PESA (Polyepoxysuccinic Acid) is most effective against two primary types of scale: carbonate scales, and to a very good extent, sulfate scales.
Its performance can be broken down by scale type as follows:
Highly Effective
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Calcium Carbonate Scale (CaCO₃):
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This is PESA’s strongest suit. It exhibits an excellent “threshold effect,” meaning a very small amount can effectively inhibit a large quantity of scaling ions from precipitating.
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It works by both distorting the crystal structure of CaCO₃ (making it non-adherent) and by keeping the scaling ions in solution beyond their normal saturation point.
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This makes it ideal for cooling water systems where calcium carbonate is the most common scale.
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Calcium Sulfate Scale (CaSO₄, both gypsum and anhydrite):
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PESA is also highly effective at inhibiting sulfate scales.
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It prevents the formation and growth of calcium sulfate crystals, which is critical in systems with high sulfate concentration or in processes like reverse osmosis (RO) and seawater desalination.
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Moderately Effective
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Barium Sulfate (BaSO₄) and Strontium Sulfate (SrSO₄) Scales:
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PESA provides good inhibition against these very hard, tenacious scales.
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While specialized antiscalants might be preferred for extremely high concentrations, PESA is often a key component in blended formulations designed to control these scales, especially in oilfield water treatment and RO systems.
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Less Effective / Not Recommended
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Phosphate-based Scales:
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This is a key limitation. PESA has poor effectiveness against phosphate scales, including:
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Calcium Phosphate (Ca₃(PO₄)₂)
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Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂)
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Calcium Phosphonates (e.g., from reacting with HEDP or ATMP)
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If phosphate is present in the water (either naturally or from a phosphonate-based corrosion inhibitor), PESA alone is not sufficient and must be blended with a polymer specifically designed for phosphate inhibition (e.g., a phosphinocarboxylic acid or a specific acrylic copolymer).
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Summary Table
| Scale Type | PESA’s Effectiveness | Key Application Context |
|---|---|---|
| Calcium Carbonate (CaCO₃) | Excellent / Highly Effective | Cooling water, RO, general industrial water systems. |
| Calcium Sulfate (CaSO₄) | Excellent / Highly Effective | RO, high sulfate cooling water, thermal desalination. |
| Barium Sulfate (BaSO₄) | Good / Moderately Effective | Oilfield recovery, RO with high Ba²⁺. |
| Strontium Sulfate (SrSO₄) | Good / Moderately Effective | Oilfield recovery, RO with high Sr²⁺. |
| Calcium Phosphate (Ca₃(PO₄)₂) | Poor / Not Effective | Systems with phosphate present (requires a blended formula). |
Conclusion
In practice, PESA is primarily valued for creating non-phosphorus, environmentally friendly treatment programs that are highly effective against the most common scales: carbonate and sulfate scales. Its ability to perform well in high-hardness, high-alkalinity water, combined with its chlorine stability, makes it a top choice for cooling water and RO pretreatment.
However, for systems with phosphate or where iron dispersion is a primary concern, it is almost always blended with other complementary polymers to create a comprehensive and robust water treatment program.