Determining the correct dosage of EDTMP·Na5 (Ethylenediaminetetra(methylene phosphonic acid) pentasodium salt) is critical because it is highly effective but also cost-sensitive.
The short answer is: There is no single universal dosage. It depends entirely on the specific application and system conditions.
Step-by-Step Dosing Determination Guide
1. Define Your Goal
What is the primary purpose?
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Scale Inhibition: To prevent CaCO₃, CaSO₄, BaSO₄ scale.
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Iron Stabilization: To keep dissolved iron in solution.
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Corrosion Inhibition: Often in combination with zinc ions.
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Oilfield Squeeze: For long-term downhole scale prevention.
2. Analyze System Water
This is the most crucial step. You must know your enemy (scaling ions). Key parameters to measure:
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Calcium (Ca²⁺)
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Magnesium (Mg²⁺)
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Barium (Ba²⁺)
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Strontium (Sr²⁺)
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Alkalinity (as CaCO₃)
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pH
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Temperature
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Iron (Fe²⁺/Fe³⁺)
3. Calculate the Scaling Potential
Use scaling indices (like the Langelier Saturation Index for CaCO₃) or specialized software. Higher scaling potential requires higher dosages.
4. Refer to General Dosage Guidelines
For Industrial Water Treatment (Cooling & Boiler Water):
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As a Scale Inhibitor: The typical dosage to threshold inhibit scale is very low.
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Active EDTMP·Na5 (100% pure): 1 to 10 mg/L (ppm) is common.
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As a Commercial Product Solution: Since the product you buy is not 100% active (e.g., it might be a 25% or 40% solution), you need to calculate the actual product dose.
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Formula:
Product Dose (mg/L) = Desired Active Dose (mg/L) / % Active of Your Product -
Example: To achieve 5 mg/L of active EDTMP·Na5 using a 25% active solution:
Product Dose = 5 mg/L / 0.25 = 20 mg/Lof the commercial product.
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As a Corrosion Inhibitor (with Zinc): Dosages are often higher, in the range of 10-20 mg/L of active product.
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For Iron Oxide Dispersion: Dosages can range from 5-15 mg/L active.
For Oilfield Scale Squeeze Treatments:
This is a specialized operation. Dosages are not in ppm, but in large volumes and concentrations.
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Concentration: The injected pill is typically a 5% to 20% solution of EDTMP·Na5 in water.
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Volume: The volume is calculated based on the wellbore geometry, formation porosity, and desired treatment life. It can range from thousands to tens of thousands of gallons.
5. Conduct Laboratory Tests
Never rely solely on guidelines for a critical system. Laboratory confirmation is essential.
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Static Bottle Test: A simple test to find the minimum effective dose that prevents scale formation under simulated conditions.
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Dynamic Loop Test: A more advanced test that simulates fluid flow, heat transfer, and shear stress, providing a more accurate dosage recommendation.
6. Monitor & Optimize in the Field
After setting an initial dose based on lab tests and guidelines, continuous monitoring is key.
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Monitor: Scaling rates, corrosion coupons, and water chemistry.
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Adjust: Adjust the feed rate up or down based on the results. The goal is to find the minimum effective dose that controls scale and corrosion cost-effectively.
Example Calculation for a Cooling Water System
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System: Recirculating cooling water.
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Goal: Prevent Calcium Carbonate scale.
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Water Analysis: High Calcium Hardness = 400 mg/L as CaCO₃.
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Product: EDTMP·Na5 liquid, 40% active.
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Lab Test Result: Suggests a dosage of 6 mg/L of active acid is required.
Calculation:
Product Dosage = 6 mg/L / 0.40 = 15 mg/L
Therefore, you would need to continuously add 15 mg/L (or 15 ppm) of the commercial liquid product to the circulating cooling water.
Important Considerations
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Overdosing: While generally safe, extreme overdosing can be wasteful and, in rare cases, lead to phosphonate precipitation with calcium (especially at high temperatures and pH).
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Compatibility: EDTMP·Na5 is compatible with most other water treatment chemicals (like polymers, biocides, and zinc). Always verify compatibility before mixing.
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Safety: Always refer to the manufacturer’s Safety Data Sheet (SDS) and technical data sheet for the specific product you are using. They often provide recommended dosage ranges.
In summary: Start with water analysis and scaling prediction, use the general guidelines (2-20 mg/L active) for initial estimates, confirm with lab tests, and fine-tune with field monitoring. For critical or complex applications like oilfield squeezes, always consult with a water treatment or production chemical specialist.