorption media. Pair SR trends with conductivity and recovery to verify whether concentration is the driver. Exported CSV and PDF records support audits, chemical optimization, and before/after change analysis. For assets, set an action band, such as SR 1.00–1.10, to trigger checks before scaling develops.

FAQs

What does SR mean here?

SR is the measured silica concentration divided by the adjusted equilibrium solubility at your temperature. SR below 1.00 suggests undersaturation, while SR above 1.00 suggests supersaturation and higher scaling potential.

What is SI and why use it?

SI is log10(SR). It compresses the ratio into a trend-friendly number: 0.00 is equilibrium, positive values indicate supersaturation, and negative values indicate undersaturation. Small SI changes can be easier to compare across time.

Should I enter silica as Si or SiO2?

Enter whichever your lab reports. If you choose “mg/L as Si,” the calculator converts it to “mg/L as SiO2” internally using molar-mass ratios, then performs the saturation calculations consistently.

How do I choose a correction factor?

Start with 1.00. If your water chemistry or operating history shows scaling at lower or higher SR values, adjust the factor to match observed behavior. Keep the factor documented so exported reports remain comparable.

Does pH change silica solubility?

Yes. At higher pH, more silica can exist as dissolved species, which often increases apparent solubility. The calculator flags high pH as a reminder and lets you reflect the effect using the correction factor.

What actions help when SR is high?

Common options include lowering recovery, blending lower-silica water, optimizing antiscalant dosing, reducing heat flux, or improving pretreatment. Use SR trends together with conductivity and recovery to confirm whether concentration is driving risk.